RISK ASSESSMENT OF AGR GRAPHITE CORES - METHODOLOGY COUPLING A STATISTICAL ANALYSIS TOOL (OPENTURNS) TO A NONLINEAR DYNAMICS MODEL (GCOEUR) OF AN AGR CORE

摘要

Studies performing a risk assessment of Advanced Gas-cooled Reactors (AGRs) under seismic loadings are of importance for the extension of the plant's lifespan. The core of the AGR reactor comprises thousands of interlocking graphite bricks, each of which has properties and dimensions that vary with time and for which there are some uncertainties. Among those uncertainties, the bricks are likely to crack and the time of cracking and subsequent morphology of the crack can vary. In order to understand as best as possible the behaviour of ageing nuclear graphite, and hence reduce the uncertainties, inspections and experiments are conducted and models are developed. In the same time, some statistical models are developed, which is the purpose of this paper. In this paper, a mechanical model of the whole core is presented. This model is developed in order to be able to take into account variable properties statistically, including the probability of bricks being cracked prior to the seismic event. The integrity of the core is determined by a number of criteria such as load, displacement and the straightness of the columns of bricks. A methodology coupling statistical tools and mechanical modelling finite-element (FE) methods has been developed to determine the distribution of kinematics of the inner core and, therefore, to assess the integrity of the inner core by consideration of different outputs.