ML19208C810
| ML19208C810 | |
| Person / Time | |
|---|---|
| Issue date: | 08/31/1979 |
| From: | NRC OFFICE OF STANDARDS DEVELOPMENT |
| To: | |
| References | |
| TASK-OS, TASK-RS-705-4 REGGD-01.XXX, REGGD-1.XXX, NUDOCS 7909270531 | |
| Download: ML19208C810 (26) | |
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U.S. NUCLEAR REGULATORY COMMISSION
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S OFFICE OF STANDARDS DEVELOPMENT August 1979 c
Division 1 DRAFT REGULATORY GUIDE AND VALUE/ IMPACT STATEMENT Task RS 705-4 o
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9 LIGHTNING PROTECTION FOR NUCLEAR POWER PLANTS D
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GO A.
INTRODUCTION 4
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_ b 3 Ae N'DesignCriterion2,"DesignBasisforProtEtibn;ggainstNatural Phenomena,"ofAppendixA,"GeneralDesignCriteriagdrNIll.earPowerPlants,"
to 10 CFR Part 50, " Domestic Licensing of Productio$ arid Utilization Facil-A vp ities," requires, in part, that structures, systems', sand
- components important to safety be designed to withstand natural phenome The design bases for ggs these structures, systems, and components are required to reflect (1) appro-ex w
priate consideration of the most severe of$th'e-natbral phenomena that have gQ been historically reported for the sitefand, surrounding area, with sufficient
.x ~ m margin for the limited accuracy, quantit D and period of time in which the D
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historical data have been accumulated;*(2) appropriate combinations of the o
effect of normal and accident conditions;pkith the effects of the natural
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phenomena; and (3) the importance ofsthe safety functions to be performed.
A i General Design Criterion 18 "JnspectionandTestingofElectricPower Systems," of Appendix A to 10 CFR Part 50, requires, in part, that electric power systems is..ortant to sa'ety be designed with a cam bility to test periodically the opera 6ility and functional performance of their components.
This regulatory gu[y xyde describes criteria acceptable to the NRC seff for thedesign, appl,ica'iog,gud testing of lightning protection systems tr ensure e -
t that electrical trarv,1[nts resulting from lightning phenomena do not iander p
wy systemsimportanftosafetyinoperableorcausespuriousoperationofsuch systems.
790927053/
1042 261 This regulatory guide and the associated value/ impact statement are being issued in draf t fonn to involve the public in the early stages of the development of a regulatory position in this area. They have not received complete staff review, have not been reviewed by the NRC Regulatory Requirements Review Comit-tee, and do not represent an official MRC staf f position.
Public coments are being solicited on both drafts, the guide (including any implementation schedule) an'd the value/ impact statement. Coments on the value/ impact statement should be accompanied by supporting CorTnents on both draf ts should be sent to the Secretary of the Comission, yI 1,1,eaf { gulatory Nuc data.
19e Comission Washington, D.C. 20555, Attention: Docketing and Service Brcnch, by WW s
Requests for single copies of issued guides and draft guides (which may be reproduced) or for placement on an automatic distribution list for single copies of future guides and draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Comission, Washington, D.C. 20555, Attention:
Director, Division of Technical Infonnation and Document Control.
B.
DISCUSSION G
To ensure the continuous and reliable functioning of systems inportant to safety, protection against lightning-induced transients must be provided for the components and structures of these systems in the plant.
Properly placed lightning rods and masts have been proven effective against direct strokes.
Further, electric systems must also be protected from lightning and other elec-trical transients (for example, switching surges) to ensure that these systems and protection systems electrically connected to them are not damaged.
Surge arresters, which function to limit overvoltages, are applied for protection against surges entering the plant site through connected transmission lines.
Surge transient periods, regardless of cause, are usually very short.
However, these periods are extremely important, since it is at such times that circuit components are subjected to the greatest stresses from excessive cur-rents or voltages and damage to camponents or systems important to safety could result.
During abnormal conditions, when transiant currents take unusual paths, high transient voltages can appear between points that are normally at or close to the same potential.
This can cause electrical stresses that damage equipmen thereby adding considerably to the effects of the initial disturbance.
Adverse consequences of abnormal voltage disturbances can be greatly reduced by correct design.
The object of this design is to reduce transient potential gradients as much as possible.
Therefore, special grounding methods must be applied where soil conditions are particularly adverse and low grour.J resistance cannot easily be achieved.
These grounding methods sometimes must take the form of a counterpoise, a continuous ground mat laid underground.
The principal goal of any ground mat design is to provide as low a resistance path to ground fault currents as is necessary to prevent discharge voltages and reflected waves from causing transient overvoltages in sensitive equipment.
A hign frequency of induced or direct lightning surges on power transmis-
!A, C [. sign lines and transformers suggests that protecUon must be provided to ensure that high-energy surges do not propagate into plant distribution and m] n a jd j J 1 3
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protection systems and cause damage to redundant systems important to safety.
Direct strokes at the plant site are of concern only if the shielding masts are bypasFM r.+J the stroke terminates on electrical equipment.
