注锌对压水堆锆合金表面污垢的影响研究

Effect of Zinc injection on the surface CRUD of PWR zirconium alloy

腐蚀产物在压水堆(Pressurized Water Reactor,PWR)锆合金表面沉积后会形成污垢(Chalk Rivers Unidentified Deposit,CRUD),降低燃料包壳换热能力,并对一回路放射性水平产生影响。注锌作为一种水化学调节方式,在国内外各核电站中正得到越来越广泛地应用。CRUD主要成分为镍铁络合物,锌作为比镍铁更活泼的金属,可能通过置换反应改变CRUD成分、或在较高热流密度的环境下析出并与镍铁形成新的金属络合物。利用人造污垢实验设备,在与PWR服役工况相近的环境下开展了注锌对人造污垢影响实验,并采用扫描电子显微镜(Scanning Electric Microscope,SEM)和X射线光电子能谱仪(X-ray Photoelectric Spectroscopy,XPS)对注锌前后CRUD的形貌、成分和氧化颗粒尺寸进行了分析。结果表明:锌主要在加热段的CRUD中析出;注锌后CRUD的镍铁比从0.58升高至0.65,氧化颗粒物孔隙率从30.15%降低至10.08%;相对于未注锌工况,CRUD开裂现象更为明显,微观形貌从疏松多孔状转变为较致密状态。本文研究成果为在运机组评估注锌对燃料性能的影响提供了参考依据。

[Background]The corrosion products deposited on the surface of pressurized water reactor(PWR)zirconium alloy will form chalk rivers unidentified deposit(CRUD),which will reduce the heat transfer capacity of fuel cladding and affect the primary radioactivity level.The main component of CRUD is ferronickel spinel whilst the zinc,as a more active metal than ferronickel,may change the composition of CRUD through displacement reaction,or precipitate in a higher heat flux environment and form a new metal complex with ferronickel.Hence zinc injection,as a hydrochemical regulating method,is being more and more widely used in nuclear power plants.[Purpose]This study aims to investigate the effect of zinc injection on CRUD of zirconium allay surface.[Methods]Experiments were conducted in artificial CRUD facility under similar PWR operation environment.Scanning electric microscope(SEM)and X-ray photoelectric spectroscopy(XPS)were employed to analyze the morphology,element and oxidized particles porosity of CRUD before and after zinc injection.[Results]The experimental results show that zinc mainly precipitates inside CRUD in heating region;after zinc injection,the nickel-iron ration of CRUD elevates from 0.58 to 0.65,while oxidized particles porosity of CRUD decreases from 30.15%to 10.08%.Compared with the non-zinc environment,the cracking of CRUD becomes more obvious,and the micro size of CRUD changes from loose porous shape to dense shape.[Conclusions]These results provide a reference for evaluating the influence of zinc injection on fuel performance of in-service PWRs.