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Modes of Combustion

Reactor accident analyses treat the reaction of hydrogen with air in the reactor containment:

These analyses usually consider three modes of hydrogen combustion:

  • • Standing flames: Combustible gas is ignited at the point that it emerges from the reactor coolant system or other source location and burns as a jet.
  • • Deflagrations: Combustible gas burns throughout a volume along a reaction front that propagates at a velocity less than the speed of sound in the unburned gas.
  • • Detonations: Combustible gas burns throughout a volume along a reaction front behind a shock wave that propagates at a velocity greater than the speed of sound in the unburned gas.

Standing flames can develop at vent points in the reactor coolant system or in reactor buildings of boiling water reactors at vent points in the reactor containment [7, 8]. Typically, standing flames are not found to produce significant containment pressurization because the rate of heat release is slow in comparison to the natural heat removal capability of the containment or reactor building. Standing flames can impose high heat loads on adjacent structures and equipment which can have ramifications on the continued progression of a reactor accident. The effects of standing flames are very specific to the reactor design and are not pursued further here.

 
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