Central spherical detector is one of the most essential and complicated support systems for the large-scale underground neutrino observatory. If a central spherical detector accident happens, the consequences may be disastrous with huge economic loss. However, there is very few published research works which focus on its quantitative risk analysis. In this paper, an improved fuzzy fault tree analysis (FFTA) method incorporated with the weakest t-norm (Tω) algorithm, the confidence level concept, and the analytic hierarchy process (AHP) approach is proposed to perform its risk assessment. By carrying out the identification of failure modes and failure reasons, fault tree (FT) model of central detector is constructed based on logical relationship among subcomponents. Fuzzy set theory is applied to obtain failure data, and Tω algorithm is exploited to eliminate fuzzy accumulation in the aggregation process. In addition, a confidence level coefficient and AHP approach are employed to enhance the reliability of the evaluation. Both importance and sensitivity analysis have been conducted to identify the critical basic events and provide improvement measures. Finally, the comparison of the occurrence possibility of detector failure is used to verify the applicability and the feasibility of proposed method. The calculated results indicate that the improved approach is more consistent with real situation and can provide a more effective engineering reference for the risk decision of central spherical detector.

Based on the algorithm of Coupled Eulerian Lagrangian (CEL), the processes of the generation of shaped charge jet (SCJ) and the penetration to the inner and outer ship side plates were simulated by the finite element analysis (FEA). Meanwhile, the residual velocity of SCJ after penetrating the side plate could be obtained. In order to compare with the FEA results, the damage caused by the SCJ to the inner and outer plates of the ship side was experimentally studied, and the residual velocity was measured successfully. The comparison demonstrated that the values of the residual velocity obtained by simulation well agreed with the experimental results. The simulation indicated that the velocity of the SCJ decreased after penetrating the inner plate. Moreover, the influences of the ship side structural details, including the inner plate thickness, the distance between the inner and outer plates and the layout of the inner plate, on its protective ability against SCJ were investigated. The research indicated that increasing the thickness of inner plate and the spacing between inner and outer plates can effectively reduce SCJ residual velocity. Replacement of the inner plate with a multilayer plate could obviously reduce the SCJ residual velocity. The simulation method could describe the process of SCJ generation and penetration accurately, and the research results could provide references for the protective structural design of the ship hull attacked by SCJ.