POSIVA 2006-08
Dissolution of Unirradiated UO2 and
UO2 Doped with 233U in 0.01 M NaCl under
Anoxic and Reducing Conditions
Kaija Ollila
December 2006
POSIVA OY
FIN-27160 OLKILUOTO, FINLAND
Phone (02) 8372 31 (nat.), (+358-2-) 8372 31 (int.)
Fax (02) 8372 3709 (nat.), (+358-2-) 8372 3709 (int.)
POSIVA 2006-08
Dissolution of Unirradiated UO2 and
UO2 Doped with 233U in 0.01 M NaCl under
Anoxic and Reducing Conditions
Kaija Ollila
VTT
December 2006
POSIVA
FI-27160
OY
OLKILUOTO,
FINLAND
Phone (02) 8372 31 (nat.), (+358-2-) 8372 31 (int.)
Fax (02) 8372 3709 (nat.), (+358-2-) 8372 3709 (int.)
ISBN 951-652-148-7
ISSN 1239-3096
The conclusions and viewpoints presented in the report are
those of author(s) and do not necessarily coincide
with those of Posiva.
Posiva-raportti – Posiva Report
Raportin tunnus – Report code
POSIVA 2006-08
Posiva Oy
FI-27160 OLKILUOTO, FINLAND
Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)
Tekijä(t) – Author(s)
Julkaisuaika – Date
December 2006
Toimeksiantaja(t) – Commissioned by
Kaija Ollila, VTT
Posiva Oy
Nimeke – Title
Dissolution of Unirradiated UO2 and UO2 Doped with 233U in 0.01 M NaCl under Anoxic and
Reducing Conditions
Tiivistelmä – Abstract
Dissolution experiments were conducted to determine the dissolution rate of unirradiated UO2 and
UO2 doped with 233U in 0.01 M NaCl solution with isotope dilution method. UO2 doped with 233U
(5, 10 %) was used to simulate the degree of D-radiation that will be present in spent fuel at 3,000
and 10,000 years after disposal. The isotope dilution method was used to decrease uncertainties
due to precipitation and sorption effects. Redox conditions were anoxic (N2, 1 ppm S2-) and
reducing (N2, metallic Fe) conditions. The effect of the ratio of the UO2 surface area to leachant
volume was investigated in the tests with unirradiated UO2 (SA/V= 11…67 m-1). The studies
reported were performed as part of the NF-PRO project of the European Commission 6th
Framework Programme (NF/PRO/F16W-CT-2003-02389).
The [238U] stayed low and reached steady state rapidly in the leaching solutions (1 ppm S2-) under
anoxic conditions. The changes in the measured 235U/238U ratios vs. time suggest higher U release
than the measured [238U] in solution and the precipitation of U. The calculated 238U release
increased as the SA/V increased. The presence of Gd (6% Gd2O3) in the solid UO2 phase did not
seem to have effect on the release of U. Under reducing conditions with an iron strip in solution,
the [238U] in solution was in many cases below the detection limit (8 ˜ 10-11 M). The calculated
238
U release, that was based on the 235U/238U changes during the test periods (60, 120 and 160
days), was higher, and increased with the SA/V. Additional tests with longer dissolution periods
are needed to confirm the effect of SA/V.
During the dissolution tests with 233U-doped UO2 samples no effects that could be attributed to the
alpha radiolysis could be observed. A low SA/V (5…7 m-1) was used in these tests due to the
small amount of the 233U-doped solid samples available for the tests. The tests showed the strong
effect of redox conditions on the results. Dissolution rates were evaluated based on the changes in
the 235U/238U ratios during the tests. They ranged between 0.7 and 1.9 ppm/yr (ppm=µg/gUO2)
under anoxic conditions (1 ppm S2-). Under reducing conditions with Fe, the corresponding rates
were 0.04 to 0.2 ppm/yr.
Avainsanat - Keywords
uranium dioxide, UO2, dissolution rate, alpha activity, 233U, alpha radiolysis, NaCl, anoxic
conditions, reducing conditions
ISBN
ISSN
ISBN 951-652-148-7
Sivumäärä – Number of pages
87
ISSN 1239-3096
Kieli – Language
English
Posiva-raportti – Posiva Report
Raportin tunnus – Report code
POSIVA 2006-08
Posiva Oy
FI-27160 OLKILUOTO, FINLAND
Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)
Tekijä(t) – Author(s)
Julkaisuaika – Date
Joulukuu 2006
Toimeksiantaja(t) – Commissioned by
Kaija Ollila, VTT
Posiva Oy
Nimeke – Title
Säteilyttämättömän UO2:n ja 233U-alfasäteilijää sisältävän UO2:n liukenemisnopeudet 0.01 M
NaCl-liuoksessa hapettomissa ja pelkistävissä olosuhteissa
Tiivistelmä – Abstract
Tässä raportissa on esitetty tuloksia liukenemiskokeista, joissa tutkittiin säteilyttämättömän UO2:n ja
alfasäteilijää sisältävän UO2:n liukenemisnopeutta 0.01 M NaCl-liuoksessa. 233U-alfasäteilijän määrät
(5, 10%) oli valittu siten, että ne simuloivat käytetyn polttoaineen alfa-aktiivisuutta 3 000 ja 10 000
vuotta loppusijoituksen jälkeen. Liukenemisnopeudet mitattiin käyttäen isotooppilaimennusmenetelmää tavoitteena vähentää saostumisilmiöiden ja sorption aiheuttamia epävarmuuksia
liukenemismittauksissa. Mittauksia tehtiin hapettomissa (N2, 1 ppm S2-) ja pelkistävissä (N2, Fe)
olosuhteissa. Kiinteän UO2 faasin pinta-alan ja eluutioliuoksen tilavuuden suhteen (SA/V) vaikutusta
tutkittiin kokeissa säteilyttämättömällä UO2:lla. Tutkimus on osa EU:n kuudenteen puiteohjelmaan
kuuluvaa NF-PRO projektia (NF-PRO/F16W-CT-2003-02389).
Hapettomissa olosuhteissa (N2, 1 ppm S2-) 238U-pitoisuudet liuoksessa pysyivät matalina ja
tasoittuivat nopeasti kokeen alussa. Liuoksessa mitatut 235U/238U-isotooppisuhteen muutokset ajan
funktiona viittaavat siihen, että U:n liukenemisnopeus on korkeampi kuin mitä liuoksessa mitatut
238
U-pitoisuudet osoittavat ja U:n saostumista tapahtuu samanaikaisesti. 235U/238U-suhteen muutoksesta laskettu U:n vapautuminen kasvoi, kun SA/V kasvoi. Gadoliniumia sisältävällä UO2:lla (6%
Gd2O3) suoritettujen kokeiden tulokset eivät eronneet merkittävästi UO2:lla suoritetuista kokeista.
Metalliraudan aiheuttamissa pelkistävissä olosuhteissa 238U-pitoisuudet olivat enimmäkseen alle
määritysrajan (8 ˜ 10-11 M). Samoin kuin hapettomissa olosuhteissa, 235U/238U-isotooppisuhteen muutokset viittaavat siihen, että U:n liukenemisnopeus on korkeampi. U saostuu tai sorboituu pinnoille
koeastiassa. U:n vapautuminen kasvoi, kun SA/V kasvoi. Liukenemiskokeiden kestot olivat kuitenkin
suhteellisen lyhyitä (60, 120 ja 160 p) ja tarvitaan kokeita pidemmillä koeajoilla vahvistamaan UO2:n
pinta-alan vaikutusta.
233
U-alfasäteilijää sisältävällä UO2:lla suoritetuissa kokeissa ei havaittu alfa-radiolyysin vaikutusta
tuloksiin. Toisaalta, kokeissa käytettiin hyvin matalaa SA/V-suhdetta (5…7 m-1), koska käytettävissä
oleva kiinteän faasin määrä oli pieni. Kokeissa näkyi voimakkaasti redox-olosuhteiden vaikutus
tuloksiin. UO2 näytteiden liukenemisnopeudet arvioitiin perustuen kokeiden aikana liuoksessa
mitattuihin 235U/238U-suhteen muutoksiin. Nopeudet vaihtelivat 0.7…1.9 ppm/v (ppm= µg/gUO2)
hapettomissa olosuhteissa (1 ppm S2-), ja 0.04…0.2 ppm/v pelkistävissä olosuhteissa.
Avainsanat - Keywords
uraanidioksidi, UO2, liukenemisnopeus, alfa-aktiivisuus, 233U, alfa-radiolyysi, NaCl, hapettomat
olosuhteet, pelkistävät olosuhteet
ISBN
ISSN
ISBN 951-652-148-7
Sivumäärä – Number of pages
87
ISSN 1239-3096
Kieli – Language
Englanti
1
TABLE OF CONTENTS
ABSTRACT
TIIVISTELMÄ
1
INTRODUCTION .................................................................................................... 3
2
EXPERIMENTAL METHODS ................................................................................. 5
2.1
Isotope dilution technique ............................................................................... 5
2.2
UO2 solid phases ............................................................................................ 5
2.3
Dissolution procedure ..................................................................................... 6
3
DISSOLUTION EXPERIMENTS WITH UNIRRADIATED UO2 ............................... 9
3.1
Pretreatment of UO2 samples ......................................................................... 9
3.2
Isotope dilution tests under anoxic conditions (N2) ....................................... 10
3.3
Isotope dilution tests under anoxic conditions (N2), 1ppm S2- ....................... 14
3.4
Isotope dilution tests under reducing conditions (Fe).................................... 17
4
DISSOLUTION EXPERIMENTS WITH 233U-DOPED UO2 ................................... 23
4.1
Isotope dilution tests under anoxic conditions (N2), 1ppm S2- ....................... 23
4.2
Isotope dilution tests under reducing conditions (Fe).................................... 28
5
SUMMARY AND DISCUSSION............................................................................ 35
REFERENCES ............................................................................................................. 37
ACKNOWLEDGEMENTS............................................................................................. 39
APPENDICES 1 - 24 .................................................................................................... 41
2
3
1
INTRODUCTION
Spent fuel arising from the operation of nuclear power reactors, e.g. in Finland and
Sweden, is planned to be disposed of in a repository to be constructed at a depth of
about 500 metres in crystalline granitic bedrock. At the end of its use, the fuel contains
about 4% by weight of fission products and about 1% of actinides with atomic number
higher than 92, the atomic number of U. In order to asses the safety of the geologic repository we need to be able to predict how much of the spent fuel might dissolve if it
comes in contact with water many years after its disposal.
It is impossible to test directly the dissolution rate of spent fuel under the conditions
expected at the time of first water contact hundreds of thousands of years after disposal.
The fuel that we have available to test has radiation levels that are much higher than
those that are relevant and the radiation type is different from that which will be important in the long term. The level of radioactivity in spent fuel decreases with time. The
fission products decay by emission of E- and J-radiation, while the decay of the actinides is dominated by D-decay. The total radiation emitted by spent fuel in the first
hundred years after discharge from the reactor is predominantly due to E- and Jradiation; for later times, the dominant activity is D-radiation (Shoesmith, 2000). Since
we do not have 100 year old spent fuel available to test, we must use substitute materials that can give insight into the effects of D-radiation on the dissolution rate of spent
fuel. We have chosen to use UO2 doped with 233U to simulate the degree of D-radiation
that will be present in spent fuel at 3,000 and 10,000 years after disposal.
It is difficult, if not impossible, to establish in a laboratory the redox conditions appropriate to the geologic repository. The best inert atmosphere glove boxes have [O2] on
the order of 0.1 ppm. That means that the O2 partial pressure is 10-7 atm, a value that is
very far from the 10-65 atm needed to ensure the thermodynamic stability of UO2. We
can lower the oxygen fugacity in test solutions by using buffer materials, but this can
also interfere with the reactions we wish to monitor. Even in the presence of buffers,
stray oxygen that diffuses into the test solution might react with the UO2 before it can
react with the buffer. This means that great care must be used in the interpretation of
experimental results and that measured [U] in solutions will be upper limits compared
with those to be expected in the repository (Werme et al. 2004). The conditions inside
the disposal canister caused by corrosion of iron can be simulated by adding metallic
iron to the test system. In general, the proportions of Fe relative to UO2 in the test system will be less than those for disposal conditions, so the effects of this difference must
be estimated.
The final objective of this experimental study is to investigate the role of solution composition and ionic strength in control of reaction rates and equilibrium state in highionic strength NaCl and NaCaCl solutions, and the effect of alpha-radiation on the dissolution rate of UO2. The ionic strength in the experiments is ranging from 0.01 to 1 M.
The measurements for dissolution rates are conducted under anoxic conditions in N2
atmosphere, and under reducing conditions produced by corroding iron. The experiments are the continuation of work begun in the In Can Processes Project supported by
the European Commission under the 5th Framework Programme (Ollila et al. 2004). All
4
the experiments described in this report were performed in dilute NaCl solution
(0.01 M). The objective of these preliminary tests is to develop methods for the measurements in high-ionic strength solutions.
