Thorium-plutonium fuel for long operating cycles in PWRs - preliminary calculations

Preliminary calculations have been carried out to investigate the possibility of extending oper- ating cycle length in PWRs by use of Thorium-Plutonium mixed oxide fuel (Th-MOX). The calculations have been carried out in two dimensions, using the fuel assembly burnup simula- tion program CASMO-5. The reload scheme and the operating parameters are modelled on the Swedish PWR Ringhals 3 and a normal UOX fuel assembly designed for this reactor has been used as a reference. Results show that an extension of the currently employed 12-month oper- ating cycle length is possible, either with a burnable absorber or with a modified fuel assembly design, assuming the same 3-batch reload scheme as currently used in Ringhals 3. The initial k∞ of the new Th-MOX fuel design was designed not to exceed that of the refer- ence UOX fuel. The power peaking factor is initially significantly lower than the reference, but slightly higher later in the life of the fuel assembly. All reactivity coefficients are within acceptable range. The worth of control rods and soluble boron are lower than the reference, as expected for a plutonium-bearing fuel.