4th SYMPOSIUM RELEASE OF RADIOACTIVE MATERIAL FROM REGULATORY CONTROL
Harmonisation of Clearance Levels and Release Procedures
20 - 22 March 2006
Hotel Hafen Hamburg
GERMANY
The role of clearance in the management of
future fusion reactors radioactive materials
V. Massaut a, L. Di Pace b, L. Ooms c, K. Brodén d, R.A. Forrest e, M. Zucchettif
a EFDA-CSU
Garching Boltzmannstrasse 2, D-85748 Garching bei Munchen, GERMANY
EURATOM/ENEA sulla Fusione, Via Enrico Fermi 45, 00044 Frascati, ITALY
c SCK.CEN, Boeretang 200, 2400 Mol, BELGIUM
d Studsvik ® RadWaste AB, SE-611 82 Nyköping, SWEDEN
e EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, U.K.
f EURATOM/ENEA Fusion Association, Politecnico di Torino, Italy
b Associazione
Abstract
Under the framework of the European Power Plant Conceptual Study (PPCS), studies
were carried out on the radioactive material management from future commercial fusion
power plants, including among others: clearance and recycling, tritiated waste, waste
categorisation, interim storage and final disposal.
The present paper is focused on the important role that clearance will have in the
management of such material flows.
From different studies, performed inside the European Fusion Technology Programme, it
is evident that fusion radioactive materials will be characterised by the following specific
aspects:

Large quantities;

Mostly solid activated and contaminated material;

Reduced radioactivity in the medium term (< 100 y), no radioactivity in the long
term, due to a careful selection of materials;

Low heat generation density and low radiotoxicity;

No transuranic elements beyond trace levels;

No proliferation concerns.
These aspects will ensure that fusion materials can be managed so as to leave reduced or
even no burden to future generations. The only present concern is the large quantities of
radioactive materials calculated to be produced. The possibility of drastically reducing this
amount is based on the clearance and recycling of material arising from a fusion power
plant.
While clearance is based on the residual content of radioactivity, recycling involves also a
mixture of socio-economic and environmental issues that are being investigated.
The present paper will be mostly focused on the important role that might be played by
well-defined and harmonised clearance criteria on fusion material management.
A categorisation based on the neutron transport and activation calculations carried out on
the four different PPCS concepts has revealed the importance that might be played by the
clearance process on the reduction of the amount of material requiring disposal.
The four investigated PPCS models span a range from relatively near term, based on
limited plasma physics and technology extrapolations, to a rather advanced concept. The
technological issues are determined by the different combinations of materials such as
armour, structural material, coolant, breeder and neutron multiplier.
The activation of the materials in all four Models decays relatively rapidly – very rapidly at
first and broadly by a factor ten thousand over a hundred years. For much of this material,
after an adequate decay time, the activity falls to levels so low that it could be “cleared”
from regulatory control. The estimated share of clearable material ranges up to about 50%
of the total mass. Exploiting to a full extent the possibility to carry out recycling would
reduce to a very limited quantity the amount of material to be disposed of.
1. Introduction: setting the scene
The concept of clearance and free release of radioactive materials were first considered by
the decommissioning industry as these concepts and the values eventually attached to
them could have a very large impact on the radioactive waste produced from dismantling
operations.
Nevertheless, the clearance or release of materials has also impacted on the design and
conceptual studies of future fusion plants. Moreover, as the fusion reaction does not
produce radioactive “ash”, most of the radioactive wastes produced come from activation
of the materials under neutron bombardment, contamination by the tritium present in the
plant and contamination of the cooling loops through erosion/corrosion and neutron
irradiation. Most of these products can be controlled by an adequate selection of the
materials facing the plasma and subject to neutron irradiation and by adequately confining
the tritium. But finally the quantity of material to be considered as radwaste will strongly
depend upon the clearance level for the different isotopes to be considered. For a fusion
plant the quantity of material can be very significant. In order to understand the issues, the
principles of fusion are summarisedl.
The fusion reaction, on which most of the research for developing a power plant is based,
is the one involving Deuterium and Tritium as the fuel. This reaction gives rise to the
production of a neutron with energy around 14 MeV:
2D
+ 3T => 4He + n + Energy
Most designs of fusion devices using this reaction concentrate on the Tokamak concept ,
based on magnetic confinement of the hot plasma (the other main research route being
studied is inertial fusion, which will not be further considered in this paper). For different
physical reasons, the possibility of generating more energy by the fusion reactions than is
input to heat the plasma is roughly linked with the size of the plasma and thus with the size
of the machine. Therefore, there is a physically inherent need to develop large machines
to be able to generate practical amounts power by thermonuclear fusion. The size of the
machines thus tends to show an increasing trend, going from small laboratory machines to
large research installations (such as JET, JT-60,…) and now increasing to a large size
research plant (ITER).
