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Conference Article: Dynamic testing and qualification.

Kleine Tebbe, A.; Schmidt, G.; Theymann, W. (Hochtemperatur-Reaktorbau GmbH, Juelich (Germany, F.R.))

Abstract

The core structure of an HTR-plant consists of the side reflector, the bottom reflector, the top reflector and the pebble bed of spherical fuel elements. Dynamically this system is a many-body structure with non-linear force-deformation couplings. The integrity of the system under seismic loads is given by radially orientated spring packs. These spring packs must be stiff against earthquake loads, but must allow radial thermal movements. To verify the seismic safety of the system, scaled-down models were tested. The results of these tests were compared with those of analytical methods. The good-natured behaviour of the pebble-bed under seismic loads has been confirmed. Due to the granular structure of the non-regular packed pebble-bed, high damping occurs during seismic excitations. With increasing depth the damping ratio decreases because of restriction of movement. We are able to describe the seismic behaviour of the pebble-bed analytically. The one- and two-dimensional test configurations of the top reflector were used to analyse resonance and lumping effects. The experimental results were verified by the computer codes CRUNCH-1D AND CRUNCH-2D. The experimental investigations of the side reflector are underway. The results show a non-critical behaviour under horizontal excitations. Small rigid-body motions of single blocks are detected, but they do not cause any global ovalisations of the complete ring structure. Finite element calculations with contact and friction between the blocks show a close agreement with the experimental results. Seismic qualification of ground mounted electrical equipment is usually performed on the basis of codes like IEEE, IEC, KTA, etc. These standards give different possibilities of the excitation mode: sinusoidal excitation in every natural frequency (continuous or sine beat) or time history excitation which covers a prescribed required response spectrum. Recently performed tests are compared regarding the usefulness and severity of the different excitation modes.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Seismic behaviour of gas cooled reactor components. Proceedings of a specialists' meeting held in Gif-sur-Yvette, France, 14-16 November 1989
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--22, pp:125-132