Study On Method And Key Technologies Of Multi-spacetime Scales Real-time Risk Monitoring For Nuclear Reactors

The safety management mode of nuclear reactors is on its way of shifting to the Risk-formed Regulation(RIR),which combines probabilistic and deterministic methods.As the probabilistic methods is systematic and comprehensive,the RIR management model enables to eliminate disadvantages of deterministic method,such as the hypotheticality and conservatism,and finally reach to a scientific decisionmaking methodology.The tool for direct application of the RIR management model is Risk Monitor(RM)system,which has been widely used in the world.The RM system is a real-time risk analysis tool,which analyzes the real-time risk caused by state change of nuclear reactor systems and equipments,which are of great significance for avoiding high-risk configuration and optimizing maintenance strategies.However,the existing nuclear reactor risk monitoring system hasn’t fully considered the characteristics of nuclear reactor safety in different data update frequency and different safety goals in different areas,especially neglected the impact of periodic characteristics of four types of data to model updating,during the dynamic construction of the nuclear reactor real-time risk monitoring model;could not fully consider the time-periodic characteristics of nuclear reactors in SSC classification,maintenance and other aspects in the process of nuclear reactor item classification;failed to improve the accuracy and effectiveness of item classification through fully utilizing the historical operation data of nuclear reactors;could not fully consider the source release risk corresponding to Level Ⅱ PSA(probabilistic safety assessment)and the off-site dose risk corresponding to Level Ⅲ PSA in the scope of risk monitoring.Thus,it cannot fulfill the latest requirements of nuclear reactor risk monitoring on the spatial scale.In view of problems found in the above research,this paper has carried out a series of key technical studies in the risk monitoring of nuclear reactors at multiple time scale and multiple space scale.The research and innovations mainly include the following aspects:1.This paper studies the multiple-time scale characteristics of nuclear reactor risk monitoring,summarizes the periodic characteristics of four types of data of nuclear reactor,classifies the data sources from real-time risk monitoring model of nuclear reactors in a multiple-time scale dynamic modeling and gives a set of dynamic modeling methods based on the above characteristics,including the reliable data update method based on dynamic events,the common cause group dynamic update method based on multiple conversion page,the post-model processing method based on recovery rules,the complex boundary condition replacement and fault tree expansion method based on multiple-switch event sets,etc.2.This paper proposes an item classification method based on the specific historical operation data of nuclear reactors,and takes the time-periodic characteristic of nuclear reactors in terms of SSC detection and maintenance into account,so as to make full use of the real SSC status data to improve the subsequent SSC maintenance and nuclear reactor safety management,and utilize the specific operation history of nuclear reactors and the latest state of SSC to improve the economy of nuclear reactors,while ensuring its safety.3.A real-time risk monitoring method for nuclear reactors is proposed,which can simultaneously support the real-time calculation of accident risks such as core damage frequency,radioactive source item release risk and off-site dose risk.It overcomes that the traditional nuclear reactor risk monitor only supports the safety assessment of firstlevel probability,that is,it can only provide the real-time calculation of core damage risk and the information directly related to nuclear power operation management such as the allowable outage time,but it fails to provide information support to issues such as radioactive source item release risk and off-site dose risk of the reactors.We’ve carried out the design and development of the multiple-space-time scale nuclear reactor RM system so as to meet the multiple-space-time characteristics of nuclear reactor safety better.Through the typical tests of nuclear reactor risk monitoring models,we have verified the function and correctness of the software system.At the same time,we have carried out a preliminary application to the actual case of real-time risk monitoring of Xi’an Pulse Reactor.The application results show that,the impact of accident source terms and off-site dose of the public and the environment in the reactor risk assessment is more convincing than that of using the core damage frequency alone.The results are more abundant than the existing risk monitoring system,and it can support the nuclear reactor safety supervision and nuclear emergency management decision-making more effectively.