Frequently Asked Questions About Fire Barriers
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What are the NRC's goals regarding fire barriers at nuclear power plants (NPPs)?
The main goal of the U.S. Nuclear Regulatory Commission (NRC) is safety, and the need to protect the public and environment have remained paramount. The NRC achieves this goal partly through the use of the defense-in-depth concept. As indicated in Appendix R to Title 10, Part 50, of the Code of Federal Regulations (10 CFR Part 50), the fire protection program extends the concept of defense-in-depth to fire protection with the following objectives: (1) prevent fires from starting; (2) detect rapidly, control, and extinguish those fires that do occur; and (3) provide protection for structures, systems, and components important to safety so that a fire that is not promptly extinguished by the fire suppression activities will not prevent the safe shutdown of the plant. Fire barriers are an important tool in achieving the third objective above.
What is a fire barrier?
Fire barriers are continuous construction assemblies, which are designed and constructed to achieve specific fire resistance ratings, limit the spread of heat and fire, and restrict the movement of smoke. Fire barriers may be structural (walls, ceilings, floors) or non-structural (radiant energy shields, raceway fire barriers).
What is an electrical raceway fire barrier system (ERFBS)?
ERFBSs are non-structural fire rated assemblies that protect the electrical cables they enclose. In NPP applications, ERFBSs are required to have a fire resistance rating of either 1 or 3 hours, based on the specific application. Common ERFBSs in use at NPPs include Thermo-Lag, Darmatt, Hemyc, MT, and 3M Interam.
Why and how are ERFBSs used?
Section III.G of Appendix R to 10 CFR Part 50, which addresses fire protection of safe-shutdown capability, requires that fire protection features be provided such that one train of systems necessary to achieve hot shutdown conditions remains free of fire damage. One acceptable means of satisfying this requirement is to enclose cables and equipment and associated non-safety circuits of one redundant train in a fire barrier having a 1-hour fire rating and install fire detectors and an automatic fire suppression system in the fire area (Section III.G.2.c). Another means is to separate cables and equipment and associated non-safety circuits of redundant systems necessary to achieve and maintain hot shutdown conditions located in the same fire area by a fire barrier having a 3-hour fire rating (Section III.G.2.a). The Hemyc ERFBS is an example of a 1-hour rated fire barrier used to protect cables and equipment and associated non-safety circuits of one redundant train. The MT ERFBS is an example of a 3-hour rated fire barrier used to protect cables and equipment and associated non-safety circuits of one redundant train.
Plants with operating licenses issued after January 1, 1979, are not required to meet the requirements of Section III.G, but they generally meet a similar commitment in their licensing basis to have 1-hour rated barriers with automatic suppression or 3-hour rated barriers for areas that contain redundant safe-shutdown equipment.
How is the Hemyc ERFBS constructed?
Hemyc is a "fire wrap" that was installed to protect electrical raceways from the effects of fire for 1 hour. Hemyc consists of a 1.5- or 2.0-inch thick ceramic fiber material (e.g., Kaowool) blanket covered with a tightly knit fire-resistant fiber material (e.g., siltemp), and all materials are sewn together with fire resistant "Astroquartz" thread.
How is the MT ERFBS constructed?
MT ERFBS is a "fire wrap" designed to protect electrical raceways from the effects of fire for a duration of 3 hours. MT consists of a layer of ceramic fiber material (e.g., Kaowool) directly over the conduit, surrounded by a metallic layer, surrounded by a energy absorbing "hydrate" layer, and lastly these three layers are enclosed in a Hemyc ERFBS. The layer of ceramic fiber around the conduit, the metallic layer, and the "hydrate" layer of heat-activated compound are the elements that differentiate the MT product from the Hemyc ERFBS.
Has the NRC approved Hemyc 1-hour rated ERFBS at NPPs in the past?
Yes. In the past, the NRC approved the use of the Hemyc ERFBS on a case-by-case basis at a licensee's specific request.
Has the NRC approved MT 3-hour rated ERFBS at NPPs in the past?
No. Only one licensee (Shearon-Harris Nuclear Power Plant, owned by Carolina Power and Light Company) is known to use the MT ERFBS in a 3-hour application. No explicit approval of the MT ERFBS was issued by the NRC.
Is the NRC changing the rule to accommodate licensees who use Hemyc ERFBSs?
No. The NRC is not changing the rule to accommodate licensees who are currently using Hemyc 1-hour rated ERFBSs. The licensees have a responsibility to follow their licensing bases, which may require them to prove that the use of Hemyc is acceptable. The NRC has issued generic communications on the Hemyc issue and is in the process of closing the issue and verifying licensees' compliance.
Can the NRC issue a violation to the licensee due to Hemyc not being in compliance with the regulation?
