Study on density, melting point, thermal expansion, creep, thermal diffusivity and thermal conductivity of the simulated rock-like oxide (ROX) fuels

摘要

A new type of fuel, that is, rock-like oxide (ROX) fuel composed of PuO(sub 2)-SZR (stabilized zirconia)-MgAl(sub 2)O(sub 4) is under development at JAERI. To prepare the data base, the simulated ROX fuel in which original PuO(sub 2) was replaced by UO(sub 2) was fabricated and brought to out-of-pile tests. Main remarks obtained within this experimental scope are: (1) It was found from the present study that the simulated ROX fuel was successfully fabricated. (2) The gas immersion density of the simulated ROX fuels had values ranging from 4.9 to 5.4 g/cc, which were of order of about 47-52% of that of UO(sub 2). SZR increased the density of while MgAl(sub 2)O(sub 4). (3) Melting point of the simulated ROX fuel was revealed to be 1,911 (+-) 39degC, about 30% lower than that of UO(sub 2) fuel. (4) The difference in linear thermal expansion (LTE) between the simulated ROX fuel and the UO(sub 2) fuel was little up to temperatures of 1,500degC. The LTE was increased with the increase of SZR. (5) The creep rate of simulated ROX fuel was strongly dependent on the amount of MgAl(sub 2)O(sub 4), where the role of Al(sub 2)O(sub 3) dissolved in MgAl(sub 2)O(sub 4) is important. The creep propensity was similar between the simulated ROX fuel and UO(sub 2) fuel. (6) The magnitude of hardness (Hv) was sensitive to the Al(sub 2)O(sub 3) contained in MgAl(sub 2)O(sub 4), hence the increase of Al(sub 2)O(sub 3) made the simulated ROX fuel more hard. (7) The difference in thermal diffusivity between the simulated ROX fuel and the UO(sub 2) was not so significant. (8) The difference in thermal conductivity between the simulated ROX and UO(sub 2) fuel is little. Degradation of the thermal conductivity occurred by the increase of SZR. (9) Among three candidates of the simulated ROX fuels studied in the present paper, the sample consisted of 26wt%UO(sub 2)-24wt%SZR-50wt%MgAl(sub 2)O(sub 4) seems to have the most feasible performance for future studies. (J.P.N.)