Working
Report
2004-06
fQuivalent flow Rates from
Canister Interior-into the Geosphere
in aKBS-3H Type Repository
Henrik
Nordman
Timo Vieno
March
2004
March
2004
POSIVA QV
FIN-27160 OLKILUOTO, FINLAND
Tel. +358-2-8372 31
Fax +358-2-8372 3709
----------------------
INSINOORITOIMISTO
SAANIO & RIEKKOLA OY
----
--
SAATE
4.2.2004
SAATE TYORAPORTIN T ARKASTAMISESTA JA HYV AKSYMISEST A
TILAAJA
SKB/Posiva KBS-3H yhteistyo
SKB Box 5864, SE 102 40 Stockholm, Sverige
Posiva Oy, 27160 OLKILUOTO
TILAUS
8206, Erik Lindgren SKB
YHTEYSHENKILOT
Aimo Hautoj arvi
Margit Snellman
TYORAPORTTI
EQUIVALENT FLOW RATES FROM CANISTER
INTERIOR INTO THE GEOSPHERE IN A kbs-3h TYPE
REPOSITORY
LAATIJA
Henrik Nordman, Timo Vieno
TARKASTAJA
~(l>-~·i- ~~
HYVAKSYJA
f41J.
6. 3. 2ML,
lhnp"-'~~
PosivaOy
Saanio & Riekkola Oy
VTT
Margit Snellman
Saanio & Riekkola Oy
Reijo Riekkola
toimitusjohtaja
Saanio & Riekkola Oy
~-----·
----
----
- -----
-JLV7T
Research organisation and address
Customer
VTT Processes, Nuclear Energy
P.O. Box 1608
FIN -02044 VTT, FINLAND
Saanio & Riekkola Oy
Laulukuja 4
00420 HELSINKI
Responsible person
Contact person
Timo Vieno
Margit Snellman
Diary code (VTT)
Order reference
PR01-110T-03
6861103-2, 104 cont.
Title and reference code for assignment
Report identification & Pages
Date
13KBS-3H; C3SU00382
PR01/7001104
12 p.
27.1.2004
Report title and author(s)
EQUIVALENT FLOW RATES FROM CANISTER INTERIOR INTO THE GEOSPHERE IN A KBS-3H TYPE
REPOSITORY
Nordman, H. & Vieno, T.
Summary
Equivalent flow rates from the interior of a damaged canister in a KBS-3H type horizontal
deposition drift into the geosphere are calculated as a function of the transmissivity of a rock
fracture intersecting the deposition drift and its distance from the defect in the canister. Equivalent
flow rate (litres/yr) gives the steady state release rate of a stable species into the geosphere in a
case where a constant concentration of one unit per litre is assumed to prevail in the canister.
The results show that in a fully saturated state, where a swollen and homogenous buffer surrounds
the canister and no significant erosion of the bentonite takes place, the boundary layer resistance
between the stagnant porewater in the buffer and the groundwater flowing in fractures intersecting
the deposition drift is a dominant transport resistance in the near-field. The diffusion resistance in
the buffer is significant for anions which have low diffusivity in the buffer thanks to anionic
exclusion. In similar flow and fracturing conditions, long-term release rates from a KBS-3H
deposition drift are lower than those from a KBS-3V deposition hole, where the upper part of the
deposition hole backfilled with the tunnel backfill as well as the tunnel may become important
release routes for long-lived radionuclides, if significant flow of groundwater takes place through
these parts of the near-field. This concerns especially cations having a high mobility in the buffer
and backfill
Publicity
Distribution
Saanio & Riekkola Oy
Margit Snellman I Saanio & Riekkola Oy
Aimo Hautojarvi/Posiva Oy
Responsible person
t; f.·
Timo Vieno
Re;;:ed l!"d approve:.
Confidential
~CJ1AA uyl~
fkhl<~~-·.
Arto Muurinen
Se;;/(k~
Group Manager
Research Manager
The use of the name of the Technical Research Centre of Finland (VTT) in advertising or publication in part of
this report is only permissible by written authorisation from the Technical Research Centre of Finland
Working
Report
2004-06
fQuivalent flow Rates from
Canister Interior into the Geosphere
in aKBS-3H Type Repository
Henrik
Nordman
Timo
Vieno
VTT Processes
March
2004
Working Reports contain information on work in progress
or pending completion.
