ASSESSMENT OF THE COMMITTED EFFECTIVE DOSE EQUIVALENT AND ITS UNCERTAINTY FROM INCIDENTAL INTERNAL TRITIUM EXPOSURE

The objective of the study was to estimate the committed effective dose equivalent from internal tritium exposure and its uncertainty in case of tritium incident at Mayak PA. According to worker's self-report, he had been exposed as a result of pouring "heavy" water over himself while performing technological operation in September 2019. Two-component exponential model of tritiated water (HTO) excretion including fast and slow phases was used to describe HTO content in the body. The individual's specific value of tritium biological half-life in the fast phase was 8.9 days, which is close to the average value of 10 days in the ICRP model. The slow-phase HTO excretion fraction is two orders of magnitude lower than the corresponding value in the ICRP model. The calculated committed effective dose equivalent (CEDE) due to tritium intake (7.4 mSv) depended mostly on fast-phase excretion. The uncertainty factor calculated as ratio of the 97.5% quantile and the mean value was equal to 1.14. The contribution of the slow-phase excretion to the CEDE due to internal exposure was as low as from 0.1 to 0.2% of total CEDE. This demonstrates that after the case of a single intake of tritium, which we studied, the CEDE is determined mostly by the excretion in the fast phase. The metabolized organically bound tritium dose fraction was in the range from 0.3 to 2.0%. The use of all the results of the measurement of HTO activity concentration in urine made it possible to obtain a lower estimate of the uncertainty of the CEDE of internal exposure in comparison with the use of only the first measurement result.