Experimental study at reduced-scale of fire spread between electrical cabinets located opposite each other

International audienceThe ability of an electrical cabinet fire to spread to neighbouring cabinets is a major concern for fire safety in nuclear power plants (NPPs). Twelve intermediate-scale fire tests were performed to determine the fire spread conditions from a burning enclosure to an opposite closed-door enclosure, for non-combustible (glazed and metallic) and combustible (made of poly(methyl methacrylate) [PMMA]) doors. The impact on these conditions of the separation distance (SD) between the enclosures, the target type contained in the closed-door enclosure and overhead electric cable trays, were especially investigated. The tests used a device mainly composed of a fire enclosure (FE) and an opposite enclosure (OE). Fire can spread to the OE with a glazed panel when the total transmitted heat flux exceeds that required for spontaneous ignition of the target. Fire can propagate to the OE with a PMMA panel only if its ignition is piloted by the flames from the FE. The tests with a PMMA panel also revealed that the most severe fire was not obtained for the minimum SD. Furthermore, fire can spread for a higher SD when overhead electric cables are used. Finally, the effects of the door type and SD on the transmittance were also addressed

Fire spreading from a real open-doors electrical cabinet to overhead multiple cable trays into a confined and mechanically-ventilated facility

International audienceElectrical cabinet fire is one of the main fire hazards in Nuclear Power Plants (NPPs). The ability of the fire to spread beyond the burning cabinet is therefore a major concern for fire safety analyses in NPPs. In the framework of the OECD PRISME-2 programme led by the French ‘‘Institut de Radioprotection et de Sûreté Nucléaire’’ (IRSN), three fire tests, named CFS-5 to CFS-7, involving a real open-doors electrical cabinet and three overhead cable trays, are performed. In this study, the main objectives are to investigate the effects of ventilation and types of electrical cable on the fire spread from the electrical open-doors cabinet to the three overhead cable trays. The fire tests are carried out into a confined and mechanically ventilated facility, named DIVA. Both CFS-5 and CFS-6 tests involve a ventilation renewal rate (VRR, defined as the room volume number renewed per hour) of 15 h-1, while the third CFS-7 test early implements a significantly lower VRR of about 1 h-1. For this last one, fire dampers are indeed shutdown 2 min 30 s after the starting of the cabinet ignition. In addition, the overhead trays are filled with two types of electrical cable used in NPPs, named cable C for the CFS-5 test and cable A for both CFS-6 and CFS-7 tests. These tests highlight that fire spreads from the real open-doors cabinet to the overhead cable trays for a VRR of 15 h-1 and whatever the type of cable. However, this last one influences the fire behaviour of the upper cable trays. The cable A trays indeed ignite once and later than the three ignitions highlighted for the cable C trays. Moreover, the cable A tray fire is longer than the three cable C tray fires. The former mainly grows after the cabinet fire while the latter match with the cabinet fire. Finally, for the CFS-7 test, the fire dampers shutdown shortens the cabinet fire and prevents the upper cable trays ignition

ETUDE DE LA PROPAGATION DU FEU SUR DE MULTIPLES CHEMINS DE CABLES ELECTRIQUES HORIZONTAUX

RESUME Les câbles électriques représentent la plus grande quantité de matière combustible présente dans les installations nucléaires. Les feux de câbles électriques constituent ainsi un des plus importants risques d'incendie sur ces installations. Les analyses de sûreté incendie doivent ainsi évaluer la propagation de feux potentiels sur des chemins de câbles électriques et la puissance du feu résultante, afin d'évaluer les dommages sur des éléments importants pour la sûreté des installations nucléaires. Le modèle FLASH-CAT permet d'évaluer simplement la propagation du feu sur un ensemble de chemins de câbles électriques horizontaux. Dans le cadre du programme OCDE PRISME-2, des essais qui ont impliqué des chemins de câbles horizontaux supportés par un mur, ont mis en évidence une croissance rapide des feux et d'importants pics de puissance. Ces essais visaient à compléter des essais de feux de chemins de câbles horizontaux localisés loin de murs et de plafonds, réalisés dans le cadre du programme CHRISTIFIRE. La présente étude propose ainsi d'étudier la capacité du modèle simplifié FLASH-CAT à évaluer la puissance du feu se propageant sur des chemins de câbles horizontaux avec un mur support. Les premières évaluations des essais PRISME-2 CFSS avec le modèle FLASH-CAT ont surestimé les mesures des délais d'inflammation des chemins de câbles ainsi que les durées des feux. Ces calculs ont aussi sous-estimé de façon significative les taux de croissance du feu et les pics de puissance mesurés lors des essais. En premier lieu, ce travail révèle en effet que des paramètres d'entrée du modèle FLASH-CAT, les paramètres de propagation, doivent être actualisés quand un mur supporte les chemins de câbles. Ces paramètres sont le délai d'inflammation des chemins de câble, l'angle de propagation et la vitesse de propagation des flammes le long des chemins de câbles. Ces paramètres ont été ainsi mesurés grâce à une méthode d'analyse des vidéos des feux (AVF), développée dans cette étude, et appliqué aux essais PRISME-2 CFSS. Cette étude montre ensuite que les prédictions du modèle FLASH-CAT avec les paramètres de propagation optimisés pour des chemins de câbles supportés par un mur, sont en accord avec les essais. La méthode AVF a été aussi appliquée à des essais de feux de chemins de câbles du programme CHRISTIFIRE. Les calculs avec le modèle FLASH-CAT et les paramètres optimisés améliorent également la prédiction de l'évolution temporelle de la puissance du feu