The conclusions and viewpoints presented in the report
are those of author(s) and do not necessarily
coincide with those of Posiva.
EQUIVALENT FLOW RATES FROM CANISTER INTERIOR INTO THE GEOSPHERE IN A KBS-3H TYPE REPOSITORY
ABSTRACT
Equivalent flow rates from the interior of a damaged canister in a KBS-3H type
horizontal deposition drift into the geosphere are calculated as a function of the
transmissivity of a rock fracture intersecting the deposition drift and its distance from
the defect in the canister. Equivalent flow rate (litres/yr) gives the steady state release
rate of a stable species into the geosphere in a case where a constant concentration of
one unit per litre is assumed to prevail in the canister.
The results show that in a fully saturated state, where a swollen and homogenous buffer
surrounds the canister and no significant erosion of the bentonite takes place, the
boundary layer resistance between the stagnant porewater in the buffer and the
groundwater flowing in fractures intersecting the deposition drift is a dominant transport
resistance in the near-field. The diffusion resistance in the buffer is significant for
anions which have low diffusivity in the buffer thanks to anionic exclusion. In similar
flow and fracturing conditions, long-term release rates from a KBS-3H deposition drift
are lower than those from a KBS-3V deposition hole, where the upper part of the
deposition hole backfilled with the tunnel backfill as well as the tunnel may become
important release routes for long-lived radionuclides, if significant flow of groundwater
takes place through these parts of the near-field. This concerns especially cations having
a high mobility in the buffer and backfill.
Keywords: equivalent flow rate, near-field, transport, KBS-3H
EKVIVALENTIT VIRTAAMAT VAURIOITUNEESTA KAPSELISTA KALLIOPERAAN KBS-3H TYYPPISESSA LOPPUSIJOITUSTILASSA
TIIVISTELMA
Tutkimuksessa on laskettu ekvivalentit virtaamat KBS-3H tyyppisessa vaakasuuntaisessa loppusijoitusreiassa sijaitsevasta vaurioituneesta kapselista kallioperaan sijoitusreikaa
leikkaavan vettajohtavan kallioraon transmissiviteetin ja etaisyyden funktiona. Ekvivalentti virtaama ilmaisee tasapainotilanteen vapautumisnopeuden radioaktiivisesti
hajoamattomalle aineelle, kun kapselin sisalla oletetaan vallitsevan vakiopitoisuus.
Tulokset osoittavat, etta saturoituneessa tilassa, jossa paisunut ja homogeeninen
puskuribentoniitti ymparoi kapselia eika merkittavaa bentoniitin erodoitumista sijoitusreiasta kallioon tapahdu, raj akerrosvastus bentoniitin stagnantin huokosveden j a
kallioraossa virtaavan pohjaveden valilla on tarkein kulkeutumisvastus lahialueella.
Diffuusiovastus bentoniitissa on merkittava anioneille, joiden diffuusiota bentoniitissa
rajoittaa anionieksluusio. Samankaltaisissa virtaus- ja rakoiluolosuhteissa pitkaikaisten
radionuklidien vapautumisnopeudet KBS-3H sijoitusreiasta ovat pienempia kuin pystysuuntaisesta KBS-3V sijoitusreiasta, jossa kulkeutumisreitit tunnelitaytteella taytetyn
sijoitusreian ylaosan seka itse tunnelin kautta voivat muodostua merkittaviksi vapautumisreiteiksi pitkaikaisille radionuklideille, erityisesti suuren diffuusiokertoimen omaaville kationeille, jos naiden loppusijoitustilan osien lavitse tapahtuu merkittavaa pohjaveden virtausta.
Keywords: ekvivalentti virtaama, lahialue, kulkeutuminen, KBS-3H
1
TABLE OF CONTENTS
Page
ABSTRACT
TIIVISTELMA
TABLE OF CONTENTS ..................................................................................... 1
PREFACE .......................................................................................................... 2
1
INTRODUCTION ...................................................................................... 3
2
TRANSPORT MODEL .............................................................................. 4
3
RESULTS .................................................................................................. 8
4
DISCUSSION .......................................................................................... 13
REFERENCES ................................................................................................. 14
2
PREFACE
This study has been performed within the Basic Design phase of SKB and Posiva' s
development programme for the KBS-3H (i.e. horizontal) disposal concept.
