深穿透跨尺度辐射场分析软件NECP-MCX研发及应用

Development and Application of Deep Penetrating Cross-scale Radiation Field Analysis Software NECP-MCX

西安交通大学核工程计算物理实验室自主研发了深穿透跨尺度辐射场分析软件NECP-MCX。针对大空间伽马射线辐射输运模拟、聚变堆停堆剂量模拟和点源屏蔽问题等新应用场景下的新问题与新挑战,在NECP-MCX中研发了对应的新方法与新功能。针对km尺度的伽马射线辐射输运问题,提出一致性共轭驱动重要性抽样(CADIS)-下次事件估计器(NEE)耦合方法,该方法能够精确高效地获得km尺度距离处的光子通量密度,计算效率比传统的NEE高6.8倍;针对聚变堆停堆剂量问题,采用粒子输运-燃耗-活化-源项耦合分析方法,获得PF线圈、TF线圈、真空室和偏滤器处停堆剂量随停堆时间的变化;对于点源屏蔽问题,提出首次碰撞源(FCS)-CADIS方法,解决CADIS方法对点源进行源偏倚的局限性,FCS-CADIS方法的计算效率比CADIS方法高2倍。

The research and development progress of NECP-MCX,a deep penetrating cross-scale radiation field analysis software independently developed by Xi’an Jiaotong University,is summarized.New methods and functions have been developed for new application scenarios such as large-space gamma ray radiation transport simulation,dose field simulation within containment,fusion reactor shutdown dose simulation and point source shielding problem.Precise calculation results of various problems and high performance indicate that NECP-MCX is able to cope with new challenges of the new application scenarios.The efficiency of consistent adjoint driven importance sampling(CADIS)and forward-CADIS(FW-CADIS)is shown in this work by calculation PCA-Replica benchmark which is a classic pressure vessel shielding problem in SINBAD(shielding integral benchmark archive and database).Both CADIS and FW-CADIS are able to improve simulation efficiency of reaction rate tallies in detectors.For the new challenge of large-space gamma ray radiation transport simulation,the CADIS-next event estimator(NEE)coupling method is implemented in NECP-MCX.By combining with CADIS,the convergence of NEE is improved as more paticles transport to the adjacent region of the detector point.With the coupling method,the point tally ability of CADIS is expanded as well,which allows CADIS method to obtain results at points.The CADIS-NEE method is able to accurately and efficiently obtain the photon flux density at km-scale distance in large-space gamma ray radiation transport simulation,and the computational efficiency is 6.8 times higher than that of the traditional NEE method.Further more,the relative standard deviation of CADIS-NEE decreases at a rate of~N 1/2 over the last half run,which means a reasonable convergence.While NEE’s relative standard deviation is not able to decrease at such stable rate in the large-space gamma ray radiation problem.For the simulation of shut-down-dose-rate(SDDR)of China Fusion Engineering Test Reactor(CFETR),NECP-MCX can obtain and visualize decay photon strength and distribution of the whole CFETR after shutdown.Then SDDR of poloidal field coils,toroidal field coils,vacuum vessel and divertor at various shutdown time can be estimated by the novel particle-transport/depletion/activation/source-term coupling analysis process in NECP-MCX.The SDDR of CFETR from just shutdown to 500 years after shutdown is evaluated with NECP-MCX.For the point source shielding problem,NECP-MCX proposes the first-collision source(FCS)-CADIS method to cope with the limitation of source biasing of the CADIS method,and the computational efficiency of FCS-CADIS method is 2 times higher than that of the CADIS method.