SAMHYCO-NET project

Project characteristics

Completion dates : 2017 to 2020
Academic partner : France CNRS-ICARE - China Shanghai University - Japan - Nagaoke University of Technology -  Norvège University of South-Eastern Norway
Research institutes : France IRSN - CEA - Spain CIEMAT - Lithuania LEI - Ukraine SSTC-NRS - South Korea KINS - Switzerland PSI - Slovenia IJS - Netherlands NRG - Germany JULICH / KIT - Canada CNSC / CNL - Japan JAEA - China SNERDI - Bulgaria INRNE - Russia SEC-NRS
Industries : France General Electric - EDF - Air Liquide - Germany Framatome

Project Background

During the late phase of a severe accident in a nuclear reactor, hydrogen (H2) is produced by the oxidation of the metal components of the damaged core by steam. These components are present either in the reactor core (fuel rod claddings and control rods) or in the corium (magma resulting from the melting of the reactor core) which, if it has penetrated the reactor vessel, interacts with the concrete raft (ICB corium-concrete interaction).

In addition to H2, this interaction leads to the massive production of carbon monoxide (CO) and other flammable gases. The accumulation of these flammable gases in the containment can lead, in the event of combustion, to pressure and temperature loads that are potentially damaging to containment structures and equipment, particularly those needed to manage a severe accident. In addition, the build-up of pressure in the containment causes the H2/CO mixture to migrate into the space between the containments of PWR 1300 and 1450 MWe and the associated buildings, leading to the formation of explosive atmospheres.

Following the Fukushima-Daiichi accident, European stress tests highlighted the existence of a risk of explosion in ventilation systems and the risk of migration of flammable gases into spaces beyond the containment, such as the reactor building ring.

It is in this context that SAMHYCO-NET was launched by IRSN, under the aegis of NUGENIA. Its aim is to gain a better understanding of the phenomena governing the combustion of mixtures containing H2/CO and its effects on safety-critical equipment. The project also aims to improve knowledge of the behaviour of catalytic recombiners under conditions representative of the late phase of a severe accident. It also aims to improve the predictive capabilities of explosion simulation tools. These advances will be used to improve severe accident management procedures, particularly in the late phase.

Lines of research

The SAMHYCO-NET project comprises 4 lines of research to achieve its objectives, all coordinated by IRSN.

Area 1: State of the art of existing experimental data and models

Coordinated by Becker Technologies with the support of IRSN, this first area aims to carry out a critical analysis of existing experimental data and numerical models on the behaviour of recombiners and the combustion of the H2/CO mixture under conditions representative of the late phase of a severe nuclear reactor accident. This state of the art will make it possible to identify the missing data, particularly with regard to reactor applications, and to specify the tests to be carried out as part of axes 2 and 3.

Area 2: Experimental and analytical study of the behaviour of catalytic recombiners in the late phase of a severe accident

Coordinated by JULICH (Germany) with the support of Becker Technologies, the aim of this line of research is to study the operational behaviour of current catalytic recombiners under the specific conditions of the late phase of severe accidents, when the corium is outside the vessel. This work focuses on the combined effects of a lack of oxygen, water vapour and carbon monoxide, as well as the negative effect of iodine on the operation of recombiners (possible poisoning of recombination sites). The calculation codes REKO-DIREKT (diffusive mass transfer approach) developed by JULICH, and SPARK (detailed chemistry on the surface of the recombiner and in the gas passing through it) developed by IRSN, will be used for theoretical modelling.

The results of this experimental programme will be used to assess the ability of existing catalytic recombiner models to take these critical conditions into account, and to propose a new recombiner model for implementation in accident analysis calculation codes.

Area 3: Experimental and analytical study of the combustion of the H2/CO/H2O mixture in the late phase of a severe accident

Coordinated by the CNRS with the support of KIT (Germany), the aim of this research area is to carry out experimental and numerical studies on the combustion of the H2/CO/H2O mixture in conditions outside the reactor vessel (after the corium-concrete interaction). The experiments carried out will help to overcome the lack of data on the propagation of flames from the combustion of the H2/CO/H2O mixture in conditions representative of the late phase of severe accidents. They will be used to improve the combustion models implemented in the calculation codes used for safety assessment.

Area 4: Improving the predictive capabilities of numerical tools for assessing the risk of explosion in the reactor building

Coordinated by IRSN with the support of CIEMAT (Spain), this area should make it possible to identify ways of improving safety procedures and severe accident management procedures on the basis of severe accident simulations carried out in the previous areas.

In addition to the experimental and analytical work, the SAMHYCO-NET project will produce reference documents on the state of the art concerning the behaviour of catalytic recombiners and combustion during the late phase of a severe accident, as well as a review of the corresponding Severe Accident Management Guidelines (SAMG).

IRSN's laboratories involved

• Laboratories : fire and explosion laboratory (LIE)
• Engineering office : B2EGR severe accident and radioactive release design and assessment office