Development of the Dual Counting Method and Internal Dose Assessment Method for Tritium and Carbon-14 at Nuclear Power Plants

At pressurized heavy water reactors (PHWRs), carbon-14 is generally produced by the irradiation of oxygen present as impurities in the moderator system from 17O(n,α)14C reaction. Because carbon-14 release from PHWRs takes place mostly as carbon dioxide (14CO2), in the case of carbon-14 release to the work area, it is easily inhaled into the body of radiation workers. Most inhaled carbon-14 is rapidly exhaled from the worker's body, but a small amount of carbon-14 remains inside the body and is excreted by urine. Internal dose assessment for carbon-14 is conducted using the measurement results of carbon-14 in urine samples of radiation workers since carbon-14 is a low energy beta emitter. In this study, the origin of carbon-14 and its metabolism through inhalation were reviewed for internal dose assessment of carbon-14 at PHWRs. In particular, the method of dual analysis of tritium and carbon-14 in urine samples was developed with the use of Liquid Scintillation Counters (LSCs) and methods for tritium measurements at the Wolsong nuclear power plants (NPPs). In addition, methods for determination of intake and internal dose assessment were established based on the measurement results of carbon-14 and its excretion rate data