The Tennessee Valley Authority (TVA, the licensee) is the holder of Facility Operating Licenses DPR-33, DPR-52, and DPR-68, which authorize operation of the Browns Ferry Nuclear Plant, Units 1, 2 and 3. The license provides, among other things, that the facility is subject to all rules, regulations, and orders of the Nuclear Regulatory Commission (NRC, the Commission) now or hereafter in effect.
The facility consists of three boiling-water reactors located in Limestone County in Alabama.
On November 19, 1980, the Commission published a new Appendix R to Title 10 to the Code of Federal Regulations (10 CFR) Part 50 regarding fire protection features of nuclear power plants (45 FR 76602). Section 50.48(a) requires that each operating nuclear power plant have a fire protection plan which satisfies General Design Criterion (GDC) 3, “Fire protection,” in Appendix A, “General Design Criteria for Nuclear Power Plants,” to 10 CFR Part 50. The approved fire protection plan is the plan required to satisfy 10 CFR 50.48(a). Specific fire protection features deemed necessary to ensure this capability are delineated in Appendix R to 10 CFR Part 50. Section III of Appendix R contains 15 subsections, lettered A through O, each of which specifies the requirements for a particular aspect of fire protection features at nuclear power plants. The Browns Ferry units are required to comply with the provisions of Sections III.G and III.J and III.O. Section III.G.2 of Appendix R to 10 CFR Part 50 requires that where cables or equipment of redundant trains of systems necessary to achieve and maintain hot shutdown conditions are located within the same fire area outside of primary containment, one of the following means of ensuring that one of the redundant trains is free of fire damage shall be provided:
a. Separation of cables and equipment and associated non-safety circuits of redundant trains by a fire barrier having a 3-hour rating. Structural steel forming a part of or supporting such fire barriers shall be protected to provide fire resistance equivalent to that required of the barrier;
b. Separation of cables and equipment and associated non-safety circuits of redundant trains by a horizontal distance of more than 20 feet with no intervening combustible or fire hazards. In addition, fire detectors and an automatic fire suppression system shall be installed in the fire area; or
c. Enclosure of cable and equipment and associated non-safety circuits of one redundant train in a fire barrier having a 1-hour rating. In addition, fire detectors and an automatic fire suppression system shall be installed in the fire area;
By letter dated October 26, 2006, as supplemented by a letter dated January 11, 2007, the licensee requested a revision to an exemption from 10 CFR 50 Appendix R, III.G.2. For the items specified in this exemption request, the licensee has selected III.G.2.b as the option for compliance with Appendix R, Section II.G.2. The exemption involves allowing intervening combustible materials, for example, fire hazards (480V reactor building (RB) vent boards 1B, 2B, and 3B; small panels in Units 1, 2, and 3, and 1-hour rated Thermo-Lag 330-1 electrical raceway fire barrier (ERFB) material), in the specified 20 feet of separation protected with fire detection and automatic water-based fire suppression between redundant safe-shutdown trains.
The redundant trains are separated by a horizontal distance of 20 feet with intervening combustibles in certain fire zones in the Units 1, 2, and 3 RBs. Start Printed Page 16833Exemptions are requested from the requirements to provide 20 feet of separation, free of intervening combustibles. The following is a list of those fire zone locations and intervening combustibles/fire hazards present within a 20-foot spatial separation zone for redundant safe-shutdown trains:
|• Unit 1 Fire Zone 1-1/1-2||565′ Elevation||480V (RB) Vent Board 1B.|
|• Unit 1 Fire Zone 1-1/1-2||565′ Elevation||1-LPLN-925-338 & 338A Process Radiation Monitor and Relay Panel.|
|• Unit 1 Fire Zone 1-1/1-2||565′ Elevation||Thermo-Lag on Conduits ES2625-II and ES2673-II.|
|• Unit 1 Fire Zone 1-3/1-4||593′ Elevation||Thermo-Lag on Conduits PP459-IA, PP460-IA, and ES125-I.|
|• Unit 1 Fire Zone 1-3/1-4||593′ Elevation||1-LPLN-925-0281A Fire Detection Panel.|
|• Unit 1 Fire Zone 1-3/1-4||593′ Elevation||1-LPLN-925-0315 Heat Detection Panel.|
|• Unit 2 Fire Zone 2-1/2-4||565′ Elevation||480V (RB) Vent Board 2B.|
|• Unit 2 Fire Zone 2-1/2-2||565′ Elevation||2-PWR-276-0007 480V Power Distribution Panel.|
|• Unit 2 Fire Zone 2-3/2-4||593′ Elevation||25-281A Fire Detection Panel.|
|• Unit 2 Fire Zone 2-3/2-4||593′ Elevation||25-316 Cable Tray Fire Detection Control.|
|• Unit 3 Fire Zone 3-1/3-2||565′ Elevation||480 V (RB) Vent Board 3B.|
|• Unit 3 Fire Zone 3-1/3-2||565′ Elevation||1-LPLN-925-336 & 336A Raw Cooling Water Effluent Radiation Monitor and Relay Panel.|
|• Unit 3 Fire Zone 3-1/3-2||565′ Elevation||1-LPLN-925-337 & 337A Process Radiation Monitor and Relay Panel.|
To justify inclusion of intervening combustibles in RB fire areas, the licensee performed fire modeling to assess potential hazards using methodology from NUREG-1805, “Fire Dynamics Tools (FDTs) Quantitative Fire Hazard Analysis Methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program,” December 2004. Enclosure 2 of the exemption request discussed the fire-risk analysis for the Units 1, 2, and 3 RBs.