The way forward towards electricity generation is envisaged as follows: JET → ITER →
DEMO → Commercial power plant; the DEMO reactor being the first one to actually
generate electricity from the fusion process. For the development of the DEMO plant, after
the construction of ITER, different concepts have already been studied in Europe, in the
Power Plant Conceptual Study (PPCS). The four investigated PPCS models span a range
from relatively near term, based on limited plasma physics and technology extrapolations,
to a rather advanced concept. The technological issues are determined by the different
combinations of materials such as armour, structural material, coolant, breeder and
neutron multiplier.
In order to have an idea of the machine size, and the main parameters related to
radioactive waste production and the clearance of materials, some important parameters
of the different machines are summarized in the table below:
Table I: general data about some fusion machines (*)
Major radius (m)
Minor radius (m)
Plasma volume (m3)
Plasma (peak) power (MW)
Quantity of tritium in the
machine (instantaneous)(g)
Total neutron production
(n/s)
Neutron load (MW/m2)
Neutron fluence (n/cm2)
General mass of the reactor
(T)
Estimated total mass of
radwaste (T)
Mass of considered waste
for clearance (T)*
JET
2.96
2.10/1.25
80
16
~30
ITER
6.2
850
~410
3 000
(max. allowed
=90)
(~2000 in buffer
storage)
DEMO like
PPCS A
PPCS AB
9.8
9.56
3.27
3564
~5500
~4250
~3000
~3000
(650 g/day)
1.5*1020
0.3-0.5
>> 2800
~2.2-2.96
1.84
~163 000
~123 700
~60 000
metal
~25 000
metal
~5000
(incl.concrete)
~70 000
(concrete)
This table puts the various issues into perspective. It helps to set the scene and to
illustrate the quantities of materials that fusion power plants will generate. Moreover,
presently it is foreseen to replace regularly (every 2 to 5 years) the components which are
subjected to the highest particle bombardment such as the so-called divertor.
Moreover, it should be stressed that if the detritiation of material is effective, then fusion
will produce mostly activated material, which, if adequately selected, could lead to the free
release of most of the material present in the plant. The possibility of releasing materials,
in large quantities (thousands of tons) is thus at the basis of the importance given to the
clearance of material from regulatory control.
2. Importance of clearance for fusion plants
Even though the construction of next large experimental reactor (ITER) has yet to begin,
the first conceptual designs have already been carried out for future power plants, since
the problems to be solved by ITER will be derived from these studies.
One of the main advantages of fusion power is that it does not produce long-term (half-life
> thousands of years) radioactive waste. However, this favourable characteristic can be
fully exploited only in a power plant design that pays careful attention to the disposition
*
Note: the quantities given here can be estimated after a certain period of decay (50 to 100 years)
and removal routes for the materials arising during operation and maintenance. The size of
the machine is important, as large amounts of materials will be produced, mainly at the
end-of-life of the plant but also during operation, as some components are intended to be
replaced during the operating lifetime. Table 1 above gives some orders of magnitude of
these amounts, which are to be counted in thousands of tons of metallic materials and
probably even more in concrete from the bioshield.
The current designs of fusion power plants takes into account these aspects and attempts
to reduce and minimize the quantity of material that needs to be considered as radioactive
waste. Nevertheless, the values of the clearance levels will have a very important impact
on these amounts of materials, and so it is necessary to consider a fusion specific
approach, or at least to take into account the fusion specific nuclides, when determining
the impact of future power plants.
3. Issues of clearance for fusion reactors
There are probably two main issues for the use of clearance in fusion reactors: the first
one concerns the presence of tritium, mostly due to the diffusion of this nuclide within the
bulk of the material and the presence of significant quantities of tritium in fusion plants. To
have an idea of the quantities of tritium, Table 1 gives also an order of magnitude of the
total quantity present in the machine for the different facilities foreseen in the mid-term.
When converting these amounts to activity, (note that 1g 3H ~ 10 000 Ci or 3.7x1014 Bq)
this issue is put into perspective.
It is indeed foreseen to detritiate the materials before proceeding with handling or removal,
as even shallow land disposal requires limiting the amount of tritium included in the waste
streams (see reference [8]). Various detritiation methods are currently being studied and
developed for metals and other materials. Nevertheless, and this is probably the most
important issue concerning clearance, the clearance levels for tritium are very variable
between different countries.
Table 2 below gives an overview of the range of clearance values applied to tritium in
different countries of the European Union, as well as the value given as a guideline in the
recent EC-RP 122 [ref]. The large variability of the clearance level for tritium, ranging from
4.10-1 Bq/g in U.K. to 1.106 Bq/g in the Netherlands, i.e. a variation of more than 6 orders
of magnitude is obvious This is probably due to the very low radiotoxicity of the inhaled (or
ingested) tritium, which is in the range of 1.8 10-11 Sv/Bq [11], and to the relatively poor
knowledge of the effect of tritium on the cells of the human body. This large variation is
also given in graphical form in Figure 1 below.
