NEA Mandates and Structures

Expert Group on Reactor Systems Multi-Physics (EGMUP)

Mandate (Document reference):

• The NSC Working Party on Scientific Issues of Reactor Systems (WPRS): Proposal for Prioritisation and Restructuring [NEA/NSC/WPRS/DOC(2020)19]
• Summary record of the 31^st meeting of the Nuclear Science Committee in September 2020 [NEA/SEN/NSC(2020)20] 
• Mandate of the Expert Group on Reactor Systems Multi-Physics (EGMUP) [NEA/NSC/WPRS/DOC(2021)2]
• Summary record of the 4^th meeting of the Expert Group on Reactor Systems Multi-Physics held on 21 February 2024 [NEA/SEN/NSC/WPRS(2024)X] (forthcoming)
• Mandate of the WPRS Expert Group on Reactor Systems Multi-Physics (EGMUP) [NEA/NSC/WPRS(2024)3]

Mandate (Document extract):

Extract from document [NEA/NSC/WPRS(2024)3]

Background

As a result of the prioritisation process, a reorganisation of the Nuclear Science Committee (NSC) activities was performed in 2020/2021 under the guidance of the NSC Bureau. This has resulted in the disbandment of the NSC Expert Group on Multi-Physics Experimental Data, Benchmarks and Validation (EGMPEBV), the Expert Group on Radiation Transport and Shielding (EGRTS), the Expert Group on Reactor Physics and Advanced Nuclear Systems (EGRPANS) and the Expert Group on Uncertainty Analysis in Modelling (EGUAM). Two new bodies have been created to replace them: the Expert Group on Physics of Reactor Systems (EGPRS) and the Expert Group on Reactor Systems Multi-Physics (EGMUP).

Scope

Under the guidance of the Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS), the Expert Group on Reactor Systems Multi-Physics (EGMUP) will advance the state-of the-art in establishing processes and procedures for certifying experimental data and benchmarking multi-physics multi-scale modelling and simulation (M&S). EGMUP will also evaluate the performance of novel artificial intelligence (AI) and machine learning (ML) applications in multi-physics M&S of reactor systems.

Coupled behaviours of two or more of the following physics will include, but are not limited to the following:

• reactor physics;
• core and system thermal-hydraulics;
• fuel performance and, in particular, integration of fuel performance codes in multiphysics packages for prototype and commercial reactor systems of current and future reactor systems (including GEN-IV designs),
• structural mechanics; and
• material science, chemistry, and thermodynamics.

The single- and few-physics modules collected in a multi-physics model should be based on the best-estimate models. They might be as precise (or high-fidelity) as derived from fully mechanistic tools using a kind of Hi2Lo techniques.

Multi-physics aspects of both steady-state and transient conditions of existing and advanced nuclear systems will be examined along with uncertainty quantification and direct (forward)- and backward- propagation through different scale (multi-scale M&S) and different physics phenomena (multi-physics M&S).

Reactor types considered include, but are not limited to the following:

• Current fleet of light-water and heavy water reactors (LWRs/HWRs) as well as present generation of fuel designs.
• Evolutionary and innovative LWR/HWR systems along with advanced and accident tolerant fuel designs.
• Next generation reactor systems including high temperature gas cooled reactors (HTGR), sodium fast reactors (SFR), lead fast reactors (LFR), gas-cooled fast reactors (GFR), and molten salt reactor (MSR) systems.
• Reactor systems of different scales including large scale reactors, small modular reactors (SMRs), and micro-reactors.
• Nuclear systems for space applications and civilian maritime propulsion
• Accelerator driven (sub-critical) and critical systems for wide range of non-power applications.
• Fusion and hybrid fusion-fission systems.

Objectives

The EGMUP will provide recommendations to the WPRS and the nuclear community on the scientific development needs (data and methods, validation experiments, scenario studies) for multi-physics and multi-scale M&S, including sensitivity and uncertainty methodology for analysis of different reactor systems and scenarios.

Guidance and protocols to qualify experimental-based benchmarks for multi-physics and multi-scale M&S, and to make use of the objective observations and integral experiments in the validation process will be developed and periodically updated.

