Deliberate Ignition of Hydrogen-Air-Steam Mixtures in Condensing Steam Environments (NUREG/CR-6530, SAND94-1676)

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Publication Information

Manuscript Completed: April 1997
Date Published: May 1997

Prepared by:
T.K. Blanchat
Sandia National Laboratories
P.O. Box 5800
Albuquerque, New Mexico 87185-1139
Operated by Sandia Corporation

D.W Stamps
University of Evansville
1800 Lincoln Avenue
Evansville, Indian 47722

A. Malliakos, NRC Project Manager

Prepared for:
Division of Systems Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code L2443

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Abstract

Large scale experiments were performed at the Surtsey Test Facility for the Nuclear Regulatory Commission to determine the effectiveness of thermal glow plug igniters to burn hydrogen in a condensing steam environment due to the presence of water sprays. The experiments were designed to determine if a detonation or an accelerated flame could occur in a hydrogen-air-steam mixture which was initially nonflammable due to steam dilution but was subsequently rendered flammable by rapid condensation of steam due to water sprays. Eleven Hydrogen Igniter Tests were conducted in the Surtsey test vessel. The Surtsey vessel was instrumented with pressure transducers, thermocouple rakes, gas grab sample bottles, hydrogen microsensors, and cameras. The Surtsey vessel contained two prototypic engineered systems: 1) a deliberate hydrogen ignition system and 2) a water spray system. The experiments were conducted under conditions scaled to be nearly prototypic of those expected in Advanced Light Water Reactors (such as the Combustion Engineering (CE) System 80+), with prototypic spray drop diameter, spray mass flux, steam condensation rates, hydrogen injection flow rates, and using the actual proposed plant igniters. The lack of any significant pressure increase during the majority of the burn and condensation events, signified that localized, benign hydrogen deflagration(s) occurred with no significant pressure load on the Surtsey containment vessel. Igniter location did not appear to be a factor in the open geometry. Initially stratified tests with a stoichiometric mixture in the top showed that the water spray effectively mixes the initially stratified atmosphere prior to the deflagration event. All of the tests demonstrated that thermal glow plugs ignite hydrogen-air-steam mixtures under conditions with water sprays near the flammability limits previously determined for hydrogen-air-steam mixtures under quiescent conditions. This report describes these experiments, gives the experimental results, and provides interpretation of the results.