In this case, the arrester, rollowing sparkover, would be subjected to surge discharge cur-rents of large magnitude and short duration which, because of the short time of application, may not stress a pt7perly applied arrester to its thermal limit.
Line surges entering as a result of shielding or backflash failures will also result in short-time current discharges that, again, do not thermally stress the arrester.
The longer-lasting switching surge stresses the thermal capabil-ity, as do several cycles of follow (pewer) current subsequent to arrester sparkover.
Available data suggest a significant frequency of lightning surges with currents on the order of 200,000 ampires.
Therefore, we have concluded that protection against a postulated design basis discharge surge of this current magnitude will provide a reasonably conservative assurance that nuclear systems important to safety will be protected against the most severe anticipated lightning-induced surges.
Lightning surges with currents larger than 200,000 amperes do occur, but at a lower frequency.
The consequences of these larger surges on plant systems important to safety would be as severe as those of any surge that is greater than the design capability of the systems being protected.
However, transmis-sion line and switchyard protection will further reduce the probability of such surges from reaching the plant systems important to safety.
Electrical transients generated from lightning phenomena and switching of clectric circuits have been a source of concern for many years.
Instrument failures, blowing of fuses in control circuits, and failures of insulation systems as a result of transients of electrical nature in nuclear power plants have increased the unavailability of systems important to safety.
The increasingly common use of highly sensitive solid state logic systems for the protection of nuclear power plants accentuates the need for closer scrutiny in the methods used for protecting such systems from transient over-voltages generated externally and propagated into the plant.
Common failure modes whereby surges of a transient nature could render redundant components of systems important to safety inoperable can be postulated.
For example, power to redundant onsite electric distribution systems is typically supplied I
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from tne offsite transmission system through a power transformer with a typi-cal Lransformation ratio of 345 kV to 4.16 kV.
In this type of system, a pri-mary-to-secondary failure in the transformer as a result of lightning or other causes could propagate the primary voltage to the secondary if the secondary is not properly grounded to hold the voltage at near normal secondary voltage.
Additionally, a lightning-induced surge originating in the primary side of the transformer can propagate to the redundant circuits in the secondary through capacitive coupling in the transformer with potentially damaging consequences to the redundant circuits in engineered safety feature sequence logics and pro-tection systems electrically connected to the offsite power system.
Insulation coordination between protector and protected equipment is of great importance in power systems.
An arrester with an impulse characteristic that is higher than that of a transformer would not be effective in protecting the transformer even at the first surge.
Therefore, it is essential that the boundary impulse voltage characteristic curve for the insulation of the pro-tected equipment be greater than the impulse voltap' characteristic curve of the protective equipment for a voltage wave of the 1.2 x 50 psec shape, i.e.,
1.2 psec to reach peak value and 50 psec to decay to half peak.
The impulse voltage characteristic c irve for the maximum surge that the protector must control can then be completely contained within the boundary impulse voltage characteristic curve of the protected equipment.
Care must be exercised in the selection of surge arresters for applica-tion in electric power systems.
Adequate protection can be provided by modern lightning arresters.
These a resters can be applied to protect the insulation and divert surges from prop Jating to sensitive equipment in the plant.
Under certain conditions, however, an arrester can be subjected to sustained rms overvoltages from which it cannot recover, thereby subjecting the power system to additional faulted conditions.
Therefore, the arrester voltage rating must be higher than the maximum expected rms line-to ground voltage under any normal or faulted condition.
Lightning arresters for a.c. power systems are rated according to the maximum line-to ground system voltage they are expected to withstand.
Of the three types of surge arresters (distribution, intermediate, and station),
the station type offers the best protective characteristics.
Its higher discharge-current capacity and its essentially flat voltage-time character-istic make it particularly suited for protecting transformer insulation o"Ro
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where the margin between operating voltage and surge strength is relatively I
low.
ANSI C62.1-1975, " Surge Arresters for Alternating-Current Power Circuits,"I describes procedures for the qualification of lightning arresters used in elec-tric power systems.
This standard, although not specifically developed for use in nuclear service, provides guidelines for the performance qualification of arresters that can be used in nuclear service.
Additionally, some sactions of ANSI C62.2-1969, " Guide for Application of Valve-Type Lightning Arresters for Alternating-Current Systems,"1 provide guidelines for the application of lightning arresters in nuclear service.
This standard also was not developed for nuclear service, and use can be made of selected sections only.
The statistical data on surge characteristics relied upon for the devel-opment of the above standards were collected in the 1940's by instrumentation of limited and questionable accuracy.
Therefore, complete endorsement of these standards is not possible at this time.
C.
REGULATORY POSITION D
Lightning protection for systems important to safety in nuclear power plants should conform to the design, inspection, and testing crir.eria presented below.
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1.
DESIGN BASIS SURGE O
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Surge protection equipment should be designed for a discharge-current surge of no less than 200,000 amperes with an 8 x 20 psec wave shape.
If analyses of local conditions indicate a high frequency of larger surge currents, selection of a larger design basis surge should be considered.
2.
SURGE ARRESTERS FOR TERMINAL EQUIPMENT PROTECTION 2.1.
