The objective of this study is to design the spent fuel storage rack (SFSR) and their support frame as well as to evaluate the structural integrity of those during and after the seismic events. The main function of these racks is to store and protect the irradiated fuel assemblies generated during the operation of the research reactor. Their support frame is used for maintaining the structural stability of these racks. The SFSRs and their support frame are classified into safety class NNS and seismic category I according with ANSI 51.1 [1] and Regulatory Guide 1.29 [2]. The design of those has been performed according to the guideline of Regulatory Guide 1.13 [3] and IAEA safety standards DS 350 [4]. Specially, the pitch among storage cells should be decided from the criticality calculation with all postulated assumptions according to the NUREG 1537 [5] (Effective Neutron Multiplication Factor, keff < 0.9), conservatively.
These racks are installed in their support frame having free standing type boundary conditions in the pool. Since the dynamic behavior of structures can be significantly affected by the water, the hydrodynamic effect is considered by using added mass. All materials of submerged racks and their support frame are made of austenitic stainless steel to prevent the corrosion. To evaluate the structural integrity of these racks and their support frame, the response spectrum analysis (RSA) and response time history analysis have been performed under the seismic loads of OBE (Operating Basis Earthquake) and SSE (Safe Shutdown Earthquake) by using ANSYS software. In addition, the possibility of impact between the side wall of the pool and the support frame is investigated by using a nonlinear time history analysis considering the structural nonlinearity such as the contact and the friction problem.
The analysis results show that the maximum stress values of these racks and their support frame under the seismic loads are within the specified code limits. Since the sliding distance calculated from the nonlinear time history analysis is less than the gap, the impact does not occur. It is confirmed that those cannot be overturned but slide under an SSE event. Therefore, any damage on the structural integrity is not expected when those are installed and utilized in the pool.
