AP1000小破口叠加重力注射失效严重事故分析

AP1000 Severe Accident Analysis of Small LOCA Coupled With Failure of Internal Refueling Water Storage Tank

应用新版MELCOR程序,建立了AP1000一二回路、非能动安全系统及安全壳隔室的热工水力模型,并以热段小破口叠加重力注射系统失效事故为例,对该严重事故进程在压力容器内阶段进行模拟计算,对缓解措施的功能进行了分析和评价。结果表明:自动卸压系统(ADS1～4)的成功实施,可使来自堆芯补水箱和安注箱的冷却水快速有效地注入堆芯,在冷却水完全耗尽前,堆芯始终处于淹没的状态。ADS4爆破阀开启后,使回路压力快速与安全壳压力平衡;非能动安全壳冷却系统对抵御严重事故下由于衰变热和非冷凝气体带来的缓慢升温升压是行之有效的措施;点火器在氢气浓度较低时点火,缓解了安全壳大空间发生全局燃爆而引发安全壳超压失效的风险,但连续点火燃烧会引起局部隔室温升远超出设计温度而危及后备缓解设施的存活。

In this paper MELCOR code was applied for modeling of AP1000 NPP primary and secondary circuits, passive safety system and containment compartment. And by applying the code, a severe accident scenario of small loss of coolant accident （LOCA） at hot leg concurrent with failure of internal refueling water storage tank （IRWST） function was selected for simulation and calculation mainly during the invessel phase, the passive mitigation measures were analyzed and evaluated. The analysis results show that the execution of ADS （automatic depressurization system）1-4, will lead to quick and effective injection of cold water from core make-up tank （CMT） and accumulators into the core, before they are exhausted, the core is kept flooded all the time. With broken of ADS4 valve, primary pressure is fast balanced to containment pressure. The passive containment cooling system （PCS） can be adopted as a counter measure to slow pressurization of containment by airborne decay heat and non-condensable gases. The ignition of H2 by igniters before the concentration of H2 are high enough to deflagrate automatically, and can alleviate the risk of containment failure from overpressure due to global deflagration, while continuously ignition may cause temperature in some compartments rise to a value that exceed much more than its design temperature. Under such condition, other system supports to severe accident mitigation are difficult to survival.