Surge arresters with a rating of 100 percent of normal line-to-line voltage should be provided to e,>tect against any anticipated overvoltage 1Copies may be obtained from the American National Standards Institute, D
1430 Broadway, New York, New York 10018.
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1042 265 m,
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conditions in grounded neutral power systems unless a lower rating is justi-fied by calculations based on position 2.2.
2.2.
For use of surge arresters with a lower rating than 100 percent in grounded neS'.ral power systems, detailed system fault calculations should be performed to determine the maximum line-to ground voltages (where zero-sequence resistance to positive-sequence reactance ratios are positive and 1.0 or less and zero-sequence reactance to positive-sequence reactance ratios are positive and
'.0 or less).
2.3.
The provisions for determining maximum line-to ground voltages identi-
?ied in section 3.1 of ANSI C62.2-1969 should be followed.
For effectively grounded neutral systems, the arrester selection curves (Fig. 1 of the standard),
may be used for estimating purposes only.
2.4.
Selection of surge arrester ratings for isolated neutral systems should be based on calculations taking into account the constants of the system, the type of fault considered, and the fault resistance.
2.5.
Station-type surge arresters with a current-discharge capability of 200,000 amperes should be installed on the primary and secondary sides of startup and unit auxiliary transformers shared by redundant systems.
For redundant systems that do not share transformers, the discharge capability recommended in section 5 of ANSI C62.1-1975 is acceptable.
2.6.
Station-type surge arresters with a current-discharge capability of 200,000 amperes should be installed at the electrical switchgear upstream of the feeder breaker connected to startup and unit auxiliary transformer second-aries that are shared by redundant systems.
For redundant systems that do not share transformers, the discharge capability recommended in section 5 of ANSI C62.1-1975 is acceptable.
2.7.
If n arresters are used in parallel to meet the 200,000-ampere recom-mendation of items 2.5 and 2.6, each arrester should be capable of withstanding 200,000/n amperes in service.
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2.8.
Qualification testing for surge arresters should be conducted in I
accordance with the requirements specified in ANSI C62.1-1975.
2Property "ANSI code" (as page type) with input value "ANSI C62.1-1975.</br></br>2" contains invalid characters or is incomplete and therefore can cause unexpected results during a query or annotation process..9.
Design tests included in section 7 of ANSI C62.1-1975 should be used but should be supplemented to include high-current-discharge tests of 200,000 amperes for arresters (or parallel combinations of arresters, see item 2.7) used to protect redundant systems important to safety that share startup or unit auxiliary transformers.
For redundant systems that do not share trans-formers, the high-current-discharge tests recommended in the standard are acceptable.
2.10.
The provisions recommended in section 3.5 of ANSI C62.2-1969 for insulation coordination of transformers external to systems important to safety, namely unit auxiliary and startup, are acceptable at a design basis discharge-current surge best suited for the particular application.
However, for redun-dant systems important to safety electrically connected to these transformers, the arrester discharge voltage from a design basis discharge current of 200,000 amperes reaching these systems should not exceed their withstand capability.
D 2.11.
Periodic testing of surge arresters should be conducted as follows:
2.11.1.
At intervals not to exceed ten years, a surge arrester of the oldest installed group of each type and rating should be removed and replaced.
The removed arresters should be tested in accordance with the performance test requirements specified in section 5 of ANSI C62.1-1975.
2Property "ANSI code" (as page type) with input value "ANSI C62.1-1975.</br></br>2" contains invalid characters or is incomplete and therefore can cause unexpected results during a query or annotation process..31.2.
If the tects discussed in item 2.11.1 reveal unsatisfactory performance that is attributed to common design or aging defects, all arresters of the same type and rating, including those installed ten years after the oldest installed group, should be replaced.
If, however, the unsatisfactory performance is attributed to a random failure unique to the arrester under test, additional ecolacements should not be required.
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3.
GROUND WIRES FOR TRANSMISSION LINE SHIELDING 3.1.
Ground wires should be provided for a sufficient distance, as deter-mined by analysis, along the transmission lines.
3.2.
Transmission lines should be shielded to maintain an angle of pro-tection that does not exceed 30.
Shielding at an angle of protection greater than 30 should be justified by analysis.
3.3.
Tower footing resistance to ground should be maintained low enough to ensure that lightning discharge transient voltages do not exceed the voltage withstand level of the insulation between tower and conductor.
3.4.
Visual inspections of ground wire continuity consistent with other planned periodic inspection programs for outdoor electrical installations should be conducted.
4.
CONVENTIONAL LIGHTNING RODS (AIR TERMINALS) FOR PROTECTION OF STRUCTURES 4.1.
Air terminals should be installed to protect switchyards, offgas stacks, fuel tanks, meteorological towers, and other components whose functional integrity is important in maintaining the safety of the plant.2 4.2.
The air terminals should be connected to the plant grounding system by electrical bonding.'7 4.3.
Air terminals should be located in such a way that all items'to be pro-tected are included in a cona of protection with a nominal angle of 40 4.4.