Under the current rule, all fire barriers must be rated in order to meet the requirements of Section III.G.2 of Appendix R to 10 CFR Part 50. For plants that are committed to Appendix R, due to the backfit applied in 10 CFR 50.48(b) (i.e., pre-1979 plants), an exemption per 10 CFR 50.12 must be obtained for barriers that are not rated. For plants licensed after 1979, plants must meet their license condition and have a fire protection program in accordance with 10 CFR 50.48(a). These plants would be considered to be in violation of their license basis if they are unable to demonstrate the ratings of their fire barriers. The NRC's description for achieving a rating for a fire barrier is presented in Generic Letter 86-10, Supplement 1. Although these barriers were tested before the issuance of Generic Letter 86-10 , Supplement 1, it is incumbent on the licensee to demonstrate that the installed material can protect electrical raceways for the required duration.
Has the NRC conducted analysis on the cost of compliance with the fire safety regulations?
The NRC has not prepared any cost analysis. Since the issue pertains to compliance with an existing regulation, cost is not a consideration.
Why were the Hemyc and MT ERFBSs retested?
The initial tests performed on the Hemyc and MT ERFBSs were for "insurance purposes only" and were found to be indeterminate because of inconsistencies in the test results. Although the initial testing followed American Society for Testing and Materials (ASTM) E-119 "Standard Test Methods for Fire Tests of Building Construction and Materials," which the NRC accepts as test criteria for fire barriers (see Generic Letter 86-10, Supplement 1), the existing body of tests was not sufficient to qualify the Hemyc or MT as rated fire barriers. Issues with the testing were whether the testing was representative of installed configurations (functionality, cable types, raceway mass, and raceway size).
Why did the NRC perform the testing?
Initially, the NRC requested that the licensees perform the ERFBS tests. The licensees claimed that they were complying with their licensing bases, and that no industry initiative was planned. The NRC also suggested that the Nuclear Energy Institute (NEI) perform the testing as an industry initiative, but NEI declined this suggestion. In order to resolve this issue, the NRC developed a test plan and tested both Hemyc and MT ERFBSs.
Why wasn't the degradation of Hemyc and MT ERFBSs dealt with faster?
The Hemyc 1-hour rated ERFBS is only used in applications where its protective quality is aided by automatic fire detection and suppression. Therefore, the degradation of the Hemyc ERFBS is not seen to be an area of major risk. In addition, the test information available at that time indicated that the barrier has some fire resistance capability, even though it may not meet the required 1-hour duration.
The MT 3-hour rated ERFBS is only used in two plants, and only one plant is known to rely on MT for a 3-hour rated barrier (the other plant relies on MT for a 1-hour rated barrier). Also, the acceptance testing showed that some configurations could pass a 3-hour ASTM E-119 time-temperature criteria.
Can licensees take no action due to the potential low risk-significance related to Hemyc and MT EFRBS?
All licensees will be expected to come into regulatory compliance, irrespective of risk-significance, within a reasonable time frame in accordance with their licensing basis. The options available to licensees are (1) replacing or upgrading the Hemyc or MT to a properly rated barrier, (2) performing a technical evaluation and submitting a license amendment (post-1979 plants) or applying for a 10 CFR 50.12 exemption (pre-1979 plants), and (3) by making changes in accordance with their license, and if necessary submitting a license amendment to demonstrate and document that the degraded condition does not pose an adverse effect (post-1979 plants). However, post- or pre-1979 plants cannot use a pure risk argument to justify no adverse condition, unless they adopt National Fire Protection Association (NFPA) Standard 805, "Performance-Based Standard for Fire Protection for Light-Water Reactor Electric Generating Plants" (NFPA 805) as their licensing basis or submit a risk-informed evaluation for NRC review.
Risk-informed approaches that consider risk-information, defense-in-depth, and safety margin are available through the use of evaluations consistent with Regulatory Guide 1.174 and NFPA 805.
How are Hemyc and MT different from Thermo-Lag?
The Thermo-Lag ERFBS, manufactured by Thermal Sciences Inc., is different from the Hemyc and MT ERFBS in a number of ways. Thermo-Lag is combustible. Neither Hemyc nor MT are combustible. This means that Thermo-Lag may act as a combustible material between two redundant cable trays. The testing for Thermo-Lag was admitted to be falsified by the testing laboratory. There is no indication of falsification related to either the Hemyc or MT testing.
The ampacity derating of electrical power cables that was applied for Thermo-Lag was incorrect. This led to issues related to insufficient derating of electrical cables. The derating factors for Hemyc and MT appear consistent with the ampacity derating factors expected for fire barrier materials of this type.
What are the regulatory actions taken to deal with barriers such as Hemyc and MT ERFBSs after the findings related to Thermo-Lag 330-1 systems?
The adequacy of fire barrier system qualification programs came into question following tests performed by Southwest Research Institute (SWRI) in 1989 on the Thermo-Lag fire barrier systems. The staff's investigation focused on the Thermo-Lag 330-1 systems because in addition to failing the SWRI tests, Thermo-Lag had been used extensively in a number of plants.
In Generic Letter 92-08, "Thermo-Lag 330-1 Fire Barriers," the staff stated that it expected the recipients to review the information in the GL to determine if it applied to other barrier materials and systems used at their facilities and to consider actions, as appropriate, to avoid problems similar to those experienced by the Thermo-Lag fire barrier systems.