One can easily understand that, with a large variation in the tritium content in solid
materials, it is not easy to finalise a design for detritiation systems, and that it can have, for
fusion plants, a direct impact on the economy of the plant and the plant operational cost.
Some coordinated approach, based on commonly accepted principles would be useful in
the context of reactor design and waste minimization studies.
Sweden
UK
EC RP 122
1.0E+00
Finland
1.0E+00
1.0E+00
1.0E+00
Netherlands
1.0E-01
1.0E-01
1.0E+00
1.0E+00
1.0E-01
1.0E+00
1.0E+01
1.0E+03
1.0E+00
1.0E-02
1.0E-01
1.0E-02
1.0E-02
1.0E-02
1.0E-02
Luxemburg
5.0E-01
5.0E+00
5.0E-01
1.0E+00
5.0E-01
5.0E+00
5.0E+00
5.0E-02
4.0E-02
5.0E-01
2.0E+00
1.0E-01
5.0E-01
1.0E+02
1.0E+03
9.0E-03
2.0E-02
1.0E-01
7.0E-02
3.0E-02
2.0E-02
4.0E-02
Italy (*)
Greece
1.0E-01
1.0E-01
1.0E+00
1.0E+00
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+00
1.0E-02
1.0E-01
1.0E-02
1.0E-02
1.0E-02
1.0E-02
Germany
Am
Pu
137
Cs
90
Sr
60
Co
65
Zn
51
Cr
3
H
238
U
232
Th
228
Th
228
Ra+
226
Ra+
210
Pb
210
Po
239
Denmark (°)
241
Belgium
Nuclide
Table 2
Clearance levels (CLs) in [Bq/g]
From [10] based on EC-RP 134
5.0E-02
4.0E-02
5.0E-01
2.0E+00
1.0E-01
5.0E-01
1.0E+02
1.0E+03
1.0E+00
1.0E+00
1.0E+01
1.0E+02
1.0E+00
1.0E+01
1.0E+03
1.0E+06
1.0E+00
1.0E+00
1.0E+00
1.0E+00
1.0E+00
1.0E+02
1.0E+02
1.0E-01
1.0E-01
1.0E+00
1.0E+00
1.0E+00
1.0E+00
1.0E+01
1.0E+01
1.0E-01
1.0E-01
1.0E-01
1.0E+01
1.0E-01
1.0E+01
1.0E-01
1.0E-01
1.0E-01
5.0E-01
5.0E-01
5.0E-01
5.0E-01
5.0E-01
5.0E-01
1.0E-01
1.0E-01
1.0E-01
5.0E-01
1.0E-01
5.0E-01
1.0E-01
4.0E-01
4.0E-01
4.0E-01
4.0E-01
4.0E-01
4.0E-01
4.0E-01
4.0E-01
1.11E+01
2.59E+00
2.59E+00
3.70E-01
3.70E-01
7.40E-01
3.70E-01
1.0E-01
1.0E-01
1.0E+00
1.0E+00
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+00
1.0E-02
1.0E-01
1.0E-02
1.0E-02
1.0E-02
1.0E-02
3.0E-02
1.0E-01
7.0E-02
3.0E-02
4.0E-02
4.0E-02
(°) for natural radionculides
(*) clearance levels proposed for the decommissioning of Caorso NPP
Figure 1 - General clearance levels for tritium (H-3) (no multi-nuclide contamination) (source [9])
A second aspect is the changes made to the clearance values over time and the impact
that these values can have on the amount of material to be treated as radioactive
materials to be recycled or disposed of as radwaste. To illustrate this aspect, one can
consider two approaches recently used for the estimation of the radioactive substances
arising at the end of life of a fusion facility, after a sufficient decay time for the removal of
short-lived radionuclides.
The first approach is rather academic and concerns the ITER facility, to be built in the next
few years in Europe. This estimate is considered as academic, as France does not apply
the free release of materials coming out of nuclear radwaste zones, and as the material
selected has beeen changed in a recent design; but the conclusions remain useful.
The estimate concerns the shielding part of the outboard vacuum vessel. The calculation
was carried out to evaluate the possible influence of the changes from the IAEA Tecdoc
855 [ref[ and the new IAEA safety guide RS-G-1.7 [ref].
Figure 2: effect of the clearance levels changes (from [12])
One can clearly see, in Figure 2, the effect of the changes. The material, which would be
clearable after a decay time of about 100 years with the “old” value, has to be treated as
radioactive material (or waste) as it would become clearable, under the new approach,
only after about 6000 years. Further analysis of this issue [12], shows that the main
radionuclide which responsible for this significant change is 63Ni for which the clearance
level was reduced by 40%. This typical academic example shows clearly how even small
changes can have an important impact on the design evaluation and the associated costs.
