Ignalina NPP Unit 2 Gas Gap Probabilistic Evaluation

One of the factors limiting RMBK service life is the closure of the gas gap between the pressure tubes and the graphite masonry. The objective of the present work is to develop a mathematical model for Unit 2 of the Ignalina nuclear power plant (NPP) reactor, in Lithuania, which estimates the probability of the presence of a gas gap for different periods of operation. The calculations are based on collected data of graphite and pressure tube diameters and burn up measurements in period 1983-2005. There were no performed enough measurements for Unit 2, but big amount of statistical data was available for Unit 1. Therefore Unit 1 data properties were analyzed and constructed model was applied for INPP reactor Unit 2. The main analysis results are gas gap existence probabilities evaluation and the issued channel measuring strategies for the next planed preventive maintenance period for Ignalina NPP. (authors)