U.S. NRC Blog

Transparent, Participate, and Collaborate

Tag Archives: Browns Ferry

Browns Ferry: A New Milestone in Nuclear Plant Fire Protection

Barry Miller
Senior Project Manager, Fire Protection Branch

The NRC recently marked a milestone with the transition of the Browns Ferry nuclear power plant to the National Fire Protection Association’s Standard 805 (NFPA 805). The license amendment, issued October 28, is significant because it marks 23 reactors at 15 plants to have completed the transition since 2010. It is symbolically important because a fire at Browns Ferry in March of 1975 prompted the NRC and the industry to focus on fire safety at nuclear power plants.

Fire Protection infographic_r13The Browns Ferry fire started when a worker used a candle to test airflow around a temporary penetration seal in the cable spreading room. The flame ignited the temporary seal material, and the fire spread to the reactor building where it burned many of the cables in systems required to safely shut down the plant.

Although plant operators were able to shut the plant down safely, the event led the NRC to promulgate prescriptive fire safety requirements (10 CFR Part 50, Appendix R). For example, plants were to ensure there was at least 20 feet of separation between trains of redundant safety systems. However, this requirement was impractical for some plants that had already been built, so in many cases licensees had to find an alternative means of achieving an equivalent level of safety.

“The fire at Browns Ferry in 1975 was a turning point for the nuclear industry,” said Bill Dean, director of the Office of Nuclear Reactor Regulation. “It put a spotlight on the risk fires can pose to nuclear safety. Many safety improvements have been made industry-wide since that time, but the adoption of NFPA 805 represents perhaps the most significant undertaking in fire safety since the institution of Appendix R. This transition means Browns Ferry has performed a full re-analysis of the fire risk at its three reactors and identified the most efficient and effective means to protect its most fire-sensitive areas.”

The NFPA 805 is a performance-based means of using advanced fire analysis tools to assess the risk of fire at various areas of a nuclear power plant. That way, a plant’s fire protection scheme can be customized to focus on the most risk-significant areas and to protect the reactor’s safety systems.

Using the NFPA 805 standard is optional. Newer plants constructed after 1975 were typically built to the prescriptive requirements. So they may opt to remain under those requirements, contained in 10 CFR 50.48 and still be in compliance with the agency’s fire protection regulations. Although NFPA 805 offers certain advantages from a risk-informed perspective, both methods provide reasonable assurance that a plant would be able to cope with a serious fire.

The following plants have now completed the transition to the NFPA 805 fire protection standard: Shearon Harris; Oconee 1, 2 & 3; D.C. Cook 1&2; Duane Arnold; Callaway; Fort Calhoun; V.C. Summer; Cooper; Nine Mile Point 1; Turkey Point 3 & 4; Farley 1 & 2; Brunswick 1 & 2; Palisades; Arkansas Nuclear One Unit 2; and Browns Ferry 1, 2 & 3.

Before the Browns Ferry Fire: Antiquated Notions That Electricity and Water Didn’t Mix

Tom Wellock
NRC Historian
 
Browns Ferry Fire: Historial Photo

Browns Ferry Fire: Historical Photo

Few events altered nuclear power regulation as much as the Browns Ferry Unit 1 fire. In March 1975, thousands of electrical cables burned for about seven and a half hours, disabling all of Unit 1’s and many of Unit 2’s emergency core cooling systems. Only creative action by plant operators prevented reactor damage, and only a resort to water hoses rather than portable CO2 fire extinguishers quenched the flames.

The NRC was just two months old when the fire started, and it enacted sweeping reforms to enhance reactor safety from fires, including fire detection, prevention and suppression.

Browns Ferry was so momentous that any discussion of fire history before it often receives little attention and is mistakenly dismissed in a few sentences: The NRC’s predecessor, the Atomic Energy Commission, didn’t consider fire a nuclear safety issue. It erred in deferring to non-nuclear standards set by property insurance companies and engineering associations. Such deference was inadequate because insurance standards were designed to limit property damage rather than prevent a reactor accident.

In fact, the fire can’t be so easily blamed on AEC inattention. The agency did believe fire was a reactor safety issue, and it insisted on special fire protection designs that proved inadequate at Browns Ferry. Its key error, then, wasn’t in deferring to non-nuclear fire insurance experts; it sometimes didn’t defer enough. Most egregiously, nuclear regulators rejected expert recommendations on fire suppression systems believing that nuclear safety considerations demanded alternative designs.

By the late 1960s, fire protection experts favored water as a fire suppressant. Tests and experience showed water was the most desirable fire suppressant even in areas with electrical equipment because of its ability to rapidly smother and cool a growing fire. Businesses used water suppression in diverse applications such as computer factories and electric cable rooms in steel mills. Even AEC weapons plants added water to supplement their CO2-based systems. Fire insurance associations recommended water-based fire suppression systems for civilian nuclear power plants.

AEC regulators and the industry disagreed. Having limited nuclear-specific data on fires, they operated from the perspective that electricity and water didn’t mix. They feared water would cause short circuits and disable backup reactor safety systems. With AEC encouragement, new plants commonly installed fixed CO2 fire extinguishing systems in electrical areas, as was done in Browns Ferry’s damaged cable spreading room. In addition, the cable spreading room was not equipped with fire hoses and water supply piping called standpipes.

firemanDavid Notley, the NRC’s first fire safety expert, noted the ironic result of the AEC’s ignorance on fire suppression. Believing that nuclear power was a special exception to standard industrial practice, regulators dismissed non-nuclear experience that might have improved reactor safety. Had water been used early in the 1975 fire, the duration of the fire, the damage to the plant and the challenge to safely shutting down the plant would have been significantly reduced.

The AEC did treat fire as a reactor safety threat, but it pursued ill-informed solutions. Chastened by Browns Ferry, the NRC expanded its fire regulations and a launched a fire research program that have measurably improved plant safety.

%d bloggers like this: