COMPLETE DOCUMENT (1862 kb) - OECD Nuclear Energy Agency

decontamination factor of more than one hundred is required for the RE fraction. A 99% purity involves
a separation factor of more than 1 000, which is at the technical limit for elements such as the
lanthanides and the actinides with very similar chemical properties. Recent developments in chemical
separation techniques have improved the prospects for solving that problem.
The adaptations to be made to the current flowsheets and their translation into technological
realities are a difficult task which is outside the scope of this report. Future reprocessing plants will
possibly include MA and LLFP partitioning rigs from the design phase on.
3.2.3.3 Fabrication of MA targets for heterogeneous irradiation in LWRs
In the medium term, only thermal reactors and particularly LWRs are available for irradiation
of MA-loaded fuel or targets. Fabrication of irradiation targets with industrially representative
quantities of MAs is difficult to accomplish even in pilot-scale hot-cell facilities.
Experience has been gained in the production of isotopic heat sources, but the present
radiologic context and the ALARA limitations to be expected from regulatory bodies on industrial
activities render industrial recycling of MAs very different from what has been done in the past for
military and space applications.
The presence of large quantities of 241 Am accompanied by 1 to 10% RE will require fully
gamma shielded and remotely operated fabrication facilities. The presence of 5% 244 Cm in an
241 Am- 243 Am target will amplify the degree of technical complexity due to the additional neutron
shielding resulting from the spontaneous fission rate and from the α-n reaction in oxide-type isotopic
targets.
3.2.3.4 Separation of long-lived fission and activation products
A number of radiologically important fission/activation products play a potentially important
role in the assessment of a geologic repository and have been considered in a P&T option. The following
nuclides have to be assessed: the fission products, 99 Tc, 129 I, 135 Cs, 79 Se, 93 Zr and 126 Sn, and the
activation products, 14 C and 36 Cl.
99 Tc is a fission product with a half-life of 213 000 years which occurs as Tc metal and TcO 2
in the insoluble residues and as pertechnetate ion in the HLLW solution. Its radioactive concentration in
spent fuel of 45 GWd/tHM is 6×10 11 Bq/tHM and its radiotoxicity is characterised by an annual limit of
intake (ALI) by ingestion of 3×10 7 Bq/year. In order to effectively address the long-term radiotoxicity
problem both fractions ought to be combined before any nuclear action is taken towards depletion by
transmutation. The extraction of soluble Tc is relatively easy. The similarity between Tc and the
platinum metals in insoluble waste and the nature of the separation methods (pyrochemical techniques)
makes this partitioning operation very difficult. Tc displays only a radiotoxicological hazard when
submitted to oxidative underground conditions (Tuff, Yucca Mountains). In reducing deep underground
aquifers the migration of 99 Tc is negligible.
129 I is separated from the HLLW during the conventional reprocessing operations. It occurs in
the scrub liquids of the dissolver. The radioactive concentration in spent fuel is 1.6×10 9 Bq/tHM and its
ALI is 2×10 5 Bq/year. The separated fraction can either be stored on a specific adsorbent or discharged
into the ocean. Since 129 I has a half-life of 16 million years it may very probably enter into a world-wide
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