Study On The Hydrogen Source During Severe Accident For PWR

Some studies have shown that hydrogen detonation is one of the major risk contributors to early containment failure in the case of a severe accident in a nuclear power plant. In the past two decades, the different aspects of this issue have been investigated in many research programs. By using the MELCOR code, this subject studies the hydrogen source for the 600MW PWR, which generates through oxidation of Zircaloy by steam and molten core concrete interaction in cavity, during the severe accident induced by large, medium and small LOCA, including the sensitivity analysis of the different break sizes and locations, and induced by station blackout, including the sensitivity of the different break sizes and timing of pump seal failure.The results of sensitivity analysis are summarized as follows: (1) For severe accident induced by large, medium and small LOCA, the peak of in-vessel hydrogen generation rate, which is until the lower head of pressure vessel is failed, is all at the range of 0.2-0.3kg/s. And the ex-vessel hydrogen generation rate is generally at the range of 0.001-0.005kg/s, and the peak of ex-vessel generation rate in some sequences is less than 0.1kg/s.(2) For severe accident induced by station blackout, the in-vessel hydrogen production is about 330kg, and ex-vessel is about 800kg when the calculation time reaches 100000s (27.8h). The peak of in-vessel hydrogen generation rate is 0.33kg/s and ex-vessel hydrogen generation rate is under 0.01kg/s.(3) The pump seals LOCAs which might happen in a station blackout sequence result in different effects on hydrogen source...