Author(s)

M. Liaukonis & J. Augutis

Abstract

Data analysis with uncertainty evaluation for the Ignalina NPP RBMK-1500 gas-gap closure evaluation M. Liaukonis1 & J. Augutis2 1 Department of Mathematics and Statistics, Vytautas Magnus University, Lithuania. 2Nuclear Safety Installation Labovatoy,Lithuanian Energy Institute, Lithuania. Abstract This paper presents data analysis with uncertainty evaluation for Ignalina NPP Unit 1 RBMK-1500 reactor core lifetime analysis. The closure of the gas gap between the pressure tubes and the graphite bricks is one of the criteria for the evaluation of the reactor core lifetime. The rate of closure of the approximately 1.5mm gaps between the pressure tubes and the graphite is largely a function of accumulated fast neutron dose and graphite operating temperatures. Historical approaches to this problem are briefly discussed and more thorough data analysis performing probabilistic model is presented. For the graphite behaviour the ABAQUS code was used. Non-linear changes of graphite have high influence for further forecast. With the data used for the calculations it was performed uncertainty analysis. It showed confidence in the results. 1 Introduction The RBMK reactor is designed to use a graphite moderator in the form of graphite bricks which surround Zirconium-Niobium channels (or \“pressure tubes”) containing the nuclear fuel and coolant. The pressure tube is initially positioned in place by a series of graphite rings that are alternately in contact with the inner bore hole of the graphite bricks and the outer perimeter of the

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