Thorium is an asset the nuclear industry does not use, and plutonium is a liability that much of the world would like to be rid of. By incorporating a thorium-plutonium mixed oxide fuel (Th-MOX) into the fuel cycle, pressurized water reactors could provide a means for the United States to address both of these issues - but only if key reactor safety parameters are not affected.

The feasibility of utilizing Th-MOX fuel in a pressurized water reactor is examined under steady-state, beginning of life conditions. With a three-dimensional MCNP model of a Westinghouse-type 17 x 17 PWR, many possibilities for replacing one-third of the UO2 assemblies with Th-MOX assemblies were considered. The excess reactivity, critical boron concentration, and centerline axial and radial flux profiles for several configurations and compositions of a one-third Th-MOX core were compared to a 100% UO2 core. A blanket-type arrangement of 5.5 wt% PuO2 was determined to be the best candidate for further analysis. Therefore, this configuration was compared to a 100% UO2 core using the following parameters: delayed neutron fraction (βeff), temperature coefficient, shutdown margin (SDM), and axial and radial nuclear hot channel factors (FZN and FRN).

The one-third Th-MOX configuration showed an undesirable reduction in βeff from 0.00716 ± 4.60E-07 for the 100% UO2 configuration to 0.00607 ± 4.30E-07. The reduction in βeff would perhaps be ameliorated by the one-third Th-MOX configuration's temperature coefficient of reactivity, which at -2.05 ± 0.02 pcm °F-1 is more favorable than the corresponding value of -1.42 ± 0.02 pcm °F-1 for the 100% UO2 configuration. The SDM of the one-third Th-MOX configuration is estimated to be 4079 ± 7 pcm, which is 28% lower than value of the 100% UO2 configuration. The FZN for the two cores were virtually identical. However, FRN for the one-third Th-MOX configuration (1.67 ± 0.28) was 20% higher than the corresponding value for the 100% UO2 configuration (1.39 ± 0.23).

These preliminary results are encouraging. However, additional investigations are required to study the impact of thermal fluid feedback and the effect of burnup and poison buildup.