Thermal and mechanical properties of (U,Er)O sub(2)

Erbium is considered as a slow burnable poison suitable for use in light water reactors (LWRs). Addition of a small amount of Er sub(2)O sub(3) to all UO sub(2) pellets will make it possible to develop super high burnup fuels in Japanese nuclear facilities which are now under the restriction of the upper limit of super(235)U enrichment. When utilizing the (U,Er)O sub(2) fuels, it is very important to understand the thermal and mechanical properties. Here we show the characterization results of (U sub(1-x)Er sub(x))O sub(2) (0 [less-than-or-equals, slant] x [less-than-or-equals, slant] 0.1). We measured their thermal and mechanical properties and investigated the effect of Er addition on these properties of (U,Er)O sub(2). All Er completely dissolved in UO sub(2), and the lattice parameter decreased linearly with the Er content. Both the thermal conductivity and Young's modulus of (U,Er)O sub(2) decreased with the Er content. These results would be useful for us in evaluating the performance of the (U,Er)O sub(2) fuels in LWRs.