Fires involving electrical cables are one of the main hazards in Nuclear Power Plants (NPPs). Cables are complex assemblies including several polymeric parts (insulation, bedding, sheath) constituting fuel sources. This study provides an in-depth characterization of the fire behavior of two halogen-free flame retardant cables used in NPPs using the cone calorimeter. The influence of two key parameters, namely the external heat flux and the spacing between cables, on the cable fire characteristics is especially investigated. The prominent role of the outer sheath material on the ignition and the burning at early times was highlighted. A parameter of utmost importance called transition heat flux, was identified and depends on the composition and the structure of the cable. Below this heat flux, the decomposition is limited and concerns only the sheath. Above it, fire hazard is greatly enhanced because most often non-flame retarded insulation part contributes to heat release. The influence of spacing appears complex, and depends on the considered fire property.

Cable fires are one of the main fire hazards in nuclear power plants. As part of the cable fire spreading (CFS) campaign of the OECD PRISME-2 programme, 3 real-scale cable tray fire testswere performed in open atmosphere (1 CFS support test, named CFSS-2) and in a confined and mechanically ventilated facility (2 CFS tests, named CFS-3 and CFS-4). This study aims at investigating the effects of confined and ventilated conditions on cable tray fires that used a halogen-free flame retardant cable-type. The CFS-3 and CFS-4 tests involved 2 ventilation renewal rates of 4 and 15 h −1 , respectively. The confined conditions lead to decrease the fire growth rate and the peaks of mass loss rate and heat release rate, compared with open atmosphere. The reductions are larger for the lower ventilation renewal rate. Furthermore, it is shown that the CFS-4 test may be classified as a well-ventilated fire and the CFS-3 test as an under-ventilated fire. For this last one, its fire characteristics and its consequences in the fire room highlight an oscillatory behaviour, with the same low frequency, for about 30 minutes.These oscillations arise from successive combustions of unburnt gases.

The paper presents an application of Video Fire Analysis (VFA) to a cable tray fire scenario, a scenario of interest to Nuclear Power Plants (NPPs) where cables constitute a substantial part of the combustible load. Five horizontal trays, each 2.4 m long and 0.45 m wide, are positioned with a 0.3 m spacing (in the vertical direction) and set-up against an insulated wall. Each tray contains 49 power PVC cables of 13 mm outer diameter. Ignition is performed with an 80 kW propane burner centrally positioned at 0.2 m below the first (i.e. lowest) tray. Thanks to a flame detection algorithm, the VFA technique allows a reconstruction of the heat release rate (HRR) profile based on the estimated temporal evolution of flame and extinction fronts at the level of each tray. The obtained profile is generally in good agreement with the HRR measurements (from oxygen depletion calorimetry). However, the time to reach the peak HRR is overestimated by approximately 100 s and the peak HRR of 3 MW is underestimated by 17%. These results are nevertheless encouraging because they provide confidence in the flame spread measurements (which are estimated for the case at hand between 2 and 5 mm/s). Therefore, a systematic application of VFA to real-scale experiments is believed to generate a valuable set of data (e.g. flame spread rates) for the development of simplified modelling.

Summary Electrical cabinet fire is one of the main fire hazards in nuclear power plants. As part of the OECD PRISME‐2 programme, four fire tests were carried out to investigate the fire spread from an open‐doors electrical cabinet to overhead cable trays and adjacent cabinets in a confined and mechanically ventilated facility. These tests, named CFS‐5 to CFS‐7 and CORE‐6, used same both cabinet (fire source) and three overhead cable trays. The trays were filled with a halogenated flame‐retardant cable‐type for CFS‐5 and one halogen‐free for the three other tests. Moreover, fire dampers were used for CFS‐7 test while CORE‐6 test implemented two additional cabinets adjacent to the fire source. Measurements such as flame and gas temperature, gas concentration, mass loss rate, and heat release rate were performed for investigating the fire spread. Cabinet fire spread to the cable trays for CFS‐5 and CFS‐6 tests. Three fast and short cable tray fires were shown for CFS‐5, while a slow and long cable tray fire was highlighted for CFS‐6. In contrast, the fire dampers shutdown for CFS‐7 test prevented ignition of the overhead cables. Furthermore, for CORE‐6 test, cabinet fire spread to the adjacent cabinets, but the upper cables were not ignited.

No abstract