5
2
EXPERIMENTAL METHODS
2.1 Isotope dilution technique
The isotope dilution technique, which is used in geochemistry to measure the concentration of elements in natural samples, can be used to determine whether a solid in contact
with solution is continuing to dissolve and reprecipitate even though the solution concentration is constant, or even decreasing.
The dissolution test of the solid UO2 sample is started in a solution that has a U content
near to that expected at equilibrium or steady state, but a 235U/238U isotopic ratio far
from that of the solid sample. As the solid sample dissolves, the material entering into
the solution has a different 235U/238U ratio from that of the original solution. Even if
precipitation occurs, the change in isotopic ratio will give the amount of the material
processed through the solution. For each measurement point we have a starting [U] and
isotopic composition of the system based on the last measurement point. From this we
can calculate the initial amounts of 235U and 238U in the solution. When the next sample
is taken and the [U] and 235U/238U in the solution are measured, we use the isotopic ratio
to calculate how much 235U and 238U have been added to the solution.
235
U/238Umeasured = (235Uinitial + 235Udissolved) / (238Uinitial + 238Udissolved)
We compare the results of the calculations with the measured concentration of each
isotope. This shows whether precipitation is occurring.
A standard reference material, U3O8, with a 235U/238U ratio of 10.354 r 0.758 was used
for the spike. The U3O8 was dissolved in acid (1 M HNO3). The spike solution was
deaerated and stored under N2 atmosphere in the glove box. An aliquot of the diluted
spike solution was added to leaching solutions.
2.2 UO2 solid phases
The undoped UO2 pellets used were commercial fuel pellets prepared by ABB and contained 2.8 % 235U. The pellets were gently crushed to fragments. The material in the size
range 1.4 to 4 mm was used in the experiments. The UO2 fragments doped with 233U
were produced by BNFL (British Nuclear Fuel Limited). The fragments were in the
size range 1.4 to 4 mm. The nominal isotopic composition of the UO2 samples is given
in Table 1. Two tests were also conducted with 6 wt% Gd2O3 doped UO2. The Gd2O3
doped UO2 pellets were prepared by ABB Atom. The pellets were crushed to fragments
(1.4 to 4 mm) for the tests.
6
Table 1. Isotopic composition of UO2 samples.
UO2 sample
0%
0%
5%
10%
[233U]
(%)
0
0
5.0
10.0
[235U]
(%)
2.82
0.71
4.5
4.5
[238U]
(%)
97.18
93.29
90.5
85.5
Gd2O3
(%)
6
-
235
U/238U
0.029
0.007
0.050
0.053
2.3 Dissolution procedure
The method of the dissolution experiments was a static batch dissolution procedure. The
solid UO2 samples were placed on a fused silica 'saucer', which was immersed in 0.01
M NaCl solution in Nalgene bottles made of polypropylene. An aliquot of spike solution was added. The total U added was ranging from 0.4 to 1.2 ppb U. Samples were
taken periodically for the analyses of [238U] and 235U/238U with ICP-MS. The duration
of the tests ranged from 20 days to 6 months. At the end of the selected tests, the remaining leaching solution after sampling was transferred to a new vessel, acidified (1 M
HNO3), and allowed to equilibrate with the acid. The purpose of this was to dissolve
any possible colloidal material or precipitate. The test vessel was rinsed with deionized
water three times. The rinse solutions were collected in a separate vessel and acidified
(1 M HNO3). 1 M nitric acid was added to the test vessel and allowed to dissolve any
precipitated or sorbed material. The saucer was rinsed with deionized water in an attempt to remove small grains that may have dislodged from the original solid. After
this, the saucer was placed in a new vessel and 1 M nitric acid was added to desorb the
U. Samples were taken from the acidified leaching solution, from the rinse solution of
the test vessel and from the acid strip solutions of the test vessel and the saucer for U
concentration and the isotopic ratio.
Previous tests with undoped and 233U-doped UO2 fragments in modified Allard
groundwater used 1 gram of fragments of solid phase in 50 ml of aqueous phase. The
ratio of UO2 geometric surface area to solution volume (SA/V) was 4 m-1 in all tests.
This resulted in very low U concentrations in the aqueous phase under reducing conditions (Ollila et al. 2004). In the measurements in 0.01 M NaCl solution, the SA/V was
increased, being 13 and 67 m-1 in the tests with UO2 fragments. Tests were also conducted with intact UO2 pellets, the SA/V being 11 and 44 m-1.
Two redox environments were used: 1) anoxic conditions under N2 atmosphere, and
2) reducing conditions achieved through the inclusion of an actively corroding iron strip
(1.5 x 3 cm) in the solution (30-40 ml). After the immersion of the iron strip in solution,
the Eh of the solution dropped rapidly to a low value, staying near - 0.4 V (relative to
the standard hydrogen electrode scale, SHE). The pH increased to 9.2 from the initial
value of 8.3. In the tests under anoxic conditions (N2), the pH stability of the solution
caused problems. It decreased from the original value of 8.3 to below 6. This is probably due to the dissolution of U and the subsequent formation of U hydroxide complexes
in the weakly buffered solution. The aqueous U concentrations increased to 10-7 ... 10-6
mol/l under these conditions. In order to stabilize the pH, 1 ppm sulfide (S2-) was added
7
as pH buffer (HS-/S2-) to the solution in the dissolution tests with longer duration.
HS-/S2- is known to be a common weak acid-base in natural waters. The addition of
sulfide also reduces the Eh of the solution (a - 0.2 V). In the restarted tests with sulfide,
the pH stayed at 8.5 ... 9.
The experimental conditions for the preliminary isotope dilution tests with undoped
UO2 samples are shown in Appendix 1. The tests under reducing conditions were conducted in triplicate at both SA/V (13, 67 m-1). The tests under anoxic conditions were
conducted in duplicate. Additional tests were conducted with Gd-doped UO2 fragments
at SA/V= 67 m-1 under anoxic and reducing conditions. The tests with intact pellets
were performed under anoxic contitions (SA/V= 11, 44 m-1).
8
9
3
DISSOLUTION EXPERIMENTS WITH UNIRRADIATED UO2
3.1 Pretreatment of UO2 samples
A pretreatment was performed for the solid samples prior to the start of the isotope dilution tests to remove any layer of oxidized or loose material that might have formed on
the samples during storage and handling under atmospheric conditions. The pretreatment steps consisted of a series of exposures of the solid samples to test solution (0.01
M NaCl) with the same composition as intended for the isotope dilution tests, with exposure times of 1 to 13 days under anoxic conditions in the absence of Fe, and with exposure times of 20 and 10 days in the presence of Fe. A similar SA/V was used as later
in the isotope dilution tests.
The results of solution analyses for U at the end of pretreatment periods in deaerated
0.01 M NaCl under anoxic conditions (N2) are given in Appendix 2, and in deaerated
0.01 M NaCl under reducing conditions in the presence of Fe strip are given in Appendices 3 and 4. The ferrous iron (Fe2+) and total Fe concentrations were also measured at
the end of the selected pretreatment periods with Fe in order to see the level of Fe(II)
ions in the leaching solutions , see Appendix 5. A ferrozine method was used (Dimmock et al. 1979).
The U concentration in solution decreased slowly in the sequential leaching periods in
the absence of Fe, being 0.2 ... 3.6 ppb in the last period of 2 days. The U concentration
in solution is higher at higher SA/V. The Gd-doped UO2 samples seemed to dissolve a
little slower. Higher [U] was measured in the predissolution periods for intact UO2 pellets than for UO2 fragments.
In the pretreatment periods with an iron strip in solution, the [U] in solution decreased,
but still showed a difference between the two SA/V, see Appendices 3 and 4. At the end
of these periods, the remaining leaching solutions after sampling were transferred to
new bottles, and the UO2 samples were transferred to new saucers and they were placed
in new test vessels with fresh leachant for the start of the new period. The used test vessels were rinsed (H2O) and acid stripped (1 M HNO3). The used saucers were acid
stripped separately. The resulting solutions were analyzed for U. After equilibration
with the acid for one week, the [U] in the leaching solutions was higher than in the first
samplings with U measurements within one day, see Appendices 3 and 4. The [U] in the
rinse and acid strip solutions of the test vessels was at the same level or higher than in
the leaching solutions. It is possible that the [U] in the acid strip solutions of the saucers
may contain some U dislodged from the original UO2 solid. In order to minimize this
the saucers were rinsed quickly with deionized water before acid stripping in order to
remove small particles as well as possible. This rinse solution was discarded. The total
recovered U in each test vessel has been calculated in Appendices 6 and 7 for both
leaching periods with Fe. The total U was also calculated excluding the U from saucers
for comparison. Table 2 gives the U in solution and the total recovered U for the UO2
samples vs. SA/V. The results show that the main part of U was in colloids, precipitates
or sorbed on the surfaces of the test vessel. When comparing the results at lower and
higher SA/V there is a clear difference in total recovered U. The difference seems to be
directly proportional to SA/V in the last leaching period of 10 days. The difference is
10
similar for UO2 pellets and fragments. The Gd-doped UO2 fragments act in the similar
way as the undoped UO2 fragments.
Table 2. U in solution and total recovered U under reducing conditions (Fe).
Sample
code
L1
L2
L3
L4
L5
H1
H2
H3
H4
H5
H6
H7
L6
H8
Solid UO2 sample/
30 ml 0.01 M NaCl
2 g UO2 fragments
"
"
"
"
10 g UO2 fragments
"
"
"
"
10 g (Gd,U)O2 fragments
"
1 UO2 pellet
4 UO2 pellets
SA/V
(m-1)
13
"
"
"
"
67
"
"
"
"
67
"
11
44
20 d
Solution
U (Pg)
0.001
0.001
0.001
0.010
0.003
0.005
0.004
0.003
0.013
0.011
0.002
0.003
0.022
0.052
10 d
Solution
U (Pg)
0.001
0.001
0.001
0.002
0.002
0.006
0.005
0.006
0.032
0.012
0.004
0.007
0.010
0.017
20 d
Total
U (Pg)
0.20
0.24
0.17
0.30
0.23
0.66
0.61
0.42
0.68
0.62
0.59
0.40
1.21
2.66
10 d
Total
U (Pg)
0.12
0.14
0.11
0.12
0.15
0.54
0.61
0.56
0.68
0.54
0.61
0.49
0.40
1.54
The determination of the ferrous (Fe2+) and the total iron concentrations in the leaching
solutions was performed at the end of the sequential pretreatment periods with Fe strip.
The results are given in Appendix 5. The Fe2+ in the sample was measured with the
ferrozine method (Dimmock et al. 1979). The total Fe was determined with the reduction of all the Fe in the sample to the Fe2+ state and the subsequent measurement of the
Fe2+ with the ferrozine method. The Fe3+ concentration can be calculated subtracting the
Fe2+ concentration from the total Fe concentration. The measured Fe2+ concentrations
ranged from 0.02 to 0.13 ppm. The total Fe concentrations were higher than the Fe2+
concentrations in many cases suggesting the presence of the Fe3+ in the solutions.
3.2 Isotope dilution tests under anoxic conditions (N2)
Two test series (I, II) were conducted consecutively under N2 atmosphere in 0.01 M
NaCl solution. Both test series included tests in duplicate at SA/V= 13 m-1 and 67 m-1
with UO2 fragments, one test with 6 wt% Gd2O3 doped UO2 fragments at SA/V= 67 m1
, one test with UO2 pellets at SA/V= 11 m-1 and one test with UO2 pellets at SA/V= 44
m-1. The leaching solutions were spiked in the first test series with 0.4 ppb U (235U/238U
ratio of 10.354 ± 0.758). The duration of the test series was 20 days. The detailed results
are given in Appendix 8. The table shows the measured [238U], 235U/238U in the samples
which were taken from the leaching solutions 1, 4 and 20 days after the start of the dissolution tests, and the [238U] calculated from the isotopic ratio change. The measured
isotopic ratio is given as the average of four ICP-MS injections.
The measured [238U] in the leaching solutions (App. 8) ranged from 0.7 to 12.7 ppb. It
was highest in the tests with pellets at higher SA/V. The 235U/238U ratio of the leaching
11
solution decreased rapidly and approached to that of the solid (0.029 for undoped UO2,
0.007 for Gd-doped UO2) at the end of all tests. The [238U] in the solutions stayed at the
same level vs. time. The comparison of the measured data with the data calculated from
the change in the isotopic ratio suggest the precipitation of U to occur. The calculated
[238U] is higher in all tests and is increasing until the end of the experimental time, see
Figures 1-3. Precipitation would seem to begin during the first days of the tests. The
calculated [238U] release increased with the SA/V.
