Compatibility of Eu2O3 and (Eu, Gd)2O3 with type 316 stainless steel

The compatibility of Eu2O3 and (Eu, Gd)2O3 mixed oxides which contain 0, 1, 5, 10, 50 and 100 mol/0 of Gd2O3, with type 316 stainless steel was examined by out-of-pile heatings. The heating temperature ranged from 550 to 1,0000C and heating time from 500 h to up to 5,000 h. Metallographic examinations of the stainless steel indicated that chemical reaction between Eu2O3 and stainless steel occurred at 6500C and that grain boundary penetration extended up to 40 μm after heating at 1,0000C for 500 h. The penetration depth δl was expressed as a function of heating temperature T as; δl = 3.08 x 104 exp(-1.72 x 104/RT), where R is the gas constant and the activation energy is given in cal/mol. Electron probe microanalysis and X-ray diffraction analysis indicated that main reaction product is europium silicate. When Gd, which is a decay product of Eu, is mixed with Eu2O3, the degree of reaction between (Eu, Gd)2O3 and stainless steel decreases as increase in concentration of Gd2O3. It was found that actually no grain boundary attack was observed even after heating at 1,0000C for 500 h when concentration of Gd2O3 in (Eu, Gd)2O3 exceeded 10 mol/0. Discussion was made of reaction mechanism of Eu2O3 and (Eu, Gd)2O3 with stainless steel. (author)