Probabilistic analyses of the reliability of feedwater system for WWER-1000

The aim of the analysis made is to determine of the probability of failure of the feedwater system (TK), identifying of the elements with the biggest contribution to the failures and developing of recommendations for the increase of the reliability of the system operation. The functions and structure of the system are described in the paper. The analysis is made using the fault tree modelling of the system TK. The code SAPHIRE is used for the analysis. The probability for failure, calculated using the fault tree model is 1.627E-2, obtained on the base of 200 minimal sections. The most significant contributions to the failure have the gauges for consumption, temperature, pressure and level. The high probability of failure is caused by the fact that they are treated as IC elements, working in a stand by regime and tested once a year. The failure of the fittings of the back up feeding device, combined with the failure of the pumps QF11-01 has also high contribution to the failures. The Fussel - Vesely analysis of the significance of the individual failures shows that the system QF11-01 had the highest contribution to the system unavailability. For the increase of the feedwater system reliability it is recommended to conduct maintenance analysis and optimization