The measured low values for isotopic ratios at the end of the first test series suggested
that the initial spike additions (0.4 ppb U) were too low. Consequently, a test series with
a higher amount of the spike, 1.2 ppb U, was restarted using the same solid samples.
Regardless of that, there was still a rapid decrease in isotopic ratio, see Appendix 9. The
measured [238U] was higher than in the first test series. The reason for the relatively
high U concentrations under these conditions was probably the instability of the pH in
the leaching solutions. The pH measurements at the end of the tests showed that pH
decreased during both contact periods from the original value of 8.3, more drastically in
the second period, see Table 3. After this, a conclusion was drawn that the addition of a
pH buffer is necessary. Sulfide, 1 ppm S2-, was added to leaching solutions in the dissolution tests with longer duration.
40
UO2 fragments,
35
SA/V = 13 m-1
[238U], ppb
30
25
20
15
10
5
0
0
5
10
15
20
25
Time, days
Figure 1. Comparison of measured [238U] (open symbols) and [238U] calculated from
the isotopic ratio changes (filled symbols). The results are data for a test in duplicate
with UO2 fragments in 0.01 M NaCl under N2 atmosphere.
12
40
UO2 fragments,
(Gd, U)O2 fragments,
[238U], ppb
-1
30 SA/V = 67 m
20
10
0
0
5
10
15
20
25
Time, days
Figure 2. Comparison of measured [238U] (open symbols) and [238U] calculated from
the isotopic ratio changes (filled symbols). The results are data for a test in duplicate
with UO2 fragments (triangles) and for a test with Gd-doped UO2 fragments (circles) in
0.01 M NaCl under N2 atmosphere.
40
UO2 pellets,
SA/V= 11 m-1
[238U], ppb
30
20
10
0
0
5
10
15
20
25
Time, days
Figure 3. Comparison of measured [238U] (open symbols) and [238U] calculated from
the isotopic ratio changes (filled symbols). The results are data for a test with UO2 pellets in 0.01 M NaCl under N2 atmosphere.
13
Table 3. Measured pH and [U] at the end of the isotope dilution tests in 0.01 M NaCl
under N2 atmosphere.
Solid sample
SA/V (m-1)
Test series I (20 d)
pH
UO2 fragments
"
"
"
(Gd,U)O2 fragments
UO2 pellets
"
13
"
67
"
"
11
44
6.8
7.0
7.8
7.0
7.6
6.8
7.2
238
U
(ppb)
1.2
1.0
5.4
2.6
1.1
5.1
9.5
Test series II (18 d)
pH
5.6
5.3
5.7
5.6
5.3
5.3
5.3
238
U
(ppb)
9.6
18.5
47.1
32.4
12.2
22.4
53.1
14
3.3 Isotope dilution tests under anoxic conditions (N2), 1ppm S2After this, a test series with the same solid samples was restarted in fresh leaching solutions containing 1 ppm S2-. The samples for analyses were taken at longer intervals after
the start of the experiments: 12, 29, 56, 109, 161 and 250 days. The addition of spike
was 0.8 ppb U.
The [238U] decreased in the leaching solutions, staying below 1 ppb in all samples except in the 29 days sample (2.8 ppb) in the test with pellets, SA/V= 44 m-1 and in the
250 days sample (1.7 ppb) in the test with fragments, SA/V= 67 m-1, see Appendices 10
and 11. The decrease in the 235U/238U ratio was slower than in the previous tests without
sulfide. This is expected because the addition of sulfide also reduces the Eh of the solution. The measured Eh was - 0.2 V. The 235U/238U of the solution reached that of the
solid in the higher SA/V test with pellets after 56 days. Hence, it was not possible to see
the change in the ratio between 56 and 250 days. The comparison of the measured 238U
data with the calculated data suggests precipitation in all tests (Figures 4-6). There is
some scatter in the calculated data of the tests with fragments at higher SA/V. The
measured data for parallel tests are in good agreement. The presence of Gd in the solid
UO2 phase does not seem to have effect on the results. There is a clear influence of the
SA/V on the calculated [238U], see Figure 7. The calculated [238U] increases as the SA/V
increases. It increases in all tests until the end of the experimental time. The measured
data also show small difference vs. SA/V, see Figure 8. The pH stayed between 8.5 and
9 in the tests.
10
UO2 fragments
SA/V= 13 m-1
[238U], ppb
8
6
4
2
0
0
50
100 150 200 250 300
Time, days
Figure 4. Measured [238U] (open symbols) and [238U] calculated from the isotopic ratio
changes (filled symbols). The results are data for a test in duplicate with UO2 fragments
in 0.01 M NaCl (1 ppm S2-) under anoxic conditions.
15
140
[238U], ppb
UO2 fragments,
120 (Gd,U)O fragments
2
-1
100 SA/V= 67 m
80
60
40
20
0
0
50
100 150 200 250 300
Time, days
Figure 5. Measured [238U] (open symbols) and [238U] calculated from the isotopic ratio
changes (filled symbols). The results are data for a test in duplicate with UO2 fragments (triangles) and for a test with Gd-doped UO2 fragments (circles) in 0.01 M NaCl
(1 ppm S2-) under anoxic conditions.
60
UO2 pellets
SA/V= 11 m-1
[238U], ppb
50
40
30
20
10
0
0
100
200
300
400
500
Time, days
Figure 6. Measured [238U] (open symbols) and [238U] calculated from the isotopic ratio
changes (filled symbols). The results are data for a test with UO2 pellets in 0.01 M NaCl
(1 ppm S2-) under anoxic conditions.
16
100
Calculated [U]
[238U], ppb
80
60
-1
SA/V= 67 m
40
20
-1
SA/V= 13 m
0
0
50
100 150 200 250 300
Time, days
Figure 7. Calculated [238U] in the leaching solution vs. SA/V. The results are average
data for tests in duplicate with UO2 fragments in 0.01 M NaCl (1 ppm S2-) under anoxic
conditions.
3.0
Measured [U]
[238U], ppb
2.5
2.0
1.5
1.0
-1
SA/V= 67 m
0.5
SA/V=13 m
-1
0.0
0
50
100 150 200 250 300
Time, days
Figure 8. Measured [238U] in the leaching solution vs. SA/V. The results are average
data for tests in duplicate with UO2 fragments in 0.01 M NaCl (1 ppm S2-) under anoxic
conditions.
17
3.4 Isotope dilution tests under reducing conditions (Fe)
Tests under reducing conditions included tests in triplicate both at SA/V= 13 m-1 and 67
m-1 with UO2 fragments, and one test with Gd-doped UO2 fragments in 0.01 M NaCl
with an iron strip in solution, see Appendices 12 and 13. All tests used fresh iron strips.
The leaching solutions were spiked with 0.8 ppb U.
The measured [238U] in small aliquots that were taken for analyses was at or below the
detection limit of the analytical method (0.02 ppb) in all tests at SA/V= 13 m-1. At
SA/V= 67 m-1, the [238U] was also close to the detection limit but measurable in most
samples. The isotopic ratio measurements caused problems because the [235U] was close
to the detection limit. A conclusion was drawn that it is not possible to measure the
change in the isotopic ratio vs. time by taking small samples at regular intervals under
these conditions.
The earlier tests in Allard groundwater under similar conditions with an iron strip in
solution had shown that the leaching solutions were inhomogeneous at the end of the
contact periods, and U sorbed or precipitated on the surfaces in test vessels was found
(Ollila et al. 2004). In order to study the amount of precipitation and sorption in 0.01 M
NaCl, tests at both SA/V were terminated after the contact times of 60, 120 and 160
days. The remaining leaching solutions after sampling were transferred to new bottles,
acidified (1 M HNO3) and allowed to equilibrate for a week. The UO2 samples were
transferred to new saucers and they were placed in new test vessels with fresh leachant
and an iron strip. The used test vessels were rinsed with deionized water, and acid
stripped with 1 M HNO3. The used saucers were rinsed with deionized water before
acid stripping with HNO3 in order to remove small particles of original UO2 solid as
well as possible. This rinse solution was discarded. The elution of U from the iron strips
was performed with NaHCO3 solution (250 ppm HCO3) under atmospheric conditions.
All these solutions were analysed for [238U], the leaching solutions and the acid strip
solutions also for 235U/238U. The U contents were measurable in all solutions. Tables 4-6
give the measured 238U amounts found in the test vessel in different solutions. The isotopic ratios were also well measurable. The measured ratios for the rinse solutions
showed more scatter in the four injections than the ratios for the other solutions. The
isotopic ratio measurements for different solutions in each test were in agreement. The
results show that it is possible to calculate the U release based on changes in the isotopic ratios measured for these solutions. The recovered total 238U from the test vessel
and calculated total 238U are at the same level in each test. This shows that minimal precipitation of the spike onto the solid UO2 sample occurred and no effect of ion exchange
was detected. The majority of U recovered was found in the acid strip solutions of the
test vessels and saucers, and in the elution solutions of the Fe strips.
There was not a clear trend in the calculated total 238U release vs. the length of the dissolution period. The U release increased, as the SA/V was increased from 13 m-1 to 67
m-1. Tests with longer contact times are needed to confirm the results.
18
Table 4. Measured and calculated total 238U release in tests. The results are data for
tests with UO2 fragments in 0.01 M NaCl under reducing conditions (Fe). Test duration:
60 days.
SA/V= 13 m-1
Leaching solution
(after equilibration
with acid)
Rinse solution of
the test vessel
Acid strip solution
of the test vessel
Acid strip solution
of the saucer
Elution solution of
the Fe strip
6
Measured
total 238U
µg/test
Measured
235
U/238U
Measured
235
U/238U
Std Dev (%)
Calculated
total 238U
µg/test
0.003
0.1022
3.2
0.3
0.009
0.1065
8.6
0.3
0.08
0.1345
0.7
0.2
0.13
-
-
-
0.05
-
-
-
0.3
average: 0.3
SA/V= 67 m-1
Leaching solution
(after equilibration
with acid)
Rinse solution of
the test vessel
Acid strip solution
of the test vessel
Acid strip solution
of the saucer
Elution solution of
the Fe strip
6
Measured
total 238U
µg/test
Measured
235
U/238U
Measured
235
U/238U
Std Dev (%)
Calculated
total 238U
µg/test
0.02
0.0512
1.3
1.0
0.04
0.0495
17
1.1
0.40
0.0430
1.1
1.6
0.21
-
-
-
0.39
-
-
-
1.1
average: 1.2
19
Table 5. Measured and calculated total 238U release in tests. The results are data for
tests with UO2 fragments in 0.01 M NaCl under reducing conditions (Fe). Test duration: 120 days.
SA/V= 13 m-1
Leaching solution
(after equilibration
with acid)
Rinse solution of
the test vessel
Acid strip solution
of the test vessel
Acid strip solution
of the saucer
Elution solution of
the Fe strip
6
Measured
total 238U
µg/test
Measured
235
U/238U
Measured
235
U/238U
Std Dev (%)
Calculated
total 238U
µg/test
0.01
0.0663
5.0
0.6
0.05
0.0560
3.6
0.8
0.24
0.0648
8.4
0.6
0.08
-
-
-
0.09
-
-
-
0.5
Average: 0.7
SA/V= 67 m-1
Leaching solution
(after equilibration
with acid)
Rinse solution of
the test vessel
Acid strip solution
of the test vessel
Acid strip solution
of the saucer
Elution solution of
the Fe strip
6
Measured
total 238U
µg/test
Measured
235
U/238U
Measured
235
U/238U
Std Dev (%)
Calculated
total 238U
µg/test
0.11
0.0461
4.2
1.3
0.04
0.0405
6.9
1.9
1.08
0.0424
1.1
1.6
0.51
-
-
-
0.075
-
-
-
1.8
Average: 1.6
20
Table 6. Measured and calculated total 238U release in tests. The results are data for
tests with UO2 fragments in 0.01 M NaCl under reducing conditions (Fe). Test duration: 160 days.
SA/V= 13 m-1
Leaching solution
(after equilibration
with acid)
Rinse solution of
the test vessel
Acid strip solution
of the test vessel
Acid strip solution
of the saucer
Elution solution of
the Fe strip
6
Measured
total 238U
µg/test
Measured
235
U/238U
Measured
235
U/238U
Std Dev (%)
Calculated
total 238U
µg/test
0.002
0.1777
13.7
0.1
0.01
0.1401
10.7
0.2
0.14
0.0850
1.8
0.4
0.04
-
-
-
0.001
-
-
-
0.2
Average: 0.2
SA/V= 67 m-1
Leaching solution
(after equilibration
with acid)
Rinse solution of
the test vessel
Acid strip solution
of the test vessel
Acid strip solution
of the saucer
Elution solution of
the Fe strip
6
Measured
total 238U
µg/test
Measured
235
U/238U
Measured
235
U/238U
Std Dev (%)
Calculated
total 238U
µg/test
0.03
0.0461
4.2
1.3
0.04
0.0405
6.9
1.9
0.40
0.0424
1.1
1.6
0.39
-
-
-
0.09
-
-
-
1.0
Average: 1.3
21
Table 7. Measured and calculated total 238U release vs. the length of the dissolution
period: ID tests with UO2 fragments in 0.01 M NaCl under reducing conditions (Fe).
