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Conference Article: Effects of high temperature neutron irradiation on the physical, chemical and mechanical properties of fine-grained isotropic graphite

Matsuo, H.; Nomura, S.; Imai, H.; Oku, T.; Eto, M. (Japan Atomic Energy Research Inst., Tokai, Ibaraki. Tokai Research Establishment)

Abstract

Effects of neutron irradiation on the dimensional change, coefficient of thermal expansion(CTE), thermal conductivity, corrosion rate, Young's modulus and strengths were studied for the candidate graphite material IG-110 of the experimental very high temperature gas-cooled reactor(VHTR) after irradiation at 585 - 1273 deg C to neutron fluences of up to about 3 x 1025 n/m2 (E > 29 fJ) in the JMTR and JRR-2, and to about 7 x 1025 n/m2 (E > 29 fJ) in the HFR. The results were compared with the irradiation behaviors of other graphites. Dimensional shrinkage was observed in the whole irradiation temperature range, showing lower value than 2 %. The shrinkage rate showed the minimum in the irradiation temperature of around 850 deg C, followed by the increase for the samples irradiated at higher temperatures. The dimensional stability of the material was clarified to be almost the same with that of H451 graphite. The CTE, thermal resistivity and Young's modulus increased in the early stage of irradiation and then only the CTE decreased while the thermal resistivity and Young's modulus levelled off with further irradiation. The neutron fluence showing the maximum CTE shifted to the lower fluence with increasing irradiation temperature. The increases of both thermal resistivity and Young's modulus were remarkable for the samples irradiated at lower temperatures. Compressive and bending strengths measured at room temperature increased after irradiation as well. The corrosion rate with water-vapor of 0.65 % in helium at high temperatures decreased owing to irradiation and the reduction was independent of irradiation temperature and neutron fluence. The activation energy for the reaction was estimated to be the same before and after irradiation.

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key words: corrosion; dimensions; graphite; htgr type reactors; irradiation; neutron beams; physical radiation effects; temperature dependence; thermal conductivity; thermal expansion; very high temperature; beams; carbon; chemical reactions; expansion; gas cooled reactors; graphite moderated reactors; particle beams; physical properties; radiation effects; thermodynamic properties
Reference:
Specialists' meeting on graphite component structural design, JAERI Tokai (Japan), September 8-11, 1986
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--11, pp:138-143