MELCOR2.2氢气点燃浓度限值敏感性分析

Sensitivity analysis of the hydrogen mole fraction limit for ignition with MELCOR2.2

严重事故工况下,堆芯燃料包壳和其他金属构件的蒸汽氧化以及熔融堆芯-混凝土相互作用是最重要的氢气释放源项。为避免安全壳内氢气爆燃和爆炸现象,有必要对氢气点火浓度的敏感性进行研究。研究使用最新版MELCOR2.2程序对大功率非能动压水堆安全壳进行系统建模,对安全壳内氢气点燃浓度限值进行了敏感性分析。分析结果表明:1)氢气可燃浓度限值设置越高,单次燃烧产生的压力峰值越明显,超过设定的可燃浓度限值,可能引起氢气爆燃和爆炸;2)氢气点燃一定程度上受其他不凝气体浓度影响,其中一氧化碳会加速氢气点燃,而二氧化碳和蒸汽的摩尔浓度增加则会稀释可燃气体。因此,氢气点燃受氢气点燃浓度限值影响较大,但安全壳内其他不凝气体组分的影响也不可忽略,应该及时做好安全壳内可燃气体的复合和稀释,有效消除可燃气体的潜在威胁。

[Background] In severe accidents, the oxidation behavior of fuel cladding and other metallic materials in core region with steam, and the molten corium-concrete interaction (MCCI) are important source items for releasing hydrogen.[Purpose] This study aims to investigate the sensitivity of the hydrogen mole fraction limit for ignition in the containment to prevent the hydrogen deflagration and explosion.[Methods] The integrated contamination model has been built systemically in large power passive pressurized-water reactor (PWR) using the latest version of MELCOR2.2 code, and the sensitivity analysis of hydrogen molar fraction limit for ignition has been carried out.[Results] The analysis results show that: 1) the higher hydrogen mole fraction limit setting the more obvious pressure peak generated by a single combustion;it will cause the hydrogen deflagration and detonation if the value exceeds the mole fraction limit;2) the hydrogen ignition is affected by other noncondensible gases to a certain extent. The increase of carbon monoxide molar fraction escalates the hydrogen ignition and, conversely, the carbon dioxide and steam dilute the flammable gases.[Conclusion] Hydrogen ignition is greatly affected by the ignition limit of hydrogen molar fraction, and as an important factor, the other noncondensible gases components in containment are non-negligible. Therefore, it is crucial to combining and diluting the combustible gases for eliminating the potential risk in containment.