Research Programs

Publications:

1. Greenspan, E., F. Ganda, D. Olander, Z, Shayer, N. Todreas, et al., “Optimization of UO₂ Fueled PWR Core Design,” Presented at ICAPP 2005, Paper 5569, Seoul, Korea, May 2005.
2. Malen, J., N.E. Todreas, and A. Romano, “Thermal Hydraulic Design of Hydride Fueled PWR Cores,” Presented at NUTHOS6, N6P216, Nara, Japan, October 2004.
3. Romano, A., C. Shuffler, J. Trant, and N. Todreas, “Application of Hydride Fuels to Enhance Pressurized Water Reactor Performance,” MIT-NFC-TR-072, August 2005.
4. Shuffler, C., “Optimization of Hydride Fueled Pressurized Water Reactor Cores,” MS Thesis, submitted to the Department of Nuclear Engineering, MIT, September 2004.
5. Trant, J., “Transient Analysis of Hydride Fueled Pressurized Water Reactor Cores,” MS Thesis, submitted to the Department of Nuclear Engineering, MIT, September, 2004.

Investigators

• Professor N. E. Todreas
• P. Diller
• P. Ferroni
• J. Malen
• A. Romano
• C. Shuffler
• J. Trant

Evaluation of Solid Hydride Fuel for Long-Lived LWR Core Design

This project is being conducted in cooperation with the University of California-Berkeley and Westinghouse to assess the benefits derivable from use of solid hydride fuel in PWR and BWR core designs. U.C. Berkeley leads the project and is responsible for the neutronic assessment. MIT is responsible for the thermal hydraulic assessment of hydride fuel. Westinghouse is responsible for materials assessment. The Hydride project will consider UZrH_1.6, UThH₂, PuThH₂, PuH₂, and PuZrH_1.6 fuels. The concentration of hydrogen atoms in these hydride fuels is comparable to that of liquid water. Hydrogen atoms moderate fast neutrons born during the fission process to thermal energies, at which they are more likely to induce subsequent fissions, thereby maintaining the chain reaction. Contemporary LWR cores depend solely upon the primary coolant to moderate neutrons into this optimum energy spectrum. The introduction of hydrogen atoms into the fuel itself permits attainment of optimum neutron moderation with a relatively low coolant volume. As a result the hydride core can have a smaller volume or higher total power in the same volume, relative to an LWR core that burns oxide fuel. In addition, thorium hydride fuels have a higher heavy metal density than oxide fuel. Estimates suggest that high heavy metal concentration and increased fuel to water ratio may increase core life and energy per fuel loading by a factor of two. The net benefit will be improved economics, improved resource utilization, reduced waste, improved safety, and improved proliferation resistance.

The MIT investigations are evaluating cores of the following types: square array, grid supported PWRs; hexagonal array, wire wrap supported PWRs; square array, grind supported BWRs. For each case cores are investigated which can be backfit into existing operating plants and cores for new plants with larger reactor vessels and higher capacity pumps.

The core designs are pursued through a parametric study to determine the optimum combination of lattice pitch, rod diameter, and channel shape for maximizing power loaded with UZrH_1.6 fuel and standard UO₂ fuel. Geometries are examined with the VIPRE subchannel analysis tool. MATLAB scripts were developed to automate VIPRE execution, permitting timely analysis of multiple combinations of geometry and operating parameters. For the thermal hydraulic analysis, steady state core performance was judged against four constraints—minimum departure from nucleate boiling ratio (MDNBR), core pressure drop, flow velocity, and maximum fuel temperature. For PWRs transient performance under loss of coolant, loss of flow and overpower conditions have also been studied. The maximum achievable power for each geometry is defined as the highest power that can be sustained without exceeding any of the constraint limits, which were chosen based on technical feasibility and safety.

Since the fuel temperature constraint has typically not been limited, upgrade square array, grid supported cores of hydride and uranium oxide have both been shown to achieve powers of 25 to 30% above the current reference PWR levels and corresponding fuel cycle costs 20-25% lower. Wire wrap supported hexagonal array PWR cores achieve power increases of 60-80%. Hydride BWR cores, because of the elimination of control channels and water rods, achieve power increases of 20-30%. The fuel cost advantages have not yet been evaluated for either of the last two cases.