During the Three Mile Island accident in 1979, hydrogen was produced by the interaction of hot fuel cladding and steam and was released into the containment building , where it ignited. Although it caused only superficial damage, it led to a concern for the safety of other water cooled reactors, specifically of Sizewell 'B' which was being designed at the time.
PWR containment fan cooler
(Photo courtesy of American Air Filters Inc.)
As part of the work done in support of the Sizewell public inquiry, I examined the phenomena associated with the generation and combustion of hydrogen. I commissioned several sets of experiments in university departments to look at such things as flame speeds in still air and turbulent air conditions for different hydrogen concentrations.
I also commissioned and oversaw a set of experiments at one of British Gas' test sites to model the effects of hydrogen combustion in PWR containment ventilation systems, particularly in the fan coolers (see picture). Air is drawn through the banks of tubes shown by a large fan and then distributed around the lower parts of the building. The concern was that turbulence generated by the fan could increase the flame speed of the hydrogen and generate pressure waves. These experiments were at 2/5 full scale and, together with the associated computer modeling, demonstrated that hydrogen did not pose a significant risk to containment structures.