Prediction of Fluid Behaviour during Reactor Transient Analysis using Coupled 1D and 3D Models

Abstract

The detailed understanding of the behaviour of a pressurised water reactor during transient operation is crucial to the design of the reactor.

Hitherto mathematical simulation effort has largely concentrated on one-dimensional loop analysis of the reactor system: this gives a reasonable understanding of the consequences of a transient, such as the blowdown. but does not yield adequate information on features such as pressure effects in the reactor vessel. For greater understanding of such effects, a three-dimensional reactor model is required.

Two- and three-dimensional transient simulations of reactor vessels and of individual components of the circuit have, in the past, been performed in order to provide pressure and temperature fields for input to structural analysis programs. Such decoupled calculations have however tended to underestimate the real situation, since boundary conditions have been specified from stand-alone loop calculations; furthermore, there has been no simple way of incorporating fluid-structure interaction effects.

This paper describes the application of the PHOENICS program to predict the fluid behaviour in a PWR during a hypothetical blowdown. The analysis features two technical novelties. The first is the use of a three-dimensional model for the reactor vessel, directly linked with one-dimensional loop models for the primary water circuits; the second is the dynamic coupling of a fluids code (PHOENICS) with a stress code (ABAQUS) to provide a first step towards the modelling of fluid-structure interaction effects.