Earthquake Safety And Assembly Dropping Analyses Of Spent Nuclear Fuel Storage Rack

Spent nuclear fuel storage rack is mainly used to storage spent fuelassemblies unloaded from a nuclear reactor. Because the spent fuel assembliesstill have certain radioactivity, it’s very important to make sure that the rack issafe during all the time in service. In this thesis, the rack and assembly systemwas analyzed under design load condition, abnormal condition and accidentcondition and safety assessment was performed based on the French standardRCC-M. Furthermore, dropping of the assembly and impact with the rackwere also studied for the safety evaluation. Main contents of the thesis are asfollows.(1) A finite element model was established for the rack and assemblysystem using the software ANSYS. Static analysis under the design load case,i.e. the action of gravity force and float force, was carried out. Deformationand stress distributions of the rack were obtained and checked according torelevant codes.(2) Based on the established finite element model and giving reseanoblesimplification for linearizing the system, model analysis was conducted and all the resonant frequencies less than50Hz were given.(3) Earthquake analysis of the rack and assembly system under bothabnormal and accident conditions were performed. Results show that thestrength of the rack can conform to the requirements of codes, but sliding andjumping of the rack might happen in some degree. However, approximatetheoretical formula calculation indicates that due to the plate around the rackand considering the resistant action of the water, no impact could happenbetween the racks or the crack and the wall of the pool. The rack is still safe.(4) In order to correctly calculate the dropping speed of the assembly inthe water, especially the speed when impact on the rack, numerical simulationwas also conducted for the dropping process of the assembly in the water.Results were compared with the theoretical approximate solution. It is foundboth methods give almost the same results, meaning that they are all effectivein simulating the dropping process.(5) Finally, impact process of the assembly with the rack was numericallysimulated. It is found that produced deformation of the rcak is so serious thatthe assembly cannot be taken out anymore. But the deformation of the rackwill not cause the leakage of the assembly and the lower support plate of therack will not touch the bottom of the pool.