基于RELAP5的反应堆失控提棒反应性引入分析

Analysis on the Reactivity of Reactor Noncontrolled Lifting Rod Based on RELAP5

失控提棒是核电厂中发生频率较高的事故。为了了解该事故发生时核功率、堆芯核通量、堆芯热流密度的表现形式,以某机组压水堆运行核电站设计数据为基础,利用RELAP5进行了反应堆失控提棒反应性引入计算分析。计算结果表明,在次临界状态、热态零功率或有功率状态下,事故过程中核功率响应,虽然在瞬态中的核功率峰值很大,但时间很短,能量释放和燃料平均温度的增加并不大。控制棒组失控提升连续引入反应性,使核功率迅速增长,但功率的增长将被负的多普勒反应性反馈所限制。在高反应性引入速率时,堆芯核通量上升很快,高核通量信号会导致停堆事件的发生。由于燃料和冷却剂系统液体热容的影响,堆芯热流密度将滞后于核通量的增加。为了避免燃料元件包壳损坏,就应该使反应堆保护系统能够在偏离泡核沸腾比(DNBR)下降到限值之前终止该事故。

Noncontrolled lifting rod is an accident occurring at a relatively high frequency in a nuclear power plant. To understand the manifestations of nuclear power,core nuclear flux,and core heat flux density at the time of the accident,based on a pressurized water reactor nuclear power plant operation design data,RELAP5 is used to analyze and calculate the reactivity of reactor noncontrolled lifting rod. The results showthat nuclear power response in the event of sub-critical state,hot zero-power state or power state,although the peak of nuclear power in transient state is very large,but due to the short time,energy release and average fuel temperature increase are not great. The uncontrolled lifting of the control rod leads continuously to the reactivity and causes a rapid increase in nuclear power,but the increase in power is limited by negative Doppler reactivity feedback. At high reactivity introduction rates,core-flux increases rapidly and high-core flux signals can cause shutdown events,but the core heat flux density will lag behind core flux increase due to the heat capacity of the fuel and cooling liquid. Therefore,in order to avoid the destruction of the fuel cell envelope,the reactor protection system should be able to terminate the accident before the DNBR drops to a limit.