摘要
Abstract
The steam generator,as a nuclear safety Class Ⅰ equipment in the primary circuit of a nuclear power plant,has its operational reliability directly related to the economic benefits and safety of the power unit.Through analyzing the collector tube DN1200 and the connecting welds №111-1 and №111-2 of the PGV-1000 steam generator used in VVER pressurized water reactor units,a design flaw similar to a"pocket"dead angle was discovered.By analyzing the overhaul data of operat-ing units such as the Novovoronezh Nuclear Power Plant in Russia,it was found that such welds are prone to structural strength loss within 5-20 years after the unit starts operation,mainly manifested as defects like cracks.The study indicates that the causes of the defects are related to multiple factors:uneven thermal shock in the dead angle area,impeded medium flow leading to accumulation of copper ions and other impurities,accelerating crack initiation and propagation;residual welding stress and structural complexity further exacerbate the damage.To address these issues,improvements in the manu-facturing process are proposed:optimizing welding techniques(such as argon protection at the root of the arc welding,sym-metrical welding to control deformation),enhancing welder certification and non-destructive testing systems,and strictly implementing post-weld heat treatment at 620-640℃to reduce residual stress.During the operational phase,it is recom-mended to add chemical agents to inhibit deposits,increase cleaning frequency,conduct regular eddy current/ultrasonic tests,and for units exceeding their designed lifespan,"pocket"passivation and operational load optimization can be adopted to delay defect deterioration.The research results provide theoretical and practical guidance for the manufacturing and opera-tion&maintenance of the VVER reactor type steam generator weld №111,and also offer references for defect control in similar structures of other reactor types.关键词
VVER压水堆/蒸汽发生器/焊接接头/缺陷机理/残余应力/运维策略Key words
VVER PWR/steam generator/welding joint/defect mechanism/residual stress/operation and maintenance strategy分类
矿业与冶金