Duration of the test
days
60
120
160
SA/V= 13 m-1
total 238U, µg
Measured
Calculated
0.3
0.3
0.5
0.7
0.2
0.2
SA/V= 67 m-1
total 238U, µg
Measured
Calculated
1.1
1.2
1.8
1.6
1.0
1.3
22
23
4
DISSOLUTION EXPERIMENTS WITH 233U-DOPED UO2
The isotope dilution tests with the UO2 samples doped with 233U (see Table 1, p. 4)
were performed similarly with the previous tests with the unirradiated UO2 samples.
The 233U-doped samples were the same solid samples which were used earlier in the
dissolution tests of the In Can Processes project (Ollila et al. 2004, Ollila & Oversby
2005, 2006). Those tests were performed in dilute synthetic bicarbonate groundwater.
The preceding test series before the tests of this study were conducted in the presence of
Fe strip.
Two test series (I, II) were conducted consecutively in 0.01 M NaCl solution first under
anoxic conditions with 1 ppm S2- in solution, which was followed by two test series (I,
II) consecutively under reducing conditions with an iron strip in solution.
A lower SA/V of 5–7 m-1 was used in these tests than in the previous tests with unirradiated UO2 samples of this study (Ch. 3). This was due to the small amount of the 233Udoped UO2 samples available for tests (1 g). Parallel tests were performed with unirradiated UO2 samples using a similar SA/V in each test series.
4.1 Isotope dilution tests under anoxic conditions (N2), 1ppm S2In the first test series, 1 g of each UO2 solid sample was immersed in 30 ml of 0.01 M
NaCl (1 ppm S2-), see Appendix 14. The samples for analyses were taken at the following times after the start of the experiments: 3, 57, 84 and 124 days. The long sampling
interval at the early stages of the tests was caused by the difficulties with the ICP-MS.
The addition of spike was 0.8 ppb U.
The measured 238U concentrations in small aliquots (2 ml) that were taken for analyses,
were lower than the measured concentrations in the tests with unirradiated UO2 samples
under similar conditions (Appendices 10-11). The [238U] was below the detection limit
in all samples, except in the first sampling. An attempt was made to measure the
235
U/238U ratios with ICP-MS using the micronebulizer, which improves the sensitivity
of the measurement. It was possible to measure the ratios, but the standard deviation
was high (6…44 %), see Appendix 14. The values should be taken as tentative ones. At
the end of the tests, the leaching solutions were removed from the test vessels and the
solid samples were transferred to new test vessels for a start of a new dissolution period.
The leaching solutions were equilibrated with acid, the test vessels and saucers of the
first dissolution period were rinsed with deionized water and acid stripped, and the resulting solutions were analysed for 238U and 235U/238U, similar to the methods used in
the reducing conditions tests of unirradiated UO2 samples (Ch. 3) , see the Appendix
15. The [238U] was still low but measurable in all these solutions. The measured values
for 235U/238U show that dissolution has happened. Figure 9 gives the measured and calculated [238U] data vs. time for the test in duplicate with the 5 % 233U-doped sample.
The difference between measured and calculated data is small. It is increasing towards
the end of the test. The calculated [238U] at different doping levels: 0% (unirradiated
UO2), 5 and 10% 233U-doped UO2 is given in Figure 10. No increase was seen vs. the
doping level.
24
The reason for the measured low 238U concentrations in the leaching solutions in this
test series, that were lower than in the tests with unirradiated UO2 samples under similar
conditions (previous chapter), may be the lower SA/V (7 m-1). On the other hand, the
preceding test series before these tests with these solid samples was conducted under
reducing conditions with iron. It is possible that the different redox conditions of the
preceding tests may have had effect on the results. A new test series was restarted under the same redox conditions (N2, 1ppm S2-) to study this.
2.0
UO2 fragments (5%
U)
233
[238U], ppb
1.5
1.0
0.5
0.0
0
20 40 60 80 100 120 140
Time, days
Figure 9. Measured [238U] (open symbols) and [238U] calculated from the isotopic ratio
changes (filled symbols) in the isotope dilution tests with 5% 233U-doped UO2 samples
(Test series I).
25
2.0
1.0
238
U, ppb
1.5
0.5
0.0
0
20
40
60
80 100 120 140
Time, days
Figure 10. Calculated [238U] vs. the doping level in the isotope dilution tests with unirradiated UO2 fragments (white symbols), 5% 233U-doped (grey symbols) and 10% 233Udoped UO2 fragments (black symbols). Results are for tests in duplicate (Test series I).
The results for the samples vs. time for the new test series are given in Appendices 16
and 17. In these tests, 1 g of each UO2 solid sample was immersed in 40 ml of 0.01 M
NaCl (1 ppm S2-) in order to increase sample volume. At least 2 ml is needed in one
sampling for analyses. The samples for analyses were taken at the following times after
the start of the experiments: 2, 13, 22, 29, 48 days. The tests were terminated after
50 days. The 238U concentrations were low but above detection limit in all samples, with
the exception of the 48 days’ sample for the 10% 233U-doped UO2 sample (1). The decrease in the 235U/238U ratio was faster than in the first series suggesting higher dissolution rate.
The measured 238U data for the 5% 233U-doped samples, compared with the calculated
data from the isotopic ratio changes are given in Figure 11.The difference between
measured and calculated data is greater with the same solid samples in these tests than
in the first test series (Figure 9). The calculated data are also higher. The results are in
better agreement with the previous tests with the unirradiated UO2 samples (e.g. Figure
4) under similar redox conditions. It is obvious that the different redox conditions of the
tests before the test series I have affected the measured data of the test series I. The mesured data in the test series II are probably more representative for the redox conditions
produced with S(II).
The data for the UO2 samples at different doping levels are compared in Figures 12–14.
The measured 238U concentrations are at the same level (” 0.2 ppb) in all tests. The
[238U] is decreasing in the beginning of the tests suggesting precipitation and stabilizes
afterwards.
26
5
UO2 fragments (5% 233U)
[238U], ppb
4
3
2
1
0
0
10
20
30
40
50
Time, days
Figure 11. Measured [238U] (open symbols) and [238U] calculated from the isotopic
ratio changes (filled symbols) in the isotope dilution test in duplicate with 5% 233Udoped UO2 samples (Test series II).
1.0
Measured [U]
[238U], ppb
0.8
0.6
0.4
0.2
0.0
0
10
20
30
40
50
Time, days
Figure 12. Measured [238U] in the leaching solutions for the unirradiated (black symbols) and 5% 233U-doped (white symbols) UO2 samples. The results are for tests in duplicate (Test series II).
27
5
Calculated [U]
[238U], ppb
4
3
2
1
0
0
10
20
30
40
50
Time, days
Figure 13. Calculated [238U] in the leaching solutions for the unirradiated (black symbols) and 5% 233U-doped (white symbols) UO2 samples. The results are for tests in duplicate (Test series II).
5
Calculated [U]
[238U], ppb
4
3
2
1
0
0
10
20
30
40
50
Time, days
Figure 14. Calculated [238U] in the leaching solutions for the 5% 233U-doped (white
symbols) and 10% 233U-doped (black symbols) UO2 samples. The results are for tests
in duplicate (Test series II).
28
The calculated [238U] is higher than the measured [238U] in all tests, and it is slowly increasing towards the end of the experimental time. The calculated [238U] data for the
unirradiated, 5% 233U-doped and 10% 233U-doped do not show any clear difference,
Figures 13-14. This does not suggest any effect of alpha radiolysis during these experiments.
An attempt was made to evaluate the total release of U in each test, Table 8. The total
238
U was calculated based on the difference between the initial 235U/238U of the spiked
leaching solution, and the measured 235U/238U ratios in the test termination samples
(Appendix 18). The total 238U release was calculated using the measured 235U/238U ratios in leaching, rinse and acid strip solutions. The average release is given in Table 8.
The total 238U amounts recovered from the test vessels are lower. This is probably
caused by the loss of material during the rinsing of the saucers. The saucers were rinsed
with deionized water prior to the acid stripping in order to rinse off small particles from
the UO2 solids. During this process, the precipitated material might have been rinsed
off. The calculated total 238U was used to calculate preliminary dissolution rates under
test conditions for the solid samples. The rates were calculated as microgram per gram
of UO2 solid (µg g-1 yr-1= ppm/yr). The values should be taken as tentative ones due to
the small amount of solid phases available for the tests. The duration of the tests was
also relatively short. No effects of radiolysis could be observed.
Table 8. Calculated total 238U dissolution per test in the isotope dilution tests in 0.01 M
NaCl (1 ppm S2-) under anoxic conditions (N2). The duration was 50 days.
UO2 sample
(1 g)
UO2 – 0% 233U (1)
UO2 – 0% 233U (2)
UO2 – 5% 233U (1)
UO2 – 5% 233U (2)
UO2 – 10% 233U (1)
UO2 – 10% 233U (2)
Calculated
total 238U, µg
0.12
0.16
0.26
0.26
0.11
0.23
6recovered
238
U, µg
0.04
0.06
0.06
0.05
0.02
0.03
Dissolution rate
ppm/yr
0.9
1.3
1.9
1.9
0.7
1.6
4.2 Isotope dilution tests under reducing conditions (Fe)
The measured data vs. time for the first and second series of tests, as well as for the test
termination samples are given in Appendices 19-21 and 22-24, respectively. 1 g of each
UO2 solid sample was immersed in 40 ml of 0.01 M NaCl with an iron strip. In the first
test series, the samples for analyses were taken at the following times after the start of
the experiments: 1, 2, 5, 13, 22 and 40 days. The test series was terminated after 125
days. In the second series of tests, the samples were taken after 1, 2, 5, 11 and 85 days.
The duration was 102 days. The addition of spike was 0.8 ppb U.
The following Figures 15, 16 and 17 give the measured [238U] in comparison with the
calculated [238U] from the isotopic ratio changes for the both test series. There are data
for the samples at the early stages of the tests, in which the U was measurable. The last
data at 125 days for test series I, and at 102 days for test series II are based on the data
29
for the test termination samples. The data for leaching solutions after equilibration with
acid was used if it was available. Otherwise the average data of the rinse and acid strip
solutions of the test vessel was used.
2.0
UO2 fragments (0%233U)
[238U], ppb
1.5
1.0
0.5
0.0
2 5
13
125
Time, days
2.0
UO2 fragments (0% 233U)
1.0
238
[ U], ppb
1.5
0.5
0.0
2 5
10
100
Time, days
Figure 15. Measured [238U] (open symbols) and [238U] calculated from the isotopic
ratio changes (filled symbols) in successive isotope dilution tests under reducing conditions (Fe) with unirradiated UO2 samples (a test in duplicate in both Figures).
Test series I: upper Figure
Test series II: lower Figure
30
2.0
UO2 fragments (5% 233U)
[238U], ppb
1.5
1.0
0.5
0.0
2 5
13
125
Time, days
2.0
UO2 fragments (5% 233U)
[238U], ppb
1.5
1.0
0.5
0.0
2 5
10
100
Time, days
Figure 16. Measured [238U] (open symbols) and [238U] calculated from the isotopic
ratio changes (filled symbols) in successive isotope dilution tests under reducing conditions (Fe) with 5% 233U-doped UO2 samples (a test in duplicate in both Figures).
Test series I: upper Figure
Test series II: lower Figure
31
2.0
UO2 fragments (10% 233U)
[238U], ppb
1.5
1.0
0.5
0.0
2 5
13
125
Time, days
2.0
UO2 fragments (10% 233U)
[238U], ppb
1.5
1.0
0.5
0.0
2 5
10
100
Time, days
Figure 17. Measured [238U] (open symbols) and [238U] calculated from the isotopic
ratio changes (filled symbols) in successive isotope dilution tests under reducing conditions (Fe) with 10% 233U-doped UO2 samples (a test in duplicate in both Figures).
Test series I: upper Figure
Test series II: lower Figure
32
In the test series I, the [238U] was low, but measurable in the first three samplings (1, 2
and 5 days), except in the 5 days sample in one test with 10% 233U-doped UO2 sample.
In the further samplings, the measured [238U] was mostly below the detection limit (Appendix 19-20). There was some scatter in the data for the test termination samples (Appendix 21). The measured data for the leaching solutions after equilibration with acid
were below detection limit. The measured data for the rinse and acid strip solutions
were not in good agreement. The reason for this is not known. It is possible that the
change in redox conditions has had an influence. The preceding test series with these
solid samples was conducted with 1 ppm S2- in solution under anoxic conditions. The
elution of the iron strips with NaHCO3 solution (250 ppm HCO3) was also performed at the end of the test series. The measured [238U] in the elution solutions was at
the detection limit of the analytical method.
