Post irradiation examination of 84F-12A capsule containing uranium-plutonium mixed carbide fuels

Two fuel pins containing uranium-plutonium mixed carbide pellets having different carbon content, (U,Pu)C1.0 and (U,Pu)C1.1, were encapsuled in 84F-12A and irradiated in JMTR up to 4.5 and 3.7%FIMA at a peak linear power of 60 and 49 kW/m respectively. The capsule cooled for ∼5 months was transported to Reactor Fuel Examination Facility and subjected to non-destructive and destructive post irradiation examinations. It was proved from the post irradiation examination that the mixed carbide fuel performance irradiated up to 4.5%FIMA was satisfied. The gamma ray scanning of the fuel pins indicated the transfer of cesium to the plenum region. (U,Pu)C1.1 fuel pellets showed two times larger fission gas release ratio than (U,Pu)C1.0 fuel pellets because the former had relatively higher open porosity. At the central part of the fuel pellets, the number of the small pores decreased and the grain growth was stimulated in (U,Pu)C1.0 fuel pellets. Slight carburization observed near the inner surface of the cladding tube did not affect the fuel pin performance itself. (author)