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Pyrolysis of spent ion exchange resins is used to reduce radioactive waste volume and to make the final waste form more stable. The weight loss of cation exchange resin after pyrolysis is only 50%, while that of anion exchange resin is 90%. Fundamental experiments were performed to investigate the reason for the small weight loss of the former. The cation resin consists of base polymer and functional sulfonic acid groups. Chemical analyses •of the pyrolysis products showed that 65% of the functional groups decomposed at about 300°C and generated S0 2 gas. However, only a small amount of the base polymer was pyrolyzed even at 600°C and the weight loss was only 50%. TheIR and XPS studies on the residue showed that 35% of the functional sulfonic acid groups was converted to sulfonyl and sulfur bridges between the base polymers during pyrolysis. These bridges made the base polymers thermally stable. Therefore, the small weight loss of the cation resin was attributed to formation of bridges, which originated from the functional groups.

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Iodine separation technology using an inorganic adsorption material has been investigated in order to apply the technology to the off-gas treatment systems of nuclear facilities. Iodine removal efficiencies were checked by laboratory experiments using simulated off-gas streams of various conditions and the developed adsorbent, silver impregnated alumina (AgA). Laboratory test results demonstrated effective iodine removal with high decontamination factors (DF's) a t relatively high temperatures ( 2 100°C). Then the removal efficiency were confirmed using actual off-gas streams sampled from the dissolver off-gas treatment system of the Karlsruhe reprocessing plant. The D F ' s were over los with the AgA bed depth of lOcm and showed little change during the adsorption period, which indicated applicability of the iodine removal technology with AgA to nuclear fuel reprocessing plants. Iodine adsorption capacity and its release property were also investigated using simulated off-gas streams. The former had a value of -0.22g/g-AgA and this value could well predict the breakthrough property. The adsorbed iodine was judged stable during the storage of AgA saturated with iodine in air at temperatures below 500°C and in water a t -20°C after changing the adsorbed iodine form from AgIO, to AgI. Thus, the separation technology provided effective and stable iodine separation from the off-gas of nuclear facilities.