BEHAVIOR OF NONLINEAR SUPPORTS ON A PWR COOLANT SYSTEM DURING A POSTULATED LOCA .1. EFFECT OF MODELING METHODS

A 4-loop Pressurised Water Reactor (PWR) primary coolant system has be en analysed for the postulated Loss of Coolant Accident (LOCA) event i n order to derive peak dynamic loads for qualifying the design of equi pment supports and pipe whip restraints. Pipe whip restraints as well as pipe and equipment supports are nonlinear by nature because of the presence of gaps and the different directional stiffnesses arising fro m snubber, steelwork and geometric and material interaction at the con crete to steel embedment. The different structural idealisations for t he supports and restraints have an influence on the dynamic response o f the structure. In the first of the two part paper a range of idealis ation models for the Steam Generator and Reactor Coolant Pump vertical columns ranging from elastic stiffnesses to bilinear stiffnesses with or without preload were examined. Due to both structural and loading complexity, the behaviour of these supports were analysed by the Nonli near Modal Superposition Method [1] and [2]. Analyses with the differe nt models that are within the capabilities of the WESTDYN [3] piping a nalysis code enabled variations in the peak dynamic loads at the suppo rts. restraints and equipment nozzles and other parameters to be deter mined and the design acceptability of the hardware established.