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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.

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