Regulatory Guide 1.75: Difference between revisions

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{{Adams
{{Adams
| number = ML13350A340
| number = ML043630448
| issue date = 01/31/1975
| issue date = 02/07/2005
| title = Physical Independence of Electric Systems
| title = Criteria for Independence of Electrical Safety Systems, Rev. 3
| author name =  
| author name = Aggarwal S
| author affiliation = NRC/RES
| author affiliation = NRC/RES/DET/MEB
| addressee name =  
| addressee name =  
| addressee affiliation =  
| addressee affiliation =  
Line 10: Line 10:
| license number =  
| license number =  
| contact person =  
| contact person =  
| document report number = RG-1.075, Rev. 1
| case reference number = DG-1129
| document report number = RG-1.075, Rev 3
| document type = Regulatory Guide
| document type = Regulatory Guide
| page count = 3
| page count = 5
}}
}}
{{#Wiki_filter:Revision 1 January 1975 U.S. NUCLEAR REGULATORY COMMISSION
{{#Wiki_filter:1 Standards promulgated by the Institute of Electrical and Electronics Engineers (IEEE) may be purchased from the IEEE Service Center,
*
445 Hoes Lane, Piscataway, NJ  08854 (800-678-4333).
REGULATORY GUIDE
The U.S. Nuclear Regulatory Commission (NRC) issues regulatory guides to describe and make available to the public methods that the NRC staff considers acceptable for use in implementing specific parts of the agencys regulations, techniques that the staff uses in evaluating specific problems or postulated accidents, and data that the staff need in reviewing applications for permits and licenses.  Regulatory guides are not substitutes for regulations, and compliance with them is not required.  Methods and solutions that differ from those set forth in regulatory guides will be deemed acceptable if they provide a basis for the findings required for the issuance or continuance of a permit or license by the Commission.
REGULATORY GUIDE 1.75 PHYSICAL INDEPENDENCE OF ELECTRIC SYSTEMS


==A. INTRODUCTION==
This guide was issued after consideration of comments received from the public. The NRC staff encourages and welcomes comments and suggestions in connection with improvements to published regulatory guides, as well as items for inclusion in regulatory guides that are currently being developed. The NRC staff will revise existing guides, as appropriate, to accommodate comments and to reflect new information or experience. Written comments may be submitted to the Rules and Directives Branch, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.
Section 505.5a. "Codes and Standards," of l0 CFR
Part
50.


"Licensing of Production arid Utiliz.ation Facilities," requires in paragraph (hi)
Regulatory guides are issued in 10 broad divisions:  1, Power Reactors; 2, Research and Test Reactors; 3, Fuels and Materials Facilities; 4, Environmental and Siting;
that protectihon systems incel (tie requirenments set forth in tihe Institute ofl Electrical and Electronics Engineers Standard,
5, Materials and Plant Protection; 6, Products; 7, Transportation; 8, Occupational Health; 9, Antitrust and Financial Review; and 10, General.
"'Criteria for Protectiun Systemis fur Nuclear Power Generating StatiolnS." (li'lE 271W . Section 4.6 of IEEE
Std
279-1971 (also designated ANSI
N42.7-1972)
requires. in part. that channels that provide signals for the same protective function be independent arid physically separated. General Design Criterion 3. "Fire Protection.'" it' Appendix A. "(Gencinal DXsiwi Criteria fur Nuclear Power Plants." to 10 CFR Part 50 requires.


in part.
Requests for single copies of draft or active regulatory guides (which may be reproduced) should be made to the U.S. Nuclear Regulatory Commission, Washington, DC
20555, Attention: Reproduction and Distribution Services Section, or by fax to (301) 415-2289; or by email to Distribution@nrc.gov.  Electronic copies of this guide and other recently issued guides are available through the NRCs public Web site under the Regulatory Guides document collection of the NRCs Electronic Reading Room at http://www.nrc.gov/reading-rm/doc-collections/
and through the NRCs Agencywide Documents Access and Management System (ADAMS)
at http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML043630448.  Note, however, that the NRC has temporarily suspended public access to ADAMS so that the agency can complete security reviews of publicly available documents and remove potentially sensitive information.  Please check the NRCs Web site for updates concerning the resumption of public access to ADAMS.


