基于MCNP的反应堆建模方法

Reactor physical modeling method based on MCNP

为了研究不可分辨共振区概率表、自由气体热散射的温度修正、热中子S(α,β)模型对MCNP模拟的反应堆有效增值因子K_(eff)、堆芯能谱以及功率分布的影响,本文提出了一种基于MCNP的反应堆临界模拟方法。使用蒙特卡罗程序MCNP5对某反应堆堆芯及周围结构进行了建模,在此基础上,通过控制MCNP5输入文件中的PHYS卡、TMP卡、MTn卡分别模拟不可分辨共振区概率表、自由气体热散射的温度修正、热中子S(α,β)模型等因素对MCNP5计算的反应堆有效增值因子K_(eff)、堆芯能谱以及功率分布的影响。结果表明,S(α,β)模型对K_(eff)、堆芯能谱以及堆芯功率分布计算均有较大影响,在反应堆堆芯建模时应加以考虑,并且忽略S(α,β)模型的影响将得到非保守的K_(eff)计算结果。此外,自由气体热散射的温度修正对K_(eff)计算也有着不可忽略的影响。

In order to study the unresolved resonance range probability tables,temperature correction of free gas thermal scattering,and neutron thermal S(α,β)on the Monte Carlo N particle transport code(MCNP)simulated reactor effective multiplication factor(K_(eff)),core energy spectrum and power distribution,this paper proposes an MCNP-based reactor criticality simulation method.The Monte Carlo program MCNP5 is used to model a reactor core and surrounding structures.On this basis,the PHYS card,TMP card,and MTn card in the input file of MCNP5 are controlled to simulate the influence of unresolved resonance range probability tables,temperature correction of free gas thermal scattering,and neutron thermal S(α,β)on the MCNP calculated effective multiplication factor-K_(eff),core spectrum,and power distribution.The results show that the S(α,β)model should be taken into account because of its great influence on the calculation of K_(eff),energy spectrum and power distribution of the reactor core,and ignoring the influence of the S(α,β)model will result in a non-conservative value of K_(eff) calculation result.In addition,the temperature correction of the free gas thermal scattering also has a non-negligible influence on the K_(eff) calculation.