SUPERCOMPUTER APPLICATION TO STRUCTURAL DYNAMIC ANALYSIS OF PWR PIPING SYSTEM

A suite of computer programs has been developed to analyse the structu ral dynamic response of the coolant circuit of the PWR Nuclear Steam S upply System in the event of an extremely hypothetical Loss of Coolant Accident or LOCA in short. This paper firstly introduces the computat ional procedures and steps of the programs to analyse the structural e ffects of this event. These programs calculate the thermo hydraulic re sponse of the two phase fluid and the propagation of the depressurisin g wave through the complex geometry of the pipe system and equipment i nternals. From these time dependent thermal hydraulic quantities, the forces arising from the depressurising wave are calculated and transla ted into time history forces and moments. These forces act on the stru ctures 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 intern als and supports upon which the integrity of the system must be assess ed. 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 qualificatio n of these structures. The nonlinear modal superposition technique use d is of recent interest as being the computationally efficient and is gradually being used in conventional plant piping analysis. However, t his method for the structural dynamic transient analysis of a large nu mber of degrees of freedom structural model with nonlinearities is sti ll computationally intensive.