The radioactivity analysis of14C and3H in graphite from the dismantled korea research reactor and its dose estimation

Abstract

A high temperature combustion method was used to analyze the 14 C and 3 H activities in graphite and the dose assessment was carried out to determine the clearance in the conservative way. By this method, the 3 H and 14 C 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 14 C in the sample. The combustion ratio was about 99% on the graphite sample with the weight of 0.1 g. Minimum detectable activity was 0.05 Bq/g for the 14 C and 0.15 Bq/g for the 3 H at the same background counting time. The recoveries from the combustion furnace were around 100% and 90% in 14 C and 3 H, respectively. The radioactivity were 2,530 ~ 3,160 Bq/g in 14 C and 1,700 ~2,040 Bq/g in 3 H 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. 60 Co, 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.