摘要
在轻水慢化次临界系统中,裂变反应产生的瞬发中子数量占次级中子绝对数量的99%以上,对堆内中子的衰减起主导作用,瞬发中子衰减参数α是核系统的重要标志性特征参数,该值的准确测量对于核临界安全具有重要意义。本文基于单群热中子扩散理论,根据裂变反应次级中子生成时间的不同,剥除高次谐波瞬发中子和缓发中子的影响得到按单一指数衰减的基波瞬发中子衰减曲线,结合数据采集参数编写算法并制作标准数据进行验证。在实验堆芯中分段测量控制棒的基波瞬发中子衰减参数,根据单一指数衰减法(S-K法)得到控制棒的积分价值曲线,并与周期法测量的积分价值曲线进行比对,两者的测量结果吻合很好;同时测量了4种不同堆芯方案中P组、A组、B组合E组对称控制棒全插时的基波瞬发中子衰减参数,由单一指数法得到反应性,数据分析表明,单一指数法的标准偏差为±0.042元,对应的百分偏差为0.6%。
In light water moderated subcritical system,accounting for the number of secondary neutrons produced by fission reactions,the total number of 99%neutrons is prompt neutron which plays a dominant role.Prompt neutron decay parameter α is an important parameter in nuclear systems,accurate measurement of this value is much more important for nuclear criticality safety.Based on one group thermal neutron diffusion theory,depending on the generation time of secondary neutrons in fission reaction,as the effect of higher harmonic fluxes of prompt neutron and delayed neutron is eliminated,we obtained a attenuation curve originating from the fundamental prompt neutron decay constant.Algorithm was written and verified with the help of data acquisition parameters and standard data.In experiments,based on the characteristic decay constant method,the integral reactivity of one control rod was obtained by measuring the prompt neutron decay parameters in each segments.For comparison,we calibrated the same control rod' integral reactivity by neutron generation methd,both measurements agree well.The symmetrical control rods' integral reactivity were measued by the characteristic decay constant method,which put in order group P,group A,group B,and group E in four different cores.Data analysis showes that the standard deviation is ± 0.042 million,corresponding to the percentage deviation of 0.6%.
引文
[1]罗璋琳,罗安仁.实验反应堆物理[M].北京:原子能出版社
[2]Marc rosselelet,Tony Williams,Rakesh chawla.Subcriticality measurements using an epithermal pulsed-neutronsource technique in pebble-bed htr configurations[C].Nucl.Energy,Vol.25,No.4-5,1998:285-294.