西安脉冲堆127I嬗变计算方法与实验验证

为了开展129I的热中子嬗变的研究，在西安脉冲堆上开展了127I靶件辐照实验。以探索实验条件，对127I靶件的嬗变率进行了蒙特卡罗计算，并与实验测量值进行了比对。利用NJOY程序，以ENDF/B VII.0库为基础，制作了127I在西安脉冲堆堆芯辐照温度下的MCNP格式截面库，与MCNP自带库(ENDF/B VI.2)同温度下截面库进行了比较，在不可分辨共振区做了改进，使用新制的截面库，利用MCNP程序对ORIGEN2数据库中的127I辐射俘获截面进行了修正，结合ORIGEN2程序分析了127I靶件在西安脉冲堆实际辐照后的嬗变率和核素的变化，研究了中子能谱和辐照时间对靶件嬗变计算的影响。使用MCNPX自带的燃耗模块CINDER90对127I靶件的嬗变情况进行模拟，结果与ORIGEN2基本一致，与实验数值有2%~3%的偏差，主要原因是MCNP计算中子通量密度存在误差。

Calculation and experimental validation of 127I transmutation rate in Xi’an pulsed reactor

In order to develop the research on 129I transmutation in the thermal reactor, 127I target was irradiated in Xi’an pulsed reactor(XAPR) to explore the condition for experiment in XAPR. The Monte Carlo method was used in the calculation of 127I target transmutation rate, and the results were compared with the experimental data. The NJOY software was used to generate 127I ace format neutron cross section at XAPR operating temperature based on ENDF/B VII.0 library. New cross section was compared with old ENDF/B VI library and developed in the unresolved resonance region. MCNP was used to modify the 127I cross section of ORIGEN2 by adopting a new cross section, then transmutation of 127I target was calculated to analyze changes of transmutation rate and nuclides, also the influence of neutron spectrum and irradiating time on transmutation was studied. The CINDER’90 software, a depletion mode of MCNPX, was also used to model the transmutation condition, the analytical result was consistent with ORIGEN2, but was a little different from the experimental data (2%-3% error) because of the deviation from the MCNP model in neutron flux calculation.