that structuress, systems. and components important to safety be desitgned anid located to I miniriZe , consistent with other safety requiremen ts, the probability and effect of fires. General Design Criterion
U.S. NUCLEAR REGULATORY COMMISSION
1 7. "Electric Power Systeins," requires. in part. that the onsite electric power supplies, including the batteries.
Revision 3 February 2005 REGULATORY GUIDE
OFFICE OF NUCLEAR REGULATORY RESEARCH
REGULATORY GUIDE 1.75 (Draft was issued as DG-1129, dated December 2003)
CRITERIA FOR
INDEPENDENCE OF ELECTRICAL SAFETY SYSTEMS


and the onsite electric distribution system have sufficient independence to performn their safety flunc- tions assuming a single failure. General Design Criterion
==A. INTRODUCTION==
21,  
Section 50.55a, Codes and Standards, of 10 CFR Part 50, Domestic Licensing of Production and Utilization Facilities, requires in 10 CFR 50.55a(h) that protection systems for plants with construction permits issued after January 1, 1971, but before May 13, 1999, must meet the requirements stated in either IEEE Std. 279, Criteria for Protection Systems for Nuclear Power Generating Stations,1 or IEEE Std. 603-1991, Criteria for Safety Systems for Nuclear Power Generating Stations.1  For nuclear power plants with construction permits issued before January 1, 1971, protection systems must be consistent with their licensing basis or may meet the requirements of IEEE Std. 603-1991. The safety systems for plants with construction permits issued after May 13,
"Protection System Reliability and Testability,"
1999, must meet the requirements of IEEE Std. 603-1991.
requires, in part.


that independence desiLued into protection systems be sufficient to ensure that no single failure results in loss of the protection function. This guide describes a method acceptable to the Regulatory staff of complying with IEEE Std 279-1971 and Criteria
Section 4.6 of IEEE Std. 279-1971 requires, in part, that channels that provide signals for the same protective function must be independent and physically separated.  Section 5.6.1 of IEEE Std. 603-1991 states, Redundant portions of a safety system provided for a safety function shall be independent of, and physically separated from, each other to the degree necessary to retain the capability of accomplishing the safety function during and following any design basis event requiring that safety function. General Design Criterion (GDC) 17, Electric Power Systems, in Appendix A to 10 CFR Part 50 requires, in part, that electric power
3. 17. and 21 of Appendix A to 10 CFR Part 50 with respect to thie physical independence of the circuits and electric equipment comprising or associated with the Class IE power system, the protection system, systems actuated or controlled by the protection system, and
'Copies may be obtained froemthe Institute ot' Electrical and Electronics Engineers, United Engineering Center, 345 East 47th Street, New York. New York 10017.


auxiliary or supporting systems that must be operable for the protection system and the systemls it actLuaeCs to perlform their saf'ety-related I'ulctions. This guide a pplics to all types of niclear power plants.
1.75-2 from the transmission network to the onsite electric distribution system shall be supplied by two physically independent circuits that are designed and located so as to minimize to the extent practical the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions. GDC 21, Protection System Reliability and Testability, requires, in part, that redundancy and independence designed into the protection system shall be sufficient to assure that no single failure results in a loss of the protection function.  GDC 22, Protection System Independence, requires that the effects of natural phenomena, and of normal operating, maintenance, testing, and postulated accident conditions on redundant channels do not result in loss of the protection function.


