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.

Tritium in environmental objects in the area affected by FSUE Mayak Production Association in 2014-15.

Comparison of tritium volume activity (VA) rates in objects of environment in the Mayak Production Association (Mayak PA) affected area in the period from 2014 to 2015 with tritium VA rates in the same or similar objects of environment measured in the period from 2001 to 2013. Water samples from environmental objects-precipitations, ponds, wells-were the material for this research. Tritium VA in various environmental objects was measured using liquid scintillation method. The results were processed using parametric and nonparametric methods of statistical analysis. In samples collected in 2014-15 from open reservoirs located in Mayak PA affected area tritium VA was 1.4 times lower than the level of tritium VA in water samples from the same reservoirs collected in 2001-03. There was no statistically significant difference between tritium VA in water samples from the same open reservoirs collected in periods 2009-12 and 2014-15. Tritium VA in the water sample from production reservoir R-2 (lake Kyzyltash) in 2015 made 11 200 Bq l-1that was 1.7 times higher than average rate in 2007-09. In water samples collected in 2014 from 11 wells and boreholes located in the affected area of Mayak PA tritium VA made in average 22 ± 5 Bq l-1. No statistically significant difference was detected in water samples taken from boreholes in 2005-06 and in 2014. Comparison of median values revealed a statistically significant 3.2 times decrease of tritium VA in samples of daily precipitations in Ozyorsk in the time interval between 2007 and 2014. In single samples of daily precipitation in 2007, 2014 and 2015 tritium VA in Ozyorsk made 1020, 145 and 3500 Bq l-1respectively that in respect exceeded the median values 29 times in 2007, 13 times in 2014 and 160 times in 2015. This could indicate irregular tritium air emissions from Mayak PA that provides ground for necessity of tritium VA monitoring not only in daily precipitation but also in air vapor condensate. Decrease of tritium VA in water samples from open reservoirs from the period of 2001-03 to 2014-15 as well as decrease of the levels of tritium VA in samples of daily precipitation from 2007 to 2014 could be an evidence of possible decrease of tritium atmospheric emission from Mayak PA.