Solubility of hot fuel particles from Chernobyl—Influencing parameters for individual radiation dose calculations

Nuclear fuel particles of Chernobyl origin are carriers of increased radioactivity (hot particles) and are still present in the atmosphere of the Chernobyl exclusion zone. Workers in the zone may inhale these particles, which makes assessment necessary. The residence time in the lungs and the transfer in the blood of the inhaled radionuclides are crucial for inhalation dose assessment. Therefore, the dissolution of several kinds of nuclear fuel particles from air filters sampled in the Chernobyl exclusion zone was studied. For this purpose filter fragments with hot particles were submersed in simulated lung fluids (SLFs). The activities of the radionuclides ¹³⁷Cs, ⁹⁰Sr, ²³⁹⁺²⁴⁰Pu and ²⁴¹Am were measured in the SLF and in the residuum of the fragments by radiometric methods after chemical treatment. Soluble fractions as well as dissolution rates of the nuclides were determined. The influence of the genesis of the hot particles, represented by the ¹³⁷Cs/²³⁹⁺²⁴⁰Pu ratio, on the availability of ¹³⁷Cs was demonstrated, whereas the dissolution of ⁹⁰Sr, ²³⁹⁺²⁴⁰Pu and ²⁴¹Am proved to be independent of genesis. No difference in the dissolution of ¹³⁷Cs and ²³⁹⁺²⁴⁰Pu was observed for the two applied types of SLF. Increased solubility was found for smaller hot particles. A two-component exponential model was used to describe the dissolution of the nuclides as a function of time. The results were applied for determining individual inhalation dose coefficients for the workers at the Chernobyl construction site. Greater dose coefficients for the respiratory tract and smaller coefficients for the other organs were calculated (compared to ICRP default values). The effective doses were in general lower for the considered radionuclides, for ²⁴¹Am even by one order of magnitude.