Determining the time to reach radiological equivalence of radioactive waste and natural uranium raw materials in the closed nuclear fuel cycle with fast reactors and with account of the main factors of uncertainty in the calculation of radiation risks

One of the most important problems in the large-scale development of nuclear energy is the management and disposal of radioactive waste (RW). The potential biological hazard of RW for human health considerably exceeds the health hazard from uranium feedstock. Due to the natural processes of radioactive decay, the potential biological hazard of RW decreases over time. However, long-term storage and disposal of long-lived RW leads to an increase in the health and environmental hazard of nuclear energy. Recently, to reduce the hazard effects, the novel approach based on the principle that hazard of RW should not exceed the hazard of natural uranium raw materials has been used. This principle is called as "radiation equivalence" if the hazards levels are assessed by the radiation dose magnitude, and "radiological equivalence" is used if the hazards are assessed by the magnitudes of lifetime radiation risks of malignant neoplasms development. Earlier papers have already given point estimates of the time to reach “radiation” or “radiological” equivalence when analyzing a scenario based on a closed nuclear fuel cycle. This article proposes a method for estimating the uncertainties in the time to achieve radiation and radiological equivalence. The results of these estimates are presented for a model scenario for the development of nuclear power, in which thermal neutron reactors are gradually being replaced by fast neutron reactors by 2100. The numerical simulation method is used. Modern radiation risk models proposed by the International Commission on Radiological Protection (ICRP) and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) are applied. The determination of equivalent radiation doses to organs and tissues was based on dose factors for radioactive substances provided for wide use by the US Environmental Protection Agency (EPA). If we assume that the maximum relative error of the initial values of the potential biological hazard of RW is about 246%, then the 95% confidence limit for achieving radiological equivalence was less than 340 years. The results of the study of the scenario for the development of nuclear energy in Russia, calculations show that since the integrity of containers with RW is maintained for 1000 years, the safety of RW for future generations will be ensured.