From 1993 to 1998, the staff addressed performance deficiencies with respect to two other fire barrier systems, Kaowool and FP-60, after determining the fire rating of these systems could not be supported by valid test results. In 1999, inspectors performing fire protection functional inspections and triennial inspections reviewed the fire endurance test program for the MT ERFBS and concluded that the test results were indeterminate. Consequently, inspectors began issuing unresolved items (URIs) on the MT ERFBS.
Since MT ERFBS are used as a 3-hour rated barrier of defense, it is recognized that other defense-in-depth methods, such as manual fire suppression provided by the fire brigade, further protect the equipment inside the MT. The MT ERFBS is expected to provide a substantial amount of protection, even if it does not qualify for the full 3-hour time period.
The staff issued Generic Letter 2006-03, "Potentially Nonconforming Hemyc and MT Fire Barrier Configurations." This Generic Letter requested that licensees evaluate their facilities to confirm compliance with the existing applicable regulatory requirements, with respect to all ERFBSs, and, if appropriate, take additional actions. All licensees responded, and all of their responses have been closed.
How can the NRC be certain that there is no danger to the public or the environment from an NPP utilizing Hemyc ERFBSs?
Hemyc ERFBSs do not affect the plants' ability to prevent, detect, or suppress a fire. They are used in addition to an automatic fire suppression system to protect the cables and equipment of one redundant safe-shutdown train. The first level of defense when a fire occurs in areas using Hemyc is the automatic suppression system. In the unlikely event that the automatic suppression systems fails, the Hemyc ERFBS will likely provide sufficient time to employ alternate fire suppression capabilities (e.g., manual suppression by the plant fire brigade) to extinguish fires, even if the Hemyc ERFBS has a less than 1-hour fire rating. The majority of fires that are expected to occur at NPPs do not generate heat rates or temperature increases that would challenge the Hemyc ERFBS. In addition, the test acceptance criterion is based on the temperature of the enclosed conduit or cable tray. When the conduit or tray reaches the temperature acceptance limit, additional time is available before the enclosed cables will fail and potentially cause a short.
In light of the test results, how can the NRC be certain that there is no danger to the public or the environment from an NPP utilizing MT ERFBSs?
The NRC has confidence that the MT barrier provides significant protection based on the following aspects: (1) the fire barrier lasted at least 87 minutes in all tested configurations before reaching the minimum cable failure temperature, (2) furnace-like temperatures would have to be achieved in plant areas and maintained for an extended period of time, and (3) even if areas reached and maintained these temperatures, there would be significant time available for manual suppression to occur before cables become damaged.
What is the closure plan for the Hemyc and MT issues?
The NRC issued Generic Letter 2006-03 to request licensees to report whether or not they rely on Hemyc and/or MT and to submit their corrective action plan to the NRC. All licensees have responded to the generic letter. The commitments from the 16 reactor units which utilize Hemyc and/or MT range from plant modifications to exemptions to dispositioning by transition to the new risk-informed, performance-based fire protection licensing basis (NFPA 805). For all non-NFPA 805 units, the NRC plans to verify that licensees have fulfilled their commitments using the fire protection inspection process. For NFPA 805 transitioning plants, the NRC will ensure closure during the staff reviews of the licensees' License Amendment Requests for the new licensing basis.
Why hasn't the NRC evaluated and qualified fire barrier materials as Chairman Selin committed to do in his testimony in 1993?
The NRC has completed the actions committed to by the Chairman and assessed fire barrier capabilities. The NRC obtained and reviewed design and test information from all fire barrier vendors and observed installed fire barrier configurations at selected NPPs. The NRC also performed small-scale fire barrier tests of selected fire barriers. Finally, the NRC issued updated guidance on fire barrier testing and acceptance criteria. However, the NRC could have identified Hemyc earlier and followed up on small-scale tests more promptly.
How is the NRC ensuring that electrical raceway fire barriers are performing as designed?
The NRC performs quarterly fire protection inspections of plant equipment conditions. Every three years the NRC performs triennial fire protection design and operational safety inspections. Licensees implement corrective action plans and put in place compensatory measures when deficiencies are identified with a raceway fire barrier design or installation.
How has the NRC research program supported fire barrier activities?
The Office of Nuclear Regulatory Research (RES) has supported NRC fire barrier activities with testing of ERFBSs. During 2005, RES performed confirmatory fire endurance testing at Omega Point Laboratories (OPL) of typical Hemyc 1-hour rated ERFBSs. Sixteen tests were performed on conduits, cable trays, junction boxes, air drops, and supports protected with Hemyc 1-hour rated ERFBS. RES has also witnessed several industry-sponsored tests of ERFBSs. In September 2009, RES published Draft NUREG-1924, "Electric Raceway Fire Barrier Systems in U.S. Nuclear Power Plants," for public comments. NUREG-1924 documents the history of Electrical Raceway Fire Barrier Systems (ERFBS) used to protect post-fire, safe-shutdown functions. This draft report documents the current state of the use of these barriers and evaluates the effectiveness of these barriers in achieving adequate protection for nuclear power plants.
Page Last Reviewed/Updated Tuesday, March 10, 2020