FULL BEPU APPLICATION FOR CHAPTER 15 OF ATUCHA-2 NPP

In the frame of the licensing process of the Atucha II PHWR (pressurized heavy water reactor) the BEPU (Best Estimate Plus Uncertainty) approach has been selected for issuing the Chapter 15 of FSAR (Final Safety Analysis Report) dealing with accident analysis. The key attributes of a methodology to perform accident analysis of a NPP for licensing purposes are: the first one should be the compliance with the established regulatory requirements. A second attribute deals with the adequacy and the completeness of the selected spectrum of events that should consider the combined contributions of deterministic and probabilistic methods. The third attribute is connected to the availability of qualified tools and analytical procedures suitable for the analysis of accident conditions envisaged for the NPP of concern. The complexity of a nuclear power plant (NPP) and of the accident scenarios may be a challenge for a conservative analysis and may justify the choice of a BEPU approach in the licensing process. This implies two main needs: (1) the need to adopt and to prove (to the regulatory authority) an adequate quality for the computational tools and (2) the need to account for the uncertainty. The purpose of the present paper is to outline key aspects of the BEPU process aimed at the licensing of the Atucha II (CNA-II) NPP in Argentina operated by Nucleoeléctrica Argentina (NA-SA). The execution of the overall analysis and the evaluation of results in relation to slightly fewer than 100 scenarios revealed the wide safety margins available for the NPP of concern. The FSAR including Chapter 15 is required by the Regulatory Body in Argentina to obtain the Commissioning license of the Plant, which reached the first criticality on June 3rd, 2014.