The article represents the approaches introduced in the RELTRAN code developed under the FTP NRS-2 to modeling the radiation consequences for the population caused by possible releases of radioactive substances into the atmosphere during the planned work on the decommissioning of nuclear facilities. One of the tasks of the RELTRAN code is to perform calculations of the consequences of radioactive releases for the population for the tasks of justifying radiation safety. Several modeling options are considered: calculations based on average concentrations over several years, calculations based on average concentrations over several years, considering the schedule of the decommissioning process, case-study modeling approach based on historical meteorological series analysis and case-study modeling approach based on historical meteorological series analysis, considering the schedule of the decommissioning process. It was obtained that, depending on the duration of the planned process and depending on the season, the results differ significantly, for medium-term work, their seasonality becomes an important factor, at the same time, work with conditionally constant emissions lasting more than 6 months has a negligible uncertainty associated with time start of work.