西安脉冲堆燃耗对中子代时间的影响研究

Study on the Influence of Depletion on Neutron Generation Time for Xi’an Pulsed Reactor

本文研究了计算反应堆中子代时间(Λ)的瞬发中子通量密度衰减法,基于反应堆仅释放瞬发中子的假设条件,研究了瞬发中子动力学方程,将Λ的计算转变为α本征值的计算问题,采用MCNP程序模拟瞬发中子通量密度的衰减特性以拟合出α值。该方法避免了抽样计算中子价值函数的复杂问题,实现相对容易。并根据西安脉冲堆(XAPR)堆芯三维燃耗分布拟合出不同燃耗深度下瞬发中子通量密度衰减系数α,计算出堆芯中子代时间。结果表明:随着XAPR堆芯燃耗的加深,中子代时间呈增大趋势,从新堆芯到第一循环末(120EFPD),Λ增大幅度为8.93%。

The neutron generation time Λ is a very important reactor kinetics parameter. It is very significant for reactor operation and safety under reactor transient conditions. The prompt neutron flux density decay method is developed in the paper. Assuming that only prompt neutrons are produced in the reactor,the prompt kinetics equation is derived. And based on the prompt kinetics equation,the calculation of Λ is converted to α eigenvalue. Then the decay of prompt neutron flux density is simulated by the MCNP code to calculate α. The complicate problem calculating neutron importance function is avoided so that the method is easier to be achieved. According to the three-dimensional burnup distribution of the Xi’an pulsed reactor, the prompt neutron flux density attenuation coefficient is fitted and the Λ is calculated. The result indicates that the Λ is enlargement along with the increase of burnup. From the new core to 120EFPD,the Λ increases by 8.93%.