[Federal Register Volume 72, Number 65 (Thursday, April 5, 2007)]
[Notices]
[Pages 16832-16835]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 07-1696]


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NUCLEAR REGULATORY COMMISSION


Tennessee Valley Authority Browns Ferry Nuclear Plant, Units 1, 
2, and 3 Docket Nos. 50-259, 50-260, and 50-296 Exemption

1.0 Background

    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.

2.0 Request/Action

    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.

[[Page 16833]]

Exemptions 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:

<bullet> Unit 1 Fire Zone 1-1/1-2....  565' Elevation.........  480V (RB) Vent Board 1B.
<bullet> Unit 1 Fire Zone 1-1/1-2....  565' Elevation.........  1-LPLN-925-338 & 338A Process Radiation Monitor
                                                                 and Relay Panel.
<bullet> Unit 1 Fire Zone 1-1/1-2....  565' Elevation.........  Thermo-Lag on Conduits ES2625-II and ES2673-II.
<bullet> Unit 1 Fire Zone 1-3/1-4....  593' Elevation.........  Thermo-Lag on Conduits PP459-IA, PP460-IA, and
                                                                 ES125-I.
<bullet> Unit 1 Fire Zone 1-3/1-4....  593' Elevation.........  1-LPLN-925-0281A Fire Detection Panel.
<bullet> Unit 1 Fire Zone 1-3/1-4....  593' Elevation.........  1-LPLN-925-0315 Heat Detection Panel.
<bullet> Unit 2 Fire Zone 2-1/2-4....  565' Elevation.........  480V (RB) Vent Board 2B.
<bullet> Unit 2 Fire Zone 2-1/2-2....  565' Elevation.........  2-PWR-276-0007 480V Power Distribution Panel.
<bullet> Unit 2 Fire Zone 2-3/2-4....  593' Elevation.........  25-281A Fire Detection Panel.
<bullet> Unit 2 Fire Zone 2-3/2-4....  593' Elevation.........  25-316 Cable Tray Fire Detection Control.
<bullet> Unit 3 Fire Zone 3-1/3-2....  565' Elevation.........  480 V (RB) Vent Board 3B.
<bullet> Unit 3 Fire Zone 3-1/3-2....  565' Elevation.........  1-LPLN-925-336 & 336A Raw Cooling Water Effluent
                                                                 Radiation Monitor and Relay Panel.
<bullet> 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.\1\ 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.
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    \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.
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    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) 
\2\ 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.
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    \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).
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    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 \3\ 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/m<SUP>2</SUP>.
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    \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.
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    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/m<SUP>2</SUP> (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/m<SUP>2</SUP> based on 
American Society of Testing and Materials (ASTM) E1321, ``Standard Test 
Method for Determining Material Ignition and Flame Spread

[[Page 16834]]

Properties'' (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.

3.0 Discussion

    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.

Special Circumstances

    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

[[Page 16835]]

the 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.

4.0 Conclusion

    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.

    Dated at Rockville, Maryland, this 29th day of March 2007.
    For the Nuclear Regulatory Commission.
Catherine Haney,
Director, Division of Operating Reactor Licensing, Office of Nuclear 
Reactor Regulation.
[FR Doc. 07-1696 Filed 4-4-07; 8:45 am]
BILLING CODE 7590-01-P