Evaluation of 14C release characteristics in Korean standard pressurized water reactor

Abstract

This paper focuses on evaluation of the characteristics of organic and inorganic 14C, which is purged to the environment via purge line of each building in Korean standard reactor. 14C has a half-life of 5730 years and emits pure beta rays. 14C is a radioactive element that is easily transferred to the environment and has considerable environmental biological effects. According to recent research, organic 14C compounds are produced in reactor coolants via deoxidizing pathways. However, in oxidizing conditions, 14C changes to an oxidized carbon form and finally to 14CO 2. The radioactivity in purge lines and the purged quantity of organic and inorganic 14C in each building at Yonggwang #5unit were measured and evaluated during the three-year period from 2006 to 2008. During normal operation the annual purge quantity is about 100 GBq/GWe-yr, lower than the annual purge quantity in European pressurized water reactors. During normal operation inorganic 14C shows a higher purge rate than organic 14C in the purge line. During the outage period, the purge of 14C shows a slightly higher rate than the purge rate in normal operation. In Korean standard reactors the portion of 14C in inorganic chemical form is higher than those in foreign nuclear power plants, and this is attributable to operation characteristics such as volume control tank purge operation during normal operation. From the evaluation of the purge quantity through the purge line, it was found that considerable 14C was purged to the environment via the fuel handling building. This evaluation study will provide useful information for establishing radiocarbon ( 14C) control policy and for purge management.