Working Group on Analysis and Management of Accidents (WGAMA)

The Working Group on the Analysis and Management of Accidents (WGAMA) focuses on the NEA activities related to potential design-basis and beyond design-basis accidents in nuclear reactors and related technologies. The accident progression includes in-vessel and ex-vessel phenomena involving system thermal-hydraulics, core damage and relocation, release and transport of radioactive materials and their physical-chemical behaviour, combustible gas generation, distribution and combustion, and molten core-concrete/structure interactions. The WGAMA also works on the safety aspects of existing nuclear reactors and related technologies as well as emerging challenges of evolutionary and innovative reactor designs and nuclear technologies, including small modular reactors. Group's priorities are based on established criteria of the Committee on the Safety of Nuclear Installations (CSNI) and in particular on safety significance and risk and uncertainty considerations.

The WGAMA objective is to assess and, where necessary, strengthen the technical basis needed for the prevention, mitigation and management of potential accidents in nuclear reactors and related technologies, and to facilitate international convergence on safety issues, safety assessments and accident management (AM) measures and strategies.

In order to fulfil these objectives, the WGAMA focuses on:

  • Exchanging technical experience and information relevant for resolving current or emerging safety issues.
  • Promoting the development of phenomena-based models and codes used for the safety analysis, including the performance of benchmarking exercises.
  • Assessing the state of knowledge in areas relevant for the accident analysis.
  • Where needed, promoting research activities aimed to improve such understanding, while supporting the maintenance of expertise and infrastructure in nuclear safety research.

The WGAMA co-ordinates its work with other NEA bodies, notably with the Working Group on Risk Assessment (WGRISK) for priority setting and potential accident sequences; the Working Group on New Technologies (WGNT) for regulatory concerns on new technologies; the Working Group on Integrity and Ageing of Components and Structures (WGIAGE) for ageing and structure integrity evaluation; the Working Group on Fuel Safety (WGFS) for issues related to fuel safety which includes accident-tolerant fuel (ATF) subjects; and the Working Group on Human and Organisational Factors (WGHOF) for human and organisational aspects of AM. Co-operation with other CSNI and CNRA working groups aim at activities based on defined/agreed priorities in both groups.

The WGAMA also works in co-ordination with the Expert Group on Core Thermal Hydraulics and Mechanics (EGTHM) of the Nuclear Science Committee (NSC) on scientific items related to advanced thermal-hydraulic methods including coupling techniques with other codes (e.g., neutronics, fuel performance, CFD).

The NEA provides a framework for establishing joint safety research projects, and the WGAMA promotes technical exchanges by creating opportunities with relevant projects, and provides technical support as appropriate.

The WGAMA co-operates with international bodies specialised in similar sets of activities to ensure complementarity and synergy: with the International Atomic Energy Agency (IAEA), the European Commission, and other international organisations and fora, as well as organisations where a memorandum of understanding (MoU) is established with the NEA.

The output of the WGAMA consists of state-of-the-art reports and other technical reports, workshops and conferences with related reports and proceedings, benchmarking exercises and joint research proposals. One or more (internal) reports are usually issued for each of the activities. A final report is issued as a CSNI report.

The activity outcomes from tentative and long-term task groups are mostly published as technical reports, which include phenomena identification ranking table (PIRT)/CSNI code validation matrix (CCVM), a technical opinion paper, a summary report and/or proceedings of a workshop, and a report of international standard problem and benchmark activities, providing status and recommendations.


Hideo Nakamura (JAEA, Japan)

Ahmed Bentaib (IRSN, France)


Martina Adorni, NEA

Related news
Publications and reports

WGAMA Members' area (password protected)

Thermal-Hydraulics related activities

Status Report on Good Practices for Analyses of Design Extension Condition without Significant Fuel Degradation (DEC-A) for Operating Nuclear Power Plants, with WGFS, Task Leaders: Jinzhao Zhang, Maxime Havet (Tractebel, Belgium). Members' area

Application Tests for Realisation of Inverse Uncertainty quantification and validation Methodologies in thermal-hydraulics (ATRIUM), Task Leaders: Lucia Sargentini, Alberto Ghione, Guillaume Damblin, Philippe Fillion (CEA, France). Members' area

ISP-51 on advanced core cooling mechanism experiments (ACME), Task Leaders: Yang Jun (HUST, China), Byung-Hyun You (KAERI, Korea). Members' area

ISP-52 on PKL experiment on Multiple SG U-tube rupture, Task Leaders: Simon Schollenberger (Framatome), Alessandro Del Nevo (ENEA). Members' area

Harmonisation of Methodologies for System Thermal-Hydraulics Experimental Meta-Data Preservation, Collection and Qualification (THEMPo), Task Leader: Alessandro Petruzzi (NINE, Italy). Members' area

CFD activities 

CFD for Nuclear Reactor Safety Phase 6 – Supporting an enlarged use, Task leaders: Phlippe Freydier (EDF, France), Pierre Ruyer (IRSN, France), Stephan Kelm (FZJ, Germany), Mingjun Wang (XJTU, China). Members' area

Thermal mixing and fatigue in a T-junction with a dead leg – benchmarking and experimental validation of CFD, Task Leaders: Kristian Angele (Vattenfall), Annalisa Manera (ETZH), Victor Petrov (PSI). Members' area
Severe Accidents relates activities

State-of-Art-Report on Behaviour of Combustible Gases in Severe Accidents, Task Leaders: Sam Gyepi-Garbrah (CNSC, Canada), Ahmed Bentaib (IRSN, France), Seong-Wan Hong (KAERI, Korea), Sanjeev Gupta (Becker Technologies, Germany). Members' area

Boundary conditions of scrubbing and remobilisation of fission products in aqueous pools during severe accidents (BCAPFIS), Task Leaders: Luis E. Herranz (CIEMAT, Spain); Sanjeev Gupta (Becker Technologies, Germany). Members' area

Status Report on the Reactor Pressure Vessel Integrity Assessment for in-vessel retention, with WGIAGE, Task Leaders: Jiri Zdarek (UJV, Czech Republic), Florian Fichot (IRSN, France). Members' area

Conferences and Workshops

Workshop on experimental validation and application of CFD and CMFD codes to Nuclear Reactor Safety Issues (CFD4NRS-9), 20-23 February 2023, College Station, United States. Task Leader: Yassin Hassan (Texas A&M, USA) 

Collaboration in ERMSAR (European Review Meeting on Severe Accident Research) Conference series: Facing ERMSAR2024, 13-16 May 2024, Stockholm, Sweden. Task Leaders: Luis E. Herranz (CIEMAT, Spain), Fabrizio Gabrielli (KIT, Germany), Sandro Paci (University of Pisa).

Collaboration with BEPU2024 (Best Estimate Plus Uncertainty 2024 Conference), 19-24 May 2024, Lucca, Italy. Task Leaders: Alessandro Petruzzi (NINE, Italy)

Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics and Severe Accidents (SWINTH-2024), Task Leader: Sanjeev Gupta (Becker Technologies, Germany). Members' area