April 2012

Key Facts

• Nuclear power plants have comprehensive fire protection systems, equipment and procedures to ensure safety as well as programs to manage combustible materials and ignition sources. No fires have significantly challenged U.S. nuclear power systems in more than 30 years.
• All nuclear plants are subject to stringent fire protection requirements established by the U.S. Nuclear Regulatory Commission to protect critical systems needed to maintain the reactor and to shut it down safely in the event of a fire large enough to threaten those systems.
• The NRC mandates that plants comply with rigid requirements issued in 1981 or with a voluntary performance-based rule issued in 2004. The voluntary rule is based on a consensus fire protection standard published by the National Fire Protection Association (NFPA), NFPA 805. One reactor has implemented the new approach. Three reactors have NRC approval to do so and are transitioning to NFPA 805. An additional 47 reactors have informed the agency that they intend to pursue the new approach.

NRC Creates Stringent Requirements
Through the early 1970s, nuclear power plants generally followed the same local fire protection codes that governed other industrial facilities. However, a 1975 fire at a nuclear power plant seriously challenged safety systems. The NRC subsequently issued detailed requirements (10 CFR 50.48 and 10 CFR 50, Appendix R) that address fire prevention and detection, fire brigade training, and other areas of fire protection. These regulations require plants to protect critical safety structures and reactor equipment “important to safe shutdown” in the unlikely event of a fire.

Nuclear power plants use various systems and features, including fire protection barriers, physical separation, and fire detection and suppression equipment to meet these requirements. The overall defense-in-depth approach to fire protection combines three major elements:

• preventing fires
• rapidly detecting, controlling and promptly extinguishing any fires that do occur, thereby limiting fire damage
• providing sufficient fire protection for structures, systems, and components important to safety so that, in the event a fire is not extinguished promptly, it will not prevent essential plant safety functions from being performed.

The NRC’s original fire protection regulations are prescriptive, telling licensees what measures to take in various areas of the plant. Since they were issued before sophisticated risk assessment techniques became available, they are not necessarily commensurate with the actual risk. Generally, they go well beyond what is needed for safety, but in some instances, requirements may not be stringent enough. Nuclear power plant operators currently are developing probabilistic assessments of fire risk to help ensure that safety measures are appropriate for the actual risk in a given area. (See below.)

A further difficulty is that these prescriptive requirements were issued after many plants had been built. While licensees building new plants can factor these requirements into their designs, those with older plants faced a significant challenge implementing the requirements on systems, structures and components already in place. For example, the NRC requires plants to protect at least one set of systems needed to shut down the plant safely. At newer plants, this protection is provided by physically separating the systems. However, plants that already were built when the rule was issued may not have the capability to separate the systems sufficiently. The NRC requires these plants to provide comparable protection with fire barriers. Absent risk assessment, the required fire barrier ratings are somewhat arbitrary. They apply equally to all areas where fire barriers are used, regardless of the actual hazard.

During the past 40 years, the NRC and the industry have found that prescriptive requirements often need fine-tuning to achieve their intended purpose in real-world applications. Given the myriad differences among U.S. reactors, a one-size-fits-all approach to regulation has inevitable limitations. The NRC has granted exemptions from these requirements in specific cases where fire protection was determined to be equivalent to the prescriptive requirements. A regulatory exemption is not a waiver. Rather, it is the exchange of one binding requirement for another that is as effective or more effective in meeting the NRC’s safety objectives and more practical for the plant to implement. Once approved, that alternative becomes binding and enforceable. The NRC rigorously enforces fire protection programs at all U.S. nuclear power plants.

NRC Develops Risk-Informed Approach to Fire Protection
In 2004, the NRC issued 10 CFR 50.48(c), a voluntary approach—also known as NFPA 805—allowing risk-informed approaches that model expected fire sizes and effects. This approach involves assessing plant design and actual fire risks in each area of a facility, taking into account such factors as the amount of combustible material, potential ignition sources and fire suppression systems. Plant owners that implement the risk-informed approach may need to install additional equipment or take other measures if the analysis calls for them.

The NRC has endorsed guidance that the industry developed to aid plants in implementing risk-informed fire protection under the 2004 rule. Two plants—Progress Energy’s Shearon Harris and Duke Energy’s Oconee—participated in a pilot program to evaluate the new approach and subsequently received NRC approval to adopt it. Harris has completed implementation, and the transition is in progress at the three-reactor Oconee site. Operators of an additional 47 reactors have informed the agency that they plan to adopt the NFPA 805 approach. The total number of reactors that have implemented the new approach or plan to do so represents 51 percent of America’s reactors.

Nuclear power plants are developing probabilistic assessments of fire risk—fire PRAs—to support implementation of risk-informed approaches in a variety of plant activities, in addition to a possible change to the NFPA 805 approach to overall plant fire protection. In addition to NRC research under way, the industry is working with the Electric Power Research Institute to achieve better realism in fire PRA.

The NRC also is making the fire protection inspection process more risk-informed. It has developed baseline inspection guidance that involves frequent inspections of fire protection programs and triennial regional team inspections of safe shutdown programs. Probabilistic safety studies and the NRC’s process for determining safety significance focus inspections on the most significant plant areas.

Conclusion
The NRC enforces strict fire protection standards at nuclear power plants to reduce the likelihood of fire and ensure that, should one occur, the plant will be able to shut down safely and remain in a safe condition. There are two alternative and equally stringent sets of fire protection requirements: the agency’s original, highly prescriptive requirements and a voluntary risk-informed approach the NRC issued in 2004. Currently, fire protection programs at most plants follow the NRC’s original fire protection requirements. Two plants have NRC approval to adopt the risk-informed approach, and 47 additional reactors have notified the agency that they plan to do so.