ETUDE DE LA PROPAGATION DU FEU SUR DE MULTIPLES CHEMINS DE CABLES ELECTRIQUES HORIZONTAUX

RESUME Les câbles électriques représentent la plus grande quantité de matière combustible présente dans les installations nucléaires. Les feux de câbles électriques constituent ainsi un des plus importants risques d'incendie sur ces installations. Les analyses de sûreté incendie doivent ainsi évaluer la propagation de feux potentiels sur des chemins de câbles électriques et la puissance du feu résultante, afin d'évaluer les dommages sur des éléments importants pour la sûreté des installations nucléaires. Le modèle FLASH-CAT permet d'évaluer simplement la propagation du feu sur un ensemble de chemins de câbles électriques horizontaux. Dans le cadre du programme OCDE PRISME-2, des essais qui ont impliqué des chemins de câbles horizontaux supportés par un mur, ont mis en évidence une croissance rapide des feux et d'importants pics de puissance. Ces essais visaient à compléter des essais de feux de chemins de câbles horizontaux localisés loin de murs et de plafonds, réalisés dans le cadre du programme CHRISTIFIRE. La présente étude propose ainsi d'étudier la capacité du modèle simplifié FLASH-CAT à évaluer la puissance du feu se propageant sur des chemins de câbles horizontaux avec un mur support. Les premières évaluations des essais PRISME-2 CFSS avec le modèle FLASH-CAT ont surestimé les mesures des délais d'inflammation des chemins de câbles ainsi que les durées des feux. Ces calculs ont aussi sous-estimé de façon significative les taux de croissance du feu et les pics de puissance mesurés lors des essais. En premier lieu, ce travail révèle en effet que des paramètres d'entrée du modèle FLASH-CAT, les paramètres de propagation, doivent être actualisés quand un mur supporte les chemins de câbles. Ces paramètres sont le délai d'inflammation des chemins de câble, l'angle de propagation et la vitesse de propagation des flammes le long des chemins de câbles. Ces paramètres ont été ainsi mesurés grâce à une méthode d'analyse des vidéos des feux (AVF), développée dans cette étude, et appliqué aux essais PRISME-2 CFSS. Cette étude montre ensuite que les prédictions du modèle FLASH-CAT avec les paramètres de propagation optimisés pour des chemins de câbles supportés par un mur, sont en accord avec les essais. La méthode AVF a été aussi appliquée à des essais de feux de chemins de câbles du programme CHRISTIFIRE. Les calculs avec le modèle FLASH-CAT et les paramètres optimisés améliorent également la prédiction de l'évolution temporelle de la puissance du feu

Ignition of electrical components contained in a closed enclosure adjacent to a controlled fire source

International audienceAbout 400 fire events occurred in OECD nuclear power plants (NPPs) between 1975 and 2010 (OECD FIRE database). About 50 fire events involved electrical cabinets which are commonly arranged in rows of adjacent cabinets in NPPs. The ability of a cabinet fire to spread to adjacent cabinets is a major concern for fire safety in NPPs. How can ignition occur in the adjacent cabinets? What is the impact on ignition of the electrical component type contained in the cabinet? What are the effects on ignition of the air gap (between the cabinets) and the cabinet ventilation mode

