Estimation of Amounts of Carbon-14 Formation in and Release from HANARO

Carbon-14 (half-life 5,730 years; beta decay to N-14 with max. energy of 156 keV, average 49 keV) is one of the potential sources causing the internal radiation exposure. The release of C-14 to the environment is regulated by a Notice of the MOST on the radiation protection. The C-14 activity in the exhaust air in the form of CO and CO2 is limited to 0.1 MBq/m3. Meanwhile, C-14 is one of the elements categorized as a group of gaseous effluents together with radioactive particulates, tritium, and radioactive iodine. The equivalent dose rate to organs from this group is limited to 0.15 mSv a year. There have been long discussions, unconcluded yet, on whether we have to monitor and control the release of C-14 from nuclear facilities. Even if the amount of C- 14 released from the PWR's has not been proven negligible, a report on the C-14 monitoring techniques indicated that the environmental monitoring at a site of heavy water power reactor is more important than that at a PWR site. The major source of C-14 in a heavy water reactor is the 17O(n,α) reaction in the heavy water. Because the HANARO research reactor uses quite amount of heavy water as the reflector-moderator, the C-14 formation in the HANARO takes attention, too. In this paper, we present the results of neutronics calculation on the C-14 formation rate in the HANARO. We also present the estimation of the release to the environment which is based on crude, but conservative assumptions