LONG-TERM MEASUREMENT OF HE-3 RELEASE BEHAVIOR FROM ZIRCONIUM-COBALT TRITIDE

Release behavior of helium-3 (He-3: tritium beta-decay product) from zirconium-cobalt (ZrCo) tritide has been investigated for three and a half years as a part of the long-term reliability and safety evaluations of ZrCo for tritium (T) use. The release fractions of He-3 from ZrCo tritide were constantly less than 3% for the initial 2 yr under the following conditions: holding temperatures 293-523 K, initial atom ratios (T/ZrCo) 0.3-1.5, and numbers of hydrogenation-dehydrogenation cycles before tritiation 1-10. After 2 yr, however a He-3 release fraction (293 K ZrCoT (1.3), cycle) has been increasing more than 25% and the ratio of residual He-3 accumulated in tritide and ZrCo (He-3/ZrCo) is about 0.2. From the above point of view, two years would be a safe storage period of ZrCo tritide without any care under these conditions.