Lifetime extension of French 900 MWe NPPs: French TSO main conclusions regarding long term sump performance during a severe accident

International audienceIn the framework of the lifetime extension of the French 900 MWe NPPs beyond 40 operating years, EDF has included, in case of severe accident, a strategy to remove the decay heat from the containment without opening the emergency containment filtered venting system. The new dedicated circuit uses an injection line with a heat exchanger connected to the cold leg of the primary coolant circuit and another feeding the sump of the reactor building and a pump qualified to extreme external hazards conditions and to severe accident situations. After the drainage of the RWST (Refueling Water Storage Tank), water is taken from the containment sump in the lower part of the nuclear reactor building using one of the filtering system implemented at the bottom of the containment. Consequently this filtering system was previously used during the LOCA phase, before reaching the severe accident phase. A cooling mobile device (ultimate heat sink) is lined on the heat exchanger by the EDF rescue team “FARN” (Nuclear Rapid Response Force). One of the major issues, common to the LOCA issue, is the clogging of the filtering system due to physical and chemical conditions which can lead to an inadequate net positive suction head (NPSH) margin for the pump during the severe accident and can affect the mechanical integrity of the strainers. Furthermore, despite the filtering system, a part of the debris bypassing the strainers is transported through the dedicated circuit: a second major issue is to ensure that these debris do not damage the pump, degrade the heat exchanger performance or clog other equipment of the circuit like valves and diaphragms.Compared to the debris released in the sump in case of a LOCA, additional debris created during a severe accident come from the core degradation, the erosion of the concrete basemat by the corium and paints damaged in the containment due to high irradiation process.EDF presented its safety demonstration based on studies and experimental program on strainer clogging. IRSN conducted the safety review of EDF safety case and performed simultaneously one severe accident test on the Viktoria loop in Slovakia. The paper will present the French background and IRSN conclusions (dated the end of March 2019) on sumps performance issue in case of severe accident for the 4th periodic safety review of 900MWe NPPs. Some open issues will be discussed

Lifetime extension of French 900 MWe NPPs: French TSO main conclusions regarding long term sump performance during a severe accident

International audienceIn the framework of the lifetime extension of the French 900 MWe NPPs beyond 40 operating years, EDF has included, in case of severe accident, a strategy to remove the decay heat from the containment without opening the emergency containment filtered venting system. The new dedicated circuit uses an injection line with a heat exchanger connected to the cold leg of the primary coolant circuit and another feeding the sump of the reactor building and a pump qualified to extreme external hazards conditions and to severe accident situations. After the drainage of the RWST (Refueling Water Storage Tank), water is taken from the containment sump in the lower part of the nuclear reactor building using one of the filtering system implemented at the bottom of the containment. Consequently this filtering system was previously used during the LOCA phase, before reaching the severe accident phase. A cooling mobile device (ultimate heat sink) is lined on the heat exchanger by the EDF rescue team “FARN” (Nuclear Rapid Response Force). One of the major issues, common to the LOCA issue, is the clogging of the filtering system due to physical and chemical conditions which can lead to an inadequate net positive suction head (NPSH) margin for the pump during the severe accident and can affect the mechanical integrity of the strainers. Furthermore, despite the filtering system, a part of the debris bypassing the strainers is transported through the dedicated circuit: a second major issue is to ensure that these debris do not damage the pump, degrade the heat exchanger performance or clog other equipment of the circuit like valves and diaphragms.Compared to the debris released in the sump in case of a LOCA, additional debris created during a severe accident come from the core degradation, the erosion of the concrete basemat by the corium and paints damaged in the containment due to high irradiation process.EDF presented its safety demonstration based on studies and experimental program on strainer clogging. IRSN conducted the safety review of EDF safety case and performed simultaneously one severe accident test on the Viktoria loop in Slovakia. The paper will present the French background and IRSN conclusions (dated the end of March 2019) on sumps performance issue in case of severe accident for the 4th periodic safety review of 900MWe NPPs. Some open issues will be discussed

Screening calculations on the vessel lower head behaviour due to an in-vessel steam explosion

International audienceThe mechanical consequences of a steam explosion on a PWR lower plenum vessel are estimated through a parametric study regarding the corium location, the kinetics to transfer the corium energy to the water and the water constitutive law

TSO Perspectives to Review a Reactor Concept based on In-Vessel melt Retention (IVR) Strategy for Severe Accident Management

