Author: Darius Lukauskas
Dissertation title: Study of the Radionuclide Composition of Radioactive Waste Streams in the Nuclear Power Plant
Fields of science: Physical sciences, Physics (02P)
Scientific supervisor: Prof. Dr. Vidmantas Remeikis
Defence of the dissertation: 2009-03-05
Continually increasing consumption of energy, expansion of new industrial branches and technology unavoidably cause problems related to the harmful impact of industrial waste on the environment and people. Due to the increasing technogenic load and declining self-regulation capabilities of the environment, the society is obliged to invest in the environment preserving development ways. Nuclear energy has no alternatives from this point of view. However, it is essential to ensure high nuclear safety and radiation protection level, resolve technological tasks of radioactive waste management, understand mechanisms of radionuclide migration in the environment and better conceive aspects of ionizing radiation impact on the environment and people. It is relevant to optimisation of occupational exposure and radiation protection of public during operation of nuclear facilities as well as processing, storing and disposal of radioactive waste. These issues are particularly relevant to decommissioning of nuclear facilities, because many new technological and radiation safety aspects concerning large radioactive waste streams are not fully clear.
The work is closely related to the main task of energy in Lithuania during this decade - safe decommissioning of the Ignalina NPP. Modern radioactive waste management, utilization and disposal technologies shall be used, ensuring long term safety and minimum impact of ionizing radiation on the environment and people.
During operation of nuclear power plants and their decommissioning, dismantling of installations and buildings, tens or more thousands cubic meters of radioactive wastes are generated. Those wastes are not equally hazardous from radiation safety and nuclear safety viewpoint due to different specific activities of radionuclide and other physicochemical characteristics. Hence, the first step in the assessment of potential radiological impact of radioactive waste is the estimation of the nuclide composition. It is an essential characteristic of operational radioactive waste and contamination of buildings and equipment for dividing radioactive waste to the streams for subsequent processing and disposal. Lists of radionuclides, indicating significant radionuclides in assessment of ionizing radiation impact on the environment and people, are compiled in various countries. The united list of significant radionuclides suitable for the whole variety of nuclear facilities does not exist. Therefore, it is relevant to assess the nuclide composition of nuclear fuel and activated materials, considering materials of nuclear fuel and reactor structures and characteristics of neutron flux, and to define safety-relevant radionuclides from the radiation safety viewpoint. It is particularly relevant to nuclear power plants with RBMK-1500 reactors, as the spent nuclear fuel operational and other radioactive waste treatment, storage and disposal technologies during decommissioning of the plant are implemented for the first time. Accumulated scientific knowledge on the theoretical and experimental evaluation of the nuclide composition of operational and decommissioning radioactive waste would be useful when selecting optimal technologies, assessing possible scenarios of radionuclide migration from repositories, predictions and outcomes of unwanted radioactive pollution. The increasing demand for nuclear energy worldwide stimulates the relevance of these problems and solution of arisen tasks requires new scientific knowledge and its creative practical implementation.