The calculated [238U] in solution is higher than the measured one for all the solid samples in the test series I (Figures 15-17, upper figures) suggesting precipitation or sorption phenomena. The difference is greatest in the tests with unirradiated UO2 (0% 233U)
and least in the tests with 10% 233U-doped UO2. The calculated [238U] in solution does
not increase, as the doping level of the solid UO2 samples is increasing. This does not
suggest any effect of alpha radiation under test conditions.
A new test series (II) was started after this under similar redox conditions to confirm
results. The measured [238U] in solution vs. time was at the same level or a little higher
in the beginning of the tests than in the test series I (Appendices 22-23). The calculated
[238U] in solution decreased in the tests, except in one test with 5% 233U-doped UO2
sample (5%-1), see lower Figures 15-17. The difference between measured and calculated data is very small for the 10% 233U-doped samples.
The calculated 238U data for the latter test series II was used in the similar way as previously to evaluate an average dissolution rate per year under test conditions for the solid
samples. The total calculated 238U in Table 9 is based on the difference between the
235
U/238U of the spiked leaching solution at the start of the tests, and the measured
235
U/238U ratios in the test termination samples (Appendix 24). The total 238U release
was calculated in the same way as for Table 8 using the measured ratios in leaching,
rinse and acid strip solutions. The average release is given in Table 9. The [238U] was
below the detection limit in the leaching solutions at the end of the tests with the 5%
233
U (1) and 10% 233U (1) UO2 samples. The [238U] in the rinse and acid strip solutions
were measurable. The total 238U amounts recovered from the test vessels are shown in
Table 9 for comparison. The 238U in the rinse solutions of the saucers was not measured.
This probably caused loss of precipitated material. The differences between the calculated and measured U release are smaller than for the experiments of Table 8. The dissolution rates based on the calculated total 238U values range from 0.04 to 0.2 ppm/yr.
No effect of the 233U doping level can be observed. In previous dissolution experiments
with the same UO2 samples in synthetic bicarbonate groundwater (Allard) in the presence of metallic iron, the measured dissolution rates were 0.12 to 0.14 ppm yr (Ollila &
Oversby 2006).
33
Table 9. Calculated total 238U dissolution per test in the isotope dilution tests in 0.01 M
NaCl under reducing conditions (Fe). Test series II. The duration was 102 days.
UO2 sample
(1 g)
UO2 – 0% 233U (1)
UO2 – 0% 233U (2)
UO2 – 5% 233U (1)
UO2 – 5% 233U (2)
UO2 – 10% 233U (1)
UO2 – 10% 233U (2)
Calculated
total 238U, µg
0.03
0.05
0.03
0.01
0.01
0.01
6recovered
238
U, µg
0.02
0.04
0.01
0.01
0.01
0.01
Dissolution rate
ppm/yr
0.10
0.20
0.10
0.04
0.04
0.04
34
35
5
SUMMARY AND DISCUSSION
Dissolution experiments were conducted with unirradiated UO2 fragments and intact
pellets in 0.01 M NaCl using isotope dilution method. The isotope dilution method was
used in order to decrease uncertainties due to precipitation (sorption) effects. The main
objective of these preliminary tests was to test methods and experimental conditions for
the measurements in high-ionic strength solutions. These experiments were followed by
isotope dilution tests to measure the dissolution rate of the 233U-doped UO2 fragments in
0.01 M NaCl. The results of this study serve as the comparison for the tests in highionic strength NaCl.
Redox environments were anoxic conditions under N2 atmosphere and reducing conditions in the presence of metallic iron. It proved to be necessary to add a pH buffer to
NaCl solution to stabilize pH under anoxic conditions. Sulfide (1 ppm S2-) was added to
leaching solutions to stabilize pH between 8.5 and 9. The S2- maintains also the Eh of
the solution negative, around -0.2 V. The immersion of an iron strip to solution rapidly
lowered the Eh of the solution (- 0.4 V).
The effect of the ratio of the UO2 surface area to leachant volume (SA/V) was investigated in the preliminary tests with unirradiated UO2. It was 13 and 67 m-1 in the tests
with fragments, 11 and 44 m-1 in the tests with pellets. The values are based on geometric surface area.
The [238U] in the leaching solutions in the tests in 0.01 M NaCl under anoxic conditions
(1 ppm S2-) was low but well measurable. U seems to stay better in the solution under
these conditions than in the presence of metallic iron. The changes in the 235U/238U ratios of the leaching solutions vs. time suggest higher U release than the measured [238U]
in solutions. The precipitation of U obviously occurs. The increase in SA/V had a clear
influence on [238U] that was calculated from the isotopic ratio changes. A small difference was seen also in the measured data. The presence of Gd (6% Gd2O3) in the solid
UO2 phase did not seem to have effect on U release.
The [238U] in the leaching solutions in the tests under reducing conditions with an iron
strip in solution was in many cases below the detection limit of the ICP-MS (8 ˜ 10-11
M). It is not possible to measure the change in the isotopic ratio by taking small aliquots
for analyses vs. time for longer contact periods due to low concentrations. A separate
test is necessary for each dissolution period in order to analyse the leaching solution that
has been equilibrated with acid (1 M HNO3) to dissolve colloidal U and/or U in precipitations, as well as the rinse and acid strip solutions of the test vessel. The [238U] and
235
U/238U were well measurable in all these solutions suggesting precipitation and/or
sorption phenomena. Great care must be taken in the tests with UO2 fragments to avoid
interference from particles of the original solid phase. The U release during a time period can be calculated on the basis of the difference between the 235U/238U of the spiked
solution at the start of the test and the 235U/238U measured in the acidified leaching solution (rinse, acid strip solution) at the end of the test. The U release was evaluated in this
way in three parallel tests at both SA/V (13 and 67 m-1). The test periods were 60, 120
and 160 days. The U release increased also with the SA/V under reducing conditions.
There was not a clear trend in the U release vs. the length of the dissolution period. The
36
total 238U in the leaching solutions at the end of the tests, that was calculated from the
change in isotopic ratio, was in agreement with the total 238U recovered from the test
vessels. This does not suggest any effect of isotopic exchange. Additional tests with
longer dissolution periods are needed to confirm the effect of the SA/V.
Finally, two consecutive test series with 0 (unirradiated), 5 and 10% 233U-doped UO2
samples were conducted under anoxic conditions (1 ppm S2-), which was followed by
two consecutive test series under reducing conditions (Fe). These tests used a lower
SA/V (5-7 m-1) due to the small amount of the 233U-doped samples available for the
tests. The measured data in the first test series under anoxic conditions (1 ppm S2-) seem
to have been affected by the redox conditions of the preceding test series, which had
been conducted under reducing conditions with Fe. The measured data in the second
test series were considered more representative for the redox conditions produced with
S(II). The calculated U release did not increase, as the 233U-doping level of the UO2
sample increased from 0 to 10%. Dissolution rates were evaluated for the solid samples
under test conditions on the basis of calculated U release. They ranged from 0.7 to 1.9
ppm/yr (calculated as µg/g UO2 solid). Corresponding rates under reducing conditions
in the presence of Fe were 0.04 to 0.2 ppm/yr. No effect of alpha radiolysis could be
observed. The results are in agreement with the earlier measurements in synthetic bicarbonate groundwater (modified, Allard) (Ollila et al. 2004).
37
REFERENCES
Dimmock N. A., Settle C and Webber H. M. 1979. The use of ferrozine for the absorptiometric determination of iron in boiler-feed water, Laboratory note no RD/L/N41/79,
Central Electricity Research Laboratories.
Ollila K., Albinsson Y., Oversby V., and Cowper M. 2004. Dissolution rates of unirradiated UO2, UO2 doped with 233U, and spent fuel under normal atmospheric conditions
and under reducing conditions using an isotope dilution method, POSIVA 2004-03,
SKB TR-03-13.
Ollila K. and Oversby V. 2005. Dissolution of unirradiated UO2 and UO2 doped with
U under reducing conditions, POSIVA 2005-05, SKB TR-05-07.
233
Ollila K. and Oversby V. 2006. Testing of uranium dioxide enriched with 233U under
reducing conditions, a paper to be published in the proceedings of the International
Symposium on the Scientific Basis of Nuclear Waste Management held in Ghent, Belgium, Sept. 12-16, 2005.
Shoesmith D. W. 2000. Fuel corrosion under waste disposal conditions, J. Nucl. Mater.
282, 1-31.
Werme L., Johnson L. H., Oversby V. M., King F., Spahiu K., Grambow B., and
Shoesmith D. W. 2004. Spent fuel performance under repository conditions: A model
for use in SR-Can, SKB TR-04-19, Svensk Kärnbränslehantering AB.
38
39
ACKNOWLEDGEMENTS
The author takes pleasure in thanking Ms. R. Zilliacus and Ms. M. Lipponen for performing the ICP-MS analyses. Dr. V. Oversby (VMO Konsult, Sweden) is gratefully
acknowledged for valuable comments.
We thank Posiva and European Commission for funding this project.
40
41
APPENDIX 1
Conditions for the preliminary isotope dilution tests with undoped UO2 samples
Sample code
Solid
Solution
Redox conditions
pH
SA/V (m-1)
L1, L2, L3
2 g UO2 fragments
30 ml 0.01 M NaCl
reducing (Fe)
9.2
13
H1, H2, H3
10 g UO2 fragments
"
"
"
67
H6
10 g (Gd, U)O2 fragments
"
"
"
67
L4, L5
2 g UO2 fragments
30 ml 0.01 M NaCl
10 g UO2 fragments
"
5.5 ... 8.3
8.5 ... 9.0
"
13
H4, H5
N2 atmosphere
(1 ppm S2-)
"
H7
"
"
"
67
L6
10 g (Gd, U)O2 fragments
1 UO2 pellet
"
"
"
11
H8
4 UO2 pellets
"
"
"
44
67
42
43
APPENDIX 2
Pretreatment without Fe strip - Measured U concentrations at the end of sequential leaching periods
(1, 1, 2, 13, 2 days) of the solid UO2 samples under anoxic conditions (N2) .
Sample
code
L1
L2
L3
L4
L5
H1
H2
H3
H4
H5
H6
H7
L6
H8
Solid UO2 sample/
30 ml 0.01 M NaCl
2 g UO2 fragments
"
"
"
"
10 g UO2 fragments
"
"
"
"
10 g (Gd,U)O2 fragments
"
1 UO2 pellet
4 UO2 pellets
SA/V
(m-1)
13
"
"
"
"
67
"
"
"
"
"
1d
U (ppb)
2.0
0.6
0.9
0.9
1.0
6.2
4.7
3.9
5.8
3.2
1.9
1d
U (ppb)
1.6
0.6
0.6
0.6
0.6
6.6
4.6
4.4
4.8
2.6
1.5
2d
U (ppb)
1.4
0.7
0.6
0.7
1.1
6.9
4.6
4.3
5.5
3.5
2.0
13 d
U (ppb)
1.6
0.7
0.6
0.4
2.0
6.1
1.7
2.3
2.4
1.9
0.5
2d
U (ppb)
0.8
0.3
0.2
0.3
0.5
3.1
1.5
1.3
1.6
1.0
0.5
"
11
44
1.0
2.5
5.3
1.2
2.3
4.5
1.5
3.0
4.5
1.1
10.7
17.3
0.7
2.1
3.6
44
45
APPENDIX 3
Pretreatment with Fe strip , first cycle - Measured U concentrations at the end of 20 days' leaching pe
riod of the solid UO2 samples under reducing conditions (Fe) .
Sample
code
L1
L2
L3
L4
L5
H1
H2
H3
H4
H5
H6
H7
L6
H8
Solution:
Acidified remainder:
Rinse:
Acid strip:
Saucer strip:
Solid UO2 sample/
30 ml 0.01 M NaCl
2 g UO2 fragments
"
"
"
"
10 g UO2 fragments
"
"
"
"
10 g (Gd,U)O2 fragments
"
1 UO2 pellet
4 UO2 pellets
SA/V
(m-1)
Solution
13
"
"
"
"
67
"
"
"
"
"
U (ppb)
0.1
0.1
0.1
1.0
0.3
0.5
0.4
0.3
1.3
1.1
0.2
Acidified
remainder
U (ppb)
1.3
3.1
2.7
1.6
0.7
2.6
3.8
2.2
2.9
4.7
3.2
"
11
44
0.3
2.2
5.2
1.2
6.3
6.2
Rinse
U (ppb)
2.0
1.8
1.1
4.1
2.5
5.0
4.4
2.2
2.2
1.9
3.9
Test vessel strip
U (ppb)
2.3
2.8
2.2
3.1
2.7
7.7
9.3
7.3
11.4
8.4
9.6
Saucer
strip
U (ppb)
3.9
3.2
1.8
5.3
5.0
14.9
9.3
6.0
11.9
11.7
8.7
2.9
12.3
23.5
4.0
29.3
71.1
10.6
-
10 ml sample from solution (acidified, 1 M HNO3)
Remaining leaching solution (20 ml) after sampling was acidified (1 M HNO3), and equilibrated with the acid for
one week
Rinse solution of the test vessel (15 ml)
Acid strip solution of the test vessel (1 M HNO3, 30 ml)
Acid strip solution of the saucer (1 M HNO3, 20 ml)
46
47
APPENDIX 4
Pretreatment with Fe strip , second cycle - Measured U concentrations at the end of 10 days' leaching
period of the solid UO2 samples under reducing conditions (Fe) .