==B. DISCUSSION==
This regulatory guide describes a method acceptable to the NRC staff for complying with the NRCs regulations with respect to the physical independence requirements of the circuits and electric equipment that comprise or are associated with safety systems.
Draft II'I"E Standard. "'Criteria t or Separation ot Class IE IEquipnment and Circuits," dated July 20. 1973.


was prepared by Ad 1l0c Subcomnmnittee 0 of the Nudear Power Enghieering Comlmittee (NPE(") of the lInstitute of Electrical and Electronics Enilneers. The dralft was subsequently miodified by NPEC
This regulatory guide contains information collections that are covered by the requirements of 10 CFR Part 50, which the Office of Management and Budget (OMB) approved under OMB control number 3150-0011. The NRC may neither conduct nor sponsor, and a person is not required to respond to, an information collection request or requirement unless the requesting document displays a currently valid OMB control number.
in August
1973 incident to the normnal process of' developing its technical content. The modified draft standard provided criteria for the separation of redundant Class IFI
equipment and circuits installed at nuclear power plants.


Inasnmuch as there was an urgent need for explicit guidance in the area of physical independence of electtic systems and in view of the considerable guidance already available from tile modified IE-E
2 Standards promulgated by the IEEE may be purchased from the IEEE Service Center, 445 Hoes Lane, Piscataway, NJ  08854.
draf't standard, the Regulatory staff prepared a document entitled, "Appen- dix I to Regulatory Guide 1.75--Physical Independence of Electric Systenms."
This Appendix, which was essentially the nmodified IEEE draft standard further modified to (a) address acceptably those portions of the standard on which there was not complete agreement.


(b)
1.75-3
describe logical extensions of the standard's provisions that were acceptable to tile Regulatory staff.


and (c)
==B. DISCUSSION==
provide clarification where necessary.
IEEE Std. 384-1992, Standard Criteria for Independence of Class 1E Equipment and Circuits,2 was prepared by Working Group SC 6.5 of IEEE Nuclear Power Engineering Committee and was approved by the Standards Board on June 18, 1992.  This standard provides criteria and requirements for establishing and maintaining the independence of safety-related equipment and circuits, and auxiliary supporting features by physical separation and electrical isolation.  Based on the results of separation testing completed by the nuclear industry on internally generated electrical faults, the following significant changes were incorporated in IEEE Std. 384-1992:  (1) separation distance criteria were reduced for certain configurations identified in IEEE Std. 384-1981, and (2) separation distance criteria were added for configurations that were not previously addressed. These configurations include cable trays and conduits, cable trays and cable in free air, and conduits and cable in free air. The underlying separation criteria are that (1) physical separation and (2) electrical isolation must be provided to maintain the independence of safety-related circuits and equipment so that the safety functions required during and following any design-basis event can be accomplished .
 
Section 5.6(3) of IEEE Std. 384-1992 provides general criteria for independence between safety- related and non-safety-related circuits. When minimum separation cannot be met, it allows an analysis of non-safety-related circuits to demonstrate that the safety-related circuits are not degraded below an acceptable level.  If the analysis is successful, the non-safety-related circuits can remain as non-safety- related circuits. However, Section 5.5.2(3) contradicts Section 5.6(3) by stating that the analyzed circuits are still called associated circuits following an analysis or test demonstrating that the safety-related cables are not degraded below an acceptable level.  The staff position is that (1) non-safety-related circuits that are not separated from safety-related circuits through the minimum separation or barriers, must be treated as associated circuits, and (2) the cables that are associated because they are powered from a safety- related source serving non-safety-related loads or share the safety signal must also be treated as associated circuits.  Both of these groups of associated circuits should not ever become associated with a redundant division through its proximity or shared signal to preserve the independence.
was endorsed by the February 1974 version of this guide.
 
