Severe Weather Risk Assessment for Loviisa Power Plant

Abstract

Severe weather related core damage risks in full and low power and shutdown modes have been assessed for Loviisa 1 PWR (WER) located at the Southern coast of Finland. The first severe weather PSA for full-power operation was completed in 1994 and updated in 1998 to be a part of a living PSA. This work continued in 2003 with an update and for refueling outages comprising sixteen shutdown and low-power plant operating states (POS). This paper describes the scope of phenomena included, frequency vs severity curves for some phenomena, plantspecific and generic data sources as well as methods for defining, modeling and quantifying initiating events, systems and accident sequences. Standard fault tree and event tree techniques were applied in the modeling using POS-specific event probabilities. The reliability and maintenance data is mostly plant-specific. The main results and risk contributors are presented, and a number of risk-based modifications of the plant and procedures are described. The results indicate drastic seasonal variations and differences in the risks between power states and cold shutdown states.