Sample
code
L1
L2
L3
L4
L5
H1
H2
H3
H4
H5
H6
H7
L6
H8
Solution:
Acidified remainder:
one
Rinse:
Acid strip:
Saucer strip:
Solid UO2 sample/
30 ml 0.01 M NaCl
2 g UO2 fragments
"
"
"
"
10 g UO2 fragments
"
"
"
"
10 g (Gd,U)O2 fragments
"
1 UO2 pellet
4 UO2 pellets
SA/V
(m-1)
Solution
13
"
"
"
"
67
"
"
"
"
"
U (ppb)
0.1
0.2
0.1
0.2
0.2
0.6
0.5
0.6
3.2
1.2
0.4
Acidified
remainder
U (ppb)
0.7
1.0
1.1
0.6
0.8
1.9
3.3
4.1
5.5
2.9
3.4
"
11
44
0.7
1.0
1.8
3.1
1.9
4.1
Rinse
U (ppb)
1.4
2.6
1.6
2.3
2.4
4.3
5.2
3.7
3.7
2.9
5.1
Test vessel strip
U (ppb)
1.4
1.4
1.2
1.2
1.6
8.4
8.4
7.6
4.9
3.7
10.3
Saucer
strip
U (ppb)
2.2
1.6
1.4
1.9
2.6
9.0
10.4
9.4
16.6
15.9
7.7
3.6
5.1
19.2
4.1
9.3
38.3
12.1
-
10 ml sample from solution (acidified, 1 M HNO3)
Remaining leaching solution (20 ml) after sampling was acidified (1 M HNO3), and equilibrated with the acid for
week
Rinse solution of the test vessel (15 ml)
Acid strip solution of the test vessel (1 M HNO3, 30 ml)
Acid strip solution of the saucer (1 M HNO3, 20 ml)
48
49
APPENDIX 5
Pretreatment with Fe strip - Measured Fe2+ and total Fe concentrations at the end of the sequential
leaching periods (20, 10 days) of the solid UO2 samples under reducing conditions (Fe).
Sample
code
Solid UO2 sample/
30 ml 0.01 M NaCl
SA/V
(m-1)
L1
L2
L3
2 g UO2 fragments
"
"
H1
H2
H3
H6
10 g UO2 fragments
"
"
10 g (Gd,U)O2 fragments
13
"
"
20 d
[Fe2+]
ppm
0.11
0.11
0.13
20 d
[Fetot]
ppm
0.14
0.14
0.14
10 d
[Fe2+]
ppm
0.02
0.02
0.06
10 d
[Fetot]
ppm
0.05
0.10
0.06
67
"
"
"
0.02
0.03
0.07
0.09
0.10
0.14
0.09
0.09
0.03
0.05
0.05
0.06
0.03
0.06
0.06
0.06
- a strip of pure iron (1.5 x 3 cm, 9 cm2) was added to each test vessel (30 ml 0.01 M NaCl) at the beginning of the leaching periods
- the analyses for Fe2+ and total Fe were performed at the end of the periods
50
51
APPENDIX 6
Sample
code
L1
L2
L3
L4
L5
H1
H2
H3
H4
H5
H6
H7
L6
H8
Pretreatment with Fe strip , first cycle - Total recovered U for the 20 days' leaching period of the solid
UO2 samples under reducing conditions (Fe).
Solid UO2 sample/
30 ml 0.01 M NaCl
2 g UO2 fragments
"
"
"
"
10 g UO2 fragments
"
"
"
"
10 g (Gd,U)O2
fragments
"
1 UO2 pellet
4 UO2 pellets
U (Pg)
0.03
0.03
0.02
0.06
0.04
0.08
Test vessel strip
U (Pg)
0.07
0.08
0.06
0.09
0.08
0.23
Saucer
strip
U (Pg)
0.08
0.06
0.03
0.11
0.10
0.30
(U Pg)
0.20
0.24
0.17
0.30
0.23
0.66
Total
Exclude saucers
(U Pg)
0.13
0.17
0.14
0.19
0.13
0.36
0.08
0.04
0.06
0.09
0.06
0.07
0.03
0.03
0.03
0.06
0.28
0.22
0.34
0.25
0.29
0.19
0.12
0.24
0.23
0.17
0.61
0.42
0.68
0.62
0.59
0.42
0.30
0.45
0.38
0.41
0.02
0.13
0.12
0.04
0.19
0.35
0.12
0.88
2.13
0.21
-
0.40
1.21
2.66
0.19
-
13
"
"
"
"
67
U (Pg)
0.001
0.001
0.001
0.010
0.003
0.005
Acidified
remainder
U (Pg)
0.03
0.06
0.05
0.03
0.01
0.05
"
"
"
"
"
0.004
0.003
0.013
0.011
0.002
"
11
44
0.003
0.022
0.052
SA/V
(m-1)
Solution
Rinse
Total
52
53
APPENDIX 7
Sample
code
L1
L2
L3
L4
L5
H1
H2
H3
H4
H5
H6
H7
L6
H8
Pretreatment with Fe strip, second cycle - Total recovered U for the 10 days' leaching period of the
solid UO2 samples under reducing conditions (Fe).
Solid UO2 sample/
30 ml 0.01 M NaCl
2 g UO2 fragments
"
"
"
"
10 g UO2 fragments
"
"
"
"
10 g (Gd,U)O2
fragments
"
1 UO2 pellet
4 UO2 pellets
U (Pg)
0.02
0.04
0.02
0.03
0.04
0.06
Test vessel strip
U (Pg)
0.04
0.04
0.03
0.04
0.05
0.25
Saucer
strip
U (Pg)
0.04
0.03
0.03
0.04
0.05
0.18
(U Pg)
0.12
0.14
0.11
0.12
0.15
0.54
Total
Exclude saucers
(U Pg)
0.08
0.10
0.08
0.08
0.10
0.36
0.07
0.08
0.11
0.06
0.07
0.08
0.06
0.05
0.04
0.08
0.25
0.23
0.15
0.11
0.31
0.21
0.19
0.33
0.32
0.15
0.61
0.56
0.68
0.54
0.61
0.40
0.37
0.35
0.22
0.46
0.06
0.04
0.08
0.05
0.08
0.29
0.12
0.28
1.15
0.24
-
0.49
0.40
1.54
0.25
-
13
"
"
"
"
67
U (Pg)
0.001
0.001
0.001
0.002
0.002
0.006
Acidified
remainder
U (Pg)
0.01
0.02
0.02
0.01
0.02
0.04
"
"
"
"
"
0.005
0.006
0.032
0.012
0.004
"
11
44
0.007
0.010
0.017
SA/V
(m-1)
Solution
Rinse
Total
54
55
APPENDIX 8
Isotope dilution experiments with unirradiated UO2 samples with short contact times (20 d) under
anoxic conditions (N2)
TEST SERIES I
The table shows the measured [238U] and the ratio of 235U/238U in the samples which were taken from the leaching solutions 1, 4 and 20
days after the start of the experiments. The leaching solutions were spiked with 0.4 ppb U (235U/238U= 10.354 ± 0.758). Finally, the 238U
calculated from the change in the isotopic ratio is given.
Sample
code
UO2 sample/
30 ml 0.01
M NaCl
1 day
(m-1)
13
(ppb)
0.78
0.3304
"
0.74
0.2468
3.7
1.7
1.2
0.0911
1.5
5.8
1.0
0.0707
2.4
8.6
10 g UO2
fragments
"
67
6.4
0.0659
0.5
9.8
5.9
0.0480
2.2
19.0
5.4
0.0390
0.9
36.4
"
2.2
0.1079
1.4
4.6
2.3
0.0600
3.4
11.6
2.6
0.0438
1.5
24.5
H7
10 g GdUO2 fragments
67
1.3
0.1382
2.0
2.7
1.7
0.0429
2.8
11.5
1.1
0.0247
2.6
34.4
L6
1 UO2 pellet
4 UO2 pellets
11
3.2
0.0824
1.2
6.7
4.4
0.0499
1.8
17.3
5.1
0.0406
1.0
31.3
44
12.7
0.0442
1.2
23.8
11.9
0.0363
0.4
50.0
9.5
0.0360
12
52.2
L4
L5
H4
H5
H8
2 g UO2
fragments
"
U
235
U/238U
235
238
238
U
calc.
(ppb)
1.2
U
(ppb)
1.6
235
U/238U
20 days
U/238U
Std Dev
(%)
3.4
SA/V
238
4 days
235
0.0943
U/238U
Std Dev
(%)
2.9
238
U
calc.
(ppb)
5.5
238
(ppb)
1.2
U
235
U/238U
235
0.0654
U/238U
Std Dev
(%)
3.4
238
U
calc.
(ppb)
9.9
56
57
APPENDIX 9
Isotope dilution experiments with unirradiated UO2 samples with short contact times (20 d) under
anoxic conditions (N2)
TEST SERIES II
The table shows the measured [238U] and the ratio of 235U/238U in the samples which were taken from the leaching solutions 1, 3 and 18
days after the start of the experiments. The leaching solutions were spiked with 1.2 ppb U (235U/238U= 10.354 ± 0.758). Finally, the 238U
calculated from the change in the isotopic ratio is given.
Sample
code
UO2 sample/
30 ml 0.01
M NaCl
1 day
(m-1)
13
(ppb)
2.5
0.3573
"
5.8
0.1708
1.0
7.7
12.4
0.0862
1.2
19.1
18.5
0.0566
2.2
39.7
10 g UO2
fragments
"
67
44.6
0.0516
1.0
48.6
50.2
0.0443
0.7
71.9
47.1
0.0390
0.8
110.5
"
29.2
0.0583
0.4
37.4
35.8
0.0462
0.7
63.9
32.4
0.0390
0.9
110.5
H7
10 g GdUO2 fragments
67
9.7
0.0848
0.6
13.8
13.2
0.0428
0.8
38.6
12.2
0.0223
0.9
126.1
L6
1 UO2
pellet
4 UO2
pellets
11
8.7
0.1360
1.8
10.2
13.4
0.0860
0.7
19.2
22.4
0.0557
0.6
41.1
44
34.0
0.0588
0.8
36.8
41.0
0.0480
0.7
57.8
53.1
0.0396
0.5
104.2
L4
L5
H4
H5
H8
2 g UO2
fragments
"
U
235
U/238U
235
238
238
U
calc.
(ppb)
3.3
U
(ppb)
4.7
235
U/238U
18 days
U/238U
Std Dev
(%)
3.6
SA/V
238
3 days
235
0.1792
U/238U
Std Dev
(%)
0.7
238
U
calc.
(ppb)
7.3
238
(ppb)
9.6
U
235
U/238U
235
0.0740
U/238U
Std Dev
(%)
0.2
238
U
calc.
(ppb)
24.3
58
59
APPENDIX 10 Isotope dilution experiments with unirradiated UO2 samples with long contact times (8 months) under
anoxic conditions (N2), 1 ppm S2The tables show the measured [238U] and the ratio of 235U/238U in the samples. The samples were taken from the leaching solutions 12, 29,
56, 109 and 161 days after the start of the experiments. The leaching solutions were spiked with 0.8 ppb U (235U/238U= 10.354 ± 0.758).
Finally, the 238U calculated from the change in the isotopic ratio is given.
Samples at 12, 29 and 56 days:
(Samples at 109, 161 and 250 days: Appendix 11)
Sample
code
UO2 sample/
30 ml 0.01
M NaCl
12 days
(m-1)
13
(ppb)
0.12
0.6997
"
0.13
0.9813
3.4
0.76
0.47
0.8004
15
0.94
0.05
0.5435
7.4
1.4
10 g UO2
fragments
"
67
0.22
0.1290
11
7.3
0.29
0.0889
11
12.2
0.56
0.0525
9.1
31.1
"
0.21
0.1229
36
7.8
0.23
0.1165
3.2
8.3
0.22
0.0790
12
14.6
H7
10 g GdUO2 fragments
67
0.08
0.1973
34
3.8
0.13
0.2281
14
3.7
0.20
0.1210
8.7
7.0
L6
1 UO2
pellet
4 UO2
pellets
11
0.16
0.4718
3.7
1.6
0.37
0.2402
3.7
3.4
0.12
0.1218
15
7.9
44
0.53
0.0716
2.9
17.1
2.8
0.0466
1.7
41.6
0.59
0.0322
1.7
-
L4
L5
H4
H5
H8
2 g UO2
fragments
"
U
235
U/238U
235
238
238
U
calc.