3
1
INTRODUCTION
KBS-3H is a novel disposal concept where the copper-iron canister and the bentonite
blocks around the canister are to be packaged in a perforated steel container. These
perforated steel containers, separated by distance blocks of compacted bentonite, will
then be emplaced in horizontal deposition drifts, having a length of approx. 200 - 3 00
metres. SKB and Posiva have conducted a prefeasibility study of the concept in 2002
and the Basic Design phase will be finalised in early 2004.
In the present study the so-called equivalent flow rates from the interior of a damaged
canister into the geosphere are calculated as a function of the transmissivity of a rock
fracture intersecting the deposition drift and its distance from the defect in the canister.
Equivalent flow rate (litres/yr) gives the steady state release rate of a stable species into
the geosphere in a case where a constant concentration of one unit per litre is assumed
to prevail in the canister. The analyses are carried out for a fully saturated state, where
a swollen and homogenous buffer surrounds the canister. The effects of the perforated
steel container, which initially contains the buffer and canister, are not considered,
either.
The analyses have been carried out with the PORFLOW code, which is a CFD
(computational fluid dynamics) tool developed to solve problems involving transient or
steady state fluid flow, heat, salinity and mass transport in multi-phase, variably
saturated, porous or fractured media (http://www.acricfd.com). The use of PORFLOW
in near-field analyses for KBS-3HN type repositories is described in Nordman & Vieno
(2003). The PORFLOW code has been verified against VTT's REPCOM code as well
as the GoldSim code used by ENRESA (Nordman & Vieno 2003, Alonso et al. 2003).
Modelling of radionuclide transport in a KBS-3V type vertical deposition hole is
discussed in detail by Vieno & Nordman (2000). The report also includes an intercomparison of the modelling concepts used in the SR 97 (Andersson 1999, Lindgren &
Lindstrom 1999) and TILA-99 (Vieno & Nordman 1999) safety assessments.
4
2
TRANSPORT MODEL
Conceptual transport model
The conceptual transport model is presented in Figure 2-1. The canister is assumed to
have a large defect in the other end. The water volume inside the canister is assumed to
be in direct contact with the innermost parts of the buffer in block B 1. In the buffer
transport of dissolved species takes place by diffusion. Modelling of transport within the
buffer is truly two-dimensional. The geometrical data is presented in Table 2-1.
-
Canister interior
Bentonite
B4
B3
-4m
-2m
Bl
B2
Om 1m 2m 3m
Six alternative
locations
for the fracture
Figure 2-1. Conceptual transport model.
The deposition drift is assumed to be intersected by a water-conducting fracture. The
distance of the fracture from the defective end of the canister is varied as shown in
Figure 2-1. The transmissivity of the fracture is varied as well.
5
Table 2-1. Geometrical and PORFLOW node data.
Canister interior
3
•
water volume: 0. 700 m
•
number of nodes: 2 in the radial and axial directions
•
transfer into the innermost element of buffer block B1: full contact (severely damaged
canister)
Buffer block B1
•
length: 0.35 m
•
inner radius: 0.53 m
•
outer radius: 0.93 m
•
number of nodes in the radial direction: 9
•
number of nodes in the axial direction: 2
Buffer block B2
•
length: 3 m
•
radius: 0.93 m
•
number of nodes in the radial direction: 11
•
number of nodes in the axial direction: 12
Buffer block B3
•
length: 4.45 m
•
inner radius: 0.53 m
•
outer radius: 0.93 m
•
number of nodes in the radial direction: 9 (the two innermost nodes in the grid are isolated)
•
number of nodes in the axial direction: 17
Buffer block B4
•
length: 3 m
•
radius: 0.93 m
•
number of nodes in the radial direction: 11
•
number of nodes in the axial direction: 4
Transfer from bentonite into the groundwater flowing in fractures
Mass transfer of dissolved species from the stagnant porewater in the bentonite into the
groundwater flowing in a fracture intersecting the deposition hole is limited by the
boundary layer (film) resistance (Neretnieks 1982, Hillebrand 1985, Nilsson et al.
