IRC提前饱和对ATWT功能影响分析及应对研究

Analysis and Solution for Effect of IRC Premature Saturation on ATWT Function

某压水堆核电厂调试启动期间核仪表系统(RPN)中间量程通道(IRC)的输出电流在核功率(Pn)小于30%FP时提前达到饱和值。首循环换料设计方案(FCRS)确定后,IRC提前饱和的主要影响因素是探测器出厂热中子灵敏度(SF)。根据未能紧急停堆的预期瞬态(ATWT)设计功能和RPN安全准则,得出IRC提前饱和造成ATWT允许信号实际阈值低于设计期望阈值是可接受的结论。IRC提前饱和时,必须在饱和点以下选择Pn作为ATWT允许信号阈值,以确保ATWT允许信号可正确触发。提出采用首循环18个月换料设计方案(FCRS18)的机组应选用SF较小的探测器,以降低IRC提前饱和问题发生的几率。

The output current of intermediate range channel(IRC) of nuclear instrumentation system(RPN) reached the saturation value prematurely when the nuclear power(Pn) was less than 30%FP during the commissioning startup of a pressurized water reactor nuclear power plant. The main influence factor of IRC premature saturation was its neutron detector manufactured sensitivity(SF), after the first cycle refuel design scheme(FCRS) determined. It can be concluded that IRC premature saturation is the reason that the actual threshold of ATWT permit signal is lower than its design expected threshold, based on the ATWT design function and nuclear instrumentation system(RPN) safety criteria. In order to ensure the correct trigger of ATWT permit signal, the threshold Pnof ATWT permit signal has to be selected as Pn under the saturation power when IRC premature saturation occurred. In order to decrease the probability of the IRC premature saturation, the IRC detector with smaller SF is sugguested for the nuclear power plants with FCRS of 18 months period(FCRS18).