Overview of the OECD PRISME 3 Project

International audienceFire hazard analyses and probabilistic fire safety analyses have demonstrated that fires may cause significant damages in nuclear power plants (NPPs). Fire modelling is nowadays applied by licensees or technical safety organisations to assess fire consequences in NPPs. Thereby, one important aspect is the availability of verified and validated fire models for such fire scenarios.Several members of the Organization for Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA) expressed their interest in participating in a joint international research project on the topic of fire events to be carried out under the auspices of the NEA. The PRISME (French acronym for “Fire Propagation in Elementary Multi-Room Scenarios”) Project was realized from 2006 to 2010, by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN, France) in its facilities specially designed for large-scale fire tests in confined environments. In the continuity of the PRISME project, PRISME 2 was launched in July 2011 ending in 2016. The main experimental results of these two projects have been summarized in OECD/NEA reports [1][2]. In parallel to the experimental campaigns, PRISME partners evaluated the capabilities of various fire simulation codes for modelling fire scenarios based on the PRISME results. Both PRISME 1 and PRISME 2 Projects highlighted the strong interaction between the fire dynamics and the mechanical ventilation. Indeed, the analysis of the tests greatly contributed to enhance the knowledge of under-ventilated fires including realistic and complex fires. An improvement in the validation process of different fire models was also noticed during these two experimental programs. From these experimental findings and modelling considerations, some grey zones have been highlighted and allowed to define the outlines of the PRISME 3 Project. Various recommendations have been provided for addressing some further phenomena not studied in the past Projects. These phenomena are smoke stratification and spread, fire propagation between electrical cabinets, and electrical cable tray fires in confined and ventilated conditions for new configurations. The ongoing PRISME 3 Project aims at addressing the above mentioned three phenomena and at providing answers to various issues of interest for nuclear safety. A total of eight countries have joined the PRISME 3 Project: Belgium (Bel V and Tractebel-ENGIE), Finland (Technical Research Centre VTT), France (IRSN as Operating Agent and Électricité de France – EDF), Germany (Gesellschaft für Anlagen- und Reaktorsicherheit – GRS), Japan (Nuclear Regulation Authority – NRA and Central Research Institute of Electric Power Industry – CRIEPI), Korea (Korea Institute for Nuclear Safety – KINS and Korea Atomic Energy Research Institute – KAERI), United Kingdom (Office for Nuclear Regulation, – ONR) and the United States of America (United States Nuclear Regulatory Commission – U.S. NRC).The objective of the first campaign, named S3 for Smoke Stratification and Spread, is to study new configurations of interest for smoke propagation in a mechanically ventilated multi-room facility with simple fire sources. This choice is relevant for a complete validation of fire models on smoke propagation. The first topic of interest is to combine vertical and horizontal smoke propagation coupled with a mechanical ventilation system. This experimental configuration allows highlighting multiple interaction mechanisms of propagation during the fire scenario. The second topic of interest concerns the issue of multiple fire sources, simulating for example a seismically induced fire incident and its consequences on smoke propagation. The fire scenario involves two fire sources ignited simultaneously and located in two adjacent rooms or in two rooms separated by another one. The distance between fires is a key parameter determining different combustion regimes with or without interaction. The third topic of interest is smoke propagation induced by an elevated fire source. This configuration leads to a complex situation for the fire dynamics, since it evolves in a hot and vitiated environment. For the S3 campaign, six fire tests have been defined in the multi-compartments facility of IRSN, named DIVA, which is composed of a mechanical ventilation system. For this campaign, three or four rooms, of volume 120 m3 and 170 m3, have been implemented.The second campaign, named ECFS for Electrical Cabinet Fire Spread, aims to better understand the fire spread from an open-door cabinet to other adjacent or opposite cabinets, connected via cable trays. Four tests in the IRSN DIVA facility have been defined including the two configurations of interest: the adjacent one and the opposite one. For each configuration two tests involving HFR (halogenated flame retardant) or HFFR (halogen free flame retardant) insulated cables will be conducted. Two cable trays have been positioned above the cabinets and inside a false floor to diversify the potential paths of the fire propagation. Furthermore, for the adjacent configuration, the fire propagation through the walls and an air gap potentially separating the cabinets is also considered. In addition to these confined fire tests, four additional tests have been specified in open atmosphere. These tests are needed for characterizing the fire source or the fire spread from one electrical cabinet to another one in a reference configuration. The comparison of the two configurations will highlight the effect of the confinement on the fire spread.The purpose of the third campaign, named CFP for Cable Fire Propagation, is twofold: in a first step, the effect of the compartment geometry will be studied by conducting three cable tray fires in a corridor. The fire dynamics on a long cable tray will then be compared to those obtained in previous PRISME Project for shorter cable tray configurations. In a last step, additional scenarios involving the effects of under-ventilated conditions and of the cable tray configuration on cable fires will be investigated. In addition, an assessment of cable fire models used within simple or complex fire numerical tools will be conducted for these specific configurations. The cable type and the air renewal rate of the compartment will be considered. Consequences of such fire scenarios on the facility will be investigated through time sequences of gas pressure, temperature and concentrations inside the facility and in the ventilation network. The campaign is composed of six tests in the DIVA facility and two tests under the SATURNE calorimeter of IRSN which is composed of an extraction hood in an open domain on 20,000 m3. The main advances of PRISME 3 will make it possible, in a first step, to increase the predictive ability of models on smoke propagation problems for substantially complex situations. With regard to electric fires, especially electric cable fires, PRISME projects will also provide a fairly complete database and can therefore be used for model improvement. All the contributions of the project will allow the community to position itself on the scenarios of interest to study in the years to come