Subsequent to the issuance of the February 1974 version of this guide, the modified IEEE draft standard upon which the guide and its Appendix were based evolved, in the normal course of standard developnment.
 
into IEEE Std 384-1974, "IEEE Trial-Use Standard Criteria for Separation of Class IE Equipment atid Circuits," (also designated ANSI N41.14). IEEE Sid
384-1974 has undergone balloting within Ad Hoc Subcommittee 6 arid NPEC and was approved by tile USNRC REGULATORY GUIDES
Copies of published quides may be obtained byV equest indicating the divisions fdett ited to the U.S, Nucle,,, Reguatinty Commiiveon. Washir.glot,. 0 C
20b55.
 
Regulatory Guides ae kt~ild Io des~cribe and matke available to the public Altelmn Director of Standards Oeveelopme.nt Commentts and %utgeest-inis tIn method% acceptable to the NRC staff of impfrrntenling specific parts of Iliae nitptoven*nI
in these guides are encoutraged and *shaltd hIe sent to the.
 
Commisslion's regutaiotr,,
to detinatet ftchni.hitueS ust.t1 by the staff in srcetlatv of the? Comlmiisin.
 
U.S
Nucleart Regulatorv Comtnlitssll.


evaluating specific ptoblemls or postulated accidents. or to provide guidance to Washingtotn. 0 C 20555. Attention Oockeling and Service Section applicants Regulatery Guides sre ntof %ubslitutes fot tegllation$ and compliance with them is not tegqired. Methods aid soluftons different from those set out irn The guides ate issued its the fallowing feti broad division%
The term associated circuits has a different connotation in this regulatory guide than it does for fire protection (Appendix R to 10 CFR Part 50). This regulatory guide defines associated circuits as non-safety-related circuits that are not physically separated or not electrically isolated from safety- related circuits by acceptable separation distance, safety class structures, barriers, or isolation devices.
the guides wtll be acceptable if Ihey provide a ba$si$i for the findings requisite to the issuance or continuance of A permit or license by the Commission.


"i Power Reactots
The associated circuits in Appendix R include both safety-related and non-safety-related circuits because they involve alternative and redundant safe shutdown equipment.  Post-fire safe-shutdown capability is distinctly different from, and credits operability of different equipment than the safety- related equipment required for emergency shutdown of a nuclear power plant.  Regulatory Guide 1.189, Fire Protection for Operating Nuclear Power Plants, provides additional guidance concerning the fire protection area.


===6. Products===
IEEE Std. 384-1992 includes an informative appendix that provides background information about the cable testing program that various public utilities conducted to support the criteria for reduced separation distance. In particular, the appendix states  and the NRC staff agrees  that the use of cable wrapping is an acceptable method to reduce separation distances, but each wrapping system should be analyzed or tested on a case-by-case basis.  This method will be subject to approval by the NRC staff.
2. Reearch and Toes Reacturs
7.


rtiansporinaort
1.75-4  
3. Fuels and Materiail lactlilies
8 Occupational Health Published guides will be tevised periodicitlly. as appropriat
 
====e. to accommodale ====
4 Envitonmental and Silinit
9 Antitrust Review comments and to reflect new informatlort or esperience
5. Materials and Plant Protection
1
 
===0. Genteral===
 
IEEE Standards Bfoard on February 28, 1974. This revision to tile guide endorses, with certain exceptions.
 
IEEE Std 384-1974.
 
The Regulatory staff does not agree with certain proisions of the trial-use standard such as those pertaining to the definition of "raceway." the routing of power cables through the cable spreading area(s) and control room, and the status of non-Class It: circuits that are not separated from associated circuits by acceptable distance or barriers. This lack of agreement is reflected in Regulator)y lositions C.1. 2. 4. 6. 7, 9. 10. and 12;
There are also several regulatory positions that are logical extensions of the Standard's provisions and reflect current Regulatory staff review practice. For example, a provision of the standard which addresses the
"'degree of separation commensurate with the damage potential of the hai.ard" does not specifically cover cable tunnels which, in the event of a fire. may not effectively separate redundant circuits or equipment. As another example.
 
the standard requires that methods of identification distinguish between redundant Class IE
systems, associated circuits, and non-Class IE systems.
 