(ppb)
1.1
U
(ppb)
0.30
235
U/238U
56 days
U/238U
Std Dev
(%)
5.4
SA/V
238
29 days
235
0.5998
U/238U
Std Dev
(%)
4.7
238
U
calc.
(ppb)
1.3
238
(ppb)
0.08
U
235
U/238U
235
0.3227
U/238U
Std Dev
(%)
7.0
238
U
calc.
(ppb)
2.5
60
61
APPENDIX 11 Isotope dilution experiments with unirradiated UO2 samples with long contact times (8 months) under
anoxic conditions (N2), 1 ppm S2Samples at 109, 161 and 250 days:
Sample
code
UO2 sample/
30 ml 0.01
M NaCl
109 days
(m-1)
13
(ppb)
0.06
0.2678
"
0.05
0.3549
22
2.2
0.09
0.2894
18
2.8
0.07
0.1703
5.2
5.2
10 g UO2
fragments
"
67
0.41
0.0467
10
41.4
0.50
0.0463
4.5
42.4
1.7
0.0365
2.6
98.6
"
0.24
0.0676
8.8
18.9
0.27
0.0569
6.5
26.2
0.50
0.0455
9.9
44.4
H7
10 g GdUO2 fragments
67
0.21
0.0449
21
23.0
0.31
0.0411
5.4
36.0
0.90
0.0167
8.2
76.8
L6
1 UO2
pellet
4 UO2
pellets
11
0.09
0.0835
19
13.4
0.10
0.0807
7.8
14.1
0.23
0.0509
8.3
33.4
44
0.35
0.0340
13
-
0.45
0.0344
9.1
-
0.63
0.0337
8.8
-
L4
L5
H4
H5
H8
2 g UO2
fragments
"
U
235
U/238U
235
238
238
U
calc.
(ppb)
3.1
U
(ppb)
0.06
235
U/238U
250 days
U/238U
Std Dev
(%)
20
SA/V
238
161 days
235
0.2050
U/238U
Std Dev
(%)
25
238
U
calc.
(ppb)
4.1
238
(ppb)
0.09
U
235
U/238U
235
0.1521
U/238U
Std Dev
(%)
12
238
U
calc.
(ppb)
5.9
62
63
APPENDIX 12 Isotope dilution experiments with unirradiated UO2 samples with long contact times (8 months) under
reducing conditions (N2), Fe
The tables show the measured [238U] and the ratio of 235U/238U in the samples which were taken from the leaching solutions 15, 32, 59, 112
and 164 days after the start of the experiments. The leaching solutions were spiked with 0.8 ppb U (235U/238U= 10.354 ± 0.758). Finally, the
238
U calculated from the change in the isotopic ratio is given.
Samples at 15, 32 and 59 days:
(Samples at 112 and 164 days: Appendix 13)
Sample
code
UO2 sample/
30 ml 0.01
M NaCl
15 days
(m-1)
13
L1
(ppb)
< 0.02
-
L2
L3
"
"
"
-
-
-
< 0.02
< 0.02
-
-
-
< 0.02
< 0.02
-
-
H1
10 g UO2
fragments
"
"
67
< 0.02
-
-
-
0.05
-
-
-
0.33
0.0810
15
-
H2
H3
"
"
0.10
0.04
0.0510
0.0876
13
45
-
0.05
0.04
0.0853
-
7.9
-
-
0.03
0.02
-
-
-
H6
10 g GdUO2 fragments
"
< 0.02
-
-
0.09
0.0865
5.6
-
0.10
0.0709
20
-
2 g UO2
fragments
"
"
U
235
U/238U
235
238
238
U
calc.
(ppb)
-
U
(ppb)
0.02
235
U/238U
59 days
U/238U
Std Dev
(%)
-
SA/V
238
32 days
235
-
U/238U
Std Dev
(%)
-
238
U
calc.
(ppb)
-
238
(ppb)
< 0.02
-
U/238U
Std Dev
(%)
-
U
235
U/238U
235
238
U
calc.
(ppb)
64
65
APPENDIX 13 Isotope dilution experiments with unirradiated UO2 samples with long contact times (5 months) under
reducing conditions (N2), Fe
Samples at 112 and 164 days:
Sample
code
UO2 sample/
30 ml 0.01 M NaCl
112 days
(ppb)
< 0.02
< 0.02
-
U/238U
Std Dev
(%)
-
67
"
"
0.19
0.45
0.0578
0.0528
12
6.8
-
0.45
0.0528
6.8
-
"
0.11
0.0389
35
-
1.00
0.0316
6.5
-
SA/V
L1
L2
L3
2 g UO2 fragments
"
"
H1
H2
H3
10 g UO2 fragments
"
"
H6
10 g Gd-UO2 fragments
(m-1)
13
"
238
U
Tests L1 and H1 were finished after 64 days' contact time.
Tests L2 and H2 were finished after 120 days' contact time.
235
U/238U
164 days
235
238
U
calc.
(ppb)
-
238
< 0.02
-
U/238U
Std Dev
(%)
-
U
calc.
(ppb)
-
U
(ppb)
-
235
U/238U
235
238
66
67
APPENDIX 14 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
anoxic conditions (N2), 1 ppm S2TEST SERIES I
The table shows the measured [238U] and the ratio of 235U/238U in the samples which were taken from the leaching solutions 3, 57 and 84
days after the start of the experiments. The leaching solutions were spiked with 0.8 ppb U (235U/238U= 10.354 ± 0.758). Finally, the 238U
calculated from the change in the isotopic ratio is given.
Sample
code
UO2
sample
(g)/
30 ml
0.01 M
NaCl
3 days
SA/
V
0%-1
0%-2
1.011
1.056
(m1
)
7
"
5%-1
5%-2
1.009
0.979
10%-1
10%-2
238
U
235
U/238U
(ppb)
57 days
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
238
(ppb)
U
235
U/238U*
84 days
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
238
(ppb)
U
235
U/238U*
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
0.09
0.07
9.9944
7.2690
6.0
44
0.07
0.1
< 0.02
< 0.02
4.3628
4.3344
23
23
0.2
0.2
< 0.02
< 0.02
4.2736
2.4219
11
30
0.2
0.3
7
"
< 0.02
< 0.02
9.0551
7.8047
37
35
0.08
0.09
< 0.02
< 0.02
4.6124
6.5558
15
9.0
0.2
0.1
< 0.02
< 0.02
3.4137
6.4491
13
7.2
0.2
0.1
1.012
7
0.02
-
-
< 0.02
-
-
< 0.02
4.9715
15
0.2
0.913
"
0.02
-
-
< 0.02
24
0.1
< 0.02
5.1240
15
0.1
238
U<
0.02
238
U<
0.02
* The isotopic ratio measurements were performed with micronebulizer.
238
U<
0.02
5.8104
68
69
APPENDIX 15 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
anoxic conditions (N2), 1 ppm S2TEST SERIES I
Test termination samples (124 days)
The table shows the measured [238U] and the ratio of 235U/238U in the samples (5 ml) which were taken from:
the leaching solutions after acidification (1 M HNO3) and equilibration with the acid (4 weeks),
the rinse solutions of the test vessels (deionized water, 1 M HNO3),
and the acid strip solutions of the test vessels (1 M HNO3).
All these solutions were stored for 4 weeks before sampling. The samples were stored additional 4 months before measurements due to
ICP-MS problems.
Sample
code
Leaching solution (30 ml)
238
U/238U
235
U/238U
Std Dev
(%)
238
(ppb)
total 238U
in solution
(ng)
(ppb)
0%-1
0%-2
0.25
0.10
8
3
0.5175
0.7697
7.3
1.5
0.14
0.09
2
1
0.3555
0.4280
2.6
2.0
0.04
0.05
total 238U
in solution
(ng)
1
2
5%-1
5%-2
0.04
0.07
1
2
1.3821
1.0620
2.1
0.7
0.05
0.11
1
2
1.2635
0.9887
3.3
2.8
0.02
0.02
10%-1
10%-2
0.03
0.04
1
1
1.5399
1.6040
2.6
4.0
0.03
-*
< 0.02
-
1.2698
-
4.2
-
0.11
0.02
U
*The rinsing of the test vessel was not performed,
the [238U] of this fraction is included in the acid strip solution of the test vessel.
235
U/238U
Test vessel strip (30 ml)
total 238U
in solution
(ng)
U
235
Test vessel rinse (15 ml)
238
238
U
Std Dev
(%)
U
(ppb)
235
U/238U
238
U
Std Dev
(%)
0.8831
0.7434
5.3
2.8
1
1
2.3913
3.2899
2.0
4.8
3
1
1.0952
3.6516
2.0
8.1
70
71
APPENDIX 16 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
anoxic conditions (N2), 1 ppm S2TEST SERIES II
The tables show the measured [238U] and the ratio of 235U/238U in the samples which were taken from the leaching solutions 2, 13, 22, 29
and 48 days after the start of the experiments. The leaching solutions were spiked with 0.8 ppb U (235U/238U= 10.354 ± 0.758). Finally, the
238
U calculated from the change in the isotopic ratio is given.
Samples at 2, 13 and 22 days:
(Samples at 29 and 48 days: Appendix 17)
Sample
code
UO2 sample (g)/
2 days
13 days
22 days
40 ml
0.01 M
NaCl
SA/V
238
U
235
U/238U*
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
238
(ppb)
U
235
U/238U
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
238
(ppb)
U
235
U/238U
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
0%-1
0%-2
1.011
1.056
(m1
)
5
"
5%-1
5%-2
1.009
0.979
5
"
0.11
0.18
1.64
1.00
-
0.5
0.8
0.05
0.12
0.9076
0.5819
4.6
4.3
0.9
1.4
0.04
0.09
0.7181
0.4191
4.7
6.1
1.1
2.0
10%-1
10%-2
1.012
0.913
5
"
0.02
0.08
5.50
1.75
-
0.1
0.4
0.02
0.04
3.7700
0.9437
12
6
0.2
0.8
0.02
0.03
2.8969
0.7819
6.8
4.5
0.3
1.0
(ppb)
0.06
0.24
3.33
0.83
-
0.2
0.9
0.02
0.07
1.9119
0.5559
9.5
3.3
0.4
1.4
0.02
0.05
0.9744
0.4474
6.0
7.6
0.8
1.7
* The 235U/238U was calculated based on the concentration measurements of 238U and 235U
72
73
APPENDIX 17 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
anoxic conditions (N2), 1 ppm S2TEST SERIES II
Samples at 29 and 48 days:
Sample
code
UO2 sample (g)/
40 ml 0.01 M
NaCl
29 days
SA/V
238
(ppb)
0.03
0.06
1.2765
0.3623
U/238U
Std Dev
(%)
13
6.8
0.4423
0.2638
4.1
3.9
1.9
3.4
0.08
0.11
9.1
1.7
< 0.02
0.04
U
0%-1
0%-2
1.011
1.056
(m-1)
5
"
5%-1
5%-2
1.009
0.979
5
"
0.06
0.08
10%-1
10%-2
1.012
0.913
5
"
0.02
0.03
235
U/238U
48 days
238
U < 0.02
0.4735
235
238
238
U
calc.
(ppb)
0.6
2.2
U
(ppb)
0.03
0.08
235
U/238U
0.9844
0.3713
U/238U
Std Dev
(%)
5.3
4.0
U
calc.
(ppb)
0.8
2.1
0.3856
0.3222
13
5.0
2.2
2.7
12
1.4
238
U < 0.02
0.5566
235
238
74
75
APPENDIX 18 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
anoxic conditions (N2), 1 ppm S2TEST SERIES II
Test termination samples (50 days)
The table shows the measured [238U] and the ratio of 235U/238U in the samples (5 ml) which were taken from:
the leaching solutions after acidification (1 M HNO3) and equilibration with the acid,
the rinse solutions of the test vessels (deionized water, 1 M HNO3),
and the acid strip solutions of the test vessels (1 M HNO3).
All these solutions were stored for 4 months before sampling and measurements due to ICP-MS problems.
