堆芯熔融下反应堆压力容器结构失效模式探讨

Study on Structural Failure Mode of Reactor Pressure Vessel Under Severe Core Meltdown Accident

利用有限元方法分析了堆芯熔融严重事故下反应堆压力容器(RPV)器壁的应力分布,探讨了RPV结构的失效模式,提出了RPV结构分层失效模型,可将RPV沿壁厚由内到外分为5个层面,即熔化区、高温蠕变主导区、压缩塑性主导区、弹性区和拉伸塑性区.分析了RPV塑性失效和高温蠕变失效的影响因素,并给出了塑性失效和高温蠕变失效的载荷条件.结果表明:内压是塑性失效的主要影响因素,随着内压增大,RPV壁内弹性层会逐渐减小,弹性层消失时对应的内压即为塑性失效的载荷条件;在蠕变条件下,当内压达到一定值后,截面塑性区、蠕变应变和塑性应变迅速增大,RPV达到极限状态,此时的内压即为高温蠕变失效的载荷条件.

To evaluate the structural integrity of a reactor pressure vessel （RPV） bearing complicated and dangerous loads under severe core meltdown accident, various analyses were conducted, including an analysis on the stress distribution across the RPV wall using finite element method, and a study on the failure mode with a multi-layered failure model proposed, suggesting that the RPV wall could be divided into five layers from inner to outer wall along its thickness, namely, molten layer, high-temperature creep dominated layer, compressed plastic dominated layer, elastic layer, and tensile plastic layer, etc. Meanwhile, factors influencing the plastic failure and high-temperature creep failure of RPV were analyzed, during which load conditions of both the failures were obtained. Results show that the internal pressure is the main factor affecting the RPV plastic failure. With the rise of internal pressure, the elastic layer in RPV wall gradually reduces, and when the elastic layer disappears, the corresponding internal pressure is considered as the load condition of plastic failure. Whereas, under creep conditions, once the internal pressure gets up to a certain value, the plastic layer, the creep strain and the plastic strain on RPV wall cross section increases rapidly, and the RPV promptly reaches its limit state, when the corresponding internal pressure is considered as the load condition of high-temperature creep failure.