PHASE-EQUILIBRIA IN THE TERNARY URU3-URH3-UPD3 SYSTEM

In order to clarify the behavior of platinum metal fission products in the nitride fuel, the reactions of UN + 3(Ru-x + Rh-y + Pd1 - x - y) [O less than or equal to (x,y) less than or equal to 1] in the pseudo- ternary and quaternary systems at 1673 K under vacuum (similar to 10(- 2) Pa) were examined. The reactions of UN + 3(Ru-x + Rh-y)(x + y = 1) and the reactions of UN + 3(Rh-y + Pd1 - y) (0.25 less than or equal t o y less than or equal to 1) produced a Cu3Au type compound. However t wo Cu3Au type compounds were obtained from the reactions of UN + 3(Ru- x + Pd1 - x) (0.25 less than or equal to X less than or equal to 0.75) . In the reactions of UN + 3(RUx + Pd1 - x - y) with a lower Pd ratio, a Cu3Au type compound was formed, but the increase in Pd ratio, (x y less than or equal to 0.33), caused the formation of two Cu3Au type compounds. Although UPd3 is crystallized to a hexagonal TiNi3 type str ucture, the Cu3Au type UPd3 phase was formed in these reactions. (C) 1 998 Elsevier Science S.A.