Architecture and management of a geological repository - Andra

3 – High Level Long-Lived WasteFigure 3.2.131,800-litre, stainless steel drum containing cemented cladding waste.They contain an average of 776 kilograms of cladding waste, made up of 80.7% zirconium-tin(zircaloy 4) alloy, 15.9% stainless steel and 3.4% nickel alloy. The package weight (drum + waste +matrix) is 3.5 tonnes on average. The residual heat rating in the packages from the cobalt-60 is todayin the order of around ten watts. It will be about three watts by 2025. The equivalent β-γ dose rate inpseudo-contact with the packages (5 cm) is currently in the order of 4 Sv/h; it will be in the order of0.5 Sv/h by 2025. Water radiolysis in the cementing matrix produces hydrogen.• Compacted cladding wasteAs indicated previously, a new method of conditioning cladding waste was introduced on the LaHague site in 2002. This involves compacting waste placed preliminarily in claddings, before beingmoved to stainless steel containers (CSD-C). The compacting process is applied to cladding wasteproduced from NUGG and PWR fuels reprocessed previously and now stored in silos and pits, andcladding waste produced from current and future reprocessing operations of fuel unloaded from thePRW reactors. As mentioned above, some packages also contain compacted technological waste fromthe site's operating and/or maintenance shops. Given the diversity and nature of the flows of waste inquestion, distinction is made between four sub-assemblies of compacted cladding waste packages(CSD-C).The first package sub-assembly contains cladding waste from UOX, enriched recycled uranium andMOX fuel reprocessing mixed with metallic and organic technological waste. The hypotheses adoptedare (i) fuel reprocessing on average eight years after unloading from reactors and (ii) average weightof 420 kilograms of conditioned waste per package (including compacting claddings). Based on thesehypotheses, the heat rating of the packages, calculated for an envelope radiological inventory of thevarious waste flows mentioned above, is around 30 watts. Thermal decay of these packages is givenin Figure 3.2.12. Package irradiation levels, initially around fifty sieverts per hour (Sv/h) is in theorder of 15 Sv/h after a ten-year cooling period. The radiolysis of the organic waste in the packagesmade up of technological waste produces hydrogen. Note also that radioactive elements other thantritium (with the symbol T or 3 H), carbon-14 ( 14 C), chlorine-36 ( 36 Cl), argon-39 ( 39 Ar) and krypton-85( 85 Kr). The finished packages weigh approximately 520 kilograms.Like the previous packages, the second package sub-assembly contains a mixture of UOX, enrichedrecycled uranium and MOX cladding waste and technological waste. It differs from the first in thetype of technological waste, here formed of metallic materials only. Unlike the first sub-assemblypackages, it does not therefore generate hydrogen through radiolysis. However, there is a risk of thewaste releasing traces of radioactive gases ( 3 H, 14 C, 36 Cl, 39 Ar and 85 Kr). This raises the question oftheir containment as close to the waste as possible; this issue is dealt with in Chapter 4.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM87/495