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Conference Article: Determination of the temperature coefficients and the kinetic parameters for the HTTR safety analysis.

Tokuhara, K. (Fuji Electric Co. Ltd., Tokyo (Japan)); Nakata, T. (Kawasi Heavy Industries Ltd, Tokyo (Japan)); Murata, I.; Yamashita, K.; Shindo, R. (Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment)

Abstract

This report describes the calculational methods which were employed to determine the temperature coefficients and the kinetic parameters for the safety analysis in the HTTR (High Temperature Engineering Test Reactor). The temperature coefficients (doppler, moderator temperature) and the kinetic parameters (prompt neutron life time. L, effective delayed neutron fraction. beta eff) are important for the point model core dynamic analysis and should be evaluated properly. The temperature coefficients were calculated by the whole core model. Doppler coefficient was evaluated under the conditions of all control rods withdrawn and the uniform change of fuel temperature. The minimum and the maximum value of the evaluated doppler coefficients in a burnup cycle are -4.6x10-5 and -1.5x10-5 DELTAK/K/deg. C respectively. The moderator temperature coefficient was evaluated under the conditions of all control rods withdrawn and the uniform change of moderator temperature. The minimum and the maximum value of the evaluated moderator temperature coefficients in a burnup cycle are -17.1x10-5 and 0.99x10-5DELTAK/K/deg. C respectively. In spite of positive moderator temperature coefficient, the power coefficient is always negative. Therefore the HTTR possesses inherent power-suppressing feed back characteristic in all operating condition. We surveyed the effects of the Xe existence, the control rods existence, the fuel temperature and the region in which the temperature was changed on the moderator temperature coefficients. The kinetic parameters were calculated by the perturbation method with the whole core model. The minimum and the maximum value of the evaluated effective delayed neutron fraction (beta eff) are 0.0047 and 0.0065 respectively. These of the evaluated prompt neutron life time (l) are 0.67 and 0.78 ms respectively. We have surveyed the effects of the fuel depletion and the core power level on these parameters, and considered these effects on the kinetic parameters. From above evaluation, we determined the temperature coefficients and the kinetic parameters.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Uncertainties in physics calculations for gas cooled reactor cores. Proceedings of a specialist's meeting held in Villigen, Switzerland, 9-11 May 1990
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--24, pp:45-53