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Conference Article: Experimental results of air ingress in heated graphite channels: A summary of American analyses of the Windscale and Chernobyl accidents

Abstract

A program was initiated at BNL, in which a series of extensive full scale air ingress experiments were performed in 10 ft. long graphite channels in the temperature range from 300 deg. C - 800 deg. C. The experiments addressed the generic question of under what conditions ''graphite burning'' would or would not occur. Several hundred measurements were made, in which temperature-time-gas composition changes along the 10 ft channels were studied as functions of the air flow rates, air composition, channel geometry, graphite reactivity, Wigner energy etc. The conditions under which CO-O₂ explosions occurred were determined experimentally. In some cases the temperature-gas composition changes with position in the graphite channels were followed for several days before individual experiments were concluded. After concluding the ''graphite burning'' studies, BNL initiated an experimental program on the consequences of high temperature fuel failure in HTGRs for the Nuclear Regulatory Commission. Following the Chernobyl accident, the Nuclear Regulatory Commission requested that the members of the BNL staff who were involved in the Windscale accident analyses and the HTGR accident evaluation program re-evaluated the safety of all reactors in the USA that contained graphite. A safety evaluation was initiated and complete which addressed, in detail, the generic (design independent) conditions under which air ingress and Wigner energy releases could lead to self-sustained graphite fires in nuclear reactors. The two programs, produced comprehensive experimental and analytical investigations of the conditions under which air ingress and Wigner releases could lead to ''graphite burning'' in nuclear reactors.

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Reference:

Technical committee meeting on response of fuel, fuel elements and gas cooled reactor cores under accidental air or water ingress conditions. Beijing (China). 25-27 Oct 1993

International Atomic Energy Agency, Vienna (Austria)

IAEA-TECDOC--784, pp:50-54