Sample
code
Leaching solution (40 ml)
238
U/238U
235
U/238U
Std Dev
(%)
238
(ppb)
total 238U
in solution
(ng)
(ppb)
0%-1
0%-2
0.22
0.24
9
10
0.2883
0.2246
30
6.8
0.31
0.26
5
4
0.1352
0.1537
1.1
5.3
0.13
0.26
total 238U
in solution
(ng)
5 (20)**
10 (40)
5%-1
5%-2
0.23
0.78
9
31
0.1267
0.1143
17
8.6
0.26
0.21
4
3
0.1691
0.2117
4.7
2.8
0.17
0.22
10%-1
10%-2
0.02
0.35
1
14
2.2551
0.1886
13
8.0
0.14
0.22
2
3
0.3894
0.1771
7.5
5.4
0.09
0.12
U
235
U/238U
Test vessel strip (40 ml)
total 238U
in solution
(ng)
U
235
Test vessel rinse (15 ml)
* The result is based on a single measurement due to ICP-MS problems.
** The values in parentheses give the total 238U measured in the acid strip solutions of the saucers.
238
238
U
Std Dev
(%)
U
(ppb)
235
U/238U
238
U
Std Dev
(%)
0.4618
0.2924
2.9
2.8
7 (40)
9 (10)
0.2177*
0.2442*
-
4 (15)
5 (10)
0.1741*
0.1251
1.9
76
77
APPENDIX 19 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
reducing conditions (N2), Fe
TEST SERIES I
The tables show the measured [238U] and the ratio of 235U/238U in the samples which were taken from the leaching solutions 1, 2, 5, 13, 22
and 40 days after the start of the experiments. The leaching solutions were spiked with 0.8 ppb U (235U/238U= 10.354 ± 0.758). Finally, the
238
U calculated from the change in the isotopic ratio is given.
Samples at 1, 2 and 5 days:
(Samples at 13, 22 and 40 days: Appendix 20)
Sample
code
UO2
sample
(g)/
40 ml
0.01 M
NaCl
1 day
SA/V
238
U
235
U/238U*
2 days
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
238
(ppb)
U
235
U/238U*
5 days
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
238
(ppb)
U
0%-1
0%-2
1.011
1.056
(m1
)
5
"
5%-1
5%-2
1.009
0.979
5
"
0.03
0.02
2.67
2.00
-
0.3
0.4
0.05
0.03
2.50
1.50
-
0.3
0.5
0.02
<
0.02
10%-1
1.012
5
0.02
4.00
-
0.2
0.04
2.00
-
0.4
10%-2
0.913
"
0.02
2.50
-
0.3
0.04
2.00
-
0.4
<
0.02
<
0.02
235
U/238U
235
U/238U
Std Dev
(%)
238
U
calc.
(ppb)
(ppb)
0.08
0.08
0.88
1.00
-
0.9
0.8
0.03
0.04
1.50
1.00
-
0.5
0.8
0.02
0.03
0.9084
0.6889
15
5.2
0.8
1.1
1.5452
1.9516
8.3
6.0
0.5
0.4
* The 235U/238U was calculated based on the concentration measurements of 238U and 235U
238
U<
0.02
2.5314
13
0.3
78
79
APPENDIX 20 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
reducing conditions (N2), Fe
TEST SERIES I
Samples at 13, 22 and 40 days:
Sample
code
UO2 sample
(g)/
40 ml 0.01
M NaCl
13 day
SA/V
238
U
0%-1
1.011
(m-1)
5
0%-2
1.056
"
< 0.02
5%-1
5%-2
1.009
0.979
5
"
< 0.02
< 0.02
10%-1
1.012
5
< 0.02
10%-2
0.913
"
< 0.02
(ppb)
< 0.02
235
U/238U
238
U<
0.02
238
U<
0.02
1.2655
238
U<
0.02
238
U<
0.02
1.5847
22 days
235
U/238U
Std Dev
(%)
-
U
calc.
(ppb)
-
-
-
6.7
-
0.60
12
238
238
U
(ppb)
<
0.02
0.02
235
U/238U
238
U < 0.02
0.2739
0.02
<
0.02
238
<
0.02
0.02
238
U < 0.02
U < 0.02
238
U < 0.02
1.3316
40 days
235
U/238U
Std Dev
(%)
-
238
U
calc.
(ppb)
-
238
(ppb)
< 0.02
13
3.0
< 0.02
14
-
1.9
-
< 0.02
< 0.02
-
-
< 0.02
14
0.6
< 0.02
U
235
U/238U
238
U, 235U
< 0.02
238
U, 235U
< 0.02
238
U < 0.02
0.6533
238
U, 235U
< 0.02
238
U < 0.02
235
U/238U
Std Dev
(%)
-
238
U
calc.
(ppb)
-
-
-
15
1.2
-
-
-
-
80
81
APPENDIX 21 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
reducing conditions (N2), Fe
TEST SERIES I
Test termination samples (125 days)
The table shows the measured [238U] and the ratio of 235U/238U in the samples (5 ml) which were taken from:
the leaching solutions after acidification (1 M HNO3) and equilibration with the acid,
the rinse solutions of the test vessels (deionized water, 1 M HNO3),
and the acid strip solutions of the test vessels (1 M HNO3).
Sample
code
Leaching solution (40 ml)
238
(ppb)
total 238U
in solution
(ng)
0%-1
0%-2
0.02
0.02
1
1
235
5%-1
5%-2
0.02
0.04
1
2
235
10%-1
0.05
2
10%-2
0.05
2
U
* 235U close to detection limit
235
U/238U
U < 0.02
U < 0.02
235
U < 0.02
U < 0.02
235
238
U, 235U
< 0.02
235
U < 0.02
Test vessel rinse (15 ml)
235
U/238U
Std Dev
(%)
238
(ppb)
total 238U
in solution
(ng)
U
Std Dev
(%)
(ppb)
0.4464
(0.2777)*
11
5
0.33
0.46
total 238U
in solution
(ng)
13
18
-
0.09
0.11
1
2
-
0.22
0.04
3
1
0.6066
1.3552
18
15
0.12
0.09
-
0.65
10
(0.3433)*
22
-
0.04
1
0.9930
5.8
U
235
U/238U
Test vessel strip (40 ml)
238
238
U
235
U/238U
238
U
Std Dev
(%)
1.5209
1.0818
3.3
2.1
5
4
4.8265
5.1764
11
4.7
0.27
11
2.0620
1.3
0.08
3
6.1426
3.8
82
83
APPENDIX 22 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
reducing conditions (N2), Fe
TEST SERIES II
The tables show the measured [238U] and the ratio of 235U/238U in the samples which were taken from the leaching solutions 1, 2, 5, 11 and
85 days after the start of the experiments. The leaching solutions were spiked with 0.8 ppb U (235U/238U= 10.354 ± 0.758). Finally, the 238U
calculated from the change in the isotopic ratio is given.
Samples at 1, 2 and 5 days:
(Samples at 11 and 85 days: Appendix 23)
Sample
code
UO2 sample
(g)/
40 ml 0.01
M NaCl
1 day
SA/V
238
(ppb)
0.56
0.35
1.28
1.98
U/238U
Std Dev
(%)
-
U
235
U/238U*
2 days
235
238
238
U
calc.
(ppb)
0.6
0.4
U
(ppb)
0.59
0.30
235
U/238U*
5 days
235
1.09
1.99
U/238U
Std Dev
(%)
-
238
U
calc.
(ppb)
0.7
0.4
238
(ppb)
0.4
0.2
U
235
U/238U
235
1.0747
1.8371
U/238U
Std Dev
(%)
3.3
7.0
238
U
calc.
(ppb)
0.7
0.4
0%-1
0%-2
1.011
1.056
(m-1)
5
"
5%-1
5%-2
1.009
0.979
5
"
0.45
0.06
1.42
9.83
-
0.5
0.1
0.38
0.05
1.49
9.80
-
0.5
0.1
0.3
0.04
1.4193
9.8810
2.4
6.0
0.5
0.1
10%-1
10%-2
1.012
0.913
5
"
0.07
0.07
8.84
9.10
-
0.1
0.1
0.05
0.06
9.44
8.52
-
0.1
0.1
0.04
0.04
9.2967
9.1146
8.9
7.0
0.1
0.1
* The 235U/238U was calculated based on the concentration measurements of 238U and 235U
84
85
APPENDIX 23 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
reducing conditions (N2), Fe
TEST SERIES II
Samples at 11 and 85 days:
Sample
code
UO2 sample (g)/
40 ml 0.01 M
NaCl
11 days
SA/V
238
(ppb)
0.20
0.08
1.0746
1.5521
U/238U
Std Dev
(%)
5.0
4.5
U
235
U/238U
85 days
235
238
238
U
calc.
(ppb)
0.7
0.5
(ppb)
0.02
0.04
235
U/238U
0.8775
U < 0.02
U/238U
Std Dev
(%)
20
-
U
calc.
(ppb)
0.9
-
U, 238U < 0.02
U, 238U < 0.02
-
-
-
-
U
0%-1
0%-2
1.011
1.056
(m-1)
5
"
5%-1
5%-2
1.009
0.979
5
"
0.16
0.02
1.2315
5.3247
4.2
9.6
0.6
0.1
< 0.02
< 0.02
235
10%-1
10%-2
1.012
0.913
5
"
0.02
0.02
7.0686
6.2929
4.1
9.9
0.1
0.1
< 0.02
< 0.02
235
235
235
U, 238U < 0.02
U, 238U < 0.02
235
235
238
86
87
APPENDIX 24 Isotope dilution experiments with alpha-doped UO2 samples (0, 5, 10% 233U) under
reducing conditions (N2), Fe
TEST SERIES II
Test termination samples (102 days)
The table shows the measured [238U] and the ratio of 235U/238U in the samples (5 ml) which were taken from:
the leaching solutions after acidification (1 M HNO3) and equilibration with the acid,
the rinse solutions of the test vessels (deionized water, 1 M HNO3),
and the acid strip solutions of the test vessels + saucers (1 M HNO3).
Sample
code
Leaching solution (40 ml)
238
U/238U
(ppb)
0%-1
0%-2
0.08
0.11
3
4
5%-1
5%-2
0.04
0.05
2
2
238
9.7
4.4
0.31
0.04
5
1
1.0376
7.7745
5.0
4.2
0.20
0.02
10%-1
10%-2
< 0.02
0.02
1
238
13
0.05
0.04
1
1
6.3060
6.2892
4.2
7.3
0.02
0.04
0.9861
0.9634
U< 0.02
1.9704
U< 0.02
2.9558
235
U/238U
Std Dev
(%)
238
(ppb)
total 238U
in solution
(ng)
2.7
3.4
0.35
1.11
1
17
U
235
U/238U
Test vessel strip (40 ml)
total 238U
in solution
(ng)
U
235
Test vessel rinse (15 ml)
238
U
Std Dev
(%)
238
(ppb)
1.0041
0.4407
3.7
3.5
0.15
0.22
total 238U
in solution
(ng)
13
18
U
235
U/238U
238
U
Std Dev
(%)
0.9952
0.5173
3.3
2.1
5
4
0.9157
2.8559
11
4.7
11
3
3.4623
3.6249
1.3
3.8
1 (2)
LIST OF REPORTS
POSIVA-REPORTS 2006
POSIVA 2006-01
Effects of Salinity and High pH on Crushed Rock and Bentonite
- Experimental Work and Modelling
Ulla Vuorinen, Jarmo Lehikoinen, VTT Processes
Ari Luukkonen, VTT Building and Transport
Heini Ervanne, University of Helsinki, Department of Chemistry
May 2006
ISBN 951-652-142-8
POSIVA 2006-02
Petrology of Olkiluoto
Aulis Kärki, Kivitieto Oy
Seppo Paulamäki, Geological Survey of Finland
November 2006
ISBN 951-652-143-6
POSIVA 2006-03
Quality Controll for Overcoring Stress Measurement Data
Matti Hakala, Gridpoint Finland Oy
April 2006
ISBN 951-652-126-6
POSIVA 2006-04
Summary of Rock Mechanics Work Completed for Posiva Before
2005
John A. Hudson, Rock Engineering Consultants, UK
Erik Johansson, Saanio & Riekkola Oy
June 2006
ISBN 951-652-144-4
POSIVA 2006-05
Expected Evolution of Spent Nuclear Fuel Repository at Olkiluoto
Editors:
Barbara Pastina, Saanio & Riekkola Oy
Pirjo Hellä, Pöyry Environment Oy
December 2006
ISBN 951-652-145-2
POSIVA 2006-06
Discrete Fracture Network Modelling of a KBS-3H Repository at
Olkiluoto
G. W. Lanyon, Fracture Systems Ltd.
P. Marschall, Nagra
December 2006
ISBN 951-652-146-0
POSIVA 2006-07
Posiva Biosphere Assessment: Revised Structure and Status 2006
A. T. K. Ikonen, Posiva Oy
December 2006
ISBN 951-652-147-9
2 (2)
POSIVA 2006-08
Dissolution of Unirradiated UO2 and UO2 Doped with 233U in
0.01 M NaCl Under Anoxic and Reducing Conditions
Kaija Ollila, VTT
December 2006
ISBN 951-652-148-7