IGNITABILITY OF HYDROGEN OXYGEN/DILUENT MIXTURES IN THE PRESENCE OF HOT SURFACES/

In the licensing process for CANDU(b) nuclear power stations it is nec essary to demonstrate tolerance to a wide range of low-probability acc idents. These include loss of moderator accidents that may lead to the formation of flammable mixtures of deuterium, oxygen, helium, and ste am in the reactor calandria vessel. Uncovered adjuster or control rods are considered as possible sources of ignition when a flammable mixtu re is present. A knowledge of the minimum hot-surface temperature requ ired for ignition is important in assessing the reactor safety These h ot surface temperatures were measured using electrically heated adjust er rod simulators in a large spherical vessel (2.3-m internal diameter ), Whereas the effects of geometry on ignition temperature were studie d in the large-scale apparatus, some of the effects, such as those pro duced by a strong radiation field were studied using a small-scale app aratus. Investigations carried out over a range of hydrogen and diluen t concentrations indicated that, although the ignition temperatures we re fairly insensitive to the hydrogen concentration, they were strongl y affected by the presence of steam. The addition of 30% steam to a dr y combustible mixture increased the minimum surface temperature requir ed for ignition by approximately 100 degrees C. Of the diluents invest igated, steam had the most effect on ignition. The effect of initial t emperature of the mixture on the ignition temperature was small, where as the effect of initial pressure was significant. The effect of subst ituting deuterium for hydrogen on ignition temperature was small. The effect of a high-intensity gamma-radiation field on the minimum hot-su rface temperature required for ignition was investigated rising a 2-dm (3) ignition vessel placed in a linear accelerator Radiation had no me asurable effect on ignition temperature, The results presented in this article will be of use in the safety analyses of other reactors or in industrial environments where a combustible mixture of hydrogen/air o r hydrogen/oxygen/diluent is present.