TVA provided an assessment utilizing fire modeling to evaluate the fire hazards due to intervening combustibles between redundant cable trains in the RBs. In this fire modeling analysis, the licensee modeled fire in Unit 1 RB Elevation 565′ in the 20-foot zone of separation between fire zones 1-1 and 1-2. Specifically, 480V (RB) vent boards 1B, 2B, and 3B are located within the 20-foot zone of separation. The fire model uses a series of empirical correlations from NUREG-1805 to show the largest fire from a vertical low voltage electrical cabinet should not produce enough radiant energy to ignite the closest redundant cable trays or intervening combustibles within the redundant trains.
The analysis is used to determine the extent of the potential fire damage associated with a realistic worst case fire scenario between Unit 1 RB fire zones 1-1 and 1-2 and the anticipated failure of cables or equipment of redundant trains of systems required for safe-shutdown. A fire scenario was postulated for the Unit 1 RB, that is, fire started in a vertical electrical cabinet (480V RB vent board 1B). This cabinet has 12 vertical sections with no vent openings. The penetrations in the cabinet consist of sealed conduits on top of the cabinet. The fire started from non-qualified Institute of Electronics and Electrical Engineering Standard (IEEE)-383 cables within the cabinet and was assumed to be limited to one cable bundle. The heat release rate (HRR)  used to calculate heat fluxes to the targets (cable trays located at radial distance of approximately 7 feet [17 feet above floor], conduits located at the bottom of the duct approximately 9 feet above the top of the cabinet, and Thermo-Lag 330-1 wrapped conduit located approximately 7 feet from the edge of the cabinet) was based on Table E-4 in Appendix E of NUREG/CR-6850 (EPRI [Electric Power Research Institute] TR-1019181), “EPRI/NRC-RES Fire PRA [Probabilistic Risk Analysis] Methodology for Nuclear Power Facilities,” November 2005.
In order to evaluate the licensee's conclusion that a cabinet fire would not result in fire damage adversely affecting the safe-shutdown capability in Units 1, 2, and 3 RB located within the 20-foot separation area, the NRC staff identified areas in which additional information was necessary to complete its evaluation. The NRC staff had discussions with the licensee on November 20, 2006, concerning use of the HRR of a single bundle cable (vs. multiple bundles) fire from NUREG/CR-6850 in fire modeling. Specifically, the NRC staff requested TVA to justify how the single bundle cable HRR assumption bounds the worst case cabinet fire scenario. On January 11, 2007 (ADAMS Accession Number ML070160050), TVA provided a revised fire model to address the NRC concerns.
In the revised fire modeling analysis, the HRR for multiple-cable bundles was assumed due to multiple conduit entries in each section of the low voltage vertical cabinet. The HRR associated with multiple-cable bundles for a vertical cabinet with non-qualified IEEE-383 cables was based on Table E-5 in Appendix E of NUREG/CR-6850. The critical incident radiative heat flux  for ignition is calculated from the cabinet fire scenario to see if ignition of the redundant cables and adjacent surrounding targets (intervening combustibles) is possible. The critical incident radiative heat flux from the maximum fire HRR, that is, 816 Kilowatt (kW), was estimated at 4.28 kW/m2.
