多普勒展宽舍弃修正对氟盐冷却球床高温堆中子学的影响分析

摘要

In epithermal energy range,the thermal motion of the target nuclides impacts the elastic scattering.The traditional constant scattering cross section approximation free gas model was adopted in Monte Carlo code to describe the scattering in epithermal energy range.Recent researches show that the bias introduced by ignoring the resonance elastic scattering increases with the temperature.The working temperature of the peb-ble-bed fluoride-salt-cooled high-temperature reactor(PB-FHR)is high,therefore it's necessary to consider the resonance elastic scattering by using the Doppler broadening rejection correction(DBRC)method.In this work,the modified Monte Carlo code MCNP5 was used to analyze the pebble unit cell of PB-FHR.It is found that the DBRC method results in an increase of capture reaction rate of 238U and a decrease of infinite multiplication coefficient(kinf)by 123-1 182 pcm.In addition,the absolute difference of kinfintroduced by the DBRC increases with TRISO packing factor and temperature.%超热区中子的弹性散射易受靶核热运动影响,传统的蒙特卡罗程序采用常数散射截面自由气体模型来描述超热区中子的散射过程.研究表明,忽略共振弹性散射效应所引入的误差随温度的升高而增加,而氟盐冷却球床高温堆工作在高温条件下,为减小共振区弹性散射计算误差,有必要在中子学计算中使用多普勒展宽舍弃修正方法以考虑其共振弹性散射效应.本文使用修改源码后的蒙特卡罗程序MCNP5对氟盐冷却球床高温堆栅元开展中子学计算,发现经多普勒展宽舍弃修正后的238U的中子俘获率增加,无限增殖因数减小123～1 182 pcm,且无限增殖因数偏差随燃料球栅元填充率及温度的升高而增大.