Thorium-Based Mixed Oxide Fuel in a Pressurized Water Reactor: A Beginning of Life Feasibility Analysis with MCNP


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.


Nuclear Engineering and Radiation Science

Keywords and Phrases

Fuels; Mixed oxide fuels; Nuclear industry; Plutonium; Space division multiple access; Temperature; Thorium; Beginning of lives; Boron concentrations; Delayed neutrons; Excess reactivity; Feasibility analysis; Hot channel; MCNP; Temperature coefficient; Pressurized water reactors; Hot channel; MCNP; Neutron flux profile; Thorium MOX

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version


File Type





© 2015 Elsevier, All rights reserved.

Publication Date

01 Feb 2015