核电站一回路管道中腐蚀产物在不同过氧化氢工况下沉积特性的实验研究

压水堆核电站停堆时主回路的化学源项控制是反应堆源项控制中的重要一环,在燃料包壳没有破损的情况下,腐蚀产物的活化可造成超过90%的堆外辐射。世界上多个核电厂的运行经验表明,较差的水化学环境是导致堆外辐射强度高的主要因素。为了综合分析并确定最优的水化学环境,进而增强核电站运行期间的辐射防护,本文基于压水堆核电站的主要运行设施及其位置排布,搭建了活化腐蚀产物沉积特性实验系统。在90°水平弯管上测试不同过氧化氢含量下主要活化腐蚀产物(Fe、Cr、Mn、Co和Ni元素)沿轴向和周向方向上的沉积情况。实验结果表明,金属元素在弯管轴向角30°~75°与周向角15°~345°的区域沉积最严重。随过氧化氢浓度的增大,沉积量先减小后增大。最低沉积量对应的最佳水化学条件为20 mL过氧化氢(浓度30%)与0.6 mg/kg氢氧化锂。沉积特性的实验研究可以为核电站运行期间降低管道中辐射强度提供指导。

Revealing the concentration of hydrogen peroxide in fuel cell catalyst layers by an in‐operando approach

To evaluate the H_(2)O_(2)‐tolerance of non‐Pt oxygen reduction reaction(ORR)catalysts as well as in‐vestigate the H_(2)O_(2)‐induced decay mechanism,the selection of an appropriate H_(2)O_(2) concentration is a prerequisite.However,the concentration criterion is still unclear because of the lack of in‐operando methods to determine the actual concentration of H_(2)O_(2) in fuel cell catalyst layers.In this work,an electrochemical probe method was successfully established to in‐operando monitor the H_(2)O_(2) in non‐Pt catalyst layers for the first time.The local concentration of H_(2)O_(2) was revealed to reach 17 mmol/L,which is one order of magnitude higher than that under aqueous electrodes test conditions.Powered by the new knowledge,a concentration criterion of at least 17 mmol/L is suggested.This work fills in the large gap between aqueous electrode tests and the real fuel cell working conditions,and highlights the importance of in‐operando monitoring methods.