The licensee determined that the maximum radiant heat flux is not sufficient to ignite non-qualified IEEE-383 cable or Thermo-Lag 330-1 wrapped on conduits or safety-related cables or equipment of redundant trains of systems for safe-shutdown, nor to adversely impact any surrounding equipment. The targets require a large amount of radiative heat to ignite. The measured critical heat flux level for representative non-qualified IEEE-383 or thermoplastic cable samples typically is in the range of 6 kW/m2 (NUREG/CR-6850, Appendix H, Table H-1). The measured critical heat flux for ignition for Thermo-Lag 330-1 ERFB material is 25 kW/m2 based on American Society of Testing and Materials (ASTM) E1321, “Standard Test Method for Determining Material Ignition and Flame Spread Start Printed Page 16834Properties” (TVA October 26, 2006 (ADAMS ML063040310)).
Based on the above evaluation, the NRC staff concludes that the ability of Units 1, 2, and 3 to achieve and maintain safe-shutdown conditions in accordance with the requirements of Section III.G.2.b to Appendix R to 10 CFR 50 is not adversely affected by the inclusion of intervening combustibles or fire hazards in certain fire zones within Units 1, 2, and 3 RBs for the following reasons:
—The fire modeling performed by the licensee provides reasonable assurance that redundant safe-shutdown trains will be maintained free of fire damage. This is because the estimated heat flux from the maximum exposure fire is less than the critical heat flux for ignition for non-qualified IEEE-383 cable or Thermo-Lag 330-1 ERFB material.
—In the event of a postulated fire in the Units 1, 2, and 3 RBs, all units can safely shut down using the alternate shutdown panel located outside each RB. The Browns Ferry Nuclear Plant Appendix R alternate shutdown strategy is described in the approved fire protection plan.
—A significant fire is unlikely due to control of transient combustibles near the redundant trains. RB volume and height would dissipate heat from a cabinet fire and not threaten redundant trains. Smoke detectors and portable extinguishers were installed for quick fire detection and suppression. All electrical cabinets in the area of concern are enclosed with no ventilation openings and the bottom of the cable tray stacks have non-combustible covers.
—A fire originating in a low voltage cabinet exposing intervening combustibles/targets (cable trays located at radial distance of approximately 7 feet, conduits located at the bottom of the duct approximately 9 feet above the top of the cabinet (17 feet above floor), and Thermo-Lag 330-1 wrapped conduit located approximately 7 feet from the edge of the cabinet) would be slow to develop. Based on the fire detection arrangement in the Units 1, 2, and 3 RBs, detection of this type of fire would occur well before the fire had time to develop into a fully developed cable tray fire scenario.
—The NRC staff reviewed the physical configuration of the Units 1, 2, and 3 RBs, the associated fire hazards (intervening combustibles) and fire protection features, and fire response procedures. This review found that a fire that initiated in one of the cabinets would likely be detected in its incipient stage, and fire-fighting activities initiated (including actuation of the automatic water-based fire suppression system) before the fire becomes fully developed, thereby limiting its potential to spread.
The NRC staff, therefore, finds the licensee's proposed exemption to permit intervening combustibles in the 20-foot separation zone for certain specified fire areas in the Units 1, 2, and 3 RBs acceptable.
The licensee indicated that all fire zones discussed previously are protected with fire detection and automatic pre-action sprinkler systems, manual fire extinguishers, and hose stations. If a fire were to occur in any of these locations it would be detected before significant flame propagation or increased temperature, radiative heat flux, and damaging smoke layering occurred. The fire brigade would then extinguish the fire using hose stations and manual fire fighting equipment. If rapid fire propagation occurred before the arrival of the fire brigade, one would expect the automatic pre-action sprinkler system to actuate and limit fire spread. Pending actuation of automatic pre-action sprinkler system, the physical separation of redundant trains is sufficient to provide reasonable assurance that one safe-shutdown train would remain free of fire damage. Therefore, the NRC staff concludes that the existing level of fire protection for the redundant safe-shutdown trains is an acceptable deviation from Section III.G.2 of Appendix R to 10 CFR Part 50.
