BWR Recirculation Line Break Simulation Tests at Two Bundle Loop

概要

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Integral blowdown refill/reflood tests have been made at the Two Bundle Loop (TBL) to clarify the BWR safety margin for the Emergency Core Cooling System (ECCS) against the recirculation line break. The tests were based on the scaling considerations of the blowdown process as affected by stored heat release from the vessel structures. The dis-cussion led to a scaling compromise of the nozzle diameter increment of the automatic de-pressurization system to compensate for the excess stored heat release in the TBL. Test results, taking the break size as a parameter, were given of a single-ended recirculation line break under a single failure of the high pressure core spray system. The comparison of the results with the previous study indicated that the uncovery period of the bundle during blowdown had a peak in the small break test of AB/V=-1.0×10<SUP>-5</SUP> m<SUP>-1</SUP> (AB: Break area, V : Vessel volume). Based on the scaling principle developed, the uncovery period of heater bundles was corrected. From the estimated uncovery period and the regression line which correlated the Peak Clad Temperature (PCT) with the integrated decay heat energy during uncovery, corrected PCT was found to be more than 500°C lower than the PCT criterion of 1, 200°C.