NEA-1772 IFPE/IFA-597-MOX.

IFPE/IFA-597-MOX

A series of tests, containing two MIMAS-MOX fuel rods, both equipped with a fuel centre thermocouple and a pressure bellows transducer, has been irradiated in the Halden Reactor since July 1997 under HBWR conditions. The objectives of the test series were to study the thermal and fission gas release (FGR) behaviour of MOX fuel and to explore potential differences in behaviour between solid and hollow pellets. One of the rods had mainly solid pellets, while the other contained only hollow pellets. Both rods had an initial Pu-fissile enrichment of 6.07%. The cladding outside diameter was 9.50 mm, and the initial fuel-clad gap was 180microns. In the course of the test, power upratings for FGR studies of the MOX fuel were planned at burnup intervals of about 10 MWd/kgMOX. The power uprating was successfully performed at ~10 MWd/kgMOX, where the fuel peak temperature of the solid pellets exceeded the FGR threshold temperature for UO2 fuel, while that of the hollow pellets remained below the threshold. For the solid fuel, the temperature at onset of FGR was consistent with the empirical threshold temperature for UO2 fuel. For the hollow fuel, gas release was observed at temperatures below the threshold. FGRs at the end-of-life were ~17% for the solid pellet rod and ~14% for the hollow pellet rod, respectively. The observed FGR has been higher than expected, and as a result of discussions in HPG meetings, IFA-597.7 was unloaded in January 2002. PIE was carried out to check in-pile pressure measurements and examine fuel structural characteristics. The discharge burn-up of the MOX fuel was 32 MWd/kgMOX as determined from in-pile power data.

Mr. Terje TVERBERG

Institutt for Energiteknikk

OECD Halden Reactor Project

P.O. Box 173

N-1751 Halden

Norway

Compilation: J.A. Turnbull