THEORETICAL ANALYSIS AND NUMERICAL SIMULATION OF THE SEISMIC RESPONSE OF LIQUID-FILLED, HEAD-SUPPORTED REACTOR VESSELS

A liquid-filled advanced reactor vessel is generally cylindrical, filled with a coolant, and closed by a head. In a number of proposed designs, the vessel is supported at the head. Multiple internals are attached to the head and submerged in the coolant. Earthquake shaking of such a nuclear reactor induces fluid-structure interaction (FSI) between the vessel, internals, and contained liquid. Appropriate closed-form (theoretical) solutions of seismic FSI can be used for preliminary design and sizing of the vessel, internals, and their supporting structures. Numerical simulations are required for final design and to support equipment qualification and seismic probabilistic risk assessment. Numerical models enable consideration of complex reactor geometries, multiple components of earthquake shaking, and nonlinear fluid responses. The models must be verified and validated, which is unique to practice in the nuclear industry. This paper presents theoretical analysis for seismic FSI of rigid and flexible head-supported cylindrical tanks and numerical simulation, for application to reactor vessels. The theoretical solutions were derived for lateral frequencies of a tank (if flexible), hydrodynamic pressures, wave heights, and reactions at the head support to small-amplitude, unidirectional, horizontal motions. Numerical models were developed for seismic FSI analysis using the Arbitrary-Lagrangian-Eulerian solver in LS-DYNA. This paper demonstrates a process of verification by comparing numerical and theoretical results for the frequencies and seismic responses of a head-supported cylindrical tank.