Modelling of Hydrogen Mixing in a Set of Complex and Connecting Rooms in CANDU Containment Using GOTHIC

摘要

Igniters are installed throughout the containment in Ontario Hydro nuclear stations for hydrogen mitigation. On LOCA signals, these igniters are automatically activated to ensure a burn of the hydrogen-air-steam mixture as it reaches its flammability limits, thereby precluding damaging burns due to the build up of sensitive and possibly detonable mixtures. Hydrogen and air in the local atmosphere in the vicinity of the igniters must be adequately distributed to ensure that the igniters are not 'blinded' by a region of non-flammable composition while a more sensitive and potentially detonable mixture forms elsewhere. To demonstrate adequate hydrogen-air distribution in the containment, Ontario Hydro has used the GOTHIC code to set up three-dimensional models of containment locations to study flow patterns and the effects of fans on mixing. This paper presents the GOTHIC predictions of hydrogen distribution following a release of hydrogen into a small room (500 m~3) which connects to a set of rooms. The rooms are small but complexly partitioned which adds complexity to GOTHIC modelling. The analysis shows the effect of fans, hydrogen release profiles and hydrogen release locations on air flow patterns and mixing in these rooms. Results show that the containment atmosphere in question is adequately mixed and the igniters are well placed. This paper also shows that GOTHIC is well suited to the modelling of rooms with complex interior partitions.