Research On The Key Technologies Of Safety Design For Spent Fuel Transportation Cask

As a clean energy, nuclear power is an inevitable choice for green development. The safety of nuclear power has become the focus of research at home and abroad, among them, transport and disposal of nuclear waste is a major existing technical obstacles. Specially, with the rapid development of China’s nuclear power industry, a large number of spent fuel needs to be shipped out and safely disposed, meanwhile, waste disposal in new or planned nuclear power plants is in urgent need of proper planning, China is still almost a blank in the design and manufacturing of large-scale spent fuel transportation cask. Therefore, self-development of large-scale and safe-reliable spent fuel cask has a very important practical significance.In accordance with the types and characteristics of spent fuel used in China, and the comparison of spent fuel transportation cask both at home and abroad, spent fuel transportation cask type for self-development and its overall structure were proposed; Corresponding points for structural design, material selection, processing, manufacturing and safety analysis of spent fuel transport cask were given; safety-analysis based development technologies for spent fuel transport cask were summarized. A model was built for the AFA2G type spent fuel and the NAC-STC type transportation cask. With this model, studies were done on several key issues of safety analysis, namely, critical safety analysis, shielding analysis, thermal analysis and stress field analysis of9m drop test, which are detailed as follows:(1) Critical safety analysis:Calculations were performed for the simple system (single fuel rod lattice cell, single fuel component and single fuel component with tube) under different initial235U enrichment and different circumstances (water of different volume fraction). Further study was conducted on the critical safety analysis of the spent fuel cask system under normal transport condition and accident transport condition. It was found that the presence of neutron absorbing material in the fuel tube can significantly reduce Keff; The cask loading spent fuel in the underwater corresponded to maximum Keff, which was the most dangerous situation in the critical safety analysis.(2) Shielding analysis:Shielding calculation was conducted for boards of common materials of spent fuel cask under252Cf radioactive source. The calculation results were validated with experimental data from Japan and show good agreement with the test results, which verified the applicability of the software. Dose rate at the cask surface were gained for normal condition and accident condition, respectively. Dose rate on both sides of the cask without neutron shield was quite great, therefore, it was recommended to use the shock absorber to fully wrap the cask in the design stage.(3) Thermal calculation and analysis:Finite element model of cask was built using ANSYS11.0. Based on this, the steady temperature field was simulated for normal transport condition. Besides, simultaneous analysis was conducted for30min,800℃fire accident, and the temperature field inside container was investigated after25h of fire.(4) Stress field analysis of9m drop test:First, based on the single-degree-of-freedom spring model, the maximum deceleration was estimated to be no more than50g during collision process between cask and the ground using energy conservation principle. Then the finite element model was built for cask and the equivalent static structure analysis was made. Finally, stress check was conducted for the cask structure according to the stress limit defined by ASME III. It was found that stress on both ends of the cask correspond to maximum value, impact load of the shock absorber played a key role on the cask stress distribution; It was obvious that the setting of both ends of the neutron absorbing layer could cause stress concentration, which needed to pay special attention.In this paper, the above key technical issures were preliminarily studied and discussed. The conclusions have reference value for the design and safety analysis of spent fuel transportation cask.