Visual inspections and conductor continuity tests consistent with other planned periodic inspection programs for outdoor electrical installations should be conducted.
2 National Standard NFPA No. 78-1968, " Lightning Protection Code," Part II, Protection of Buildings and Miscellaneous Property, provides acceptable nethods (or the. detailed installation 9f lightning rods.
Copies.nay be obtained from th'e'; National Fire Protection Association, 470 Atlantic Avenue, Boston, Massachusetts 02210.
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D.
IMPLEMENTATION This proposed guide has been released to encourage public participation in its development.
Except in those cases in which an applicant proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method to be.desci-ibed in the active guide reflecting public comments will be used "., the evalua ; ion of applications for construction permits docketed after the implementati a date to be specified in the active guide.
Implementation by the staff will in no case be earlier than April 1980.
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DRAFT VALUE/ IMPACT STATEMENT l
1.
THE PROPOSED ACTION 1.1 Description Electrical transients resulting from lightning phenomena and switching of electrical circuits have hampered the perfortunce of sensitive electronic equipment and insulation systems for many years.
The history of instrument failures (Refs. 1 through 29), blowing of fuses in control circuits, and failures of insulation systems suggest that transients of electrical nature can increase the risk of system unavailability beyond acceptable levels.
The increasingly common use of highly sensitive solid state logic systems for the protection of nuclear power plants accentuates the need for closer scrutiny in the method used for.otecting such systems from transient over-voltages.
The staff has not reviewed the surge protection aspects of nuclear power plants and therefore is not thoroughly familiar with the present practices used for the protection of systems important to safety from transient over-voltages.
Published literature and industry standards (Refs. 30 and 31) on tne subject reveal that surge protection is based largely on statistical methods developed for conventional nonnuclear systems principally on a cost-benefit basis; no sper M1 consideration has been given for the protection of nuclear plant systems important to safety.
There is evidence to support the concern that common failure modes can exist in the nuclear plant safety systems whereby surges of a transient nature could render redundant components inoper-able.
For example, power to redundant safety systems is typically supplied from the offsite power transmission system through a transformer with a typical transformation ratio of 345 kV/4.16 kV.
Therefore, a primary-to-secondary failure in the transformer could propagate the primary voltage to the secondary, if the secondary is not properly designed (Ref. 18).
Additionally, a surge originated in the primary side of the transformer can prof. agate to the redun-dant circuits in the secordary through capacitive coupling in the transformer, with potentially damaging consequences.
Such high volteges occurring even for short durations could destroy sensitive equipment on onsite distribution buses l
s 1042 210 10
and render onsite power supplies inoperable.
Additionally, protection system I
components electrically connected to these supplies could be rendered inoperable.
The frequency of induced or direct lightning surge on the primary side of a transformer could be high, based on statistical data collected on strikes per mile of transmission line per year (Refs. 32 and 33).
In the event of such occurrence, the propagation of the surge to plant distribution systems is a certainty if appropriate protection is not installed on both sides of the transformer.
The propagation of high surges through transformer windings could occur as a result of the following:
a.
If the surge rise time is shorter than the arrester's response time, a significant amount of the surge will propagate past the arrester before it is safely carried to the ground by the arrester (Ref. 34).
b.
In a successfully.enponding surge arrester the voltage drop devel-oped between phase and ground is a function of the magnitude of the current surge arrested and the resistance to ground (IR drop).
Therefore, a successful discharge of a current surge of 200,000 amperes through a 10-ohm resistance will develop a voltage drop of 2,000,000 volts on the primary side of the transformer wi',h the propagation of a significant fraction of that voltage (Ref. 35), electrostatically, to the secondary through transformer capacitance (if the secondary is not properly grounded) with potentially damaging conse-quences to systems electrically connected to this secondary.
Substantial effort is being expended to determine a conservative
" design basis surge" for lightning and some switching surges (Refs. 34 and 36-39).
The significant parameters that define a surge are rise time to peak value, peak value, and time to half peak value.
Rise times, peak values, and frequency distribution of lightning surges are presently under study by NRC, by NASA and the University of Florida, and by DOE (Refs. 34 and 37).
However, the internationally accepted rise times appear acceptable at this time fo' our purposes, and when results are made available from the above studies, we will reevaluate our present position.
The frequency of thunderstorm days for various locations is depicted in an isokeraunic map of unknown origin widely used by meteorologists (Ref.
32).
However, an updating of this map may be necessary at t5is time in order to ensure its validity (Refs. 34 and 37).
Surge protection for safety systems in nuclear power plants can be achieved if the following system protection is implemented:
11 f
a.
Installation of suitable ground wires running the length of the transmissi n line for a reasonable distance from the plant site to protect I
against the effects of direct lightning strikes on power transmission lines.
b.
Conventional lightning rods strategically located to protect switchyards, offgas stacks, meteorological towers, fuel tanks, and other com-ponents whose functional integrity is important for maintaining safe plant operation.
c.
Installation of high-energy-absorption surge arresters on cri-tical lines entering the plant.
d.
Installation of surge arresters on the primary and secondary sides of power transformers.
e.