To fulfil the above the expert group will provide the following:

• standardised benchmark models with detailed uncertainty evaluations and uncertainty methodology guidelines;
• guidance on best practices to combine high fidelity and low fidelity simulation tools within a multi-physics M&S framework;
• framework and consensus recommendations for validating multi-physics simulations including validation protocols and guidelines;
• sensitivity and uncertainty methods to facilitate quantification and ranking of coupled physics;
• evaluation methods for uncertainty impacts of the following parameters on multi-physics simulations:
  • data (e.g. geometry, materials, boundary, and initial conditions),
  • numerical methods and computational algorithms,
  • mathematical models of the physical processes and phenomena;
• training opportunities to demonstrate validation principles and practices; and
• demonstrations of the validation recommendations for specific applications.

To support its activities, the group will collect and evaluate multi-physics data from available integral facilities and Nuclear Power Plant (NPP) experimental data. Analytical and numerical benchmarking will also be used to fulfil the objectives.

Working Methods

The EGMUP will report to the WPRS. The EGMUP will meet once per year, with additional meetings in support of particular activities, such as task forces of the EGMUP.

EGMUP’s deliverables will be developed in task or benchmark groups, whose work will be organised in a project-like manner with outcomes and milestones.

Interactions

The EGMUP will liaise closely with other relevant NEA bodies, in particular the WPRS Expert Group on Physics of Reactor Systems (EGPRS) and the Expert Group on Reactor Core Thermal-hydraulics and Mechanics (EGTHM) as well as those bodies operating under the guidance of the Nuclear Science Committee (NSC), and the Committee on the Safety of Nuclear Installations (CSNI) and the Committee on Nuclear Regulatory Activities (CNRA). The objective will be to ensure that the respective programmes are complementary and to provide advice and support where required and undertake common work where appropriate. Links with the NSC Working Party on Materials Science Issues in Nuclear Fuels and Structural Materials (WPFM) will assist with issues related to fuel performance and structural materials analysis. Close collaboration with the NSC Working Party on Scientific Issues of Advanced Fuel Cycles (WPFC) and its expert groups will be maintained.

The preservation and management of knowledge specific to the areas of interest will be coordinated through relevant frameworks under the auspices of the OECD-NEA Nuclear Science Committee.

Deliverables

The deliverables of EGMUP are technical reports, proceedings of seminars or workshops, state-of-the-art reports, and technical or collective opinion papers, databases, and comparison or benchmark studies. The EGMUP will also organise specialist meetings and workshops to further its objectives. The detailed list of deliverables will be tracked in the semi-annual NSC progress reports.

Priority for the 2024-2026 period is given to developments, reports, and benchmarks set forth hereunder:

• High-level recommendation report on multi-national efforts in the development and benchmarking of advanced multi-physics and multi-scale M&S tools including a summary of findings of the Expert Group on Multi-physics Experimental Data, Benchmarks and Validation (EGMPEBV).
• Development of a handbook on evaluated experimental-based benchmarks suitable for the phenomenological validation of the multi-physics and multi-scale tools, models, and data libraries.
• Completion (including comparative analysis) of the following benchmarks:
  • Multi-Physics Pellet Cladding Mechanical Interaction Validation (MPCMIV) benchmark and developing validation protocol for multi-physics transient calculations;
  • TVA WB1 Multi-Cycle Depletion performance benchmark and developing validation protocol for multi-physics cycle depletion calculations;
  • Rostov-2 VVER-1000 Multi-Physics Multi-Fidelity Transient benchmark;
  • Phase III of the LWR-Uncertainty Analysis in Modelling (UAM) benchmark;
  • Phase III of the SFR-UAM benchmark.
• Archiving of legacy benchmarks:
  • Kalinin-3 benchmark;
  • Phase II exercises (transient exercises) of MHTGR benchmark;
  • Oskarshamn-2 transient benchmark.
• Initiating activities on the benchmarking of the multi-physics and multi-scale M&S tools suitable for conceptual design and safety case studies of the advanced, including small and micro modular, nuclear systems and the elements of their fuel cycle.
• Supporting the annual organization of the International School on Simulation of Nuclear Reactor Systems (SINUS).

• Organising yearly UAM and other multi-physics benchmark workshops and enhance a dissemination of the results of the Expert Group activities through relevant international scientific conferences.