Finlandia série de vues II: voyages d'excursion en Finlande - [p. i]

Helsingfors : Finlandia [1907]

Vuosihuollon aikainen jäähdytteen boorihappopitoisuuden laimeneminen Loviisan ydinvoimalaitoksen riskianalyysissä

This master's thesis examines scenarios, which can lead to a reactivity excursion due to boron dilution events in Loviisa nuclear power plant. This thesis also describes how the boron diluted slugs are modelled in the Probabilistic Risk Assessment (PRA) model. At the current model, the valuation of the reactivity risk due to boron dilution has been very conservative, and therefore the reactivity risk during an outage is as much as 9 % of Core Damage Frequency (CDF) and Large Release Frequency (LRF). The main objective of the thesis is to decrease the annual core damage and Large Release Frequency by reducing conservative assumptions in the probabilistic modelling of boron dilution events. The core behavior during boron dilution events was modelled and reported in 2011 by Fortum using three-dimensional core model of Apros. The results of these analyses were reported same year by Fortum. According to the reported results and the analyses made by StarNode visualization program, it seems that some changes could be made in the boron dilution fault trees of the PRA model. As a result, the reactivity risk was decreased to 0.7 % of the annual CDF. In the other words, the total annual CDF and LRF were decreased 8.5 % due to the changes made in the PRA model. However the analyses made by Apros include some uncertainty. The accuracy of the analyses should be validated before making these changes in the official PRA model.