Installation of low-energy-absorption surge suppressors in onsite distribution systems and critical instrument power supplies.
The proposed action is the development of design guidance on accept-aule criteria for the protection of nuclear systems important to safety from surges that can appear on the components and systems listed above.
The likeli-hood of damaging surges propagated through field wiring to redundant systems important to safety is extremely low and need not be addressed.
Elevated ground potentials resulting from the discharge of high current I
surges to ground may adversely affect the performance of sensitive integrated circuit components used in reactor protection systems.
Therefore, designs that use integrated circuit components must be evaluated and designed to ensure that ground potentials do not adversely af fect their perforn'arce.
- 1. 2 Need for the Proposed Action The potential consequences on the public safety are of such significance that it seems imperative for the staff to include in their review of systems important to safety the protection of such systems from electrical surges gen-erated externally or internally.
To accomplish this goal, general guidance is required to bring to the attention of the design engineer and the NRC reviewer the significant areas that need particular scrutiny in the design of systems important to safety and to provide acceptable methods for surge protection for such systems.
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- 1. 3 Value/ Impact of the Proposed Action 1.3.1 NRC Operations The benefit gained by the proposed action is to secure additional staff awareness of the significant areas that require additional review and to ensure that current knowledge of surge phenomena is considered in the design of sys-tems important to safety.
Additional review time will be required and the reviewing staff should become thoroughly familiar with the technical aspects of surge protection and its compatibility with the systems being protected.
The Inspection and Enforcement staff should also become familiar with the staff requirements to ascertain that installations are made in accordance with accepted design criteria.
Research to support our proposed action is currently under way (Refs. 34 and 37) to ascertair equipment tolerance to surges, surge characteristics, surge amplitudes, and frequency.
Also, funding for technical assistance may be required to evaluate the level of protection afforded by present designs.
1.3.2 Other Government Agencies The activities of FAA, NASA, and DOE are being evaluated (Refs. 34 and 37) for the purpose of obtaining information on efforts expended by these agencies in addressing protection against electrical surge phenomena.
The information available at these agencies is being used as background for our effort.
There is no impact anticipated on these agencies as a result of our proposed action.
1.3.3 Industry A close scrutiny of surge protection for sensitive instrumentation, ade-quate insulation coordination, and sufficient conventional lightning protection for components exposed to direct lightning will reduce inadvertent failures of plant equipment and thus increase plant availability.
Surge protection is assumed an integral part of good engineering design.
Therefore, the differential cost for implementing all our proposed provisions for a 200,000-ampere level of protection at a 345 kV switchyard will be as follows:
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a.
Purchase cost of arresters for startup and unit auxiliary transformers and onsite switchgear at $25/kV:
$31,000 I
b.
Approximate installation cost:
$31,000 c.
Approximate cost for periodic surveillance per plant site at $25,000/ test for 40 years:
$175,000 TOTAL
$237,000 A more accurate cost evaluation could be made if the present protection level were known.
1.3.4 Public The value to the public will be in the direction of more reliable and safe nuclear power at a moderate financial cost.
1.4 Decision on the Proposed Action In view of the potential risks associated with electrical surges on equip-ment, guidance should be issued to identify acceptable design criteria for consideration in the design and installation of nuclear systems important to safety.
2.
TECHNICAL APPROACH 2.1 Technical Alternatives Alternative methods for addressing surge protection for redundant systems important to safety that could limit common-mode failures resulting from high-energy surges on single transmission lines would require:
a.
Strict implementation of electrical 'ndependence of offsite as well as onsite transmission and distribution systems to ensure that single surge events do not propagate to redundant trains of systems important to safety, or b.
Underground transmission of offsite power to plant systems to mini-mize the likelihood of direct lightning strikes entering the plant distribution systems.
1042 274 14 s
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2.2 Discussion and Comparison of Technical Alternatives I
2.2.1 Redundant Offsite Power Sources The implementation of redundant offsite power sources will limit the expo-sure of protection systems to certain common-mode failures resulting from surges initiated in (a) primary-to-secondary transformer failures, (b) switching at the primary side of the transformer, and (c) lightning surges on the primary side of the transformer.
2.2.2 Underground Transmission Underground transmission will limit the direct strikes on the power trans-mission to plant auxiliaries.
However, the common-mode failures associated with transformer failures and switchin[' will not be eliminated with this alter-native design unless redundancy is also maintained in the underground circuits.
2.3 Decision on Technical Approach The proposed action discussed in Part 1 should be undertaken.
The tech-nical alternatives described in item 2.2 are not feasible at this time in view of the limitations in independence requirements expressed in General Design Criterion 17 of Appendix A to 10 CFR Part 50.
3.
PROCEDURAL APPROACH 3.1 Procedural Alternatives Potential SD procedures that may be used to promulgate the proposed action and technical approach include the following:
Regulation Regulatory guide ANSI standard, endorsed by a regulatory guide Branch position NUREG report
)
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3.2 Value/ Impact of Procedural Alternatives l
A NUREG is not a viable alternative because it will not contain the kind of guidance required to interpret the existing regulations.
