Probabilistic Safety Assessment Research For Fusion Reactor

At present,the energy problem has become a focus of global concern.Fusion energy has always been considered as one of the most developing potential sustainable clean energy sources.As the largest international scientific cooperation plan,the International Thermonuclear Fusion Experiment Reactor(ITER)plans to build and run a sustainable burning tokamak fusion experimental reactor to maintain fusion for long periods of time and test the integrated technologies,materials,and physics regimes necessary for the commercial production of fusion-based electricity.The construction of ITER marks the fusion research come into the stage of engineering research.The probabilistic safety assessment(PSA)is one of the important methods for the safety evaluation of nuclear facility.It has been widely used in the design,operation and maintenance of nuclear energy systems.The fusion PSA can quantitative analysis the accident sequence and the frequency of its occurrence through risk modeling for fusion facility.These works provide technical support for the nuclear power plant and safety supervision departments.But the probabilistic safety assessment for fusion facility mainly carried out for some sub-system of fusion reactor at present.A new probabilistic safety analysis method for fusion reactor was proposed in this paper,mainly research work are as follows:(1)Based on the design and safety features of ITER,a new methodological framework of fusion safety assessment which based on probability was given.The new methodological framework includes the determination of probability safety goals for fusion reactor,Initiation event analysis,accident sequence analysis,system reliability analysis and risk assessment.(2)Probability safety goals are the premise and foundation of probability safety assessment,but there is lack of probabilistic safety goals for fusion reactor at present stage.Based on the safety characteristics of fusion reactor,according to the basis and development process of current probabilistic safety goals for nuclear power plants in service,the probability safety goals for fusion reactor was proposed in this paper.This safety goal gives the risk acceptability of fusion reactor at all operation stage though Dose VS frequency method(3)According the different reactor response process,the postulated initiation event list which analyzed in ITER accident analysis reports,were grouped.The event tree analysis was used to establish the event tree model for each postulated initiation event group.The radiological releases to the environmental during each accident sequence were analyzed in this paper.The frequency of each accident sequence was analyzed through reliability analysis.The Fault tree models were established for VVPSS and DS in this paper.(4)According to the analysis result of ITER accident sequence,the maximum individual effective dose at the boundary of ITER is calculated according to the radiation dose of each radioactive material and the CCDF curve of ITER at the site boundary was given.The research results showed that the cumulative frequency of ITER small dose accident is higher,but it still meets the established probability safety goals.Within the range of over 0.1 mSv,the cumulative frequency of ITER drops sharply,which is unlikely to cause the large radioactive consequences.The radioactive consequences of ITER under the most serious accident conditions are lower than the off-site standards,which is consistent with the safety requirements of the fusion reactor to eliminate off-site emergency.Those work provide an effective method for the fusion reactor PSA;the probabilistic safety goals for fusion reactor was given and answer the question that"how safe is safe enough" in fusion reactor;the social risk of ITER was assessed which validates the effectiveness of this method.The conclusions provide some valuable reference for risk assessment and safety supervision of fusion commercial reactor in the future.