Some Topics on Improvement in Production Technology and Fission Product Behavior of HTTR Coated Particle Fuel

摘要

In collaborations of the Japan Atomic Energy Research Institute (JAERI) and the Nuclear Fuel Industries, Ltd. (NFI), various improvements have been made on the production processes of coated fuel particles and fuel compacts, in order to reduce the failure fraction of the fuel for the High Temperature Engineering Test Reactor (HTTR). Irradiation performance of the fuels recently produced by the improved technology was successfully demonstrated by the 13th OGL-1 fuel assembly irradiation, performed in an in-pile gas loop, OGL-1.rnIn the field of fission product behavior, a peculiar distribution of ~(110m)Ag was noticed in its radial profile in the graphite sleeve; the concentration of this nuclide was markedly reduced with increasing concentration of metallic impurities including ~(60)Co. This behavior may be ascribed to competitive co-sorption of Ag and the impurities for the trapping sites on the surface of open pores in the graphite material. Obtained results so far suggest that this nuclide should be retained effectively in the highly-purified graphite sleeve under the HTTR conditions.rnAs for the ZrC-coated particle fuel being developed as an advanced HTTR fuel, much better retention of Cs was observed than for SiC-coated particles in isochronal annealing experiments at temperatures between 1500 and 2300℃; while relatively poor retention of Ru was observed for ZrC-coated particles in this temperature range.