A similar calculation was also carried out for PPCS (Power Plant Conceptual Study) plant
model C (using a dual coolant lithium-lead blanket) for which the change from Tecdoc 855
to the Safety Guide RS.G.1.7 led also to a longer decay time to reach the clearance level,
changing from about 100 years to 10 000 years for a portion of the vacuum vessel [7].
Here also the main nuclide responsible was 63Ni in the short-term and then 14C at longer
times.
In general, the estimated share of clearable material in a shut down fusion plant, after
about 100 years of decay period, ranges up to about 50% of the total mass [ Luigi?]. A
large part of the remaining material can probably be recycled, providing the necessary
technology and processes are put in place. But this proportion can depend strongly of the
clearance levels attached to fusion relevant radionuclides.
It has to be noted that most of the nuclides relevant for fission (e.g. 60Co, 63Ni, 54Mn, 14C,
152Eu,) are also relevant for fusion purposes. Nevertheless, regarding the very hard
neutron spectrum of fusion plant, some specific radionuclides can appear to be more
important than in fission facilities [7]. Moreover, the aspect of tritium clearance level is
specific to fusion as the amounts of tritium in fusion plants are several orders of magnitude
larger than in any fission power plants.
4. Conclusions.
This paper is intended to make the clearance, radioprotection and radioactive waste
community aware of the implication that decisions taken for the fission industry can also
have repercussion for future installations like fusion plants.
Thermonuclear fusion power is still in the development phase, one of the objectives of
research is to minimize the burden for future generations, created by the production of
today’s energy. Therefore, the minimisation of radioactive waste production is an important
goal driving the development road map for future fusion plant.
The clearance of materials from fusion plays a primary role, as it would allow a drastic
reduction in the amount of waste to be disposed of, and designers and developers are
committed to produce materials and plants which give rise mostly to clearable materials
(allowing for a certain period of radioactive decay). Therefore in parallel to the necessary
developments and attention paid in the design of the plant to avoiding activating materials,
it is also important to have very clear and stable procedures and levels for the clearance of
materials, and that fusion specific radionuclides, including tritium, should be taken into
account in the definition of clearance level and dose distribution scenarios.
References
[1]
A conceptual study of commercial fusion power plants
Final Report of the European Fusion Power Plant Conceptual Study (PPCS)
EFDA-RP-RE-5.0
April 13th, 2005
[2]
JET
[3]
Waste Issues and Detritiation activities at Culham
A.Perevezentsev & J. Williams
Active operations, UKAEA Culham
[4]
Categorisation of Active Materials from PPCS Model Power Plants
R. Forrest, N. Taylor & R. Pampin
Euratom/UKAEA fusion assoc. Culham Science Centre
IAEA Technical Meeting, Vienna, 5-7 July 2005
[5]
Neutron transport and activation calculations for PPCS plant model AB
R. Pampin
UKAEA/TW4-TRP-002 Deliverable 2e
Revision 1, April 2005
[6]
Assessment of tritium control in PPCS model AB blanket systems
Report on the task EFDA TW4-TRP-002-D2b
RAPPORT DM2S SERMA/LCA/RT/05-3614/A
Wilfrid Farabolini, CEA
14/12/2005
[7]
Current Challenges Facing recycling and clearance of fusion radioactive materials
L.A. El-Guebaly et al.
Fusion Technology Institute, University of Wisconsin
UWFDM-1285
November 2005
[8]
Evaluation of the radiological consequences of tritium present in radioactive waste
components from fusion reactors
EFDA Technology Workprogramme Task TW4-TSW-001-D1b Waste and
decommissioning strategy: Waste disposal criteria
Rrestricted contract report SCK•CEN-R-4051, 04/DMa/P-62
Dirk Mallants
December, 2004
[9]
State of the art in the field of recycling and clearance.
Safety criteria, regulations and implications for the fusion industry
EFDA task TW4-TSW-001/ENEA/D2 (Rev.0)
FUS-TN-SA-SE-R-132
L. Di Pace
September 2005
[10] ENEA part of the Art.5.1.a. task, and reminder of former results and reports
L.Di Pace ENEA CR Frascati
Presented at the Final Meeting of the contracts TW3-TSW-001 and -002 and TW4TSW-001 and -002
Garching, January 17th, 2006
[11] Le tritium
Communiqués IRSN
Available on:
http://www.irsn.org/vf/04_act/04_act_1/04_act_archives_ipsn/04_act_communiques_2002/04_act_020128.shtm
28/01/2001
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(Activation calculations for the ITER port cells and ACP assessment)
FUS-TN-SA-SE-R-135
G. Cambi, D.G. Cepraga, M. Frisoni
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