ReviewThe working group on the analysis and management of accidents (WGAMA): A historical review of major contributions
Introduction
The Working Group on the Analysis and Management of Accidents (WGAMA) was created on December 31st, 1999, by combining two previous Primary Working Groups of PWG-2 and PWG-4, each of them were primarily in charge of in-vessel and ex-vessel thermal-hydraulics and severe accident phenomena in nuclear power plants (NPP). It is one of the nine working groups (WGs) of the Committee for the Safety of Nuclear Installations (CSNI), which is responsible for the promotion of Nuclear Safety among the 33 member states of the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development (OECD/NEA). Fig. 1 shows the CSNI WG structure and OECD/NEA joint projects; the WGAMA is highlighted.
The overall WGAMA objectives are to assess and strengthen the technical basis needed for the prevention, mitigation and management of potential accidents in NPP and to facilitate international convergence on safety issues and accident management analyses 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, assesses the state of knowledge in areas relevant for the accident analysis and, where needed, identify and fosters research activities aimed to improve such understanding, while supporting the maintenance of expertise and infrastructure in nuclear safety research. The intention is always to make significant contributions to the regulatory decision-making on prevention and management of accidents, reactor safety capacity building, continuously improving the state of knowledge and knowledge management.
The specific scope of the WGAMA extends over a number of fields associated with both current and advanced reactors: reactor coolant system thermal-hydraulics; in-vessel behaviour of degraded cores and in-vessel protection; containment behaviour and containment protection; and fission product (FP) release, transport, deposition and retention. Such a vast scope requires involving large resources, which in numbers translates into more than 100 registered WG members (the largest CSNI WG), over 200 scientists and engineers involved in the running of activities and in excess of 25 technical reports published in the last 5 years, most of which have already been heavily referenced via web referencing and downloaded from the NEA/CSNI document directory (https://www.oecd-nea.org/nsd/docs/indexcsni.html).
The present paper gives an introduction of WGAMA by briefly reviewing the main technical contributions completed since its inception in the fields of thermal-hydraulics, computational fluid-dynamics (CFD) and severe accidents. The WGAMA history has been split into three time periods: decade preceding the Fukushima-Daiichi accident (2000–2010), in which WG's activities and dynamics got consolidated; the next five years (2011–2015), which were heavily influenced by the Fukushima-Daiichi accident; and the present times (2016–2019), in which the group is looking ahead based on the recent and past experience since its inception. Given the limited extension of this article, only the most significant contributions are here shortly described, but a more thorough overview may be done by going through the NEA/CSNI document directory (https://www.oecd-nea.org/nsd/docs/indexcsni.html).
Section snippets
Thermal-hydraulics
The safety of NPPs is demonstrated and assessed through deterministic safety analysis with conservative inputs, to confirm adequate margin to an acceptance criterion well below the failure point, namely of the nuclear fuel. The use of best-estimate (BE) computer codes, combined with conservative or realistic input data, has also been gaining acceptance at the latter part of the 20th century. The code scaling capability and uncertainty methods developed in the same period evolved simultaneously,
The Fukushima DAIICHI years (2011–2016)
The five year period from 2011 to 2016 was soon heavily conditioned by the Fukushima-Daiichi accident that happened on March 11th, 2011. This clearly marked the activities that WGAMA faced with; nevertheless, the momentum in other areas was also kept as briefly reported below.
Thermal-hydraulics
The NEA has been conducting a series of thermal-hydraulic experimental programs through joint collaborations among interested member countries since 2001 on a number of facilities such as SETH,3 PKL.4 These projects produced data in the integral test facilities to benchmark system codes for current and new PWR design concepts. Subsequently in 2014,
Final remarks
A summary of the industrious production of WGAMA in the area of analysis and management of accident in the last 20 years has been outlined. The text is loaded with references in which substantial support may be found. As a result, around 50 technical reports (status reports and state of the art reports, workshop proceedings, code benchmarking reports, uncertainty quantification reports, best practice guidelines, and expert opinion papers) have been cited at the end of this paper.
The research
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors are indebted to CSNI for their support and NEA for articulating all the necessary means to conduct the WGAMA activities in the best conditions possible. Likewise, thanks all the members of the WGAMA bureau for the technical discussions shaping up and pushing forward the WGAMA work. Last but not least, the authors show their deepest appreciation to all those who actively contribute to the WGAMA activities.
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