ELSMOR – towards European Licensing of Small Modular Reactors: Methodology recommendations for light-water small modular reactors safety assessment

Decarbonization of energy production is key in today’s societies and nuclear energy holds an essential place in this prospect. Besides heavy-duty electricity production, other industrial and communal needs could be served by integrating novel nuclear energy production systems, among which are low-power nuclear devices, like small modular reactors (SMRs). The ELSMOR (towards European Licensing of Small Modular Reactors) European project addresses this topic as an answer to the Horizon 2020 Euratom NFRP-2018-3 call. The consortium includes 15 partners from eight European countries, involving research institutes, major European nuclear companies and technical support organizations. The 3.5-year project, launched in September 2019, investigates selected safety features of light-water (LW) SMRs with focus on licensing aspects. Providing a comprehensive compliance framework that regulators can adopt and operate, the licensing process of such SMRs could be optimized, helping their deployment. In this prospect, as a result of ELSMOR’s work, this article gives an overview of the specific issues that LW-SMRs may bring about in the different domains of nuclear safety, in terms of: Methodological standpoints: safety goals, safety requirements, safety principles (defence-in-depth implementation); Main safety functions of reactivity control, decay heat removal and confinement management; Severe accident management; Other safety issues particular to SMRs: use of shared systems; performing of multi-unit probabilistic safety assessment (PSA); refuelling, spent fuel management, transport and disposal management. In this article, adequate methodologies are developed to deal with these issues and to help assess the safety of LW-SMRs. This work gives a precious synthesis of the safety assessment issues of LW-SMRs and of the associated methodologies developed in the context of the ELSMOR European project. The removal of fossil fuels in energy production is very important in today’s societies and nuclear energy plays an essential role in this. Besides large-scale electricity production, other industrial and communal needs could be solved by using new nuclear energy production systems, among which are low-power nuclear devices, like small modular reactors (SMRs). The ELSMOR (towards European Licensing of Small Modular Reactors) European project looks at this topic as an answer to the Horizon 2020 Euratom NFRP-2018-3 initiative. This project includes 15 partners from eight European countries, involving research institutes, major European nuclear companies and technical support organizations. The 3.5-year project, started in September 2019, investigates selected safety features of light-water (LW) SMRs with a focus on the licensing aspects. Providing a comprehensive compliance framework that regulators can use and operate, the licensing process of such SMRs could be optimized, helping their deployment. With this prospect, this article gives an overview of the specific subjects that LW-SMRs may bring in the different areas of nuclear safety (in particular: safety goals, safety requirements, nuclear safety functions: reactivity control, decay heat removal and confinement management, etc..). In this article, methods are developed to deal with these new subjects and to help assess the safety of LW-SMRs. This work gives an overview of the safety assessment issues of LW-SMRs and of the associated methods developed in the context of the ELSMOR European project

3-D TRANSIENT COUPLED SIMULATION OF SUPERPHENIX WITH PARCS/ATHLET

Most safety criteria for Sodium cooled Fast Reactors (SFR) are local core parameters. Thus, application of 3-D neutron kinetic and thermal-hydraulic coupled codes including detailed modelling of core expansion effects is mandatory for best estimate evaluations of safety margins. A recently published benchmark based on measurements performed at the Superph´enix (SPX) reactor offers the opportunity to validate codes and methods for SFR safety assessment. In this paper, the SPX core is modelled in ATHLET and PARCS. Explicit models for axial and radial core expansion effects for 3-D coupled calculations were recently implemented in PARCS. In ATHLET, axial thermal expansion of structures (strongback, vessel, control rod drive line) influencing the relative position of the control rod in the active core is modelled. The newly implemented models are tested on a transient initiated by a reactivity insertion of -50 pcm. A point kinetic simulation is also performed to compare with the 3D solution. Both ATHLET-point kinetic model and ATHLET-PARCS simulations deliver similar power responses during the transient but with an offset. By analysing the different feedbacks in the point kinetic model, it can be concluded that models of expansion of the different structures are well implemented. In the future further analysis of different transients of the benchmark are planned

3-D TRANSIENT COUPLED SIMULATION OF SUPERPHENIX WITH PARCS/ATHLET

Most safety criteria for Sodium cooled Fast Reactors (SFR) are local core parameters. Thus, application of 3-D neutron kinetic and thermal-hydraulic coupled codes including detailed modelling of core expansion effects is mandatory for best estimate evaluations of safety margins. A recently published benchmark based on measurements performed at the Superph´enix (SPX) reactor offers the opportunity to validate codes and methods for SFR safety assessment. In this paper, the SPX core is modelled in ATHLET and PARCS. Explicit models for axial and radial core expansion effects for 3-D coupled calculations were recently implemented in PARCS. In ATHLET, axial thermal expansion of structures (strongback, vessel, control rod drive line) influencing the relative position of the control rod in the active core is modelled. The newly implemented models are tested on a transient initiated by a reactivity insertion of -50 pcm. A point kinetic simulation is also performed to compare with the 3D solution. Both ATHLET-point kinetic model and ATHLET-PARCS simulations deliver similar power responses during the transient but with an offset. By analysing the different feedbacks in the point kinetic model, it can be concluded that models of expansion of the different structures are well implemented. In the future further analysis of different transients of the benchmark are planned

Aleksandar Pavkovic/Peter Radan, "Creating New States. Theory and Practice of Secession", Aldershot 2007

Dietrich F. Aleksandar Pavkovic/Peter Radan, "Creating New States. Theory and Practice of Secession", Aldershot 2007. Politische Vierteljahresschrift. 2009;50(2):346-348