engleski

Coupled Code Calculation of Rod Withdrawal at Power Accident

The Rod Withdrawal At Power (RWAP) accident is analyzed for NPP Krško as part of activity related to possible Resistance Temperature Detectors (RTD) bypass removal. The RWAP accident can be Departure from Nucleate Boiling (DNB) or overpower limiting accident depending on initial power level and rate and amount of reactivity addition. By replacing the RTD bypass manifold system with fast-response thermowell (TW) RTDs, the Reactor Coolant System (RCS) temperature measurement time may change what affects the time delays for overtemperature (OTΔT) and overpower (OPΔT) trips. The analysis is performed first using point kinetics model as implemented in RELAP5/MOD3.3 code. Both RCS temperature measurement configurations (RTD bypass and TW RTD) with different RCS temperature measurement delays as well as different reactivity insertion rates were addressed in the analyses. For most critical scenario the calculation is repeated using coupled code based on RELAP5 and PARCS. As part of the coupled code calculation core wide DNBR calculation is performed, and at the end of the calculation COBRA based model is used to determine minimum DNB ratio (DNBR) for hot pin in fuel assembly experiencing peak power.

RWAP; DNBR; RELAP; PARCS; COBRA

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