THE IMPACT OF PHENOMENOLOGICAL UNCERTAINTIES ON AN ACCIDENT MANAGEMENT STRATEGY

Using lower cavity flooding as an accident-management tool to prevent 'core-on-the floor' is evaluated. Three phenomena that impact the effe ctiveness of lower cavity flooding are chosen for evaluation: (1) reac tor vessel lower head failure, (2) ex-vessel steam explosions in a BWR , and (3) buoyancy-driven recirculation for a PWR. The merit of the se lected management strategy and the impact of uncertainties in phenomen ological behavior is evaluated using the method of influence diagrams. The probability of a particular outcome can depend on the state-of-kn owledge uncertainties of the model parameters. The probabilities are e stimated by making many calculations with a response surface that is g enerated from several results of a particular model and covers the pos sible ranges of its parameter uncertainties, using randomly sampled va lues of its parameter uncertainties. This allows knowledge about uncer tainties to be transformed to probabilities with a minimum of subjecti vity. The approach shows the effects of uncertainties in the parameter s by changing their state-of-knowledge distributions.