Hot Topic: GRS Research on Fire Protection in Nuclear Power Plants
The NEA is an official institution within the Organisation for Economic Co-operation (OECD) that facilitates and coordinates the cooperation of states with advanced nuclear infrastructure. This is to promote and improve areas such as nuclear safety, technology, science or legislation. The NEA maintains several specialised standing technical committees, two of which are directly related to NPP safety: the CNRA (Committee on Nuclear Regulatory Activities) and the CSNI (Committee on the Safety of Nuclear Installations).
- to exchange technical information,
- to promote collaboration between research, development, engineering and regulation organisations,
- to review the state of knowledge on selected topics of nuclear safety technology and safety assessments, including operating experience, and
- to promote coordination of work aimed at maintaining competence in nuclear safety.
Arcing faults as a potential cause of fire
In a HEAF scenario, two successive phases are typically distinguished, each with its own damage patterns. The first phase is characterised by an extremely short and rapid release of energy from the arc of typically 100 kcal/m2. This energy release can result in
- a complete functional failure of the affected component,
- the ejection of hot projectiles from damaged electrical components or the component housing, and
- a subsequent fire due to the extremely high temperatures.
HEAF events can affect safety in nuclear power plants
Based on these findings, a first series of large-scale experiments took place under the auspices of the OECD/NEA as early as from 2012, which confirmed the observations from operating experience. The experts and representatives of the authorities involved in this project concluded from this that arcing faults should be taken into account in the fire hazard analysis as well as in the fire-related parts of a probabilistic safety analysis (PSA) for an adequate safety assessment of nuclear facilities. In addition, regulatory guidelines for the control of arcing faults and for fires caused by them would be required.
Results of high interest to the nuclear regulatory authorities
The current planning of the OECD/NEA experiments and supplemental testing specifically covering the situation in US nuclear power plants reflects the efforts to approach the overall phenomenon of arcing faults in a step-by-step procedure. Both experimental test series are carried out by the Office of Research of the US regulatory authority, the Nuclear Regulatory Commission (NRC).
In a first step, the focus is on HEAF events in the presence of aluminum, as is typical for US components – regardless of whether the aluminum is located in the respective component itself or is part of its enclosure. The experiments will reflect both the thermal conditions of such scenarios and the pressure build-up and deposition of (possibly conductive) waste products on surfaces due to arcing faults in bus bars or switchgear cabinets. The scientists expect quantitative results regarding the impacts of arcing faults on corresponding components (so-called targets) in rooms with electrical equipment and cables.
For details on the HEAF 2 experimental setup see: