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Conference Article: Analytical method of fractional release of fission products from fuel elements of HTTR.

Sawa, K.; Shiozawa, S. (Japan Atomic Energy Research Inst., Oarai Research Establishment, Oarai, Ibaraki (Japan). Dept. of HTTR Project); Fukuda, K. (Japan Atomic Energy Research Inst., Tokai Research Establishment, Tokai, Ibaraki (Japan). Dept. of Fuels and Materials Research); Ichihashi, Y. (Japan Atomic Energy Research Inst., Oarai Research Establishment, Oarai, Ibaraki (Japan). Dept. of JMTR Project)

Abstract

Japan Atomic Energy Research Institute (JAERI) is now proceeding with the construction of the HTTR (High Temperature Engineering Test Reactor). A fuel assembly of the HTTR is made up of fuel rods and an hexagonal graphite block. The fuel consists of microspheres of low-enriched UO2 with the TRISO coating. The TRISO coatings consist of a porous pyrolytic carbon (PyC) buffer layer followed by an isotropic PyC layer, a SiC layer and a final (outer) PyC coating. The coated fuel particles are incorporated into fuel compacts with a matrix consisting of binder and graphitic filler. The fuel rod, which is composed of fuel compacts and a graphite sleeve, is contained within vertical holes of a graphite block. In order to evaluate the amount of fission products released from the HTTR fuel elements during normal operation, analytical models to calculate fractional releases of noble gases, iodines and metallic fission products have been developed. Fractional releases of noble gases and iodines are calculated based on the release data, (R/B) of 88Kr which are obtained from the sweep-gas capsule irradiation tests. The transport of metallic fission products through the kernel, coatings, fuel compact matrix and graphite sleeve is modeled as a transient diffusion process. The sorption of metallic fission products on the fuel compact matrix and the graphite sleeve is also modeled. These analytical models have been verified by comparison with measured fractional releases in the Oarai Gas Loop-1 fuel irradiation test etc. at Japan Materials Testing Reactor and have been concluded to be applicable to the safety design of the HTTR. The paper summarizes the analytical models to calculate fractional releases of fission products and introduced the major results of the verification.

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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:55-61