Supercomputer application to structural dynamic analysis of PWR piping system

Abstract

A suite of computer programs has been developed to analyse the structural dynamic response of the coolant circuit of the PWR Nuclear Steam Supply System in the event of an extremely hypothetical Loss of Coolant Accident or LOCA in short. This paper firstly introduces the computational procedures and steps of the programs to analyse the structural effects of this event. These programs calculate the thermo hydraulic response of the two phase fluid and the propagation of the depressurising wave through the complex geometry of the pipe system and equipment internals. From these time dependent thermal hydraulic quantities, the forces arising from the depressurising wave are calculated and translated into time history forces and moments. These forces act on the structures and are input to a structural lumped mass model and analysed by a dynamic piping analysis code. Resulting from this analysis are the time dependent impact forces at pipe whip restraints and system internals and supports upon which the integrity of the system must be assessed. This paper also discusses the modelling of the nonlinear supports and restraints, and the sensitivity analysis to find a computationally acceptable and sufficiently precise model for the design qualification of these structures. The nonlinear modal superposition technique used is of recent interest as being the computationally efficient and is gradually being used in conventional plant piping analysis. However, this method for the structural dynamic transient analysis of a large number of degrees of freedom structural model with nonlinearities is still computationally intensive.