Methodology for Rationing Internal Exposure from Plutonium: Problems and Solutions

Purpose: The presented materials are devoted to the development of a methodology for rationing the impact of plutonium intake by the amount of annual excess risk, which should not exceed 1 ×10-3. It is shown that the existing approach to the rationing of plutonium by the expected effective dose does not reflect the actual levels of personnel exposure and, therefore, does not provide the necessary level of radiation safety at plutonium processing plants. Results: Using data from epidemiological surveillance of a cohort of employees of the Mayak software, an assessment of the excessive relative risk per unit dose of radiation exposure for each of the plutonium-239 deposition organs was performed in order to describe the dependence of mortality from lung, liver and skeletal cancer on the dose of alpha radiation of plutonium-239. Equivalent doses to plutonium deposit organs and the annual excess risk generated by these doses for various plutonium intake scenarios are calculated based on the results of monitoring the activity of plutonium in urine. When calculating the annual effective dose based on the results of monitoring the annual equivalent dose, it is necessary to take into account the dependence of the weighing coefficients for the plutonium deposit bodies on the age of the employee at which the exposure occurred, and when assessing the magnitude of the radiation risk, the dependence of the risk coefficient on age. Conclusion: The use of the annual excess risk value as a controlled and normalized indicator for the individual dosimetry control of internal radiation from the plutonium intake is the most correct. The proposed approach to rationing can be used for acute and chronic inhalation intake of plutonium, as well as for the intake of plutonium through damaged skin.