熔融物作用下压力容器下封头热应力分析方法研究
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摘要
堆芯熔融物滞留(IVR)策略是核电厂针对严重事故的一项重要缓解措施。采用有限元方法对IVR策略期间反应堆压力容器(RPV)下封头在熔融物作用下的力学行为进行研究,通过对熔融物传递给压力容器壁面的热载荷和力学载荷进行研究,计算得到下封头的温度场和应力场分布,幵对热膨胀和内压等对结构力学响应的影响进行了研究,对材料的弹性和弹塑性行为进行了比较。结果表明,热膨胀产生的应力和变形远大于容器自重、熔池压力和冷却水压力产生的结果;内压大于1 MPa时其对结构的力学响应有显著影响;熔融物作用下压力容器下封头将产生不可忽视的塑性变形,采用弹塑性方法进行分析更为合理。
The in vessel retention(IVR) strategy is an important mitigation measure for serious accidents in nuclear power plants. In this paper, the finite element method is used to study the mechanical behavior of the reactor pressure vessel(RPV) lower head under the action of the melt during the IVR strategy. According to the thermal and mechanical loads distribution characteristics that the core melt transferred to the pressure vessel wall, the temperature field and stress field distribution of the lower head were obtained by calculation, and the effects of thermal expansion, internal pressure and other loads on the mechanical response of the structure were investigated. The comparison between the elastic and elasto-plastic behavior of materials was conducted as well. Results show that the stress and deformation caused by thermal expansion are much larger than those of the vessel dead weight, molten pool pressure and cooling water pressure; when the internal pressure is greater than 1 MPa, it has a significant effect on the mechanical response of the structure; under the action of the core melt, the structure will produce certain plastic strain that cannot be ignored, and the elasto-plastic analysis method is more reasonable.
The in vessel retention(IVR) strategy is an important mitigation measure for serious accidents in nuclear power plants. In this paper, the finite element method is used to study the mechanical behavior of the reactor pressure vessel(RPV) lower head under the action of the melt during the IVR strategy. According to the thermal and mechanical loads distribution characteristics that the core melt transferred to the pressure vessel wall, the temperature field and stress field distribution of the lower head were obtained by calculation, and the effects of thermal expansion, internal pressure and other loads on the mechanical response of the structure were investigated. The comparison between the elastic and elasto-plastic behavior of materials was conducted as well. Results show that the stress and deformation caused by thermal expansion are much larger than those of the vessel dead weight, molten pool pressure and cooling water pressure; when the internal pressure is greater than 1 MPa, it has a significant effect on the mechanical response of the structure; under the action of the core melt, the structure will produce certain plastic strain that cannot be ignored, and the elasto-plastic analysis method is more reasonable.
引文
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[2]KOUNDY V,DURIN M,NICOLAS L,et al.Simplified modeling of a PWR reactor pressure vessel lower head failure in the case of a severe accident[J].Nuclear Engineering and Design,2005,235:835-843.
[3]KYM?L?INEN O,TUOMISTO H,THEOFANOUS TG.In-vessel retention of corium at the Loviisa plant[J].Nuclear Engineering and Design 1997,169:109-130.
[4]THEOFANOUS T G,LIU C,ADDITON S,et al.Invessel coolability and retention of a core melt[J].nuclear engineering and design.1997,169:1-48.
[5]JAE H P,YONG H J.An assessment methodology for in-vessel corium retention by external reactor vessel cooling during severe accidents in PWRs[J].Annals of Nuclear Energy,2001,28:1237-1250.
[6]ESMAILI H,KHATIB-RAHBAR M.Analysis of likelihood of lower head failure and ex-vessel fuel coolant interaction energetics for AP1000[J].Nuclear Engineering and Design,2005,235:1583-1605.
[7]WILLSCHüTZ H G,ALTSTADT E.Generation of a high temperature material data base and its application to creep tests with French or German RPV-steel:Technical Report,FZR-353[R].Dresden,Germany:Forschungszentrum Rossendorf,2002.