General Design Criterion 2 of Appendix A to 10 CFR Part 50 is the regulation covering the sub-ject technical issue.
Therefore, a regulatory guide is required to provide the staff acceptable methods for implementing this regulation.
At present there is no ANSI standard addressing surge protection for redund-ant systems important to safety that could limit common-mode failures resulting from high-energy surges on single transmission lines.
However, a standard would be the most viable option for future consideration because the technical resources and experience of industry will provide a valuable contribution in the develop-ment of consistent requirements for all plant designs.
A branch position will not be a viable alternative because of its limited scope and distribution.
- 3. 3 Decision on Procedural Approach A regulatory guide should 5e prepared, e.id licensees as well as applicants should be requested to evaluate thei" ct:.ye protection and make appropriate modifications, if needed, to ensure minimum protection requirements.
4.
STATUTORY CONSIDERATIONS 4.1 NRC Authority Authority for this guide would be derived from the licensing authority a i safety requirements of the Atomic Energy Act through the NRC regulations, in particular, General Design Criterion 2 of Appendix A to 10 CFR Part 50, which requires, in part, that structures, systems, and components important to safety be designed to withstand natural phenomena.
The design bases for these struc-tures, systems, and components are required to reflect (a) appropriate consid-eration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data s<
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16
have been accumulated, (b) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena, and (c) the importance of the safety functions to be performed.
4.2 Need for NEPA Assessment The proposed action is not a major action as defined by 10 CFR g 51.5(a)(10),
and does not require an environmental impact statement.
5.
RELATIONSHIP TO OTHER EXISTING OR PROPOSED REGULATIONS OR POLICIES The proposed action is considered as part of the implementation of the requirements set forth in General Design Criterion 2 of Appendix A to 10 CFR Part 50.
There are no potential conflicts or overlaps with other agencies antici-pated as a result of the proposed action.
The Standard Format and Content of Safety Analysis Reports and the Stand-ard Review Plan should be revised to address the necessity for evaluation of surge protection for safety-related systems.
Backfitting requirements should be determined upon completion of the guide, with priority placed on plants located in areas with a high frequency of thun-derstorm activity.
6.
SUMMARY
AND CONCLUSIONS Failures in a number of installations (Refs. 1 through 17 and 19 through
- 29) suggest that the high energies release' by lightning have the potential to cause severe damage to sensitive systems important to protect the health and safety of the public.
Therefore, a regulatory guide identifying a consistent set of design criteria for surge protection for nuclear power plants is appro-priate at this time.
However, a reevaluation may be necessary at a later date upon completion of the NRC, DOE, and the NASA-University of Florida Studies, whQhareaimingtomoreaccuratelydefinerisetimes,peakvalues,andfre-quency for lightning surges.
I 1042 277 t-y 17
7.
ALTERNATIVE REGULATORY POSITION During the preparation of the proposed guide, a differing technical position was developed by a staff member of the Division of Systems Safety, Office of Nuclear Reactor Regulation.
The staff member has expressed his technical position as a proposed alternative regulatory position, which is included as Attachment A to this draft value/ impact statement.
Public review of, and comments on, the proposed alternative regulatory position are also requested.
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1042 278 18
REFERENCES 1.
QUAD CITIES 2, "Offgas System Explosion (Lightning)," BBS-73-44, March 3, 1973.*
2.
OYSTER CREEK 1, "Three Power Transformer Fuses for Diesel Generator No. 2 Were Blown (Lightning)," Rept. 73-13, June 21, 1973.
3.
VERMONT YANKEE 1, "Offgas System Explosion (Lightning)," LER A0-73-16, June 12, 1973.
4.
FT. CALHOUN 1, " Loss of Offsite Power (Lightning)," Rept. 73-4, September 26, 1973.
5.
FT. CALHOUN 1, " Loss of Offsite Power (Lightning)," LER 50-285/77-4, February 10, 1977.
6.
MILLSTONE 1, "Lorr af Offsite Power (Lightning)," Rept. 71-12, June 25, 1971.
7.
MONTICELLO 1, " Loss of Offsite Power (Lightning)," Rept. 76-8, June 26, 1976.
8.
VERMONT YANKEE 1, " Process Computer and Miscellaneous Equipment Rendered D
Inoperable, Unit Scrammed (Lightning)," LER A0-74-11, July 5, 1974.
9.
YANKEE R0WE, " Actuation of Undercurrent Relays on Two Main Coolant Loops Resulted in Reactor Scram (Lightning)," Rept. 50-29/72-08, August 27, 1972.
10.
INDIAN POINT 2, Unusual Occurrence, PNO-77-126, July 14, 1977.
11.
PALISADES, Unusual Occurrence, PNO-77-170, September 24, 1977.
12.
INDIAN POINT 2 and 3, Unusual Occurrence, PNO-77-172, September 26, 1977.
13.
FARLEY 1, " Loss of Offsite Power and Loss of Reactor Coolant Flow and Rod Position Indication (Lightning)," LER 77-012/01T-0, September 16, 1977.
