Working Group on Analysis and Management of Accidents (WGAMA)

The Working Group on the Analysis and Management of Accidents (WGAMA) addresses 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 addresses 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 (SMRs). Priority setting is 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 assesses and, where necessary, strengthens 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:

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

The WGAMA reports to the CSNI and assists the Committee with its work. The WGAMA provides answers to questions from the CSNI and the Committee on Nuclear Regulatory Activities (CNRA).

The WGAMA is led by a Chair, a Vice-Chair and a Bureau designated and acting according to the OECD guidelines. The WGAMA also has a Group of Advisors, composed of senior international experts, that can be appointed and called by the chairpersons to provide advice on specific issues.

The programme of the WGAMA is carried out by small task groups (TGs), each set up for performing a specific programme activity under the WGAMA’s supervision. All activities have a co-ordinator or a leader who is responsible for work performance.

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 engages with the following international bodies specialised in similar sets of activities to ensure complementarity and increase synergy: the International Atomic Energy Agency (IAEA), the European Commission, other organizations where a memorandum of understanding (MOU) is established with the NEA, such as the American Nuclear Society (ANS), the CANDU Owners Group (COG), the Central Research Institute of Electric Power Industry (CRIEPI), the Electric Power Research Institute (EPRI), and other international organisations.

The WGAMA produces state-of-the-art reports and other technical reports, workshops (WSs) 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. Final reports are issued as CSNI reports.

The activity derived from tentative and long-term TGs are mostly published as technical reports, which include phenomena identification ranking table (PIRT), CSNI Code Validation Matrix (CCVM)), a technical opinion paper (TOP), a summary report and/or proceedings of WS, and a report of international standard problem (ISP) 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, Germany), Alessandro Del Nevo (ENEA, Italy). Members' area

ISP-53 based on the IRSN reflooding COAL experiments, with WGFS, Task Leader: Nicolas TREGOURES (IRSN, France).  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

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), 17-20 June 2024, Dresden, Germany, Task Leader: Sanjeev Gupta (Becker Technologies, Germany). Members' area

Workshop on Experimental Validation and Application of CFD and CMFD codes to Nuclear Reactor Safety Issues (CFD4NRS-10), 10-12 December 2025, in Ibaraki (Mito and Tokai). Task Leader: Dr. Yasuteru SIBAMOTO (JAEA, Japan)

Transfer of Thermal-Hydraulic and Severe Accident Knowledge Gained Through CSNI Activities (THICKET-5), February 2025, Lucca (Italy). Task Leaders: Alessandro Petruzzi (NINE, Italy), Hideo Nakamura (JAEA, Japan), Thambiayah Nitheanandan (CSNC, Canada), Hideo Nakamura (JAEA)