基于GOTHIC 3D的内置冷却管双坩埚堆芯捕集器瞬态模拟研究

Transient Investigation of Conceptual Twin Crucible Type Core Catcher Design with Embedded Cooling Tube Using GOTHIC 3D Model

为进一步探究内置冷却管的双坩埚式堆芯捕集器在给定冷却壁面热流密度瞬态分布的边界条件下,自冷却水灌注冷却流道起始,至形成稳定两相流自然循环并达到热平衡阶段的瞬态三维冷却性能,开发了基于安全壳热工水力学信息生成(GOTHIC)的三维分布参数热工水力模型。通过使用不同形状封堵及开孔模块的搭建和分布参数热构件依异形表面的贴覆,实现了双坩埚捕集器异形流道三维流动换热过程的瞬态模拟。通过模拟分析、计算结果的后处理及相关模型分析,证实了该双坩埚捕集器在两相流自然循环启动后,形成了良好的带热能力,在假定条件下,其带热能力提升至13.4 MW;三维计算结果亦可为该捕集器的优化设计提供有价值的参考,同时亦证实了GOTHIC 3D程序对于三维两相流热工水力问题的模拟分析能力。

In case of a severe accident,the lower head of the reactor pressure vessel will be melted when the corium cannot be effectively cooled after melting.Under the EVR(ex-vessel corium retention)strategy,the molten corium will be released into the core catcher,where it can be sufficiently cooled,so that a large release of radioactive materials to the environment,after the molten materials melting through the basement of the containment,can be avoided.A twin crucible type core catcher with cooling tubes embedded in the molten pool to enhance cooling efficiency was conceived for a pressurized water reactor.As an EVR strategy,the core catcher first cools the molten pool through both the side walls of the inner crucible and the embedded cooling tubes under natural circulation of cooling water supplemented from a lower tank in IRWST(internal refueling water storage tank),before the top flooding triggered,so that all the melt is surrounded by water and thus can be retained and cooled for a long time.It is evident that the coolability of the core catcher before the top flooding might be thepredominant challenge for this conceptual design.In order to study the 3D transient coolability of the conceptual twin crucible type core catcher design,from the initiation of the water injection into the cooling channels to the establishments of first a two-phase natural circulation and then a thermal equilibrium,under given heat flux distributions from the wall,a 3D full scale distributed parameter model was built and analyzed with GOTHIC(generation of thermal-hydraulic information for containments)8.3(QA)code.By means of multiple blockages built inside a subdivided volume,the irregular shape flow channels of the twin crucible,can be modeled.With the mapped cell spanning method and the built-in heat transfer correlation package,covering the portion of the boiling curve spans single phase to pre-CHF(critical heat flux),of GOTHIC8.3(QA),the transient investigation of a 3D flow and two phase heat transfer can be realized.Through the simulation and analysis,post processing of the calculation results and discussions of related models,a sound heat removal capability of the conceptual core catcher design was proved.Under postulated conditions,the heat removal power can be improved to 13.4 MW.The results also show meaningful suggestions for the design and optimization on the transient two-phase natural circulation characteristics of the conceptual core catcher,and the capability of GOTHIC 3D model for three-dimensional thermal-hydraulic phenomena.