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Conference Article: Dose Rate Effects of Ion-Irradiated Isotropic Nuclear Graphite

Se-Hwan Chi, Gen-Chan Kim, Jong-Hwa Chang, HTGR Project, KAERI, Daejeon, KOREA

Abstract

During an operation, graphite core components in the HTGR experience radiation damage due to high energy neutrons. Depending on the relative location to the fuel, the changes in the thermal, physical, and mechanical properties of the graphite core components due to an irradiation may exhibit dose rate effects. To investigate the dose rate effects, specimens made of isotropic nuclear graphite were irradiated to varying dose levels by several dose rates with 2 MeV C+ ions. The changes in the mechanical property and internal molecular bonding structure due to an irradiation were investigated by the micro-hardness test and Raman spectroscopy. The investigated dose rate ranged from 3.50 x 10-7 - 1.3 x 10-3 dpa /sec. The peak damage was calculated to have appeared at 2.40 um in depth. Results show that the lower the dose rate, the higher the radiation damage for both measurements. Thus, an increase in the hardness was higher with a decrease in the dose rate in the micro-hardness test, and the ratio of the intensity of D and G-band , i.e., D/G , was higher with a decrease in the dose rate in the Raman spectroscopy. The FWHM was also wider with a decrease in the dose rate. Even though these experiments are limited, the present results seem to show that the radiation sensitivity of the nuclear graphite increased with an increased dose level and with a decreasing dose rate.

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key words: Nuclear graphite, Radiation damage, Dose rate effect, HTGR, Raman spectroscopy.
Reference:
Proceedings of the Conference on High Temperature Reactors, Beijing, China, September, 22-24, 2004
International Atomic Energy Agency, Vienna (Austria)
HTR-2004, pp:1-9