NEUTRON-INDUCED DAMAGE IN NEAR-STOICHIOMETRIC SPINEL CERAMICS IRRADIATED BELOW 200-DEGREES-C AND ITS RECOVERY DUE TO ANNEALING

Mg-Al spinel ceramics with different stoichiometry (Al2O3/MgO = n; n = 1.00, 1.01, 1.10 and 1.48) were irradiated with fast neutrons up to 3 .8 x 10(23) n/m(2) (E > 0.1 MeV) at 170 degrees C, and 5.7 x 10(23) n/ m(2) at 190 degrees C in the Japan Materials Testing Reactor. There wa s no obvious difference in property change between the two irradiation conditions. The amount of macroscopic length change due to these irra diations increased almost linearly with increasing Al2O3 content. Thes e specimens were isochronally annealed up to 1000 degrees C. During th e annealing, macroscopic length of the specimens started to decrease a t around 200 degrees C and reduced monotonically up to 550 degrees C. After that, the length increased slightly up to 650 degrees C and then decreased again up to 800 degrees C, showing a small peak. These fina l values corresponded to the length of the specimens before the irradi ation. The shrinkage in length between 200-550 degrees C and 650-800 d egrees C may be attributed to the recombination of Frenkel pairs of an ions, and the expansion in length between 550-650 degrees C to the ord er-disorder transition of cation distribution. (C) 1998 Elsevier Scien ce B.V. All rights reserved.