Approach to assessing monitoring operational intervention levels after an accident at a nuclear power plant using the RODOS system

The paper presents a comprehensive analysis of the IAEA's methodology for calculating the operational intervention levels (OILs) to protect the public in the aftermath of a radiation disaster based on monitoring data. Developing the OILs assessment approach involves outlining specific indicators based on accident scenario characteristics, geographical location of nuclear power plants, timing after releases, and dose criteria established by the Russian regulatory documents. The paper highlights the feasibility of using a unified computation tool to solve interconnected tasks, such as "prediction of radiological consequences" and "development of monitoring OILs". A methodological approach to assessing monitoring OILs using RODOS models, designed for predicting the consequences of a radiation accident, has been developed. This approach includes three stages: assessing the radiological significance of a scenario, evaluating monitoring OILs for different generic criteria, and justifying the recommended values of OILs. Calculations were performed to show how the new methodology can be used based on the data for the most severe possible accidents at VVER-440, VVER-1000, VVER-1200, and BN-800 reactors. The results showed that the maximum radiation doses for the prospective BN-800 and VVER-1200 reactors do not exceed the dose criteria for evacuation of the public. The dynamics of OILs were computed for the most severe accident scenario at the VVER-440 reactor, using the "ambient dose rate" metric and "evacuation" dose criteria for effective and thyroid exposure, which are justified in the Russian NRB-99/2009. The OILs obtained through the presented methodology have been compared to the aggregated values of the same indicator calculated using the IAEA methodology in a "ground scenario". Further research is needed to validate monitoring techniques for potential accidents at Russian nuclear power plants. The research should consider regional conditions and the Russian regulatory framework.