The radioactivity analysis of 14C and 3H in graphite from the dismantled korea research reactor and its dose estimation

A high temperature combustion method was used to analyze the 14C and 3H activities in graphite and the dose assessment was carried out to determine the clearance in the conservative way. By this method, the 3H and 14C were simultaneously trapped in the nitric acid and carbosorb, respectively. Accordingly, the sample preparation time for the measurement was reduced to the half. The combustion temperature was more than 800 degrees in centigrade for obtaining total tritium and 14C in the sample. The combustion ratio was about 99% on the graphite sample with the weight of 0.1 g. Minimum detectable activity was 0.05Bq/g for the 14C and 0.15Bq/g for the 3H at the same background counting time. The recoveries from the combustion furnace were around 100% and 90% in 14C and 3H, respectively. The radioactivity were 2, 530 ∼3,160Bq/g in 14C and 1, 700 ∼2,040 Bq/g in 3H at this experiment. The experimental uncertainty was less than 6% in both radionuclides where the furnace recovery was dominant factor. An individual effective dose from beta and gamma radionuclides was estimated by consideration of the scenario of inhalation, ingestion and external exposure. 60Co, the radioactivity of which was measured by using HPGe detector, had a predominant effect in estimating the effective dose. The estimation showed that the graphite wastes from the dismantled research reactor should be disposed of as a low level radioactive waste rather than clearance.