Hertzian indentation of advanced lmfbr fuels with simulated burn-up

Hertzian indentation fracture of advanced fast breeder reactor fuel materials mixed carbonitrides, (U_0.8, Pu_0.2)C_0.8N_0.2, and nitrides (U_0.8Pu_0.2)N was evaluated to yield the fracture surface energy, γ, and the fracture toughness, K_Ic. Both technological grade fuels and fuels with added fission products to chemically simulate burn-up values of 3 and 10 at.% were used. As in previous self-diffusion studies on the same materials, identical behavior (identical critical loads, P_c for crack formation) was observed for 3 and 10% b.u. Simulated M(C, N), whereas the 10% b.u. Simulated MN showed a cracking behavior identical with that of the undoped MN. In contrast, the 3 at.% b.u. Simulated MN showed lower P_c values. This is compatible with differences in fission product solubilities in these materials. The effect of fission products on γ was < 20% whereas γ increased from (U, Pu)(C, N) to (U, Pu)N by up to 80 to 90%, depending on content in fission products.