HTGR Knowledge Base

Conference Article: Calculational methods of power distribution in the HTTR and verifications

Nakata, T. (Kawasaki Heavy Industries Ltd, Tokyo (Japan)); Tokuhara, K. (Fuji Electric Co. 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 of the power distribution in the High Temperature Engineering Test Reactor (HTTR. 30MW in thermal output and 950 deg. C in reactor outlet coolant temperature) which was designed by Japan Atomic Energy Research Institute (JAERI), and the verifications of these methods. In the HTTR, an accurate determination of power distribution is one of the important design requirements. We have designed the power distribution by zoning the fuels and burnable poisons (BP) in order to keep the maximum fuel temperature as low as possible. Additionally we precisely evaluated the power distribution in a fuel block by considering the spatial fine structures. Radially these fine power distributions were calculated on the representative planes by using the 120-degrees rotational model of CITATION, which could consider the spatial heterogeneity caused by the fuel rods and BP rods in a fuel block. Then we could obtain the local power peaking factor which was defined by the ratio between finely and coarsely determined power distribution. The maximum value of the local power peaking factor is about 7% and it gradually decreases with depletion. We evaluated axially the effect of local power spikes due to the block end graphite, and we have considered 4% as these spikes for the fuel temperature calculation. On the other hand, we have verified these methods by the analysis of copper reaction rate measurements in the Very High Temperature Reactor Critical Assembly (VHTRC) experiments. The agreement between calculation and experiment was good. From these results, it was confirmed that the power distribution in the HTTR could be predicted with sufficient accuracy by our calculational method, and could meet the design requirements.

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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:53-59