International audienceIn-Vessel melt Retention (IVR) is a Severe Accident (SA) mitigation measure applied in some Pressurized Water Reactors (PWRs) in order to cool down molten fuel (corium) inside the Reactor Pressure Vessel (RPV) by flooding the reactor cavity and cooling the RPV external surface with water. The safety demonstration provided to a national safety authority to support a reactor concept crediting the IVR strategy to enhance safety of an existing plant or to license a new generation design can be based on both deterministic and Probabilistic Risk Assessment (PRA). Experimental data can be used to support analyses or to validate models implemented in computer codes. This paper provides Technical Safety Organisations (TSOs) perspectives to review IVR as SA mitigation measure applied in NPP. The paper is structured as it is advised in the European Technical Safety Organisations Network (ETSON) Technical Safety Assessment Guide ETSON/2013-003

Les accidents de fusion du cœur des réacteurs nucléaires de puissance: État des connaissances

Ouvrage sous copyright IRSNInternational audienceFor over thirty years, IPSN and subsequently IRSN has played a major international role in the field of nuclear power reactor core melt accidents through the undertaking of important experimental programmes (the most significant being the Phébus-FP programme), the development of validated simulation tools (the ASTEC code that is today the leading European tool for modelling severe accidents), and the coordination of the SARNET (Severe Accident Research NETwork) international network of excellence. These accidents are described as «severe accidents» because they can lead to radioactive releases outside the plant concerned, with serious consequences for the general public and for the environment.This book compiles the sum of the knowledge acquired on this subject and summarises the lessons that have been learnt from severe accidents around the world for the prevention and reduction of the consequences of such accidents, without addressing those from the Fukushima accident, where knowledge of events is still evolving.The knowledge accumulated by the Institute on these subjects enabled it to play an active role in informing public authorities, the media and the public when this accident occurred, and continues to do so to this day.Depuis plus de trente ans, l'IPSN puis l'IRSN joue un rôle majeur au plan mondial dans le domaine des accidents de fusion de cœur de réacteurs nucléaires de puissance par la réalisation de programmes expérimentaux importants (le plus marquant étant le programme Phébus-PF), le développement d'outils de simulation validés (le logiciel ASTEC qui est aujourd'hui le logiciel de référence européen) et par la coordination du réseau d'excellence international SARNET (Severe Accident Research Network). Ces accidents sont qualifiés "d'accidents graves" car ils peuvent conduire à des rejets radioactifs en dehors de l'installation accidentée avec des conséquences graves pour les populations et l'environnement.Ce livre compile la somme des connaissances acquises sur ce sujet et tire également les enseignements des accidents graves survenus dans le monde pour la prévention et la réduction des conséquences de tels accidents, sans aborder ceux encore trop partiels, de l'accident de Fukushima.Les connaissances accumulées par l'Institut sur ces sujets lui ont permis de jouer un rôle actif dans l'information des pouvoirs publics, des médias et du public lors de cet accident

Les accidents de fusion du cœur des réacteurs nucléaires de puissance: État des connaissances

Ouvrage sous copyright IRSNInternational audienceFor over thirty years, IPSN and subsequently IRSN has played a major international role in the field of nuclear power reactor core melt accidents through the undertaking of important experimental programmes (the most significant being the Phébus-FP programme), the development of validated simulation tools (the ASTEC code that is today the leading European tool for modelling severe accidents), and the coordination of the SARNET (Severe Accident Research NETwork) international network of excellence. These accidents are described as «severe accidents» because they can lead to radioactive releases outside the plant concerned, with serious consequences for the general public and for the environment.This book compiles the sum of the knowledge acquired on this subject and summarises the lessons that have been learnt from severe accidents around the world for the prevention and reduction of the consequences of such accidents, without addressing those from the Fukushima accident, where knowledge of events is still evolving.The knowledge accumulated by the Institute on these subjects enabled it to play an active role in informing public authorities, the media and the public when this accident occurred, and continues to do so to this day.Depuis plus de trente ans, l'IPSN puis l'IRSN joue un rôle majeur au plan mondial dans le domaine des accidents de fusion de cœur de réacteurs nucléaires de puissance par la réalisation de programmes expérimentaux importants (le plus marquant étant le programme Phébus-PF), le développement d'outils de simulation validés (le logiciel ASTEC qui est aujourd'hui le logiciel de référence européen) et par la coordination du réseau d'excellence international SARNET (Severe Accident Research Network). Ces accidents sont qualifiés "d'accidents graves" car ils peuvent conduire à des rejets radioactifs en dehors de l'installation accidentée avec des conséquences graves pour les populations et l'environnement.Ce livre compile la somme des connaissances acquises sur ce sujet et tire également les enseignements des accidents graves survenus dans le monde pour la prévention et la réduction des conséquences de tels accidents, sans aborder ceux encore trop partiels, de l'accident de Fukushima.Les connaissances accumulées par l'Institut sur ces sujets lui ont permis de jouer un rôle actif dans l'information des pouvoirs publics, des médias et du public lors de cet accident