Report of the collaboration project for research and development of sphere-pac fuel among JNC-PSI-NRG (II); Irradiation tests and post irradiation examinations (Joint research)

Nakamura, Masahiro  ; Ozawa, Takayuki   ; Morihira, Masayuki ; Kihara, Yoshiyuki

The collaboration project concerning sphere-pac fuel among JNC (Japan Nuclear Cycle Development Institute, now Japan Atomic Energy Agency), Swiss PSI (Paul Scherrer Institut) and Dutch NRG (Nuclear Research and Consultancy Group) was performed from 1996 till 2005. The target of this project is comparative irradiation tests of sphere-pac fuel in the HFR (High Flux Reactor) in Petten in the Netherlands with pellet fuel and vipac fuel. Total 16 fuel segments (8 pins) containing 5%Np-MOX sphere-pac segments were irradiated. No fuel failure was occurred. Restructuring of sphere-pac fuel was quickly progressed in early stage of irradiation, and formation of the central hole was almost completed within 48 hours steady state irradiation. According to the results of the power-to-melt test, the power to melt linear heat rates were estimated as 60kW/m for the sphere-pac fuel and as 73kW/m for the pellet fuel under HFR irradiation conditions. Irradiation behaviors of the vipac fuel and Np-MOX sphere-pac fuel were basically similar to that of the MOX sphere-pac fuel. However, the central hole of the Np-MOX sphere-pac fuel was larger than that of MOX sphere-pac fuel in the restructuring test. It suggests that the thermal conductivity of Np-MOX fuel is smaller than that of MOX fuel.