A sensitivity study of the critical flow models used in RELAP4/MOD5 blowdown analysis of a General Electric BWR
Carle, Mark Vearil
Robinson, Gordon E.
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This study utilizes the RELAP4/MOD 5 Computer Code to analyze the effects of critical flow modeling on the thermal-hydraulic transient response of a General Electric boiling water reactor to a major primary coolant line rupture. Included in the study is a presentation of the equations, assumptions, and limitations of the critical flow models available for use in RELAP4. Additionally, an evaluation of a temporary solution to a RELAP4 coding error associated with stagnation properties calculation is presented. The results of this investigation indicate that; (1) a solution to the stagnation properties calculational error that exists in the RELAP4 code, when applied to the Evaluation Model, (RELAP4-EM) provides a conservative evaluation, relative to the Standard model (RELAP4-SM) regardless of which of the five critical flow models available in the code is selected; (2) of the five critical flow models available for use in RELAP$, the Moody model and the Henry-Fauske model are nearly equivalent in the relative degrees of conservatism. Following these models, in order of relative degree of conservatism, are the Modified Momentum/Homogeneous Equilibrium model and the Sonic model; (3) in order to best alleviate the stagnation properties codeing error, the flow areas for the volumes immediately upstream from the recirculation line rupture should be increased such that the area ration (break flow area/upstream volume flow area) is 0.7.
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