Improved assessment of fire spread over horizontal cable trays supported by video fire analysis

Fire safety analyses in nuclear power plants need to assess the heat release rate (HRR) of potential cable fires. This study deals with the FLASH-CAT model which assesses the HRR of a fire spreading over horizontal ladder cable trays. As part of the OECD PRISME-2 project, fire tests which involved horizontal trays supported by a wall, highlighted fast fire growth and large HRR peak. This study investigated the ability of the FLASH-CAT model to predict the HRR for such configuration. The first assessments of the PRISME-2 tests with the FLASH-CAT model significantly delayed the ignition and under-estimated the fire growth rate and the HRR peak. A video fire analysis method was developed and contributed to propose updated input parameters, such as the ignition time and the horizontal spread rate, for cable tray configurations with a wall. In addition, modifications in the model which affect the burning cable tray area and the local fire duration are also discussed. The assessments of the PRISME-2 experiments with the modified FLASH-CAT model and the proposed input parameters are consistent with the measured HRR. In addition, the modified model also gives acceptable predictions of the HRR for numerous tests of the CHRISTIFIRE programme

Experimental investigation of the effects of a sidewall and cable arrangement on a horizontal cable tray fire in an open atmosphere

International audienceThe 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 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 in 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

EFFECTS OF CABLE TRAY CONFIGURATION ON FIRE SPREAD

International audienceFires involving electrical cables are one of the main fire hazards in Nuclear Power Plants (NPPs). The aim of this work is to study the impact of cable tray configuration on fire spread over multiple cable trays. Two real-scale cable tray fire tests were thus carried out as part of the OECD PRISME-2 Project (CORE campaign) for studying the effect of a protected cable tray (CORE-2) and slanted ladder cable trays (CORE-3) on the main fire characteristics. By considering new configurations, these tests completed the preliminary CFSS tests of the PRISME-2 project which involved five horizontal ladder cable trays. The CORE-2 test implemented the same horizontal trays set-up except that the lower tray was a protected cable tray. Compared with the five ladder cable trays set-up, the protected cable tray delayed the ignition of about 16 min and led to decrease the total mass loss (TML). Furthermore, the fire growth rates and the heat release rate (HRR) were slightly higher for the CORE-2 test. The CORE-3 test used five horizontal ladder cable trays 1 m long followed by five slanted ladder cable trays 2 m long with a 30 degree angle. This configuration shortened the ignition of about 4 min, led to similar TML and increased the fire spread over the cable trays meaningfully and the HRR peak compared with the horizontal ladder trays configuration. Finally, the other fire characteristics such as the average effective heat of combustion or the gas and soot yields were not affected by the presence of the lower protected cable tray or the ladder cable trays orientation (horizontal or slanted)

