The Behavior of ThO{sub 2}-Based Fuel Rods During Normal Operation and Transient Events in LWRs
- Massachusetts Institute of Technology (United States)
- Idaho National Engineering and Environmental Laboratory (United States)
The thermal, mechanical, and chemical behavior of both thorium and uranium dioxide (ThO{sub 2}-UO{sub 2}) and thorium and plutonium dioxide (ThO{sub 2}-PuO{sub 2})-based fuels during in-service and hypothetical accident conditions in light water reactors (LWRs) is described. These fuels offer the possibility for increased proliferation resistance and a reduction in the stockpile of weapons-grade and reactor-grade PuO{sub 2} as well as being a more stable waste form. The behavior is described for three different designs of ThO{sub 2}-based fuels: a homogeneous mixture of ThO{sub 2}-UO{sub 2}, a microheterogeneous arrangement of the ThO{sub 2} and UO{sub 2}, and a homogeneous mixture of ThO{sub 2}-PuO{sub 2}. The behavior was calculated with widely known LWR analysis tools extended for ThO{sub 2}-based fuels: (a) MATPRO for calculating material properties, (b) FRAPCON-3 for calculating in-service fuel temperature and fission-gas release, (c) VIPRE-01 for calculating the possibility for departure from nucleate boiling, (d) HEATING7 for calculating in-service two-dimensional temperature distributions in microheterogeneous fuel, (e) SCDAP/RELAP5-3D for calculating the transient reactor system behavior and fuel behavior during loss-of-coolant accidents, and (f) FRAP-T6 for calculating the vulnerability of the cladding to cracking due to swelling of the fuel during hypothetical reactivity-initiated accidents.The analytical tools accounted for the following differences in ThO{sub 2}-based fuels relative to 100% UO{sub 2} fuel: (a) higher thermal conductivity, lower density and volumetric heat capacity, less thermal expansion, and higher melting point; (b) higher fission-gas production for {sup 233}U fission than {sup 235}U fission, but a lower gas diffusion coefficient in the ThO{sub 2} than in the UO{sub 2}; (c) less plutonium accumulation at the rim of the fuel pellets; (d) greater decay heat; (e) microheterogeneous arrangement of fuel; and (f) more-negative moderator temperature and Doppler coefficients and a smaller delayed-neutron fraction. The newly developed models for ThO{sub 2} were checked against data from the light water breeder reactor program. Calculations by these analytical tools indicate that the in-service and transient performance of homogeneous ThO{sub 2}-UO{sub 2}-based fuels with respect to safety is generally equal to or better than that of 100% UO{sub 2} fuel. The in-service and transient temperatures in the most promising neutronic design of microheterogeneous ThO{sub 2}-UO{sub 2}-based fuel are greater than the temperatures in 100% UO{sub 2} fuel but are still within normal LWR safety limits. The reactor kinetics parameters for ThO{sub 2}-PuO{sub 2}-based fuel cause a higher transient reactor power for some postulated accidents, but in general, the margin of safety for ThO{sub 2}-PuO{sub 2} fuels is equal to or greater than that in 100% UO{sub 2} fuels.
- OSTI ID:
- 20840210
- Journal Information:
- Nuclear Technology, Vol. 147, Issue 1; Other Information: Copyright (c) 2006 American Nuclear Society (ANS), United States, All rights reserved. http://epubs.ans.org/; Country of input: International Atomic Energy Agency (IAEA); ISSN 0029-5450
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
FISSION PRODUCTS
FUEL RODS
HOMOGENEOUS MIXTURES
HYPOTHETICAL ACCIDENTS
MELTING POINTS
MIXED OXIDE FUELS
NUCLEATE BOILING
PLUTONIUM
PLUTONIUM DIOXIDE
REACTOR SAFETY
THORIUM
THORIUM OXIDES
TRANSIENTS
URANIUM 233
URANIUM 235
URANIUM DIOXIDE
WASTE FORMS
WATER COOLED REACTORS
WATER MODERATED REACTORS