Last update on December 2018
SAMHYCO-NET is an international project that IRSN coordinates within the support of the European platform NUGENIA. Launched in October 2017 for three years, this project aims to improve the knowledge concerning on one hand the risk of explosion combustible gases produced during a late-phase severe accident, on the other hand the performance of existing means to prevent this risk and to limit the related consequences. The outcomes of SAMHYCO-NET will enable improving the procedures for managing late-phase severe accidents.
Context and objectives
During a severe accident in a nuclear power plant, hydrogen (H2) can be produced from exothermal oxidation of metallic components from the core damaged by water steam. These components come either from the reactor core (fuel cladding or fuel assembly canisters) or from the corium (magma coming from the reactor meltdown). If the corium breaks through the vessel, it is in interaction with the concrete apron (molten core concrete interaction, MCCI). During MCCI, a large amount of carbon monoxide (CO) is produced in the reactor pit, in addition to H2 and other gases. As a consequence, local concentrations of H2 and CO can exceed the flammability limit of the mixture and induce strong dynamic pressure loads which may threaten the containment structures and technical equipment, including safety important systems (SISs). Along the accident, the containment over-pressurization may promote the H2/CO migration from the primary containment to the interspace annular between double-walled concrete enclosure of 1300 MWe and 1450 MWe PWR and to connected buildings, where formation of flammable atmospheres may also result in gas explosions.
After the Fukushima-Daichi accident, the European stress tests report highlights the need to consider a possible explosion hazard inside the venting system as well as the potential flammable mixture migration into spaces beyond the primary containment, e.g. the annulus of the reactor building.
In this context, IRSN launched SAMHYCO-NET, under the auspices of
NUGENIA. This project aims to better understand phenomena ruling over H2/CO combustion and its effects on safety important systems. It also aims to improve the knowledge on passive autocatalytic recombiners (PARs) behavior under representative ex-vessel conditions. Eventually, it aims to improve the predictability of the numerical tools used to simulate explosions. These progresses will be used to improve the procedures for managing late-phase severe accidents.
To address these issues, SAMHYCO-NET consists of four research areas coordinated by IRSN.
Area 1: State of the art of existing experiments data and modeling
Coordinated by Becker Technologies with the support of IRSN, this area concerns the review and the critical assessment of the existing experiments and modeling regarding recombiner behavior and H2/CO combustion in representive conditions of a late phase of a severe accident on LWR. The review and the critical assessment will be made based on the available data as the OECD/CCVM report. This WP will deal also with the review of the existing SAMG regarding late phase of SA on LWR. The outcomes of WP1 will used to define the missing initial and boundary conditions relevant for SA late phase.
Area 2: Experimental and analytical investigations of PARs behavior under ex-vessel conditions
Coordinated by JULICH (Germany) with the support of Becker Technologies, this area aims to investigate the operational behavior of PARs under ex-vessel conditions including the combined effect of oxygen starvation, steam, and carbon monoxide. The iodine poisoning effect will also addressed (possible poisoning of recombination sites). The complementary computer codes REKO-DIREKT (diffusive mass transfer approach), developed by JULICH, and SPARK (surface and gas phase combustion chemistry) developed by IRSN will be used for theoretical modelling.
The results of the experimental program will be used to assess the ability of the existing PAR models to address these challenging conditions and to propose new PAR model to be implemented in the accident analysis codes.
Area 3: Experimental and analytical investigations of H2/CO/H2O under ex-vessel conditions
Coordinated by CNRS/ICARE with the support of KIT (Germany), this area aims to perform experimental and numerical studies of H2/CO/H2O combustion under representative ex-vessel conditions. The experiments thus carried out will fill the lack of data on H2/CO/H2O flame propagation under representative ex-vessel conditions. They will be used to enhance the combustion modeling and extend their validation domain.
Area 4: Improving the predictability of the numerical tools used for explosion hazard evaluation inside the reactor containment
Coordinated by IRSN with the support of CIEMAT (Spain), this area aims to identify possibilities to enhance safety procedures and severe accident management guidelines based on Severe accidents simulation.
In addition to the experiments and analytical work, the project aims to provide reference documents on the status of experimental and analytical activities related to PAR behaviour and combustion in late phase of a severe accident and a review of the corresponding SAMGs.