Containment thermal-hydraulics of current and future LWRs for severe accident management



The presence of a stratification in a NPP containment is a source of concern, as pockets of hydrogen in high concentration could lead to a deflagration or detonation risk, which might challenge several equipment necessary for safety functions and even the containment structural integrity. The objectives of the project are two folds: one is to establish whether in a test sequence representative of a severe accident in a LWR, well chosen from existing plant calculations, a hydrogen (helium) stratification can be established during part of the transient starting from the initiation of the loss of coolant accident (LOCA) blowdown until the end of bulk hydrogen release from the reactor vessel into the containment, and the second is how this stratification can be broken down by the operation of Severe Accident Management systems (SAMs); sprays, coolers and Passive Auto-catalytic Recombiners (PARs). Experiments will be performed at “small scale” TOSQAN (IRSN, Saclay), "medium scale" in the MISTRA (CEA, Saclay) and PANDA (PSI, Villigen) facilities and at "nearly prototypical scale" in the KMS (NITI, St Petersburg). Any possible core concrete interaction and radiolysis of sump water generate additional hydrogen in the containment. However, this source of hydrogen is believed not cause any preferential accumulation of hydrogen in the containment atmosphere but may cause a gradual increase in the bulk hydrogen concentration. The steam and non-condensable gas to be released from the core concrete interaction and steam to be generated from the boiling sump will not cause any generation of high momentum jet. Therefore, the scope of the ERCOSAM project will not cover the post in-vessel release phase of a severe accident.

Tests without mitigation systems (spray, containment cooler or heat source simulating the behaviour of a hydrogen recombiner) and with those systems active will be performed, to assess their efficiency in breaking up the stratification and promoting homogenization of the atmosphere.

Although to be coupled at the technical and administrative levels, the research will be conducted by two consortiums in two parallel running projects; ERCOSAM, which is to be partially funded by Euratom and SAMARA which is to be funded by ROSATOM. One consortium is composed of Paul Scherrer Institut (PSI) (Switzerland), Institute for Radiological Protection and Nuclear Safety (IRSN) and Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA) (France), Karlsruhe Institute of Technology (KIT), former Forschungszentrum Karlsruhe GmbH (FzK) (Germany), Nuclear Research & Consultancy Group v.o.f. (NRG) (The Netherlands) from countries in the West Europe and Atomic Energy Canada Limited (AECL) (Canada) and the second by the Russian organizations: Nuclear Safety Institute of the Russian Academy of Sciences (IBRAE RAN) and State Research Center of Russian Federation – Institute for Physics and Power Engineering (SSC RF-IPPE). These two strongly interlinked and coordinated research projects, ERCOSAM and SAMARA, will foster cooperation and provide means to reach a common safety goal.

Both individual projects will be technically coupled under a project name ERCOSAM-SAMARA and in short ‘ERCO-SAMA’.

Participant no.

Participant organisation full and short names


1. (coordinator)

Paul Scherrer Institut, PSI



Institute for Radiological Protection and Nuclear Safety, IRSN



Commissariat à l’Energie Atomique et aux Energies Alternatives, CEA



Karlsruhe Institute of Technology, KIT



Nuclear Research & Consultancy Group v.o.f., NRG

The Netherlands


Atomic Energy Canada Limited, AECL



Nuclear Safety Institute of the Russian Academy of Sciences , IBRAE RAN

The Russian Federation


State Research Center of Russian Federation – Institute for Physics and Power Engineering, SSC RF-IPPE

The Russian Federation


New comers in 2011


Juelich Research Center



Afrikantov OKBM

The Russian Federation


This research project as a whole will establish integrated research and the aim is to reduce the remaining uncertainties in the area of containment thermal-hydraulics regarding current and future LWRs for severe accident management in European countries and Russia. The integrated research will be devoted to the creation of an experimental database on the physical phenomena occurring in the containment of light water reactors during postulated accident sequences involving core damage and will demonstrate the maturity of the main computer programs developed for containment thermal-hydraulic analysis.

The proposed project offers the creation of high quality database needed for investigating:

Effect of Complexity of the Geometry: Effect of a) different size of test vessels with one or more inner compartments, b) different interconnecting geometry between compartments, c) different injection locations, and d) different location of Spray nozzles, coolers and PAR models, and e) differences in the type of coolers on the steam and non-condensable gases distribution in the containment compartments;.

Complex Thermal-Hydraulic Phenomena: a) bulk and wall condensation, b) natural and forced convective flows due to the low and high momentum vertical jets, c) convective flows generated by spray droplets, d) buoyancy driven mixing of light gas, and e) inter-compartmental gas transport.

The proposed project will serve:

Generation of High Quality Database Prototypical to Accident Evolution: The relative importance of individual phenomena on the natural evolution of the steam and noncondensable gas distribution during idealized four phases of an accident transient: a) the blowdown phase of a LOCA when only steam will be injected into air filled containment; b) the injection of two-components mixture (helium and steam) into existing two component (air-steam) atmosphere during the core degrading phase of the severe accident; c) redistribution of hydrogen by buoyancy driven mixing of accumulated hydrogen (if occurs) until the time when severe accident management (SAM) devices start operating, and d) the last phase during which convective flows created by the SAM devices (spray, cooler and PAR[1] operation) interact with hydrogen.

Demonstration of the Effectiveness of Mitigation Systems: Effects of convective flows created by the active and passive mitigation systems, such as cooler, spray system and recombiners on promoting destabilization of hydrogen pockets; interactions of such hydrogen pockets with two convective flows created by simultaneous operation of several similar or different mitigation systems such as two recombiner units. Determination of time durations for the optimal operation of sprays and coolers during which these systems might be promoting the destabilization, beyond which adverse effects become more important due to the efficient steam condensation and increase in the relative hydrogen concentration.

Demonstration of Further Possibilities for Severe Accident Management (SAM) Measures for Mitigating Hydrogen Risk: PARs, igniters, inertization and containment venting are the established measures generally in use in a large number of current LWRs. Use of PARs as the main SAM is generally foreseen in the advanced reactors under construction. Many large dry containment designs are equipped with containment sprays. Mainly all the containment designs are equipped with fan coolers. The use of sprays and coolers (without the fan operation) could potentially expand the SAM possibilities using the existing hardware, however, the effectiveness and operational limits should be known. The latter constitutes the two thirds of the proposed area of investigations.

Demonstration of Predictive Capability of State of Art Analytical Tools: Lumped Parameter (LP) codes, in-house and commercial Computational Fluid Dynamic (CFD) codes of the organizations in EU, Switzerland and Canada and the Russian Federation will be used for the pre- and post-test calculations and scenario analyses with the aim of validating the containment codes as reliable predictive tools, able to be applied to reactor cases. A synthesis report to be produced will integrate the outcome of test results from the facilities as well as the code analysis and point out to strengths and deficiencies in the predictive capabilities of the tools.

Generation of best practice: The proposed integrated research program will facilitate a common shared platform to develop best practice at the European level (scaling parameters, test procedure, documentation, instrumentation accuracy, test repeatability, etc.) for performing experiments.

Optimized use of International resources: The proposed project further offers fostering optimized use of the resource in Europe, Canada and in the Russian Federation in this important safety area.


[1] Since the tests will use helium as the hydrogen simulant, the ‘Recombiner’ unit will be a simulator of a real recombiner by creating a plume at specified temperature and flow rate.