Research On Reliability Design Of Nuclear Control Rod Drive Mechanism

The safe and stable operation of nuclear power plants has been a great concern of the government,society and enterprises.The control rod drive mechanism(CRDM)is a very important safety equipment in nuclear reactors,which is responsible for several important functions such as power regulation,startup of reactor and safety control under accident.It drives the control rod assembly to move up and down in the reactor core to adjust the reactor's reaction rate to ensure the safety of the reactor.In order to realize the steady and sound development of China's nuclear power industry,to promote the continuous improvement of domestic nuclear power equipment R & D,manufacturing level and market competitiveness,it is imperative to study the reliability techniques applicable to the CRDM and enhance the reliability of the CRDM.In this paper,under the support of "R & D Service Project of China Demonstration Fast Reactor CRDM",using the CRDM as the research object,the reliability design system is established according to the design and development process and the actual situation of the enterprise.The key reliability technology has been studied,which has laid a solid theoretical and practical foundation for the reliability research of the CRDM.The main research contents are as follows:(1)Based on the characteristics and requirements of the CRDM,the reliability design system of the control rod drive mechanism is established according to the three basic tasks and the reliability theory and methods,which integrates the engineering design and reliability design and analysis of the CRDM.Depending on the design goals of each design phase the reliability tasks of each design and development phase can be determined,so that the reliability design and analysis can be done in an orderly and efficient manner which has laid a foundation for the design of the CRDM to meet the design requirements.(2)Aiming at the issue of failure mode analysis of CRDM,this paper,based on the analysis of the defects of traditional RPN method,puts forward the method of criticality analysis using fuzzy OWA operator and DEMATEL method,which takes into account the weighting of risk factors and the interrelationships between failure modes.The example shows that this method can reduce the frequency of repeated RPN values compared with the traditional RPN method,and can identify the sequence of failure modes that can't be identified by the traditional RPN method,which highlights the validity and correctness of the method.(3)There are a lot of uncertain factors and information in the early design stage of the control rod drive mechanism,and the reliability data is extremely scarce.In this paper,a new method is proposed to solve the problem,which combines the interval analysis theory with the analytic hierarchy process(AHP)and fuzzy evaluation.Finally,the feasibility and effectiveness of the proposed method are verified by the reliability allocation of the CRDM.(4)In order to settle a dispute that the quantitative analysis of fault tree is difficult to carry out when the probability of basic events are unknown,this paper on the basis of the combination of fuzzy set theory and expert experience presents a method to evaluate the probability of basic events.The result,the probability of occurrence for the top event and the probability importance of basic events to the top event,is obtained when applying this method to the reliability analysis of fast falling rod with signal triggering in non-seismic condition,which verifies the feasibility and practicability of the method.