Evaluation and mitigation of tritium memory in detritiation dryers

In atmospheric detritiation, and other tritium processes, tritium is adsorb ed on zeolites (molecular sieves) in the form of tritiated water. Regenerat ion removes almost all the physically adsorbed water, but a proportion rema ins permanently in the zeolite and binder structure as chemically bound wat er or hydroxyl groups. Exchange between adsorbed water and bound water mean s that tritiated water is retained in the structure after regeneration. At the end of its life, the zeolite therefore constitutes a tritiated waste. F urthermore, if an atmosphere detritiation dryer (ADD) gets highly contamina ted from a tritium spill, retained tritium contaminates both the small amou nt of vapour leaving the bed during the next drying cycle, and the water pr oduced in the subsequent regeneration. This report first describes experime nts to measure the tritiated water retained in at 5A zeolite bed after stan dard regeneration treatments, and then investigates strategies to mitigate the effect: more thorough regeneration and isotope swamping or elution. The effect of zeolite aging after thermal cycling is also seen. (C) 1999 Elsev ier Science B.V. All rights reserved.