Perspective Compounds for Immobilization of Spent Electrolyte from Pyrochemical Processing of Spent Nuclear Fuel

Immobilization of spent electrolyte–radioactive waste (RW) generated during the pyrochemical processing of mixed nitride uranium–plutonium spent nuclear fuel is an acute task for further development of the closed nuclear fuel cycle with fast neutron reactors. The electrolyte is a mixture of chloride salts that cannot be immobilized directly in conventional cement or glass matrix. In this work, a low-temperature magnesium potassium phosphate (MPP) matrix and two types of high-temperature matrices (sodium aluminoironphosphate (NAFP) glass and ceramics based on bentonite clay) were synthesized. Two systems (Li0.4K0.28La0.08Cs0.016Sr0.016Ba0.016Cl and Li0.56K0.40Cs0.02Sr0.02Cl) were used as spent electrolyte imitators. The phase composition and structure of obtained materials were studied by XRD and SEM-EDS methods. The differential leaching rate of Cs from MPP compound and ceramic based on bentonite clay was about 10−5 g/(cm2·day), and the rate of Na from NAFP glass was about 10−6 g/(cm2·day). The rate of 239Pu from MPP compound (leaching at 25 °C) and NAFP glass (leaching at 90 °C) was about 10−6 and 10−7 g/(cm2·day), respectively. All the synthesized materials demonstrated high hydrolytic, mechanical compression strength (40–50 MPa) even after thermal (up to 450 °C) and irradiation (up to 109 Gy) tests. The characteristics of the studied matrices correspond to the current requirements to immobilized high-level RW, that allow us to suggest these materials for industrial processing of the spent electrolyte.

Radiation-Hygienic Investigations of Experimental Production of Mixed Nitride Uranium-Plutonium Fuel at JSC SChC. Part 1: Methods and Results

Purpose: To present the methods and results of studies of the factors of radiation exposure to workers involved in the manufacture of mixed uranium-plutonium nitride (MUPN) fuel at the complex experimental installations CEI-1 and CEI-2 of JSC SChC. Material and Methods: Regularities of the formation of external exposure doses have been revealed based on the study of the dynamics of the ambient dose equivalent rate (ADER) of photon and neutron radiation at the CEI-1 and CEI-2 workplaces, as well as instrumental individual dosimetric control of the equivalent doses to workers. In order to assess the inhalation intake and possible doses from internal irradiation, studies of the physicochemical properties of radioactive aerosols were carried out. Results: It has been found that the main sources of penetrating radiation in the premises of CEI-1 are boxes where tablets are pressed, chips and rejected tablets are crushed, as well as temporary storage of products is occurred. The highest ADER values have been measured in those boxes, where the radiation exposure was due to radioactive contamination caused by past activity, and is not associated with fabrication of MUPN fuel. A significant contribution of neutron exposure to individual doses of workers was measured, which exceeded the contribution of gamma exposure at some workplaces of the CEI-1. At CEI-2, a non-functioning exhaust ventilation pipe passing over the premises was found to be a powerful source of external radiation. This pipe contained a significant amount of radioactive material. Assessment of the contribution of gamma exposure from the ventilation pipe to the external exposure of workers reached 85% at some workplaces. Studies of the physicochemical properties of radioactive aerosols have revealed a high reactivity of MUPN compounds, leading to instant oxidation of the thoracic fraction of MUPN fuel aerosols under contact with air. The complex morphological and dispersed composition of aerosol particles in combination with a complex chemical composition caused by the aging processes of aerosols, can lead to a fundamental difference in the biokinetics of MUPN aerosols, the process of dose formation and, consequently, the degree of radiological hazard compared to those adopted in the ICRP models for U and Pu. The results of the current radiation-hygienic research are of a preliminary nature, since the object of this research is an experimental installation, which was used to develop a new technology for the production of MUPN fuel. The instrumental and methodological approaches to assess the factors of radiation exposure to workers tested at these experimental installations, will be used in the future to conduct similar studies during the pilot industrial operation of new modules for fabricating and refurbishing of MUPN fuel.

Problems of Assessing the Health Status of Personnel Working in Conditions of New Technologies for Nuclear Fuel Production

Purpose: To identify the problem of assessing the health status of personnel working under the conditions of new technologies for the production of nuclear fuel. Material and method: The object of the research was the general morbidity of workers in the production of mixed nitride uranium-plutonium fuel (MNUP-fuel). The material for the study was the data presented in the «Health Passports». The paper used the method of comparative analysis of the overall morbidity of workers in the production of MNUP-fuel and workers in enterprises dealing with nuclear fuel. Results and analysis: At present, in our country, within the framework of the «Breakthrough» project, new technologies are being developed for the fabrication and refurbishment of mixed uranium-plutonium (MNUP) fuel. In the absence of radiation and hygienic standards for the content of fuel products in working rooms, in order to assess the influence of production factors, along with the radiation dose, the incidence of personnel is studied as an integral indicator of health. A study of the incidence of 50 workers in the production of MNUP fuel revealed: Relatively high incidence of general morbidity – 1122 diseases per 100 people or an average of 93.5 diseases per 100 people per year, regardless of the length of service. The leading diseases in the overall morbidity structure are diseases of the respiratory system – 26.0 % (1st place), eyes – 13.4 % (2nd place), musculoskeletal system – 11.4 % (3rd place), circulatory system – 10,9 % (4th place), injuries and poisoning – 8.4 % (5th place), digestive organs and genitourinary system – 7.7 % and 7.0 %, respectively (6th place), which make up 84.7 % of the total morbidity. Obviously, the effective dose of 4.6 mSv/year cannot be the only reason for the high morbidity in workers in complex radiochemical production, but characterizes only the influence of one of the many nonspecific factors of production. The existing system for assessing the health of personnel working in radiochemical production, in addition to analyzing the risks of deterministic and stochastic effects, should include an assessment of the overall morbidity of personnel.