14 FARLEY 1, " Loss of Offsite Power and Inadvertent Safety Injection (Lightning)," LER 78-033/01T-0, June 6, 1978.
15.
RANCHO SECO, " Lightning on Main Transformer (Damaged Winding),"
January 14, 1978.
16.
PILGRIM 1, " Loss of Offsite Power (Lightning)," LER 78-035-01X-0, August 6, 1978.
AReports of events submitted to the NRC by licensees of nuclear power plants are available for inspection at or may be obtained by written request to the Commission's Public Document Room, 1717 H Street, NW., Washington, D.C.
20555.
1042 279 1,
17.
CRYSTAL RIVER 3, " Meteorological Instrumentation Failure (Lightning),"
I LER 78-036/03L-0, July 16,1978.
18.
BEAVER VALLEY 1, " Transformer Failure," LER 78-043/01T-0, July 28, 1978.
19.
MONTICELLO 1, " Power to Reserve Transformer Lost (Lightning),'
Rept. LER 78-012/03L-0, June 16,1978.
20.
VERMONT YANKEE 1, " Air Samplers Inoperable; Fuses Blown (Lightning),"
Rept. R0 78-18/3L, June 25, 1978.
21.
VERMONT YANKEE 1, " Battery Charger CA-1 Failure; Stack Gas Monitoring System Failure, Motor Control Center 89B Failure (Lightning)," Repts.
78-13/3L, 78-14/3L, and 78-15/3L, June 19, 1978.
22.
INDIAN POINT 3, " Loss of Offsite Power (Lightning)," Rept. 77-3-5, May 6, 1977.
23.
' ERMONT YANKEE 1, "Of fgas System Explosion (Lightning)," August 31, 1973.
Letter from R. T. Carlson (NRC, IE) to G. W.
Reinmuth (NRC, IE) dated September 18, 1973.
24.
VERMONT YANKEE 1, "Offgas System Explosion (Lightning)," September 3, 1973.
Letter from R. T. Carlson (NRC, IE) to G. W. Reinmuth (NRC, IE) dated Septen,ber 18, 1973.
25.
PEACH BOTTOM 2 and 3, " Stack Flow Transmitters Failure (Lightning),"
Rept. 50-277-75-54 and A0-75-54.
26.
D.C. COOK 1, " Seismic Recorders Failure (Lightning)," Rept. A0-50-315/
75-16, April 24, 1975.
27.
PEACH BOTTOM 2, " Blown Fuses in Stack Sampling System (Lightning),"
Rept. 2-76-51/1T, July 17, 1976.
28.
PEACH BOTTOM 2, " Stack Flow Recorders Failure (Lightning)," Rept. 2-76-45/
3L, June 20, 1976.
29.
D.C. COOK 1 and 2, " Loss of Offsite Power (Lightning)," September 1, 1977.
Memorandum from Executive Director for Operations to Commissioners Hendrie, 3ilinsky, Kennedy, and Bradford dated September 6, 1977.
30.
ANSI C62.1-1975, " Surge Arresters for Alternating-Current Power Circuits,"
American National Standards Institute, New York, N.Y.
31.
ANSI C62.2-1969, " Guide for Application of Valve-Type Lightning Arresters for Alternating-Current Systems," American National Standards Institute, New York, N.Y.
32.
Westinghouse Electric Corporation, Transmission and Distribution Refer-ence Book, East Pittsburgh, PA, 1964.
'U!
1042 210 h-20 a
.-------,y 33.
R. H. Golde, "The Frequency of Occurrence and the Distribution of Lightning Flashes to Transmission Lines," American Institute of Electrical Engineers, Transactions, Vol. 64, pp. 902-910, 1945.
34.
H. Wayne Beaty, " Researchers Gather Lightning Data," Electrical World, PP. 52-54, August 2, 1978.
35.
A. Greenwood, Electrical Transients in Power Systems, Wiley, New York, 1971.
36.
G. A. Brown, " Joint Frequency Distribution of Stroke Current Rise and Crest Magnitude to Transmission Lines," IEEE Power Engineering Committee, Power Apparatus and Systems, No. F77017-7, Janua ry/Feb rua ry, 1978.
37.
"An Unusual Lightning Flash at Kennedy Space Center," Science, Vol. 201, No. 4350, July 7, 1978.
38.
J. C. Cronin, R. G. Colclaser, and R. F. Lehman, " Transient Lightning Overvoltage Protection Requirements for a 500 kV Gas-Insulated Substation,"
IEEE, Power Engineering Committee, Power Apparatus and Systems, Vol. 97, No. 1, pp. 646-652, January / February 1978.
39.
S. Szpor, " Comparison of Polish Versus American Lightning hacords,"
IEEE Power Engineering Committee, Power Apparatus and Systems, Vol. 88, No. 5, pp. 646-652, May 1969.
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,1
ATTACHMENT A C.
