Hydrogen combustion experiments in a 1/4-scale model of a nuclear power plant containment

Abstract

Hydrogen combustion experiments were carried out in a Froude-modeled 1/4-scale facility, reproducing the geometry of a nuclear power plant containment building, to evaluate the performance of a hydrogen mitigation system based on the controlled combustion concept. Hydrogen burning was initiated by a distributed ignition system using glow plug igniters. The objective of the study was to obtain data on the combustion phenomenology and on the thermal environment produced by the burning of hydrogen as might occur during a recoverable degraded core accident. The thermal environment was characterized through measurements of three quantities: gas temperatures, gas velocities, and radiant heat fluxes. Several highly-instrumented tests were performed in the test facility with the internal geometry adjusted so as to reproduce four possible plant configurations. Following a preassigned release history, hydrogen was introduced at the bottom of the test volume through spargers and vent holes located below the surface of a body of water modeling the suppression pool existing in the plants. Two hydrogen injection histories were used during these tests, simulating two different accident recovery scenarios. The dominant combustion mode observed during the tests involved diffusion flames anchored at the surface of the pool. Other types of combustion, involving lifted diffusion flames and localized burning, were observed at low-oxygen conditions and low hydrogen injection rates, respectively. Other than mild localized initial lightoff burns, deflagrations did not occur in the tests. For oxygen concentrations down to 8%, the distributed ignition system was successful at maintaining the background hydrogen concentration below 4.5–5% by volume.