The Small Modular Reactors (SMR) have rapidly been developed in different countries due to their many advantages and applications. Although these reactors have many benefits related to designs, there are challenges in developing these reactors including how to license these reactors. This challenge stems from the various innovations of SMR designs. As an example, for the SMRs that don’t use the traditional water coolant (such as Helium, Sodium, Lead-Bismuth, or molten salt), the licensing challenge is more difficult due to the lack of familiarity. The precise and clear existing definition of the water-cooled reactor regulatory requirements is an advantage of the light water SMRs in comparison to assessing other SMRs, however, the comprehensive activities have not been carried out to licensing issues for SMRs due to the diversities of these reactors. Also, it should be noted that in the previous generation reactors, the licensing was based on decision-making related to deterministic and probabilistic safety assessments in nuclear power plants and almost all of their licenses are approved based on conservative analysis. But in recent years, the decision-making methods based on the best estimate and realistic approach have received more attention. Thus, the method called the Best Estimate Plus Uncertainty (BEPU) approach is selected for licensing issues dealing with accident analysis in FSAR. The BEPU approach is generally based on postulated initiating event selection and analyzing these events based on best estimate models by considering uncertainty evaluations. The evolution process ahead of BEPU includes achieving qualified computational tools along with valid uncertainty methods, quality demonstration of results, and finally acceptability by the licensing authority. The BEPU has been applied the most in the coming years to evaluate the safety-related modeling for several reactors (for instance, chapter 15 of the FSAR in Atucha-II NPP). Now using the BEPU approach in licensing for PWRs is a mature technology and ready for industrial application. But, due to the fact that most of the reactors of the previous generation were licensed based on conservative methods, the vendors and even the regulatory bodies have resistance against the re-evaluation of the safety assessments based on the BEPU approach. Besides the license renewal for the past generation reactors, the BEPU approach has the capability and is highly recommended to be applied to license the SMRs. However, given the challenge of licensing SMR reactors, the choice of conservative methods in the licensing process for the SMRs is a kind of drawback as roll-back. Since none of the SMRs have been operated yet, it is necessary to use the BEPU approach to prepare FSAR chapters of SMRs in a fundamental development for licensing. The main objective of the current study is to clarify the possibility of applying the BEPU approach in the licensing process of SMRs. The challenging issue during SMR licensing using the BEPU approach is data sufficiency for multi-scale validation, which should be solved using available data from past experiences (in the case of availability) or new experiment facilities. For the potential licensing issue based on the BEPU approach, the pre-application phase should be considered, allowing vendors to interact with the regulatory body before the formal submission of a licensing application. As the NRC has started its work on licensing non-light water reactors and prepares draft regulatory guide “DG-1353”, it’s recommended that they also consider the proven BEPU approach to be a part of the design and licensing procedures. This paper summarizes the current status of the extension BEPU approach for SMRs according to the review of past experiences and a framework for extending this method in the process of safety assessments and licensing of SMRs.
Heading Toward Configuration of BEPU Approach into Licensing Process of SMRs
D’Auria Francesco
Ultimo
Supervision
2021-01-01
Abstract
The Small Modular Reactors (SMR) have rapidly been developed in different countries due to their many advantages and applications. Although these reactors have many benefits related to designs, there are challenges in developing these reactors including how to license these reactors. This challenge stems from the various innovations of SMR designs. As an example, for the SMRs that don’t use the traditional water coolant (such as Helium, Sodium, Lead-Bismuth, or molten salt), the licensing challenge is more difficult due to the lack of familiarity. The precise and clear existing definition of the water-cooled reactor regulatory requirements is an advantage of the light water SMRs in comparison to assessing other SMRs, however, the comprehensive activities have not been carried out to licensing issues for SMRs due to the diversities of these reactors. Also, it should be noted that in the previous generation reactors, the licensing was based on decision-making related to deterministic and probabilistic safety assessments in nuclear power plants and almost all of their licenses are approved based on conservative analysis. But in recent years, the decision-making methods based on the best estimate and realistic approach have received more attention. Thus, the method called the Best Estimate Plus Uncertainty (BEPU) approach is selected for licensing issues dealing with accident analysis in FSAR. The BEPU approach is generally based on postulated initiating event selection and analyzing these events based on best estimate models by considering uncertainty evaluations. The evolution process ahead of BEPU includes achieving qualified computational tools along with valid uncertainty methods, quality demonstration of results, and finally acceptability by the licensing authority. The BEPU has been applied the most in the coming years to evaluate the safety-related modeling for several reactors (for instance, chapter 15 of the FSAR in Atucha-II NPP). Now using the BEPU approach in licensing for PWRs is a mature technology and ready for industrial application. But, due to the fact that most of the reactors of the previous generation were licensed based on conservative methods, the vendors and even the regulatory bodies have resistance against the re-evaluation of the safety assessments based on the BEPU approach. Besides the license renewal for the past generation reactors, the BEPU approach has the capability and is highly recommended to be applied to license the SMRs. However, given the challenge of licensing SMR reactors, the choice of conservative methods in the licensing process for the SMRs is a kind of drawback as roll-back. Since none of the SMRs have been operated yet, it is necessary to use the BEPU approach to prepare FSAR chapters of SMRs in a fundamental development for licensing. The main objective of the current study is to clarify the possibility of applying the BEPU approach in the licensing process of SMRs. The challenging issue during SMR licensing using the BEPU approach is data sufficiency for multi-scale validation, which should be solved using available data from past experiences (in the case of availability) or new experiment facilities. For the potential licensing issue based on the BEPU approach, the pre-application phase should be considered, allowing vendors to interact with the regulatory body before the formal submission of a licensing application. As the NRC has started its work on licensing non-light water reactors and prepares draft regulatory guide “DG-1353”, it’s recommended that they also consider the proven BEPU approach to be a part of the design and licensing procedures. This paper summarizes the current status of the extension BEPU approach for SMRs according to the review of past experiences and a framework for extending this method in the process of safety assessments and licensing of SMRs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.