先进非能动核电机组一回路冷却剂流量系统化测量方法

Systematic measurement method for primary coolant flow rate in advanced passive nuclear power units

压水堆一回路冷却剂流量是防止偏离泡核沸腾的重要参数。三代先进非能动(Advanced Passive,AP)技术核电机组采用低泄漏堆芯装料模式,因堆芯出口温度温差梯度加大,导致量热平衡法流量测量计算的不确定度增加。为了保证核电机组一回路冷却剂流量精准测量,验证其满足设计与监管要求,提出了以伯努利方程为基础模型的系统化测量计算方法。在调试不同阶段,分别执行一回路主设备压差测量、冷热段弯管流量计压差测量;在首次50%、75%、90%、100%的功率平台,进行量热平衡试验计算。通过热试和满功率阶段的实体工艺流体测量值,对冷热管的弯管流量系数进行计算标定。围绕不确定度最小化,权重计算一回路冷却剂总体积流量。本方法测量计算的一回路冷却剂流量值相对误差小于4%,装料后总流量介于最佳预期流量的95.8%~104%之间;NAPs计算体积流量值不确定度低于1.9%,该方法为其他机型冷却剂流量的精准测量提供了一种示范思路。

[Background]The primary coolant flow rate is essential in preventing departure from nucleate boiling.The implementation of a low-leakage core loading pattern in advanced passive(AP)technology-based nuclear power units has increased the temperature difference gradient at the core outlet,resulting in elevated uncertainty in the flow rate calculations when using the heat balance method.[Purpose]This study aims to validate a measurement and calculation method based on the Bernoulli equation model for accurately determining the primary coolant flow rate in AP nuclear power units,hence meeting the design and regulatory requirements.[Methods]First of all,measurements were conducted for the primary loop main equipment and bend pipe flowmeter pressure differentials during the commissioning phases.Calorimertic balance tests were performed at power levels of 50%,75%,90%,and 100%.Then,the bend pipe flowmeter coefficients were calibrated using the flow rate values obtained from the hot function test and 100%rated thermal power(RTP).Finally,based on weighted factors,the total flow rate values for the reactor coolant system(RCS)were calculated with emphasis on the minimization of uncertainties.[Results]The proposed measurement and calculation method yields primary coolant flow rate values with a relative error of less than 4%.The total flow rate after loading is within the range of 95.8%to 104%of the expected optimum flow rate.The uncertainty of the volumetric flow rate calculated from NAPs is lower than 1.9%,demonstrating a novel approach for precise measurements in other units.[Conclusions]The method of this study offers an advanced perspective for reactor coolant precise measurements in other units,with primary coolant flow rate values exhibiting minimal relative error and volumetric flow rate values from NAPs demonstrating low uncertainty.