Modeling the performance of high burnup thoria and urania PWR fuel

Fuel performance models have been developed to assess the performance of ThO₂-UO₂ fuels that can be operated to a high burnup up to 80-100MWd/kgHM in current and future Light Water Reactors (LWRs). Among the various issues raised in high burnup fuel applications, the pellet rim effect, fission gas release (FGR), and response to reactivity initiated accidents (RIA) were of special interest in this work. These phenomena were modeled by modifying the NRC licensing codes FRAPCON-3 for normal operation and FRAP-T6 for transient conditions. These models were verified and compared to the results of previous thorium fuel studies and high burnup uranium fuel evaluations. The buildup of plutonium in the outer rim of LWR UO2 pellets has been observed to create a region of high fuel burnup, fission gas buildup and high porosity at the fuel rim. The power distribution of the thoria and urania fuel was calculated using a neutronics code MOCUP. Due to the lower build-up of Pu-239 (less U-238 in ThO₂-UO₂ fuel) and flatter distribution of U-233 (less resonance capture in Th-232), thoria fuel experiences a much flatter power distribution and thus has a less severe rim effect than UO₂ fuel. To model this effect properly, a new model, THUPS (Thoria-Urania Power Shape), was developed, benchmarked with MOCUP and adapted into FRAPCON-3. Additionally a porosity model for the rim region was introduced at high burnup to account for the larger fuel swelling and degradation of the thermal conductivity. The mechanisms of fission gas release in ThO₂-UO₂ fuel have been found similar to those of U0₂ fuel. Therefore, the general formulations of the existing fission gas release models in FRAPCON-3 were retained.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Nuclear Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Long, Yun, 1972-

Advisor dc:contributor.advisor

• Mujid S. Kazimi.

• Nuclear Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30000

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30000