Study on tritium release from solid breeding materials using the research reactor “YAYOI”

Abstract

Tritium release behavior from solid breeding materials was studied in order to clarify the mechanism of migration process. In-situ tritium release experiments (TTTEx) and in-situ luminescence measurements from radiation defects using the research reactor YAYOI at the University of Tokyo played important roles in these studies combining with off-pile experiments and modeling studies. In in-situ tritium release experiments, intra-grain and grain boundary diffusivities were separately evaluated. The chemical from of the released tritium was found to be determined by the oxygen potential in the system. Surface reaction, which often becomes the rate determining step in tritium release, was intensively studied. The surface reaction rate was found to be determined by the oxygen potential in the system and swamping reaction with H 2 or H 2O. It was also suggested that at low oxygen potential bonding strength of surface -OT differs from that at high oxygen potential. This was also supported by off-pile infrared absorption study of surface -OH. Tritium surface reaction model (DAD) was constructed based on these results. The tritium residence time agreed well with experimental results. In order to study the behavior of radiation defects and its interaction with tritium migration behavior, in-situ luminescence measurement and tritium release experiments under reactor irradiation at high temperature and under controlled atmosphere were conducted. As a first step, defects behavior under irradiation was studied.