1991 ). SR 97 and TILA-99 employ the same approximation for this resistance, as
discussed in detail by Vieno & Nordman (2000). With the TILA-99 notations, the
equivalent flow rate is:
(2-1)
where
2bv is the volume aperture of the fracture (m)
r2
is the radius of the deposition hole (0.93 m)
Dw is the molecular diffusion coefficient in water (2·10-9 m2/s)
u
is the velocity of water in the fracture (m/s).
Alternatively, approximating that u = Qfrac I (2r2 2bv), where Qrrac is the flow rate in the
fracture intersecting the deposition drift, it is obtained that
6
Qbl
= 2 ~2 Dw Q frac 2bv
(2-2)
The flow rate in the fracture depends on the hydraulic gradient and on the transmissivity
(T) of the fracture, which may be related to the aperture of the fracture by Qrrac ,. . , T ,. . ,
(2bv)3 . The transfer coefficient Qb1 thus depends on the transmissivity by Qb1 ,...., (T) 213 .
In the present analyses the hydraulic gradient around the deposition drift is assumed to
be 1% after the closure of the repository and a reference fracture intersecting the drift is
assumed to have a transmissivity of 10-8 m2/s and a volume aperture of 250 J..Lm.
Table 2-2 then shows the transfer coefficient Qbl as well as some related quantities as
a function of the transmissivity of the fracture varied from 10-9 to 10-7 m2/s.
Table 2-2. Transfer coefficient (Qbl) from the buffer element at the mouth of the rock
fracture into the groundwater flowing along the fracture as a function of the
transmissivity of the fracture.
Transmissivity Flow rate
of fracture
in fracture Otrac
(m 2/s)
(litres/yr)
Aperture
2bv
(J..Lm)
Advection Transfer
velocity u coefficient
(m/yr)
(litres/yr)
1·1 o-9
0.59
120
2.7
0.19
3·1 o-9
1.8
170
5.7
0.39
1-1 o-s
5.9
250
13
0.87
3·1 o-s
18
360
26
1.8
1·1 o-7
59
540
58
4.0
Qbl
Omitting of transfer resistance in the bentonite at the mouth of the fracture
There is a diffusion resistance also in the bentonite at the mouth of the fracture. In
principle, the diffusion resistance is similar to the diffusion resistance in the buffer at the
outer mouth of a small hole in the canister, discussed in Section 3.1 ofVieno & Nordman
(2000). However, here the geometry is a half of cylinder, whereas in the case of a small
hole it is a half of a sphere. The diffusion equation for a stationary situation and half
cylindrical geometry is
ac
ac
J=-De·A(r)· Br =-De·(2nr2·nr)· Br
(2-3)
where
J
C
r2
A(r)
r
De
is the mass flow rate (atoms/yr)
is the concentration (atoms/m3 )
is the radius of the deposition drift (0.93 m)
is the diffusion area in the bentonite at the distance of r from the fracture
(2nr2 ·rtr)
is the distance from fracture (m)
is the effective diffusion coefficient in the bentonite (Table 3-1 ).
7
The solution is
(2-4)
where bv is half of the volume aperture of the fracture.
From the solution of Equation 2-4 the effective flow rate in the bentonite at the mouth of
the fracture can be approximated by
Q
ben
= 2 Jr2 ·r .
2
D
e
ln(r; / bv )
(2-5)
where ri is the width of the outermost element in the PORFLOW input at the surface of
bentonite (0.05 m).
For a neutral species with De of 1·1 o-Io m2/s and for a fracture with 2bv of 250 J.lm, Qben is
about 10 litres/yr, which is a significantly higher flow rate (implying thus a lower
transport resistance) than Qb1 (c.f. Table 2-2). For a cation with a higher De the flow rate
Qben would be even higher, but for an anion with a low De it would be lower.
