反应堆瞬时短周期与反应性引入速率约束问题研究

Toward the instantaneous short reactor period and rate constraint of reactivity insertion

核反应堆在反应性引入过程中会出现瞬时短周期现象,可能触发周期保护系统,从而出现非必要停堆问题。瞬时短周期受反应性引入速率影响较大,但同时与当前缓发中子先驱核浓度相关,一般难以量化。本文从点堆方程出发,基于两次保守假设,剥离出缓发中子先驱核浓度因素,推导出了简洁的瞬时短周期与反应性引入速率约束公式;并验证在该反应性速率约束下,瞬时短周期永远大于目标周期值,可以避免意外触发周期保护问题,为反应堆运行中的控制棒提升速率约束提供了理论依据。

[Background]The reactor period will dramatically decrease at the beginning of reactivity insertion in the nuclear reactor,which may trigger the protection system of the reactor period and lead to unnecessary shutdown.The instantaneous short reactor period is influenced greatly by the inserting rate of reactivity,but also related with the present delayed neutron precursors,which is difficult to quantify.[Purpose]This study aims to explore the relationship between the instantaneous short reactor period and the inserting rate of reactivity from a theoretical perspective.[Methods]A point reactor model was used to deduce the inserting rate of the reactivity function using the variable factors of reactivity,reactor period,and reactor dynamic parameters,with some conservative assumptions to omit the effect of delayed neutron precursors.The relationship between reactivity insertion rate and transient period of reactor was derived after analysis on the short period phenomenon.Then,the formula of relationship was verified for several transient cases.[Results]The results show that the reactor periods are all larger than the aim reactor periods for all transient cases when using the rate constraint of reactivity insertion in the aforementioned formula.According to the proposed theoretical framework,unnecessary shutdown during an instantaneous short reactor period can be avoided.[Conclusions]A theoretical framework proposed in this study can be applied to the control of rod withdrawal rate during the operation of nuclear reactors.