COMPLETE DOCUMENT (1862 kb) - OECD Nuclear Energy Agency

data are not of direct application to the long-term risk assessment but are the fundamental basis for the
assessment of the radiotoxicity ranking of radionuclides.
Based on this criterion, the long-term radiotoxic inventory depends on the source term which
is determined by the type of fuel (LWR-UO 2 , LWR-MOX, FR-MOX), the burn-up and the storage time
(up to a million years). These fuels contain the actinides and the long-lived fission products as major
radiotoxic constituents.
In terms of hazard factors the following ranking can be made [167] for spent fuel seven years
after discharge from the reactor.
238,239,240,241,242 Pu > 241,243 Am > 242,244,245,246 Cm >> 237 Np
However the short-term radiotoxic inventory of some fission products is comparable to that of
the actinides within a time horizon up to 100 years. Beyond 300 years only the long-lived fission
products remain radioactive ( 99 Tc, 93 Zr and 135 Cs) and constitute a radiotoxic inventory which is roughly
1 000 times smaller than that of the actinides. 129 I is in terms of effective dose coefficient (Sv/Bq)
comparable with the actinides but its radiochemical concentration in the spent fuels, expressed in
Bq/THM, is much lower. In vitrified HLW from reprocessing, the 129 I inventory is negligible.
Among the actinides the most important are Pu, Am and Cm, the effective dose coefficients
[165,166] are given in the next Table II.16.
Table II.16. Effective dose coefficients of actinides FD RN [165,166]
Element Nuclide Sv/Bq (ingestion)
Uranium
Neptunium
Plutonium
Americium
Curium
235 U 4.6×10 -8
238 U 4.4×10 -8
237 Np 1.1×10 -7
238 Pu 2.3×10 -7
239 Pu, 240 Pu 2.5×10 -7
241 Am, 243 Am 2.0×10 -7
243 Cm 1.5×10 -7
244 Cm 1.2×10 -7
245 Cm, 246 Cm 2.1×10 -7
The long-lived fission products have toxicities which are very variable as shown in Table II.17.
In the case of the OTC all radionuclides contribute to the source term and the long-term
radiotoxic inventory is mostly due to Pu, MAs and some LLFPs. However, the conditioning operations
can provide artificial barriers which are potentially capable of confining the radionuclides within their
package for thousands of years. After this time interval nothing can be predicted except that the
solubility of the actinides (except Np) is generally very low whereas the long-lived fission products,
particularly 135 Cs, 129 I and in some cases 99 Tc, display high mobilities in the geosphere.
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