福岛核电厂3号机组严重事故模拟分析

本文应用MELCOR程序，通过建立全厂详细的模型，对福岛第一核电厂3号机组在地震发生后3 d内的严重事故进程进行了模拟分析并与电厂实测数据进行了比较，再现了从事故开始到堆芯失效坍塌直至氢气爆炸在内的主要严重事故现象。基于文中假设的模拟计算得到的趋势与电厂现有实测数据较为一致，结果表明：地震发生后约36 h反应堆水位降至堆芯活性区顶部。操纵员未能及时成功对安全壳和反应堆进行快速卸压，以在堆芯底部出现裸露前向反应堆补充冷却水，使得堆芯出现严重的锆水反应，大部分燃料包壳已破损而导致易挥发的放射性裂变产物的释放；但此时堆芯整体依然维持可冷却几何形状；在消防水泵向反应堆注入冷却水期间，由于冷却注入流量出现中断，导致堆芯进一步熔毁坍塌；碎片迁移至下腔室后，进一步的锆水反应(金属 水反应)新增的氢气泄漏并积聚在反应堆厂房上部，引发了安全壳厂房的爆炸；72 h内，堆芯内约50%的锆合金发生了氧化，压力容器下封头未发生失效。

Severe Accident Simulation and Analysis for Fukushima NPS Unit 3

In the paper the simulation of severe accident progression within first 3 days for Fukushima Daiichi NPP unit 3 was performed with application of MELCOR code. The detailed modeling of the whole plant system was made to achieve it. The resulted parameters were compared with those monitored. The major physical phenomena from the accident initiation to reactor core degradation until hydrogen explosion were reproduced in simulation. The simulation results based on assumption as defined agree well with those measured. The results indicate that the reactor water level drops down to top of core active part at 36 h since the earthquake. Operators fail to depressurize the containment and reactor at an earlier time, by the time water injection into reactor through fire pump, the core claddings are already severely oxidized, and ruptures of claddings bring up release of volatile fission product at 40.7 h. Suspended supply of fire pump water (55.5-63.2 h) leads to further degradation and relocation of core materials. Upon slumping of debris into lower plenum, more H₂ from Zr-water (or metal-water) reaction releases and accumulates over upper space of reactor building, finally results in H₂ detonation; up to 72 h，around 50% of zircalloy is oxidized, and the lower head of RPV is intact from rupture.