Precipitation of plutonium compounds in irradiated magnesium alloy fuel element cans

Abstract

Thin foils which contain the inner surface of irradiated fuel element cans have been cut with an ultramicrotome. transmission electron microscopy revealed numerous fine precipitates within 25 μm of the inner surface of irradiated AL80 (Mg/0.8 wt% Al) cans but very few in irradiated ZR55 (Mg/0.5 wt% Zr) cans. Alpha-counting of foils showed that plutonium had penetrated into the can wall to differing extents in the two materials; it was confined to the region containing the precipitate in an AL80 can irradiated at 405 °C but had diffused about 1 mm into a ZR55 can irradiated at 300 °C for half the time. some of the precipitate particles in AL80 have been identified as PuAl 3 by electron diffraction. It is concluded that the precipitation of plutonium-aluminium compounds at the inner surface prevents plutonium diffusing through the can wall of AL80 clad fuel elements during irradiation.