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TagsNuclear Regulatory Commission Mains Electricity Electrical Substation Electricity Physical Quantities
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Total Pages72
Table of Contents
List of Figures and Tables
Executive Summary
Abbreviations and Acronyms
1. Introduction
2. Lightning-Related Operating Events
3. Key Issues of Lightning Protections
4. Review of Applicable Standards
5. Assessment of Lightning Protection Requirements
6. Recommendations
7. References
Document Text Contents
Page 1


Technical Basis for
Regulatory Guidance on
Lightning Protection in
Nuclear Power Plants

Oak Ridge National Laboratory

U.S. Nuclear Regulatory Commission
Office of Nuclear Regulatory Research
Washington, DC 20555-0001

Page 2


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Page 36

Table 3. Units in AEOD/E605 review

Plant Name Number of
Events Per Plant

Big Rock Point, Brunswick 1, Byron 1, Catawba 1, Connecticut Yankee, Cooper, 1
Davis-Besse, D. C. Cook 1, Duane Arnold, Fitzpatrick, Hatch 1, McGuire 2,
Shoreham, Summer 1, Turkey Point 3, Vermont Yankee, Waterford 3
Arkansas Nuclear One 2, Farley 2, Grand Gulf 1, Maine Yankee, Peach Bottom 3, 2
Pilgrim, Susquehanna 1, Susquehanna 2, St. Lucie 2, Wolf Creek
Yankee Rowe 3
Browns Ferry 1, Crystal River 3 5
McGuire 1, TMI 2 6

All plants affected were in the mid-western and eastern regions with the majority east of the Mississippi
river. In general, plants with high number of lightning events are located in areas of high mean annual
ground flash density (greater than 10 flashes/km2). There are exceptions such as Yankee Rowe, Pilgrim,
and Vermont Yankee which, though located in a low flash density zone (2 flashes/km2), have experienced
multiple lightning induced events. The report attributes that situation to less than adequate design or
installation of lightning protection equipment of those plants. The LER data indicate that the peak
lightning-related events occur in June and July, which is of course when thunderstorms prevail. Winter
months are a minimum with only one occurrence in December.

Offsite power systems are the most affected by lightning-induced events (47 percent). Seven (24 percent)
of the offsite power events led to a reactor trip. Six events led to inadvertent emergency diesel start up.
With one or two exceptions, most of the loss of offsite power was localized to the plant switchyard (i.e.,
lightning strike in the switchyard led to failure).

Events related to safety-related instrumentation accounted for about 15 percent of the total events.
Typical were blown fuses and inadvertent activation of systems such as tripping of control rod drive
systems. The reactor tripped in 67 percent of the safety-related instrumentation events. Note that the
lightning transients crossed multiple channels of safety-related systems; however, the failures were fail
safe. A case of lightning striking containment resulted in voltage transients that failed four power
supplies plus actual damage to numerous instruments.

Events affecting meteorological, weather, and environmental systems account for 19 percent of the total
events. Events affecting radiation, gas, and effluent flow monitors account for 11 percent of the total
events. Events affecting air intake tunnel halon system account for 8 percent. ORNL Conclusions
Mid-western and eastern plants experience most of the lightning events. There is a direct correlation
between regional lighting strike density and number of events experienced by a nuclear plant. Data from
the short period of this analysis suggest that the number of lightning-related events is relatively constant.
Several plants in low lightning density zones experienced an unusually high number of events suggesting
that they have an inadequate level of lightning protection. No safety-related systems were damaged
during the period of this study. The sensitivity of signal level measurement systems makes them
susceptible to spurious actuation during lightning strikes. Licensees moved to improve these susceptible
systems when significant damage occurs or other compelling factors are present. The author of thy report
concludes that no further action regarding lightning events is recommended based on the five-ye, study.


Page 37

2.23 NRC Information Notice 85-86

Information Notice 85-86, Lightning Strikes at Nuclear Power Generating Stations [10], was issued in
1986 for all nuclear power reactor facilities holding a license or construction permit. The purpose is to
alert recipients of potentially significant problems of reactor trips and instrumentation damage cause by
lightning strikes. No actions are required regarding the notice. The notice concentrates on the effects of
lightning-induced surges on solid-state circuitry amd summarizes lightning events at five operating plants:
Zion units I and 2, Salem unit 1, Kewaunee, Byron unit 1, and Arkansas unit 2.

Lightning transients damaged safety-related systems and induced transients in the low-voltage power
supplies that resulted in control rod drops. Corrections actions were made to the affected, yet reactor trips
have still occurred for other as yet uncorrected systems.

