Approach to Analyze Potentially Limiting Hot Low Power BWR Control Rod Drop Accident
Conference
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OSTI ID:21229330
- Westinghouse Electric Sweden AB, SE-721 63, Vaesteraas (Sweden)
- Vattenfall Braensle AB, SE-162 87 Stockholm (Sweden)
- Forsmarks Kraftgrupp AB, SE-742 03 Oesthammar (Sweden)
The methodology for RIA evaluations for the BWR units Forsmark 1 and Forsmark 2 was developed to guarantee that no prompt criticality can occur. However, the current methodology does not take void effects into account, and is thus only applicable for cold or hot zero power but not for non-zero power. During calculations for a planned power up-rate the hot low power scenario became the limiting one. The reason is that when evaluating the control rod worth, based on steady state calculations with the rod fully inserted and fully withdrawn, steady state T/H conditions are assumed and local voiding after withdrawal counteracts some of the reactivity inserted. The true dynamic control rod worth will therefore be under predicted. Dynamic 3D analyses with the code POLCA-T show that prompt criticality may occur for static control rod worths as low as 400 pcm. In order to avoid impractical and time-consuming dynamic cycle specific evaluations, a method of predicting the maximum enthalpy based on static calculations at hot low power has been developed. This is based on local control rod worth expressed in pcm/% of control rod withdrawal and calculated with a constant void distribution (no T/H feedback after withdrawal) between each step of withdrawal. The calculations are performed at 2 % of nominal power; at higher power levels the void quenches the transient much faster and the resulting fuel enthalpies do not challenge any limit. (authors)
- Research Organization:
- American Nuclear Society, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
- OSTI ID:
- 21229330
- Country of Publication:
- United States
- Language:
- English
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