摘要
目前,计算α本征值(中子时间常数)的方法主要有两种。一是引进一个与α有关的k(α),使计算α本征值转化成一个计算k(α)的反问题,然后确定α,使其满足k(α)=1,这种方法在次临界计算中常常因为截面出负而失效。二是从α本征值的概念出发,计算中子密度(数)随时间的分布,取稳态后多个时间段拟合α,这种方法的主要缺点是中子密度截断时间和用于拟合α的时间段的选取需要经验或者多次重复,缺乏一个统一的标准,选择不慎会严重影响结果。本文利用瞬发中子寿命(r)给出了一个评判标准:计算中子密度时截断时间取50r,用于拟合α的时间段取(30r,50r)。
Two methods are widely used to calculate the a eigenvalue for the moment. The first one is to search a a value satisfying the condition that k（α） is equal to 1 ,which is introduced to neutron transport equation in advance. It is frequently invalidated in subcriticality because that cross section is less than O. The second one is called dynamic fit method. Neutron density with time N（t） is calculated by MCNP program beforehand, and then a value is fitted according to its definition a= dN/（Ndt）. Some experience or repetitions are required to estimate the truncation time of neutron density and select the time interval during which a value is fitted. The answer can be badly affected by the unapt selection of time interval. This paper gives a means to solve the problem by the prompt neutron lifetime （τ）. Fitting a value between 30 τ and 50τ is recommended in this paper.
出处
《核科学与工程》
CSCD
北大核心
2007年第2期182-186,共5页
Nuclear Science and Engineering
关键词
次临界
瞬发中子寿命
α本征值
MCNP
subcriticality
prompt neutron removal lifetime
a eigenvalue
MCNP