Conservatively the transport resistance in the bentonite at the mouth of the rock fracture
is, however, omitted for all species. The transport resistance of the modelled system thus
consists of the (2-dimensional) diffusion in the buffer and the boundary layer resistance
represented by Qbi·
8
3
RESULTS
The behaviour of the near-field transport system is illustrated by means of three stable
elements (Table 3-1) representing a neutral, non-sorbing species N-S, a non-sorbing anion
(A) and a sorbing cation (C). Note, however, that the distribution coefficient (Ki) does not
affect the steady state equivalent flow rates presented below. The KI value affects only the
temporal behaviour of the transport system, i.e. how soon the steady state is obtained. The
release rate from the near-field into the geosphere is calculated in the saline and non-saline
conditions for solubility-limited inputs: a constant concentration of one unit per litre is
assumed to prevail in the canister interior. Similar illustrations have been made in Vieno
& Nordman (1999, 2000) and Nordman & Vieno (2003).
Table 3-1. Stable elements used to illustrate the behaviour of the near-field transport system.
Speciation
Buffer I non-saline
• Kc! (m 31kg)
•
•
f:
De (m 21s)
Buffer I saline
3
• Kc! (m 1kg)
•
•
f:
De (m 21s)
N-S
A
c
Neutral
Anion
Cation
0
0.43
1·10-10
0
0.05
5·1 o- 12
0.1
0.43
5·10-9
0
0.43
1·10-10
0
0.05
1·1 o- 11
0.002
0.43
1·10-9
The resulting equivalent flow rates for the three stable species in the non-saline as well
as saline conditions are presented in Tables 3-2 to 3-6 and Figures 3-1 to 3-5 as
a function of the transmissivity and distance of the rock fracture intersecting the
deposition drift.
Below each table, the respective equivalent flow rates obtained in the TILA-99
assessment (Vieno & Nordman 1999) as well as in the more recent study (Vieno &
Nordman 2000), where a similar canister model as in the present study was used, are
shown. In these studies, the transfer coefficient from the buffer in a KBS-3V type
deposition hole into the rock fractures was
in the median flow scenarios with non-saline (ns50) and saline (sal50) ground•
water: 0.2 litres/yr (corresponding thus to a fracture with a transmissivity of
approx. 1o-9 m 2/s in the present study, c.f. Table 2-2)
•
in the very high flow scenario with saline groundwater (vhflowsal) 3 litres/yr and
for non-saline groundwater (vhflowns) 5 litres/yr (corresponding thus to a fracture
with a transmissivity of approx. 1o-7 m 2/s in the present study, c.f. Table 2-2)
In addition a significant flow of groundwater was assumed to take place through the
upper part of the KBS-3V deposition hole (backfilled with the tunnel backfill) and in the
deposition tunnel (see Section 11.6 of TILA-99). The transport routes via these parts of
the near-field were the dominant transport routes for several long-lived radionuclides.
By investigating the obtained equivalent flow rates as a function of the distance of the
rock fracture from the damaged end of the canister and by comparing the total
equivalent flow rates in Tables 3-2 to 3-6 to the corresponding values of the boundary
layer flow rate Qb1 in Table 2-2, it is seen that the boundary layer resistance is the
9
dominant transport resistance for the neutral species and cation. Diffusion resistance
within the buffer is an important resistance only for the anion with the low diffusivity in
the buffer.
The equivalent flow rates from the KBS-3H deposition drift are lower than those from
the KBS-3V deposition hole in similar flow and fracturing conditions. The reason is that
the backfilled sections in the upper part of the deposition hole and tunnel become
important transport routes for stable species as well as for long-lived radionuclides. This
concerns especially cations with the assumed high diffusivity in the buffer and backfill
(Table 3-5 and 3-6, Figures 3-4 and 3-5).
Table 3-2. Equivalent flow rate from canister interior into geosphere (Qeq) for neutral species.
Transmissivity Qbl
of fracture
2
(m /s)
(litre/yr)
o-9
3·1 o-9
1·1 o-8
3·1 o-8
1·1 o- 7
1·1
Oeq
(1/yr) into fractures at different distances from the canister defect
-4 m
-2 m
Om
1m
2m
3m
0.19
0.16
0.17
0.18
0.18
0.18
0.17
0.39
0.30
0.34
0.38
0.36
0.35
0.33
0.87
0.54
0.66
0.82
0.76
0.70
0.64
1.8
0.80
1.1
1.6
1.4
1.2
1.1
4.0
1.1
1.7
3.3
2.5
1.9
1.6
TILA-99:
sal50/ns50 3.9 litres/yr, vhflowsal 7.0 litres/yr, vhflowns 9.0 litres/yr
Vieno & Nordman (2000): sal50/ns50 3.2 litres/yr, vhflowsal 5.3 litres/yr, vhflowns 6.5 litres/yr
Table 3-3. Equivalent flow rate from canister interior into geosphere (Qeq) for anion in nonsaline water.