REGULATORY POSITION Conformance with the principles and requirements of the following standards (as applicable) provides acceptable methods for complying with General Design Criteria 2 and 18 of Appendix A and with Appendix B to 10 CFR Part 50 with respect to the design, qualification, construction, installation, and testing of systems and components providing protection against lightning for light-water-cooled nuclear power plants, subject to the following:
National Fire Protection Association (NFPA) No. 78-1975, " Lightning Protection Code,"* Part II, Protection of Buildings and Miscellaneous Property, and Part III, Protection of Structures Containing Flammable Liquids and Gasses; ANSI C62.1-1975, American National Standard, " Surge Arresters for Alternating-Current Power Circuits";** and ANSI C62.2-1969, American National Standard, " Guide for Application of Valve-Type Lightning Arresters for Alternating-Current Systems."**
1.
PROTECTION OF STRUCTURES Lightning protection should be provided against direct strokes to struc-tures and exposed equipment installations, including containment, auxiliary buildings, off gas stacks, fuel tanks, meteorological towers, and other compo-nents important for maintaining the safety of the plant.
The systems and equipment that provide this protection should conform with the principles and ACopies may be obtained from the National Fire Protection Association, 470 Atlantic Avenue, Boston, Massachusetts 02210.
4 1042 282 1
requirements of NFPA No. 78-1975, subject to the following:
Sections 2101(d),
2102(c) through (i), and 2122(b) should be replaced by the following:
Aluminum l should not be used as a conductor or structural support member.
2.
PROTECTION OF SWITCHYARD EQUIPMENT AGAINST DIRECT STROKES Overhead ground wire shielding, augmented by air terminals and masts as necessary, should be provided to protect all switchyard com snenM : f the power system (including overhead-line power circuits from the switchyard to other plant structures) against direct lightning strokes.
The complete shielding system, including the overhead components, interconnecting conductors, and ground-ing system, should be designed and installed in accordance with establishe's conservative design principles and practices of tne electric utility industry, and the ground resistance should not exceed one ohm.
In adcition, the design should provide a shielding effectiveness such that shielding failure stroke current (Imax, the current in a lightnir.g strike that bypasses the shielding and strikes a live component directly) will not exceed 15,000 amperes as defined by the relation I
h+y
- 7.1 1 75 0
- r
=
s max 2(1 - sin O )
s where the maximum strike distance (rs m ) is function of shield wire height (h), live component height (y), and shield angle (O ).
All dimensions are in s
meters; I is in kA.
3.
PROTECTION OF TRANSMISSION LINES AGAINST DIRECT STROKES Overhead ground wire shielding should be provided to protect all transmis-sion lines terminating in the switchyard against direct lightning strokes.
This shielding system should be provided over the entire length of the line; however, it should definitely be provided for a minimum distance of one-half ADetails for determination of shielding effectiveness using this method are con-tained in a paper by G. W. Brown, " Lightning Performance - I Shielding Failures Simplified," IEEE Transactions on Power Apparatus and Systems, Vol. PAS-97, No.
January / February 1978.
This paper specifically addresses transmission line shielding, but the methodology is readily applicable to switchyard shielding.
c p" c p. n r 1042 283 2
9
- I i
g
5.
SURGE PROTECTION FOR CLASS 1E SWITCHGEAR Station-type surge arresters should be provided for all Class 1E switchgear components that are connected to exposed overhead lines either directly or through a short length of cable.
These arresters should conform to the following:
5.1. The arresters should be selected and applied in conformance with Regu-latory Positions C.4.1, C.4.2, and C.4.3 above.
5.2. The arresters should be installed in the circuit upstream of the feeder breaker; and the physical arrangement should be such as to preclude damage to the switchgear in the event of arrester failure.
6.
PERIODIC SURVEILLANCE OF LIGHTNING Fh0TECTION SYSTEMS Periodic surveillance of lightning protection syster.is and components addresse in Regulatory Positions C.1 through C.5 should be performed, consistent with other planned periodic surveillance programs for outdoor electrical installations.
As a minimum, this periodic surveillance should include:
6.1. Visual inspectior, augmented by conductor continuity terts and ground resistanc'e measurements as deemed necessary to ascertain the functional capability of the systems providing protection against direct strikes to structures, switchya components, and transmission lines.
6.2. Visual inspection of the surge arrester installation to determine if there is evidence of physical damage, surface contamination, or other deteriora-tion in the arrester or its line and ground connections that could result in failure of surge protection.
The visual inspection should be augmented by con-ductor continuity tests and ground resistance measurements as deemed necessary to ascertain the functional capability of the surge arrester installations.
~
1042 285 4
x
(
(,,e
6.3. A check of the surge arrester discharge counter reading and leakage D
grading current reading for each arrester.
A permanent record of these data should be maintained, and an assessment of arrester functional capability should be determined by comparison with previous reaoings and with the recommendations of the manufacturer in this regard.
If the functional capability of an arrester is deemed to be marginal, it should be replaced in accordance with established maintenance procedures for this type of equipment.
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1042 286
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UNIT E D STATES NUCLIAM REGULATORY CO MUf SSION I
l a AsmucT08. o. c. 2osss Of f ICI AL BustNE55 u s MUCLE AR RE GUL ATOR Y C O ""S' 0 "
PE N ALT Y F OR PRiv ATE USE, $300 LJ 4
1042 287
.