Postirradiation examination of JOYO MK-I core fuel PPJX13; Destructive examination of fuel elements

Yamanouchi, Sadamu; Kuwajima, Y.; Namekawa, Takashi; Inui, T.; Kondo, M.; Tani, Y.; Usui, Keiji; Nagai, Shuichiro

The JOYO MK-I core fuel subassembly PPJX13 was irradiated in JOYO MK-I core (location; 000) from 50 MW test through 75 MW 6th cycle. The average burnup was about 40,100 MWD/MTM. Five fuel pins was selected in the subassembly. Destructive examination items were metallographic examination (fuel and cladding), micro-hardness measurement, cladding density measurement and burnup measurement. The following results were obtained; (1) Central void of about 250Mm, columner grain region, equiaxed region (gas bubble region) and densified equiaxed region was formed by fuel restrusting. (2) Fuel and Cladding residual gap width were 20 m 89 m. Fuel-cladding chemical interaction was 13 m at the maximum cladding temperature. (3) Carbide precipitation along the grain boundary and twinning zone were observed at high temperature position in cladding. Cladding micro-hardness indicated high value at low temperature position. (4) The cladding density change of 1.10% were observed in R material. (5) Burnup measurement by Nd isotope analysis using mass spectrometer showed 5.22 atom % at the center position of the center fuel pin.