Transm issivity Qbl
of fracture
2
(m /s)
(litre/yr)
o-9
3·1 o-9
1·1 o- 8
3·1 o- 8
1·1 o- 7
1·1
Oeq
(1/yr) into fractures at different distances from the canister defect
-4 m
-2 m
Om
1m
2m
3m
0.19
0.052
0.080
0.16
0.12
0.094
0.076
0.39
0.060
0.10
0.28
0.18
0.13
0.096
0.87
0.066
0.12
0.46
0.25
0.16
0.11
1.8
0.069
0.13
0.64
0.29
0.17
0.12
4.0
0.071
0.14
0.80
0.32
0.18
0.12
TILA-99:
ns50 0.44 1/yr, vhflowns 3.5 1/yr
Vieno & Nordman (2000): ns50 0.32 1/yr, vhflowns 0.83 1/yr
Table 3-4. Equivalent flow rate from canister interior into geosphere (Qeq) for anion in saline
water.
Transmissivity Qbl
of fracture
2
(m /s)
(litre/yr)
o-9
3·1 o-9
1·1 o- 8
3·1 o-8
1·1 o-7
1·1
Oeq
(1/yr) into fractures at different distances from the canister defect
Om
1m
-2 m
0.19
0.081
0.11
0.17
0.15
0.12
0.11
0.39
0.10
0.16
0.32
0.24
0.19
0.15
0.87
0.12
0.21
0.60
0.38
0.26
0.20
1.8
0.13
0.24
0.94
0.50
0.31
0.22
4.0
0.14
0.27
1.3
0.59
0.35
0.24
TILA-99:
sal50 0.69 litres/yr, vhflownsal 3.1 1/yr
Vieno & Nordman (2000): sal50 0.52 litres/yr, vhflownsal1.3 litres/yr
2m
3m
-4 m
10
Table 3-5. Equivalent flow rate from canister interior into geosphere (Qeq) for cation in nonsaline water.
Transmissivity Qbl
of fracture
(m 2/s)
(litre/yr)
aeq
(1/yr) into fractures at different distances from the canister defect
-4 m
-2 m
Om
1m
2m
3m
9
0.19
0.19
0.19
0.19
0.19
0.19
0.19
9
0.39
0.39
0.86
0.39
0.39
0.87
0.39
0.87
0.87
0.39
0.87
0.39
0.87
1.8
3.8
1.8
3.9
1.8
3.9
1.8
3.9
1.8
3.9
1·10"
3·10"
1·10"8
3·1 o-8
0.87
1.8
7
4.0
1·10"
1.8
4.0
TILA-99:
ns50 38 litres/yr, vhflowns 68 litres/yr
Vieno & Nordman (2000): ns50 36 litres/yr, vhflowns 64 litres/yr
Table 3-6. Equivalent flow rate from canister interior into geosphere (Qeq) for cation in saline
water.
Transmissivity Qbl
of fracture
(m 2/s)
(litre/yr)
aeq
(1/yr) into fractures at different distances from the canister defect
-4 m
-2 m
Om
1m
2m
3m
1·1 o-9
0.19
0.19
0.19
0.19
0.19
0.19
0.19
9
0.39
0.38
0.38
0.39
0.38
0.87
0.82
0.85
0.87
0.39
0.86
0.85
0.38
0.84
8
1.8
1.6
1.8
1.7
1.7
1.7
7
4.0
3.1
1.7
3.5
3.9
3.7
3.6
3.5
3·10"
1·1 o-8
3·1 o-
1·10"
TILA-99:
sal50 17 litres/yr, vhflownsal 24 litres/yr
Vieno & Nordman (2000): sal50 15 litres/yr, vhflownsal 21 litres/yr
3
2.5 .
