On the role of simulation codes in regulatory activities. Challenges and R&D needs

Simulation codes are essential tools in Nuclear Safety. Calculations are needed to assess the safety of nuclear power plants and to verify compliance with safety requirements. Nuclear regulatory bodies must assess the codes, the methodologies for their use, and the calculations performed with them by licensees in support of their safety analyses. One important way for assessing the validity, quality, consistency, and conclusions of licensee assessments is for regulators and Technical Support Organizations (TSO) alike to resort to independent analysis, including detailed TH calculations. This regulatory task requires high technical expertise and capabilities, such as the ones needed for the development of simulation codes and computerized diagnostic tools specific for regulatory assessment. These tools are not to have the same focus and scope as their industry counterparts, since the objective is shifted from design (for the licensees) to verification of safety requirements. (for regulators/TSOs). This paper has been written by members of the technical staff of Spain’s Nuclear Safety Council, with a double purpose: -To review challenges and needs for Regulatory Bodies concerning the licensing processes where thermohydraulic system codes and related methodologies and calculations are involved.-To review new and advanced methodologies, mainly related to Risk-Informed Regulations, where TH simulation codes are used.