Pursuant to 10 CFR 50.12, the Commission may, upon application by any interested person or upon its own initiative, grant exemptions from the requirements of 10 CFR Part 50 when (1) The exemptions are authorized by law, will not present an undue risk to public health or safety, and are consistent with the common defense and security; and (2) when special circumstances are present. These include the special circumstances that the underlying purpose of the rule is satisfied by the requested revision to the exemption, since the existing fire protection features and analyses demonstrate that the quantity of intervening combustibles permitted in the 20-foot separation zone does not affect the ability of the existing fire protection features to provide an equivalent level of protection as required by 10 CFR 50, Appendix R, Section III.G.
Authorized by Law
This exemption revision allows the existence of the specified intervening combustibles in the 20-foot separation zone identified previously. As stated above, 10 CFR 50.12 allows the NRC to grant exemptions from the requirements of 10 CFR 50.48 and Appendix R to 10 CFR 50. The NRC staff has determined that granting of the licensee's proposed exemption will not result in a violation of the Atomic Energy Act of 1954, as amended, or the Commission's regulations. Therefore, the exemption is authorized by law.
No Undue Risk to Public Health and Safety
The underlying purpose of 10 CFR 50.48 is to limit fire damage to structures, systems, and components (SSCs) important to safety so that the capability to shut down the plant safely is ensured. Compliance with the applicable provisions of Appendix R to Part 50 ensures that one train of cables and equipment necessary to achieve and maintain safe-shutdown are maintained free of fire damage. Based on the above, no new accident precursors are created by allowing the specified intervening combustibles into the 20-foot separation zone identified previously, thus, the probability of postulated accidents is not increased. Also, based on the above, the consequences of postulated accidents are not increased. Therefore, there is no undue risk to public health and safety.
Consistent With Common Defense and Security
The proposed exemption revision would allow the specified intervening combustibles into the 20-foot separation zone identified previously. This revision to the fire protection plan and existing exemptions has no relation to security issues. Therefore, the common defense and security are not impacted by this exemption.
In accordance with 10 CFR 50.12(a)(2), special circumstances are present whenever application of the regulation in the particular circumstances is not necessary to achieve the underlying purpose of the rule. The underlying purpose of 10 CFR 50.48 is to limit fire damage to SSCs important to safety so that the capability to shut down the plant safely is ensured. Compliance with the applicable provisions of Appendix R to Part 50 ensures that one train of cables and equipment necessary to achieve and maintain safe-shutdown are maintained free of fire damage. As the existence of Start Printed Page 16835the intervening combustibles should not affect the capability of the installed suppression and detection system to detect and mitigate a fire, the underlying purpose of 10 CFR 50.48 and Appendix R is achieved. Therefore, the special circumstances required by 10 CFR 50.12(a)(2) for the granting of an exemption from 10 CFR 50.48 and Appendix R to 10 CFR 50 exist.
Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12, the revision to the exemption is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security. Also, special circumstances are present. Therefore, the Commission hereby grants the TVA a revision to the exemption from the requirements of Section III.G.2 of Appendix R to 10 CFR 50 for the Browns Ferry Nuclear Plant, Units 1, 2 and 3.
Pursuant to 10 CFR 51.32, the Commission has determined that the granting of this exemption will not have a significant effect on the quality of the human environment (22 FR 9036).
This exemption is effective upon issuance.Start Signature
Dated at Rockville, Maryland, this 29th day of March 2007.
For the Nuclear Regulatory Commission.
Director, Division of Operating Reactor Licensing, Office of Nuclear Reactor Regulation.
1. The Units 2 and 3 configuration are very similar and the results of this analysis are applicable to 480V (RB) vent board 2B and 480V (RB) vent board 3B.Back to Citation
2. HRR is the rate at which heat energy is generated by burning. The HRR of a fuel is related to its chemistry, physical form, and availability of oxidant. When an object burns, it releases a certain amount of energy per unit of time. For most materials, the HRR of a fuel changes with time, in relation to its chemistry, physical form, and availability of oxidant (air), and is ordinarily expressed as kW (kJ/sec) or Btu/sec and denoted by Q (1,000 kW = 1 MW or 1 BTU/sec = 1.055 kW).Back to Citation
3. The incident heat flux (the rate of heat transfer per unit area that is normal to the direction of heat flow—it is a total of heat transmitted by radiation, conduction, and convection) required to raise the surface of a target to a critical temperature is termed the critical heat flux. Below this heat flux an object will typically not ignite while above this heat flux the time to ignition will decrease with the increasing heat flux.Back to Citation
[FR Doc. 07-1696 Filed 4-4-07; 8:45 am]
BILLING CODE 7590-01-P