Prevention, mitigation and management of potential accidents in nuclear power plants


The NEA Working Group on the Analysis and Management of Accidents (WGAMA) held its annual meeting in person on 11-13 September 2023 to discuss its ongoing work and activities related to potential accident situations in nuclear power plants. The meeting brought together over 80 delegates from 20 member countries, as well as representatives from the International Atomic Energy Agency (IAEA) and the European Commission

The working group aims to assess and enhance the technical basis needed for the prevention, mitigation and management of potential accidents in nuclear power plants. It also facilitates international collaboration on the management of accidents and strategies. In this context, the group currently focuses on three main fields: nuclear thermal-hydraulics, computational fluid dynamics (CFD) for nuclear reactor safety and severe accidents.

During the meeting, participants discussed the group’s 14 ongoing activities in the three main fields with the aim of assessing progress and identifying the next steps.

One key question that was discussed was how to progress on the CSNI Code Validation Matrix (CCVM). Carrying out safety assessments by using T/H safety analysis codes is key for the safe operation of nuclear power plants. Several CCVMs have thus been prepared to ensure the codes are validated with a large amount of appropriate experimental data, which may cover reactor accident responses specific to the reactor design. Validation matrices were established for integral effect tests and separate effects tests. They were supplemented later for VVER reactor phenomena and severe accidents, such as in-vessel core degradation and containment phenomena. Reaching a consensus that these matrices constitute a commonly recognised set of data for code validation was a major achievement for the group. Once anticipated accident conditions are included in the CCVM and the relevant database ranges to properly address the advanced reactor designs are established, the CCVM should become a true asset for the development and validation of analytical tools. Such a rigorous approach should be necessary also for evolutionary and innovative reactor designs including SMRs. The WGAMA recommends establishing or updating a CCVM specifically for the reactor design of concern to avoid any lack in the safety assessment, based on the reactor prototype condition tests and/or the properly scaled simulation experiments.

The group also discussed proposals for three potential new activities: a new workshop on Experimental Validation and Application of CFD and CMFD codes to Nuclear Reactor Safety Issues (CFD4NRS-10); a seminar on Transfer of Thermal-Hydraulic Knowledge Gained Through CSNI Activities (THICKET-5) and an International Standard Problem (ISP) based on the IRSN reflooding COAL experiments.

Another highlight of the meeting was the session dedicated to the NEA’s nuclear safety research experimental activities, including the next phase of the Fukushima Daiichi nuclear power plant Accident Information Collection and Evaluation (FACE). The group agreed to support new joint projects on LEaching Studies on samples characteristic of SA damaged Core (LESSAC) and SYStem THERmal hydraulics (SYSTHER). SYSTHER is an attempt to create a platform to address thermal-hydraulic nuclear safety priorities, for both existing and advanced reactor designs, including SMRs.

The direction of the WGAMA’s next meeting will be shaped by input gathered from participants and through co-operation with international organisations and other NEA groups.

For more information on the working group, click here. 

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