Hydrogen distribution and combustion

Hydrogen generated during accident conditions may pose a serious threat to water-cooled reactors. Once released into the containment atmosphere, hydrogen can form a combustible or explosive mixture with air. Ignition of this flammable mixture will initiate a combustion process that may damage relevant safety systems and can even jeopardise the integrity of the containment wall. In the worst case scenario, the safety function of the containment can be lost. The control of the hydrogen risk is therefore a key safety issue for nuclear power plants.

The hydrogen risk assessment methodology employed by NRG is based on a combination of two approaches. A system code still acts as the main workhorse for analysing large numbers of accident scenarios, while a CFD-based model, with high 3-dimensional resolution, is used for more detailed analyses of a selection of critical scenarios. For the CFD analyses, NRG uses a commercial CFD code complemented by specially developed user-defined sub-models required for steam condensation/evaporation, multi-component diffusion, hydrogen recombiners, spray systems and combustion. The developed methodology provides all the information to design, review, update, and/or optimise a hydrogen mitigation and monitoring system.

NRG has performed hydrogen distribution and hydrogen deflagration analyses for the Dutch Borssele nuclear power plant. These have been accepted by the Dutch regulatory body KFD.