Design And Evaluation On In-Service Decontamination System Of Mechanical Equipment In Pressurized Water Reactor

With independent research and design for the construction of Hualong One PWR nuclear power plant,China's nuclear energy R&D and design level have risen to a new stage.New system and equipment require in-service inspections and maintenance during reactor shutdown,and equipment or components that need to be removed from the reactor are often exposed to radioactive contamination.In order to ensure that maintenance personnel are not exposed to excessive radiation dose during operation,the components must be decontaminated prior to dismantling or repairing the equipment to reduce the surface and internal radioactive intensity of the equipment,that means in-service decontamination.The design of in-service decontamination is of great significance and value for the safety and economy of nuclear power plant operation and maintenance.In-service decontamination is different from other types of decontamination.There are special requirements for decontamination methods,conditions,and inspection standards.At present,the main decontamination methods at home and abroad are physical and chemical decontamination methods.By analyzing and comparing the advantages and disadvantages of different decontamination methods and process features,the following work was done.The decontamination process is based on chemical decontamination and assisted with physical methods.It is selected the types and main components of the chemical decontamination agent suitable for the process.For new decontamination system,It is analyzed and designed from the main principles of system operation,the function and structure of the decontamination equipment,the flow of the decontamination system,the operational control and the measures taken under the accident conditions,and the layout of the system,to meet the requirements of the decontamination process and the safety of personnel's radiation protection.Based on the qualitative analysis,the main process parameters of the system were analyzed and calculated,and the main design indicators and monitoring quantities of the system operation were determined,including the hydraulic characteristics of the nozzle,the flow resistance analysis of the air filtration facility,the ultrasonic parameters design and so on.It is specially studied the mechanism of the airtightness and safe opening and closing the lid of the chemical decontamination equipment during operation,and is proposed the structural design of linkage control with the damper to improve the safety of the apparatus.According to the feedback of the running power station,the design of the filter components of the main pump hydraulic component is improved,which greatly reduces the probability of hot spots in the decontamination process.According to the relevant national standards and operation experience of operating power plants,a principle of evaluation of decontamination effect was determined,and the design of decontamination system was tested to a certain extent through the decontamination work of a nuclear power plant.The results showed that the decontamination achieved the expected effect.Through the research and analysis of in-service decontamination,a program for Hualong One nuclear power plant decontamination system was designed,and summarizing the major problems facing the future development of in-service decontamination,and expounding the direction and focus of development in future.It is provided technical support for the standardization design of decontamination system and equipment,and also provided technical guidance and program selection for the construction design of the decontamination system of Hualong One nuclear power plant in future.