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Conference Article: The assessment of the integrity of AGR core during an earthquake

Abstract

The seismic response of the core has been calculated using an idealisation having several hundred thousand degrees of freedom. The individual graphite bricks are idealised as rigid masses, whilst contact spring elements are used to represent the load transmissions or impacts that can take place between the bricks. The necessary input information for the contact spring elements (i.e. stiffness, damping and friction), has been obtained from test work. Whilst the dynamic response of the core itself is non-linear, the supporting steel structures are linearly elastic. Consequently, the dynamic characteristics of the supporting structures are evaluated with the non-linear core structure uncoupled, and are then used with the non-linear core model in a step-by-step explicit time history analysis. The paper discusses the analytical model and presents results from some of the predictions of core dynamic response to earthquakes. The development of criteria for graphite impacts, based on the J integral, is described. Impact tests on a range of brick slices have been used to give data on brick or key cracking under repeated impacts. Dynamic analysis of plane stress finite element models of these test geometries has been carried out in order to establish a qualified analysis method which can be used to extrapolate the test data to impact damage in the core. This analysis method is applied to finite element models of the core bricks in which the loadings due to operating conditions, environmental and ageing effects are included. In the presence of any existing state of stress at any time during the operating life, the damage due to repeated impacts defined by the time-history seismic response of the core may then be estimated through a cumulative damage procedure.

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Reference:

Specialists' meeting on graphite component structural design, JAERI Tokai (Japan), September 8-11, 1986

International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors

IWGGCR--11, pp:29-36