Lightning strike entered containment penetration and damaged pressure transmitters. Reactor trip

Electrical storm resulted in loss of two of four instrument busses causing spurious safety injection and
blown fuses.

Lightning strike to containment caused reactor trip due to transient voltages in instrument and control
cabling. Failure of four containment power supplies including a redundant pair resulted in partial control
rod drop. Thirty plant instruments were damaged. Deficiencies in containment penetration were a
common denominator to the incident.

Lightning strike induced spurious signal in core protection system channels resulting in a trip from
departure-from-nucleate-boiling ratio. No equipment damage was reported.

2.3 Industry Reports

2.3.1 Nuclear Safety Analysis Center Report 41

Nuclear Safety Analysis Center Report (NSAC) 41, Lightning Problemss and Protection at Nuclear
Power Plants [11 ] reviews lightning protection features at four sample nuclear power plants. Note that
plant identities were not revealed. The goal of the NSAC project was to assess the effectiveness of
existing lightning protection (up to 1981). NFPA 78-1975 (now superseded by NFPA 780) was used as
the evaluation basis. Adherence to the NFPA code is not a licensing requirement of nuclear plants;
however, it is a widely accepted standard for lightning protection. That is why the investigators
constructed a check sheet based on the NFPA document.

The review showed that two plants have higher levels of lightning protection. Neither of these plants
reported lightning-caused events. The two plants with less lightning protection experienced significant
lightning-caused upsets and damage. This comparison strongly suggests that high-quality lightning
protection systems lower the risk to lightning-caused problems.


Page 71

(9-2004) (Assigned by NRC, Add Vol., Supp., Rev.,
NRCMD 3.7 and Addendum Numbers, If any.)

(See histructions on te reverse) NUREG/CR-6866


Technical Basis for Regulatory Guidance on MONTH YEAR
Lighting Protection in Nuclear Power Plants J



P. D. Ewing R. A. Kisner K. Korsah M. R. Moore J. B. Wilgen R. T. Wood NUREG/CR

7. PERIOD COVERED (Inctusive Dates)

8. PERFORMING ORGANIZATION -NAME AND ADDRESS (IfNRCpovdeDiion, OfficeorRegion, US. Nuc sarRegulatoryCornmisionandmaig address;ifcontractor,
provide name and mazeV address.)

Oak Ridge National Laboiratory
Managed by UT-Battelle, LLC

9. SPONSORING ORGANIZATION - NAME AND ADDRESS (if NRC, type 'Same as above', If contractor, provide NRC Division, Office or Region, US Nuclear Regulatory Commission,
and mailen address.)

Division of Engineering Technology
Offfice of Nuclear Regulatory Research
U. S. Nuclear Regulatory Commission
Washington, DC 20555-0001


C. E. Antonescu, NRC Proiect Manager
11. ABSTRACT (200 words or less)

Oak Ridge National Laboratory (ORNL) has been engaged by the U.S. Nuclear Regulatory Commission
(NRC) Office of Nuclear Regulatory Research (RES) to develop the technical basis for regulatory
guidance to address design and implementation practices for lightning protection systems in nuclear
power plants (NPPs). With the advent of digital and low-voltage analog systems in NPPs, lightning
protection is becoming increasingly important. These systems have the potential to be more vulnerable
than older, analog systems to the resulting power surges and electromagnetic interference (EMI) when
lightning hits facilities or power lines. This report documents the technical basis for guidance on the
protection of nuclear power structures and systems from direct lightning strikes and the resulting
secondary effects. Four Institute of Electrical and Electronics Engineers (IEEE) standards are
recommended for endorsement to address issues associated with the lightning protection of nuclear power
plants and their equipment and personnel: IEEE Std 665-1995 (R2001), IEEE Guide for Generating
Station Grounding; IEEE Std 666-1991 (RI 996), IEEE Design Guide for Electric Power Service Systems
for Generating Stations, IEEE Std 1050-1996, IEEE Guide for Instrumentation and Control Equipment
Grounding in Generating Stations; and IEEE Std C62.23-1995 (R2001), IEEE Application Guide for
Surge Protection of Electric Generating Plants.

12. KEY WORDS/DESCRIPTORS (List words orphrases mtat willassist researchers h locatingthe port.) I3 AVAILABILflY STATEMENT

I&C, Instrumentation and Control, Lightning, Surge Protection, EMI, Electromagnetic Interference, unlimited
Grounding, Lightning Protection 14. SECURITY CLASSIFICATION

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