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Nuclear Fuel Cycle (NFC) Technology and Policy Program

Comparison of Code Results for PWR Thorium/Uranium Pin Cell Burnup

X. Zhao, P. Hejzlar, and M.J. Driscoll

MIT-NFC-TR-027 (November 2000)

Abstract

As part of an effort to evaluate the potential benefits of using thorium in LWR fuel, initially under a strategic nuclear research collaboration between MIT and INEEL and more recently as NERI projects at MIT/INEEL and Purdue/ANL, comparisons were made between state- of-the-art codes used to perform core burnup calculations with thorium fuel. The results reported here com­pare CASMO-4, HELIOS, SCALE and MOCUP (MCNP+ORIGEN).

The pin cell problem analyzed here represents a fuel pin in a standard 17x17 Westinghouse fuel assembly. The usual all-UO2 pellets are replaced by ThO2-UO2 pellets having 75 w/o Th, 25w/o U, the latter at 19.5 w/o U-235 enrichment. This is typical of the compositions considered for modern, thorium-based fuel cycles. Comparisons were made under hot full power conditions to a burnup of 60 MWd/kg.

The eigenvalue comparison as a function of burnup is favorable: the maximum difference is about 2%, which occurs at high burnup, and the average absolute difference is less than 1%. The isotope concentration comparisons are better than a set of MOX fuel benchmarks and comparable to a set of uranium fuel benchmarks reported in the literature. The actinide and fission product data sources used in the MOCUP burnup calculations for a typical thorium fuel are documented. Reasons for code differences are analyzed and discussed.