Applications for Thorium in Multistage Fuel Cycles with Heavy Water Reactors

Abstract

Certain characteristics of heavy water reactors (HWRs), such as a more flexible neutron economy compared to light water (due to reduced absorptions in hydrogen), online refueling capability, and having a thermal neutron spectrum, make them potentially attractive for use with a thorium fuel cycle. Three options that combine HWRs with thorium-based fuels are considered in this paper: a Near-Term option with minimal advanced technology requirements, an Actinide Management option that incorporates the recycle of minor actinides (MAs), and a Thorium-Only option that uses two reactor stages to breed and consume ²³³U, respectively. Simplified, steady-state simulations and corresponding material flow analyses are used to elucidate the properties of these fuel cycle options. The Near-Term option begins with a low-enriched uranium oxide pressurized water reactor (PWR) that discharges spent nuclear fuel, from which uranium and plutonium are recovered to fabricate the driver fuel for an HWR that uses thorium oxide as a blanket fuel. This option uses 28% less natural uranium (NU) and sends 33% less plutonium to disposal than the conventional once-through uranium fuel cycle on an energy-normalized basis. The Actinide Management option also uses spent nuclear fuel from a PWR using enriched uranium oxide fuel (both a low- and high-enrichment variant are considered), but the uranium is recycled for reuse in the PWR while the plutonium and MAs are recycled and used in conjunction with thorium in an HWR with full recycle. Both enrichment variants of this option achieve a more than 95% reduction in transuranic actinide disposal rates compared to the once-through option and a more than 60% reduction compared to closed transuranic recycle in a uranium-plutonium–fueled sodium fast reactor. The Thorium-Only option breeds a surplus of ²³³U in a thorium-based HWR to supply fissile material to a high-temperature gas-cooled reactor, both of which recycle uranium and thorium. This option requires no NU and produces few transuranic actinides at steady state, although it would require a greater technology maturation effort than the other options studied. Collectively, the options considered in this study are intended to illustrate the range of operational missions that could be supported by fleets that integrate thorium and HWRs.

Keywords:

• Thorium fuel cycle
• heavy water reactor
• actinide management
• uranium-233

Acknowledgments

Various components of this work were improved by feedback from T. K. Kim [Argonne National Laboratory (ANL)], Temitope Taiwo (ANL), Jeff Powers (ORNL), Eva Sunny (ORNL), Blair Bromley (CNL), Mark Floyd (CNL), Ed Hoffman (ANL), and Brent Dixon (Idaho National Laboratory). This work has been supported by the DOE, under the NEUP. The work is being carried out as project number DE-NE0000735, “Development of Fuel Cycle Data Packages for Thorium Fuel Cycle Options.” Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government, Vanderbilt University, or ORNL.

Notes

^a The hazardous components of fuel fabrication losses are generally managed as greater-than-class-C waste rather than high-level waste⁴⁸; in any case, they represent only a small portion (0.2%) of the total Pu losses of the fuel cycle.