Overview of the OECD PRISME 3 Project

International audienceFire hazard analyses and probabilistic fire safety analyses have demonstrated that fires may cause significant damages in nuclear power plants (NPPs). Fire modelling is nowadays applied by licensees or technical safety organisations to assess fire consequences in NPPs. Thereby, one important aspect is the availability of verified and validated fire models for such fire scenarios.Several members of the Organization for Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA) expressed their interest in participating in a joint international research project on the topic of fire events to be carried out under the auspices of the NEA. The PRISME (French acronym for “Fire Propagation in Elementary Multi-Room Scenarios”) Project was realized from 2006 to 2010, by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN, France) in its facilities specially designed for large-scale fire tests in confined environments. In the continuity of the PRISME project, PRISME 2 was launched in July 2011 ending in 2016. The main experimental results of these two projects have been summarized in OECD/NEA reports [1][2]. In parallel to the experimental campaigns, PRISME partners evaluated the capabilities of various fire simulation codes for modelling fire scenarios based on the PRISME results. Both PRISME 1 and PRISME 2 Projects highlighted the strong interaction between the fire dynamics and the mechanical ventilation. Indeed, the analysis of the tests greatly contributed to enhance the knowledge of under-ventilated fires including realistic and complex fires. An improvement in the validation process of different fire models was also noticed during these two experimental programs. From these experimental findings and modelling considerations, some grey zones have been highlighted and allowed to define the outlines of the PRISME 3 Project. Various recommendations have been provided for addressing some further phenomena not studied in the past Projects. These phenomena are smoke stratification and spread, fire propagation between electrical cabinets, and electrical cable tray fires in confined and ventilated conditions for new configurations. The ongoing PRISME 3 Project aims at addressing the above mentioned three phenomena and at providing answers to various issues of interest for nuclear safety. A total of eight countries have joined the PRISME 3 Project: Belgium (Bel V and Tractebel-ENGIE), Finland (Technical Research Centre VTT), France (IRSN as Operating Agent and Électricité de France – EDF), Germany (Gesellschaft für Anlagen- und Reaktorsicherheit – GRS), Japan (Nuclear Regulation Authority – NRA and Central Research Institute of Electric Power Industry – CRIEPI), Korea (Korea Institute for Nuclear Safety – KINS and Korea Atomic Energy Research Institute – KAERI), United Kingdom (Office for Nuclear Regulation, – ONR) and the United States of America (United States Nuclear Regulatory Commission – U.S. NRC).The objective of the first campaign, named S3 for Smoke Stratification and Spread, is to study new configurations of interest for smoke propagation in a mechanically ventilated multi-room facility with simple fire sources. This choice is relevant for a complete validation of fire models on smoke propagation. The first topic of interest is to combine vertical and horizontal smoke propagation coupled with a mechanical ventilation system. This experimental configuration allows highlighting multiple interaction mechanisms of propagation during the fire scenario. The second topic of interest concerns the issue of multiple fire sources, simulating for example a seismically induced fire incident and its consequences on smoke propagation. The fire scenario involves two fire sources ignited simultaneously and located in two adjacent rooms or in two rooms separated by another one. The distance between fires is a key parameter determining different combustion regimes with or without interaction. The third topic of interest is smoke propagation induced by an elevated fire source. This configuration leads to a complex situation for the fire dynamics, since it evolves in a hot and vitiated environment. For the S3 campaign, six fire tests have been defined in the multi-compartments facility of IRSN, named DIVA, which is composed of a mechanical ventilation system. For this campaign, three or four rooms, of volume 120 m3 and 170 m3, have been implemented.The second campaign, named ECFS for Electrical Cabinet Fire Spread, aims to better understand the fire spread from an open-door cabinet to other adjacent or opposite cabinets, connected via cable trays. Four tests in the IRSN DIVA facility have been defined including the two configurations of interest: the adjacent one and the opposite one. For each configuration two tests involving HFR (halogenated flame retardant) or HFFR (halogen free flame retardant) insulated cables will be conducted. Two cable trays have been positioned above the cabinets and inside a false floor to diversify the potential paths of the fire propagation. Furthermore, for the adjacent configuration, the fire propagation through the walls and an air gap potentially separating the cabinets is also considered. In addition to these confined fire tests, four additional tests have been specified in open atmosphere. These tests are needed for characterizing the fire source or the fire spread from one electrical cabinet to another one in a reference configuration. The comparison of the two configurations will highlight the effect of the confinement on the fire spread.The purpose of the third campaign, named CFP for Cable Fire Propagation, is twofold: in a first step, the effect of the compartment geometry will be studied by conducting three cable tray fires in a corridor. The fire dynamics on a long cable tray will then be compared to those obtained in previous PRISME Project for shorter cable tray configurations. In a last step, additional scenarios involving the effects of under-ventilated conditions and of the cable tray configuration on cable fires will be investigated. In addition, an assessment of cable fire models used within simple or complex fire numerical tools will be conducted for these specific configurations. The cable type and the air renewal rate of the compartment will be considered. Consequences of such fire scenarios on the facility will be investigated through time sequences of gas pressure, temperature and concentrations inside the facility and in the ventilation network. The campaign is composed of six tests in the DIVA facility and two tests under the SATURNE calorimeter of IRSN which is composed of an extraction hood in an open domain on 20,000 m3. The main advances of PRISME 3 will make it possible, in a first step, to increase the predictive ability of models on smoke propagation problems for substantially complex situations. With regard to electric fires, especially electric cable fires, PRISME projects will also provide a fairly complete database and can therefore be used for model improvement. All the contributions of the project will allow the community to position itself on the scenarios of interest to study in the years to come