Review of current Severe Accident Management (SAM) approaches for Nuclear Power Plants in Europe

The Fukushima accidents highlighted that both the in-depth understanding of such sequences and the development or improvement of adequate Severe Accident Management (SAM) measures are essential in order to further increase the safety of the nuclear power plants operated in Europe. To support this effort, the CESAM (Code for European Severe Accident Management) R&D project, coordinated by GRS, started in April 2013 for 4 years in the 7th EC Framework Programme of research and development of the European Commission. It gathers 18 partners from 12 countries: IRSN, AREVA NP SAS and EDF (France), GRS, KIT, USTUTT and RUB (Germany), CIEMAT (Spain), ENEA (Italy), VUJE and IVS (Slovakia), LEI (Lithuania), NUBIKI (Hungary), INRNE (Bulgaria), JSI (Slovenia), VTT (Finland), PSI (Switzerland), BARC (India) plus the European Commission Joint Research Center (JRC). The CESAM project focuses on the improvement of the ASTEC (Accident Source Term Evaluation Code) computer code. ASTEC,, jointly developed by IRSN and GRS, is considered as the European reference code since it capitalizes knowledge from the European R&D on the domain. The project aims at its enhancement and extension for use in severe accident management (SAM) analysis of the nuclear power plants (NPP) of Generation II-III presently under operation or foreseen in near future in Europe, spent fuel pools included. In the frame of the CESAM project one of the tasks consisted in the preparation of a report providing an overview of the Severe Accident Management (SAM) approaches in European Nuclear Power Plants to serve as a basis for further ASTEC improvements. This report draws on the experience in several countries from introducing SAMGs and on substantial information that has become available within the EU “stress test”. To disseminate this information to a broader audience, the initial CESAM report has been revised to include only public available information. This work has been done with the agreement and in collaboration with all the CESAM project partners. The result of this work is presented here.JRC.F.5-Nuclear Reactor Safety Assessmen

Overview and outcomes of the OECD/NEA benchmark study of the accident at the Fukushima Daiichi NPS (BSAF), phase 2 – Results of severe accident analyses for unit 2

This is the second paper in a series of 3 in which results of severe accident analyses for Unit 2 of Fukushima Daiichi are presented, gained in phase 2 of the OECD/NEA project “Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF)”. Nine organizations of six countries (CNL Canada; CRIEPI, IAE, JAEA and NRA Japan; IRSN France; KAERI Korea; NRC/DOE/SNL U.S. and VTT Finland) submitted results of their calculated severe accident scenarios for Unit 2 of Fukushima Daiichi using different severe accident codes (ASTEC, MAAP, MELCOR, SAMPSON, THALES-KICHE). The present paper describes the findings of the comparison of the participants’ results for Unit 2 against each other and against plant data, the evaluation of the accident progression and the final status inside the reactors. Special focus is on reactor pressure vessel status, melt release and fission product behavior and release. Unit 2 specific aspects will be highlighted and points of consensus as well as remaining uncertainties and data needs will be summarized

HYDROGEN MANAGEMENT STRATEGIES AND ANALYSIS CODES IMPLEMENTED BY THE OECD/NEA MEMBER COUNTRIES

In the follow-up to the Fukushima accident, the OECD/NEA CSNI initiated an activity within its member countries to review and assess their hydrogen management strategies under severe accident conditions and the associated computer codes used for the hydrogen safety analysis. A CSNI report, titled Hydrogen Management and Related Computer Codes, was thereafter published by OECD/NEA in 2014 June, consisting of information contributed by 15 OECD/NEA member countries. This paper summarizes the major findings obtained in the activity. The state of knowledge on hydrogen generation, distribution, combustion and mitigation is presented. The corresponding computer codes that are used by the member countries for hydrogen safety analysis are discussed, including code capabilities and validation status assessed against the hydrogen behavior associated with generation, distribution, combustion and mitigation. The hydrogen management strategies are presented based on the literature findings. The status of hydrogen management systems implemented by the member countries are discussed, including national requirements, mitigation measures and their implementation status, and considerations on the interaction of engineering safety systems with hydrogen behavior during severe accidents. The CSNI report has provided a basis for assessing severe accident management strategies and identifying gaps in code capabilities and validations, and providing insights for model enhancement and application. It is expected to be a useful handbook for nuclear safety authorities, research institutions, and utilities.JRC.F.5-Nuclear Reactor Safety Assessmen

CSNI Post-Fukushima Activity on Hydrogen - Part II: Computer Codes and Validations

This paper provides an overview of the status report on Hydrogen Management and Related Computer Codes published by CSNI in 2014 June with a focus on part II of the report on computer codes. An assessment of the capabilities and validation status of eleven computer codes used by the member countries for hydrogen analysis was assessed against a list of phenomena defined for hydrogen generation, distribution, combustion and mitigation. The general approaches employed by these codes to model hydrogen behavior and the code performance in recent international benchmarks are discussed. The purpose of this paper is to identify gaps in model capabilities and validations, and to provide insights for model enhancement and application.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes

CSNI Post-Fukushima Activity on Hydrogen - Part I: Hydrogen Management

This paper provides an overview of the status report on Hydrogen Management and Related Computer Codes published by CSNI in 2014 June. It focuses on part I of the status report on hydrogen management, covering the state of knowledge on hydrogen generation, distribution, combustion and mitigation, hydrogen management strategies and measures implemented in various nuclear power plants under severe accident conditions (e.g., national requirements, mitigation systems and their implementation status, management strategies), and the post-Fukushima actions undertaken by the member countries. The status report is expected to be a useful handbook for nuclear safety authorities, research institutions, and utilities.JRC.G.I.4 - Nuclear Reactor Safety and Emergency Preparednes

Simulation of multiphysics in a NPP containment using combined codes with different spatial resolution

In this paper the possibilities of multiphysics simulations related to nuclear reactor safety by coupling models respectively codes of different spatial resolution are discussed. One type of models is realized recently in the so called lumped parameter (LP) code COCOSYS (the Containment Code System) [1]. The other type of models are based on 3D Navier-Stokes equations and 3D heat conduction equations. A special realization of such models for containment applications is done in the recently developed code CoPool [2]. The aim of this work is to increase the accuracy of containment simulations by interaction of both types of models