Validation of the new ICRP model for inhalation intake of tritium in the form of tritiated water

Publication 134 of the International Commission on Radiological Protection introduces an updated biokinetic model for internal exposure to tritium, which highlights the need to transition to individualized dose assessment based on this model in dosimetric monitoring. The aim of the study was to validate ICRP Publication 134 for estimating inhalation intakes of tritium based on measurements of tritium activity concentration in urine and tritiated water concentration in workplace air. Materials and Methods. Five participants were involved in the study and stayed twice in a tritium work area at a 13-day interval; each stay lasted 6 h. The air temperature and humidity were measured, air condensate samples were collected using a Peltier element, and urine samples were obtained. Urine sampling continued on subsequent days after the exposure. The model validation was performed by comparing model-derived estimates with experimental values of tritium activity concentration in urine and condensate samples under identical HTO intake scenarios. Results and Discussion. The ICRP Publication 134 model provides estimates of HTO inhalation intake comparable to those obtained with the ICRP Publication 56 model; however, within the first 12 h after prolonged tritium intake, Publication 134 more accurately reflects the dynamics of uptake and elimination. For more accurate assessment of tritium intake based on urine samples collected one week or later after exposure, correction for the tritium effective half-life is required. It is easier to perform the correction using the Publication 56 model. The breathing rates assumed in the study for sedentary work (0.54 and 0.39 m[3] /h for men and women, respectively) led to underestimation of intake compared with estimates based on urine data, whereas breathing rates corresponding to light work resulted in intake estimates exceeding those derived from urine measurements. Conclusion: The validation results for the new ICRP tritium model showed that the new model has advantages over the old one only when interpreting urine concentration measurement results obtained in the first 12 hours after the onset of intake, which is extremely important for monitoring accidental intake.

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