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The work deals with the influence of a sidewall and cable arrangement on the behavior of a fire involving horizontal cable trays in the framework of fire safety assessments in nuclear installations. The analysis is based on large‐scale fire tests performed in the open atmosphere in the frame of the OECD Nuclear Energy Agency (NEA) PRISME 3 project and on the corresponding simulations applying the FLASHCAT model for predicting the fire heat release rate. The fire configuration consists of five horizontal trays filled with PVC‐insulated power cables. The parameters investigated are the presence or absence of a sidewall and the cable arrangement (loose or tight bundles). The results show that the presence of a sidewall increases the fire HRR in comparison to a scenario without a sidewall. This effect is due to the increase of the flame spread velocity on the lower trays. Regarding cable arrangement, a tight configuration in bundles reduces the fire HRR in comparison to a scenario with a loose arrangement. This result is due to the reduction of the fire heat release rate per unit of area (HRRPUA) as well as the flame spread velocity. The performance of the FLASHCAT model in predicting the effects of the sidewall and the cable arrangement was also assessed on the basis of the fire tests and satisfactory agreements are reported. The presented analysis demonstrates that the fire scenario with horizontal cable trays against a sidewall and with a loose cable arrangement represents a conservative scenario for fire risk assessment. In addition, on the basis of these experiments, the effect of cable arrangement is more substantial than the sidewall effect. [ABSTRACT FROM AUTHOR]

Electrical cabinet-related fire events are among the most recorded fire events in nuclear power plants. As part of the OECD PRISME-3 project, four fire tests were carried out to highlight the fire spread paths from an open-door electrical cabinet (CC) to two adjacent closed-door electrical cabinets (ACs). The cabinets, separated by a double wall with an air gap, were connected by overhead and subfloor cable trays. These last ones were filled with either a "low" or "well-qualified" (LQ or WQ, respectively) cable type. Each cable type was used for two tests. In addition, tests were conducted either in open atmosphere conditions (two) or in confined and mechanically ventilated conditions (two). These tests highlighted three fire spread paths from the CC to the ACs. Regarding the first one through the double wall with an air gap, several ignitions of electrical components (used as targets) occurred in the ACs when the wall temperature near the ignited target exceeded 600 °C (or the heat flux incident to the target was higher than 26 kW/m2) whatever the test conditions. Furthermore, the two other fire spread paths through the overhead and subfloor cable trays were highlighted only if the LQ cable type was used. • Three fire spread paths were shown between adjacent cabinets separated by a double wall and connected by cable trays. • The fire spread paths were highlighted for the two studied test conditions. • Determination of the temperature and heat flux criteria leading to the fire spread via the double wall. • Impact of the cable type on the fire spread paths via the cable trays. [ABSTRACT FROM AUTHOR]

This study investigates the behaviour of a fire propagating over a long length of electrical cables, in order to assess the maximum burning length and the associated heat release rate of the travelling fire. It is part of the research work conducted in the framework of the OECD/NEA PRISME 3 project for a better assessment of fire propagation over cable trays in nuclear installations. The fire scenario consists of a set of 3 horizontal cable trays 6 m long, positioned in the corridor of a mechanically ventilated large-scale compartment. The parameters of the study are the nature of the cables (thermoset or thermoplastic types) and the distance of the cable trays from the ceiling. The determination of the fire heat release rate (HRR), the total burning length, the velocity of the flame front, the heat release rate per unit area (HHRPUA) and the effective heat of combustion (EHC) of the cable fires are given. For the configuration studied (3 cable trays and a given load), fire HRRs of 160 kW and 520 kW corresponding to burning lengths of 2 m and 3 m and corresponding to velocities of 0.4 mm/s and 0.9 mm/s are obtained for thermoset cables. For thermoplastic type cables (made of polyvinyl chloride), a power of 730 kW corresponding to a burning length of 3.5 m and corresponding to a velocity of 1.9 mm/s is reported. The order of magnitude for HRRPUA and EHC were respectively ranged between 50 kW/m2 and 150 kW/m2 and 20 MJ/kg and 25 MJ/kg for the two cable types. • Large scale fire tests of long cable trays. • Flame spread velocity of travelling fire over long cable length. • Effect of distance from the ceiling and cable type. [ABSTRACT FROM AUTHOR]

This study deals with the effect of ventilation flow rate and the ventilation configuration on the behavior of a cable tray fire in a confined and mechanically ventilated enclosure. Results are based on large-scale fire tests performed within the framework of the OECD Nuclear Energy Agency (NEA) PRISME projects. The fire source, identical for all tests, consisted in five horizontal cable trays measuring 3 m in length, stacked vertically and filled with halogen-free flame retardant cable-type, non-powered cables. The installation consists of two rooms connected by an open doorway. Two ventilation configurations were considered with two different arrangements of the inlet and outlet branches. The analysis demonstrates the effects of ventilation flow rate and air intake position on the fire heat release rate (HRR). Decreasing the ventilation flow rate reduces the maximum HRR and delays combustion on the trays, which burn one after the other rather than simultaneously. This result is the consequence of oxygen vitiation near the cable trays, which reduces the horizontal flame spread on each cable tray. The analysis also discusses the phenomenon of low frequency oscillatory behavior of fire in a ventilated enclosure. The results highlight that the conditions of occurrence of oscillations combine two criteria: a low ventilation flow rate to favor the release of unburnt gases and an appropriate configuration of the ventilation air intake to generate ignition of premixed gases. • Description of large-scale cable tray fire tests in mechanically ventilated enclosure. • Significant effect of the position of the air intake on the fire development. • The ventilation configuration influences the flame spread velocities and consequently the fire HRR. • Occurrence of oscillatory behavior in case of low oxygen environment. [ABSTRACT FROM AUTHOR]

This work deals with under-ventilated pool fires in confined and mechanically ventilated enclosures. The objective is to demonstrate the suitability of reduced-scale experiments to investigate under-ventilated combustion regimes in the case of a mechanically ventilated enclosure, by analysing combustion regimes at two different scales. The fire scenario consists in a dodecane liquid pool fire located in a mechanically ventilated room. Reduced-scale experiments concern a 0.031 m2 pool size inside a 1.875 m3 enclosure and large-scale experiments concern a 0.4 m2 pool size inside a 120 m3 enclosure. The varying parameter is the ventilation flow rate, which allows the fire behaviour to be investigated, from free-burning to confined situations. At both scales, results show that the burning rate decreases with the ventilation flow rate and a linear relationship between oxygen concentration and fuel mass loss rate is revealed. Comparison between the well-stirred reactor model and the experimental results shows good agreement for both scales. The work demonstrates the suitability of the reduced-scale approach to reproduce the combustion process in a vitiated environment, provided that appropriate dimensionless parameters are used: a reduced heat-release rate, a thermal ratio parameter and the global equivalence ratio. • Multi-scale analysis of pool fires in a mechanically ventilated enclosure. • Reduced and large-scale experiments. • Identification of main scaling parameters. • Identification of the burning rate regime in a vitiated environment. [ABSTRACT FROM AUTHOR]