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Conference Article: Analytical method and result of fission product release from core during a depressurization accident of HTTR

Sawa, K.; Tazawa, Y.; Shiozawa, S. (Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Dept. of HTTR Project); Mikami, H. (Fuji Electric Co., Ltd, Tokyo (Japan). HTR Project Dept.)

Abstract

This paper describes the analytical method and the result of the fission product release from the core during the depressurization accident of the HTTR (High Temperature Engineering Test Reactor) to be constructed by Japan Atomic Energy Research Institute. In the safety evaluation of the HTTR, a double-ended rupture of the coaxial pipe of the primary cooling system is postulated as the design basis depressurization accident. The thermal response of the core after a depressurization in the graphite-moderated gas-cooled reactor such as the HTTR is very slow because of the large heat capacity of the graphite. Therefore, the fuel temperature remains high during about hundred hours after the depressurization accident, which induces additional fission product release from the heated fuel by diffusion. Thus, the amount of the additional fission products released should be taken into account in the safety evaluation of the HTTR. In order to calculate the amount of the additional fission products released from the core during the depressurization accident, the HTCORE code has been developed. It determines the time-dependent amounts of fission product nuclides that escape from the core. The amount of the additional fission products released from the core into the containment vessel during the depressurization accident of the HTTR is calculated by HTCORE code to be 4.8 x 1013 MeV centre dot Bq for noble gases, 5.5 x 1013 Bq for I-131 and 2.6 x 1012 Bq for Cs-137.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Behaviour of gas cooled reactor fuel under accident conditions. Proceedings of a specialists meeting held in Oak Ridge, 5-8 November 1990
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--25, pp:117-123