核电厂氧化运行期间冷却剂中^(58)Co活度浓度的现场监测

On-site monitoring the activity concentration of nuclide ^(58)Co in coolant during PWR oxygenation shutdown

氧化运行期间,通过化学连续取样测定冷却剂中^(58)Co的活度浓度峰值和达到氧化运行结束条件的时间(活度浓度<25 GBq·t-1)时,会产生大量放射性废液。为减少取样产生的放射性废液,设计利用高纯锗就地γ测量系统在管道外进行γ谱测量,获得^(58)Co特征峰净计数率随停堆时间实时变化数据,藉此预判^(58)Co活度浓度达到峰值时间和氧化运行结束时间,然后进行取样分析。在某核电站氧化运行期间,利用系统进行γ谱连续测量,判断^(58)Co活度浓度峰值时间是停堆后33h39min(±10min),氧化运行结束时间是停堆后57h(±10 min);连续取样数据测量判断^(58)Co活度浓度峰值时间是停堆后33 h 34 min,氧化运行结束时间是停堆后57 h 9 min。两种方法判断达到峰值和氧化运行结束时间误差都在10 min以内。

[Background] During the oxidation operation of a reactor, the max active concentration of 58Co in the coolant and the time to the end of the oxidation operation(activity concentration <25 GBq·t-1) are compulsory. The current chemical sampling method produces large amounts of radioactive waste liquid. [Purpose] This study aims to reduce the current radioactive waste liquid by establishing an external γ spectrum monitoring system. [Methods] The HPGe γ measurement system is used to measure the γ spectrum of the coolant outside the pipeline. The net count rates of the 58Co characteristic peak varition with time were obtained after reactor shutdown. These data can be used to predict the time to reach the maximum active concentration of 58Co in the coolant and the time to reach the end of the oxidation operation, and then performed a sample analysis. [Results] During the oxidation operation of a nuclear power plant, this monitoring system was used to continuously measure the γ spectrum outside the pipeline. The time of the maximum activity concentration of 58Co was predicted to be 33 h and 39 min after shutdown, and the oxidation operation end time predicted to be 57 h after shutdown. By continuously coolant sampling data, the time of the maximum activity concentration of 58Co was 33 h and 34 min after shutdown, and the oxidation operation end time was 57 h and 9 min after shutdown. Two time errors are in normal range(less than 10 min). [Conclusions] The external monitoring method can reduce the sampling frequency significantly and reduce the amount of radioactive waste generated by sampling analysis.