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Figure II.34 Cavern-convection scenario, evolution of individual dose rate
for the most important nuclides (I-129*: refers to full 129 I inventory in spent fuel)
10 -6
Total
Dose rate (Sv/year)
10 -7
10 -8
10 -9
10 -10
I-129
Np-chain
Se-79
10 -5 10 3 10 4 10 5 10 6
I-129*
U-Ra-chain
Am-chain
Th-chain
10 -11
C-14
10 -12
Tc-99
Time (year)
In 1988, a comparative performance study (PAGIS) was undertaken within the framework of
the European Commission in order to assess the long-term impact of the disposal of HLW resulting
from a conceptual 10 GWe reactor park operated for 30 years. The equivalent of 8 180 tHM glass
canisters (about 900 m 3 vitrified HLW) were considered as the radioactive source term (fission
products, minor actinides and corrosion products). The calculations were refined in the PACOMA [193]
and EVEREST [194] projects.
The actinides Am and Cm and the daughter product 240 Pu decay completely within the first
10 m of the clay layer. This is not the case with 237 Np or with uranium if it were disposed of. The
maximum annual dose due to the presence of 237 Np is about 0.02 µSv/year when the use of drinking
water from a well in the upper aquifer near the clay layer is considered as the main pathway. According
to the same scenario, the doses due to 135 Cs and 99 Tc amount to 0.015 µSv/year and 0.15 µSv/year,
respectively. Figure II.36 shows the contribution of the different nuclides.
In a climate change scenario, where water underlying the clay layer might be used for drinking
purposes, the dose to man due to 129 I would reach the tolerance level of 0.2 mSv/year if all the iodine
waste (as AgI) recovered from the effluents of the reprocessing plant were stored in the clay repository.
Since 95 to 99% of 129 I is separated from the HLW during the reprocessing operations and
discharged in the ocean, only 1 to 5% is supposed to be associated with the cladding materials, so the
dose resulting from the leaching and migration of 129 I in the near field comes from MLW and would
amount to 30 µSv/year. Partitioning of 129 I during reprocessing and washing of the hulls in order to
minimise the residual quantities of iodine is therefore very important. Conventional transmutation of
iodine waste by n-γreaction in LWRs has proved not to be very effective. Selective transmutation
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