~
2
Neutral species
c
C'
~
'
1.5
Saline & non-satine .
.. ' '' •.......... '
0.5
OL-----_L--~--~~~~~------~--~~~~~~
1~
1~
T (m2/s)
1~
Figure 3-1. Equivalent flow rate Qeq (litreslyr) for neutral species from the interior of
a severely damaged canister into a rock fracture intersecting the deposition drift as
function of the transmissivity of the fracture and its distance from the damaged end of
the canister.
11
1.5 r;::::====:::;:-~-~---:~~---=r------:-----r--~---:---.---~-n
Om
1m
2m
3m
-
-4m
Anion
.,
tT
0
__.......--
Non-saline
0.5 f- ··
~~
__
.........
--
............------
........... ........... ; ... .. .......... :........... , ........ ; .... .. , .. ... .;. .... : ....:____
... ,/......_;..o,..C. .............. ; ............... ; ......... .. : .......
; ...... ; ......; ..... ; ... .:..-J
....----=
::
----·
~~i_.,-__;__--'---o-~~
Figure 3-2. Equivalent flow rate Qeq (litreslyr) for anion in non-saline water from the
interior of a severely damaged canister into a rock fracture intersecting the deposition
drift as a function of the transmissivity of the fracture and its distance from the
damaged end of the canister.
- - Om
- - 1m
-
2m
-
3m
-
-4m
.,
tT
0
Q L-----~--~--~_L_L~~'~i_______ L_ _~--~~~~~
1~
1~
1~
T (m2/s)
Figure 3-3. Equivalent flow rate Qeq (litreslyr) for anion in saline water from the
interior of a severely damaged canister into a rock fracture intersecting the deposition
drift as a function of the transmissivity of the fracture and its distance from the
damaged end of the canister.
12
4
-
3.5
;;
Om
1m
2m
3m
-4m
(j
3
Cation
!)
2.5
Non-saline
I
/
1.5
0.5
~:-
~
----
...--
,...,.. ,_....
....V
!
(f
0~~
I
f
/
0
10-9
Figure 3-4. Equivalent flow rate Qeq (litreslyr) for cation in non-saline water from the
interior of a severely damaged canister into a rock fracture intersecting the deposition
drift as a function of the transmissivity of the fracture and its distance from the
damaged end of the canister.
4
-
3.5
-
Om
1m
2m
3m
-4m
h
~
.
.
~' '
;(/ / /
3
Cation
2.5
~
/J~
Saline
~
2
/
/~
11)
0
1.5
0.5
;.<'
..,-
-----:----:
_.,.
,.,.
~
,...... '..lP~
7/
,
Figure 3-5. Equivalent flow rate Qeq (litreslyr) for cation in saline water from the
interior of a severely damaged canister into a rock fracture intersecting the deposition
drift as a function of the transmissivity of the fracture and its distance from the
damaged end of the canister.
13
4
DISCUSSION
The results confirm that in a fully saturated state, where a swollen and homogenous
buffer surrounds the canister and no significant erosion of the bentonite takes place, the
boundary layer resistance between the stagnant porewater in the buffer and the groundwater flowing in fractures intersecting the deposition drift is a dominant transport
resistance in the near-field. The diffusion resistance in the buffer and thus the distance
between the defect in the canister and the fracture intersecting the deposition drift is
significant for anions which have a low diffusivity in the buffer thanks to anionic
exclusion. In similar flow and fracturing conditions, long-term release rates from
a KBS-3H deposition drift are lower than those from a KBS-3V deposition hole, where
the upper part of the deposition hole backfilled with the tunnel backfill as well as the
tunnel may become important release routes for long-lived radionuclides, if significant
flow of groundwater takes place through these parts of the near-field. This concerns
especially cations having a high mobility in the buffer and backfill.
The steady state equivalent flow rate gives a fully representative picture of the transport
only in the long term and for long-lived radionuclides. The maximum release rates of
medium- and short-lived radionuclides as well as of radionuclides in decay chains are
determined by the transient behaviour of the system depending on the transport times
and half-lives of the nuclides. Furthermore, when there is only a small defect in the
canister wall, the dominant transport resistance in the near-field is provided by the small
size of the defect.
14
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