Neutron Irradiation Effect on Isotopically Tailored 11B4C

Abstract

The present investigation was carried out to elucidate the effects of neutron irradiation on the dimensional change and thermal conductivity of isotopically tailored (B4C)-B-11. The specimens used in the present investigation are 99% B-11-enriched (B4C)-B-11, 91% B-10-enriched (B4C)-B-10, and beta-SiC. (B4C)-B-10 was sampled from an irradiated material used as a neutron absorber in a "JOYO" MK-II control rod. The (B4C)-B-11 and SiC specimens were irradiated in the experimental fast reactor "JOYO" to fluences of 1.94 x 10(26) n/m(2) (E > 0.1 Me V) at 530 degrees C and 3.12 x 10(26) n/m(2) (E > 0.1 Me V) for (B4C)-B-10, with a B-10 burnup of 47.3 x 10(26) cap/m(3). Measurements on changes in dimensions and thermal conductivity, as well as postirradiation annealing Lip to 1400 degrees C, were carried out. The results of such measurements indicated that the changes in the dimensions and thermal conductivity of neutron-irradiated (B4C)-B-11 were substantially smaller than those of (B4C)-B-10 and SiC. Postirradiation annealing measurements for (B4C)-B-11 showed that the thermal conductivity was almost completely recovered at 1400 degrees C. The changes in thermal conductivity by annealing were analyzed in terms of phonon scattering theory. The onset of recovery of the thermal conductivity of (B4C)-B-11 agreed well with irradiation temperature; however, the recovery of length did not coincide with irradiation temperature.