LWR MOX fuel irradiation tests; HBWR irradiation with the instrument rig, IFA-514/565

Ozawa, Takayuki   

IFA-514 irradiation test was performed in Halden Reactor (HBWR) in Norway to study the irradiation performance of LWR MOX fuels. The fuel specifications for this irradiation test were decided in accordance with those of BWR 8 8 fuels, and plutonium content of MOX fuels was 5.8 wt.%. Six MOX fuel rods, of which parameters were pellet geometry (solid or annular) and surface roughness (grinded or as-sintered), were irradiated to the assembly average burn-up of 45 GWd/t, and the instrument data during irradiation, i.e,. cladding elongation, fuel stack elongation, fuel center temperature, and rod inner pressure, were obtained, and subsequent post-irradiation examinations indicated no remarkable corrosion and deformation on the irradiated fuel rods. The irradiation for three of six fuel rods irradiated in IFA-514 irradiation tests were continued to the assembly average burn-up of 56 GWd/t in IFA-565 irradiation tests, and the results of this irradiation test inditated no remarkable corrosion and deformation on the irradiated fuel rods. The FP gas release behavior of LWR MOX fuels was similar to that of BWR UO and ATR MOX fuels, and no difference was confirmed in the FP gas release behavior. Also FP gas release rate of annular pellets (13 %) was lower than that of solid ones (16 %), and no difference in the effect of pellet geometry, i.e. solid and annular, on PCMI behavior was confirmed since no evidence of remarkable PCMI taking place was observed in any fuel rod from the instrument data of fuel stack elongation and the results of ceramography, but the pellet geometry is expected to have an effect of the cladding diameter change reduction since the cladding diameter change of annular fuel rods was less than that of solid ones.