Computational modelling of nuclear installations has been widely used for many years to justify nuclear and radiation safety. The computer codes used for computational modelling allow predicting the behaviour of nuclear facilities in any operating conditions and in the event of accidents.

In Russian regulatory practice, a review of simulation computer codes is provided. Following Russian Federal law "On nuclear energy use", SEC NRS as a TSO of Russian nuclear regulatory authority (Rostechnadzor), performs such review. Rostekhnadzor established the procedure for the review and requirements for computer codes and justification of simulation models.

The comprehensive implementation of modern digital technologies in all nuclear energy use activities leads to further developing the computer codes review framework. For example, the current Requirements for computer codes, which were approved by Rostechnadzor in 2000, do not contain criteria for evaluating such innovative calculation tools as multiphysical computer programs, CFD-codes, and software tools that use artificial neural networks in the mathematical model. However, such innovative calculation tools have already found wide application in the justification of modern Russian nuclear installations' safety.

Besides, the requirements for computer programs contain a detailed description of the verification/validation methods. Still, they do not answer how the verification/validation findings are used to evaluate the accuracy of transient and accident simulation results presented in the safety analysis reports.

In 2020, the SEC NRS developed a draft of updated Requirements for computer codes to clear the shortcomings mentioned above. At the same time, the updated Requirements are harmonized with up-to-date IAEA publications and ASME standards, and their development took into account the reports prepared by the NEA/OECD EGMPEBV Expert Group, the ETSON Technical Safety Assessment Guides, as well as the results of bilateral cooperation between SEC NRS and IRSN.

Development of the regulatory documents in the Russian Federation involves a broad discussion with interested organizations. In December 2020, the updated Requirements were discussed at a meeting with the participation of more than 20 organizations of the Russian nuclear industry. The meeting results will be taken into account when finalizing the updated Requirements, which is planned to be submitted to Rostechnadzor for approval in the second quarter of 2021.