Analyzing the rod drop accident in a BWR with high burnup fuel
The response of fuel in a boiling water reactor to the rod drop accident (RDA) was studied using the RAMONA-4B computer code. Calculations of this design-basis event has been done conservatively because there was margin to the fuel failure criterion of 170 cal/g. Because high burnup fuel may fail at much lower fuel enthalpies, the best-estimate of the enthalpy and the uncertainty is of interest. In part of this study, calculations assessed the sensitivity to reactor conditions such as control rod pattern, inlet subcooling, and fuel burnup. It was shown that fuel enthalpy at any location in the region surrounding the dropped rod depends on the rod worth, the distance from the dropped rod, and the burnup of the fuel. The study also calculated the sensitivity to parameters whose modeling introduces significant uncertainty which may increase with burnup. These parameters are the control rod worth, Doppler reactivity coefficient, delayed neutron precursor fraction, and fuel specific heat. The results of the sensitivity studies were used in a model to determine the random uncertainty in the fuel enthalpy. The standard deviation for the calculated fuel enthalpy was estimated to be 37%. Therefore, the limiting bundle fuel enthalpy might be 75% higher than calculated. The effect of the fuel rod enthalpy distribution within a bundle was also investigated. RAMONA-4B calculates the fuel bundle average enthalpy and estimates must be made of a bundle peaking factor to determine the fuel rod enthalpy. A fit of RAMONA-4B bundle powers was used to estimate the local power peaking. It was determined that the peaking factor could be 25% higher than the factor usually assumed for RDA analysis. Combining this error with the random error means that for this analysis the actual fuel rod enthalpy could be 100% larger than calculated by RAMONA-4B. This is much larger than the uncertainty in most parameters calculated with best-estimate methods for design-basis events. 10 refs., 3 figs.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States); Nuclear Regulatory Commission, Washington, DC (United States)
- Sponsoring Organization:
- Nuclear Regulatory Commission, Washington, DC (United States)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 448053
- Report Number(s):
- BNL-NUREG-63663; CONF-970315-1; ON: DE97001876; TRN: 97:006431
- Resource Relation:
- Conference: ANS international topical meeting on light water reactor fuel performance, Portland, OR (United States), 2-6 Mar 1997; Other Information: PBD: 1997
- Country of Publication:
- United States
- Language:
- English
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