Chemical Characteristics of C-14 Released from YGN-4

Full text of publication follows: C-14 is resulting from the activation reaction of oxygen, nitrogen and carbon in the fuel and coolant of PWR. The amount of Carbon-14 released from PWR is small and not easy to detect, it is not used as a main monitored nuclide released in PWR in general. Korea Hydro and Nuclear Power Company (KHNP) had monitored Carbon-14 at five main ventilation lines of Yonggwang-4 from 2003 for 2 years. In order to monitor C-14, KHNP devised C-14 sampling instrument which can collect CO2 and hydrocarbons separately. It is composed of three main components, that is, primary CO2 sampler, a hydrocarbon oxidation assembly and a secondary CO2 sampler. The primary CO2 sampler has one water bubbler and two NaOH bubblers. To analyze C-14 in NaOH, CO3 ion was precipitated as CaCO3 or BaCO3 using CaCl2 and BaCl2 and performed mass analysis. But it was difficult due to over-precipitation by OH ion. This problem was solved by pH control using buffer solution NH4Cl and adding some heat to the solution. The collecting efficiency was calculated to 92% and the test result was verified by C-14 tracer (NaHCO3). According to the analysis results, the total activity is estimated to be 0.147 TBq/GWe.Yr. This activity would be about 67% of world's PWR average: 0.22 TBq/Gwe (UNSCEAR 2000) The area of highest concentration is the Fuel Building (RMS 035, which reaches 98% of total activity) followed by the Reactor Building, the Radwaste Building and the Auxiliary Building. The ventilation time of the Reactor Building is 3.3 hours per month, and 720 hours for the others (continuous) In the point of chemical form, the results show CO2 is dominant chemical form in fuel building, while methane compound is dominant in other areas. (authors)