Fire Protection for Nuclear Power Plants

Background

The March 22, 1975, fire at the Browns Ferry Nuclear Power Plant (near Decatur, Ala.) 

fundamentally changed how the NRC dealt with fire protection at U.S. nuclear power plants. Plant 

workers accidentally started the fire when checking fire barrier penetration seals for leaks in the room 

where electric cables entered the reactor building. The workers used a lit candle to check for air leaks. 

An air leak caused the candle flame to ignite both seal material and the cables passing through it.

Firefighters extinguished the fire almost seven hours later. More than 1,600 electrical cables 

were affected, 628 of which were important to plant safety. The fire damaged cables for power, control 

systems and instrumentation, affecting reactor safety systems. The fire-damaged cables prevented 

operators from monitoring the plant normally. Operators had to perform emergency repairs on fireaffected systems in order to shut the reactor down safely.

Investigations after the fire revealed shortcomings in both the plant’s fire protection designs and 

its procedures for responding to a fire. The event demonstrated that a fire in certain locations at a nuclear 

plant could damage redundant safety systems and components, making it difficult to shut the reactor 

down safely.

Fire Protection Regulations

Today, the NRC’s fire protection regulations 

reasonably ensure a reactor can safely shut down in 

the event of a fire by:

• Minimizing the potential for fires and 

explosions;

• Rapidly detecting, controlling and extinguishing 

fires that do occur; and

• Ensuring that plant operators have redundant 

shutdown equipment available despite a fire, 

minimizing the risk of significant radioactive 

releases to the environment.

Nuclear power plants use multiple layers of fire protection for their safety systems. These layers 

include fire barriers (such as insulation) and fire detection/suppression systems (such as smoke detectors
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and sprinklers). Every plant must have a fire protection plan outlining the fire protection program, 

installed fire protection systems, and the means to assure the reactor can be safely shutdown in the event 

of a fire. The NRC lists these requirements in 10 CFR Part 50.48(a). The NRC regularly inspects how 

plants achieve and maintain the reactor’s safe shutdown capability in the event of a fire.

Today, nuclear plants have two approaches for managing fire safety:

• Deterministic fire protection ensures reactor shutdown systems will survive an assumed serious 

fire. The NRC developed this approach when the best fire risk tools available to staff and the 

industry looked at an entire system. The NRC lists deterministic requirements in 10 CFR 

50.48(b) and Appendix R of 10 CFR Part 50. Regulatory Guide 1.189 provides plants an 

acceptable approach to meeting these requirements.

• Risk-informed, performance-based fire protection considers risk insights down to the 

individual component level, as well as other factors, to better focus attention and resources on 

design and operational issues according to their safety importance. This approach relies on a 

required outcome rather than requiring a specific process or technique to achieve that outcome. 

The NRC lists these requirements in 10 CFR 50.48(c).

The NRC approved the risk-informed and performance-based fire protection rule in July 2004.

The regulation incorporates National Fire Protection Association (NFPA) Standard 805, with some 

exceptions. NRC staff issued Regulatory Guide 1.205 to help licensees move to an NFPA 805-based fire 

protection program. The NRC guide also endorses the Nuclear Energy Institute’s NEI 04-02 document, 

because its methods acceptably implement NFPA 805 and comply with the regulatory guide. The staff 

issued Revision 2 to RG 1.205 in May 2021.

The NRC first approved risk-informed fire protection for the Shearon Harris plant in North 

Carolina in June 2010. The agency has approved 26 additional NFPA 805-based programs since then, 

with no additional plants expected to apply for transition to the risk-informed standard.

Significant Fire Protection Issuesfor Operating Reactors

The NRC oversees nuclear power plant 

fire protection through the Reactor Oversight 

Process. This includes routine fire protection 

inspections once a quarter, as well as more 

intensive inspections once a year and once every 

three years. The NRC analyzes these findings to 

determine where a plant can improve its fire 

protection performance.

Fire Barrier Testing: These fire-resistant 

materials separate redundant series of fire safety 

equipment located within a fire area. Nuclear 

plant fire barriers include: Thermo-lag,
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Hemyc/MT, Kaowool and FP-60. The NRC tested these materials in full-scale fires; the materials used 

to protect cables did not perform as designed. One Hemyc test found the barrier’s outer covering could 

shrink during a fire, opening joints in the material and potentially allowing the fire to damage cables 

inside. The NRC contacted 11 plants using Hemyc so the licensees could take appropriate compensatory 

actions. The NRC’s Generic Letter 2006-03 asked the affected plants several questions requiring both 

evaluation of all their fire barriers and permanent corrective actions. All the plants’ responses described 

the adequacy of their Hemyc and other fire barriers installed at their plants. The NRC’s review of the 

responses concluded these fire barrier issues have been accounted for, closing out the generic letter.

Post-Fire Operator Manual Actions: Plants must protect at least one set of plant safe shutdown 

equipment from fires using a combination of physical separation, barriers, and methods to detect and 

control or extinguish fires. Plant procedures can list operator manual actions to recover other safe 

shutdown equipment that could be damaged during a fire. In some cases, however, plants 

inappropriately substituted manual actions for fire protection features on one set of safe shutdown 

equipment. The agency clarified its expectations on manual actions in Regulatory Issue Summary RIS2006-10.

Fire Protection for New Reactors

The NRC ensures fire safety at new reactors by applying lessons from currently licensed reactors. 

In Regulatory Guide 1.189, new reactor design fire protection criteria exceed current standards, as

approved by the Commission, by assuming that a fire in any one area will disable all the equipment there.

The agency’s draft proposed Part 53 rulemaking, "Risk-Informed, Technology-Inclusive Regulatory 

Framework for Advanced Reactors," includes fire protection guidance for both light-water cooled and

non-light-water reactors. Both Part 53 and the ongoing advanced reactor content of application project

and the technology-inclusive content of application project will continue developing fire protection

guidance for future applications, in accordance with the Commission-approved enhanced criteria for new 

reactor designs.

Source Documents

More information on fire protection is available on the NRC’s website . The NRC’s regulations 

for nuclear power plants can be found in Title 10 of the Code of Federal Regulations . Fire protection 

regulations are detailed in Section 50.48 of 10 CFR and Appendices A and R to Part 50.

Involved Industry Organizations

National Fire Protection Association

Nuclear Energy Institute

Institute of Electrical and Electronics Engineers, Inc.

Electric Power Research Institute

January 2024