Evaluation on chemical state of irradiated rock-like oxide fuels by nuclear and chemical modeling

Chemical forms of fission products in irradiated ROX fuels were calculated by the SOLGASMX-PV code, and the resultant phase equilibrium and the oxygen potential in the fuel were evaluated in order to assess the irradiation be havior of the ROX fuels. For the ROX fuel with reactor grade Pu, the oxygen potential increased to about -140 kJ mol(-1) at EOL when all the Pu in the fresh fuel was tetravalent. In the case of fresh fuel which was partially reduced with the [Pu3+]/[Pu+4]=10/90, the oxygen potential increase was sup pressed to about -400 kJ mol(-1) On the other hand, the oxygen potential of the ROX fuel with weapon grade Pu never exceeded the value of about -400 k J mol(-1). The difference of oxygen potentials was caused by difference of Am amount produced by Pu conversion. The oxygen potential of the irradiated fuel was controlled by the phase equilibria among FPs. The equilibrium bet ween metallic Mo and MoO2 controlled the oxygen potential to about -400 kJ mol(-1). (C) 2001 Published by Elsevier Science Ltd. All rights reserved.