During a severe accident in a LWR, water may interact with hot core materials and hydrogen may be produced and released into the containment. Hydrogen may react with the oxygen of the containment atmosphere and flames, deflagrations or detonations may jeopardize the containment integrity. The current research efforts are concentrated on:
- the prevention of hydrogen combustion through pre- and post-accident inerting procedures
- the prevention and mitigation of hydrogen combustion through H2-O2 recombiners
- the mitigation of hydrogen combustion and explosion through deliberate ignition.
The objective of the project is to assess the present knowledge of hydrogen explosion problems in LWRs, the improvement of modelling techniques and the investigation of measures to reduce the risk resulting from hydrogen. Attention is focused upon the post-inerting techniques in all reactors and the pre-inerting techniques in future reactors. Recombining and deliberate ignition techniques are considered as well. Computer codes are developed for the prediction of hydrogen distribution and combustion.
University of Munich implemented the containment code RALOC, version 2/86, on its computer system and developed and tested a specific subroutine describing the injection of liquid pressurised carbon dioxide and its following evaporation and sublimitation inside the containment.
Prediction of Hydrogen distribution
Framatome started calculations of hydrogen stratification in the containment dome with the field code TRIO/VF. In order to test important options of the code, a simple calculation (only a quarter of the dome was represented) was performed to see the response of the code.
Prediction of Hydrogen combustion
University of Pisa analysed the experimental data obtained in 10 deflagration tests carried out in the glass vessel of the VIEW facility; specifically:
- experimental measurements were processed relating to pressures and temperatures which had been recorded during the tests;
- the burnt volume and the flame surface were evaluated at each instant, on the basis of the video recordings of the flame propagation taken by a video camera from two points of view which were orthogonal to each other. An analytical model has been developed to simulate vented deflagrations. The tests aim to validate the model and, vice versa, the model applied to the tests will provide an assessment of the burning velocity in vented deflagrations.
Siemens/KWU applied the 3D thermal hydraulic code COMMIX, with extensions for combustion and transport of concentrations developed, to an experiment at the Battelle containment mock up containing all possible physical effects as ignition phase, weak deflagration and jet ignition. Three dimensional calculations with a fine discretisation gave promising results with respect to the pressure transient.
An updated version has been produced for the chapter on Hydrogen Explosion Mitigation in the 1991 CEC/IAEA State of the Art Report "Hydrogen in Water Cooled Nuclear Power Reactors", (report EUR 14037). A state-of-the-art report about combustion phenomena and H2 distribution is also in preparation with the collaboration of GRS/Cologne.
As far as R&D is concerned the emphasis is both on the prediction of hydrogen distribution and combustion and on the examination of inerting procedures, namely pre- and post-accident inerting. Different inerting procedures are compared taking into account the state of the plant (containment pressure, injection temperature, chemical corrosion, etc.) and the safety characteristics (whether active or passive). Munich University is implementing the code RALOC for post-accident inerting analysis calculations of liquid pressurized CO2.
Pisa University is examining, both experimentally (upgraded VIEW facility) and analytically, the burning rates and the H2-O2 recombining mechanisms of air-H2 in connection with the techniques of deliberate ignition and passive catalytic recombination, respectively.
KfK is developing a 3D model of fast turbulent deflagration in collaboration with the Kurchatov Institute and TH Aachen: buoyancy driven natural convection is also looked at through results from the experimental facilities of HDR, Battelle Model Containment and Phebus. More generally investigations are carried out by all partners to assess and validate the modelling of hydrogen distribution and combustion effects against experimental data.
A probabilistic threat assessment analysis is carried out at NNC/Cheshire with emphasis on the influence of the H2 distribution in the containment.
KFA/Jülich is investigating prevention techniques for deflagration-to-detonation (DDT) events by computing minimum energy levels as a function of turbulence and reaction rates.
SIEMENS/Erlangen, together with FRAMATOME, are looking at H2 explosion mitigation techniques using recombiners and igniters in a multi-compartment configuration: for that purpose they are developing a field code for the modelling of the H2 stratification.
Madrid University is investigating post-accident active containment techniques by inert gas injection: they are also performing a sensitivity analysis of the MELCOR code.
Funding SchemeCSC - Cost-sharing contracts
WA16 8QZ Knutsford