By implication, associated circuits assiged to different redundant divisions should also be identified. However.
 
the provision is implicit. An explicit provision should be provided.
 
I.)tailed bases are included herein for those regulatory positions that are significantly at variance with the standard's provisions. The remaining regulatory positions are logical extensions. or clarifications. of the standard's provisions.


==C. REGULATORY POSITION==
==C. REGULATORY POSITION==
IEEE Std 384-1974 sets forth criteria for the separation of circuits and equipment that are redundant.
Conformance with the requirements of IEEE Std. 384-1992, Standard Criteria for Independence of Class 1E Equipment and Circuits, provides a method that the NRC staff considers acceptable for satisfying the agencys regulatory requirements concerning physical independence of the circuits and electrical equipment that comprise or are associated with safety systems, subject to the following:
(1)
Sections 7.1.2.1, 7.1.2.4, and 7.2.2.3 of IEEE Std. 384-1992 should be supplemented as follows:
The breaker or fuse that is automatically opened by fault current may be used as an isolation device, provided that (a) the fault current under bolted and arcing fault conditions (assuming multiple faults of all non-safety-related loads and load current of all safety-related circuits) will cause the nearest circuit breaker or fuse to interrupt the fault current prior to initiation of a trip of any upstream protection device, and (b) periodic testing of circuit breakers (visual inspection of fuses and fuse holders) during every refueling must demonstrate that the overall coordination scheme under multiple faults of non-safety-related loads remains within the limits specified in the design criteria for the nuclear power plant.


The determination of which circuits and equipment are redundant and the degree of redundancy required is outside, the scope of this guide and the standard. The standard also sets forth criteria relating to tests and analyses for determining the flame-retardant character- istics of proposed cable installations. The criteria are acceptable provided such tests and analyses are based on realistic premises and are otherwise fully applicable to the actual cable installations.
(2)
The summary results of the analysis performed to meet the requirements of IEEE Std. 384-1992, for example, to comply with Sections 5.5.2, 5.6, 6.1, etc.,
should be included in the final safety analysis report for the nuclear power plant.


The guidance in IEEE Std 384-1974, "IEEE Trial-Use Standard Criteria for Separation of Class IE Equipment and Circuits," dated Match
(3)
15,
Section 6.1.1.2 of IEEE Std. 384-1992 should be supplemented as follows:
1974, is generally acceptable to the Regulatory staff and provides an adequate basis for complying with IEEE Std 279-1971 and the Commission's General Criteria 3, 17, and 21 of Appendix A to 10 CFR Part 50 with respect to the physical independence of the circuits and electric equipment comprising or associated with the Class IE
Cable splices in raceways should generally be avoided to the extent that it is practical to do so.
power system, the protection system, systems actuated or controlled by the protection system, and auxiliary or supporting systems that must be operable for the protection system and the systems it actuates to perform.


their safety-related functions, subject to the following:
(4)
I. Section 3, Isolation Device, should be supplemented as follows: "(Interrupting devices actuated only by fault current are not considered to be isolation devices within the context of this document.)"
Section 5.6(3) of IEEE Std. 384-1992 should not be construed as allowing less than minimum separation of non-safety-related circuits from safety-related circuits to be justified by analyses without treatment of the affected non-safety-related circuits as associated circuits.
Basis: Loigcal extension of the Standard ' prow isons.


The standard defines "isolation device'" in terms of preventing ,nalfinct ions in one section of a circuit from causing unzacceptable influences in other sections of the circuit or other circuits. Under the postulated conditions of a loss-of coolant accident, loss of offsite power, and a cable tray' fire. the proximity of circuits energi2ed from re'dundant Class IE power sources could lead to concurrent high fault currents (e.g. short to ground)
(5)
which, in turn, threaten the redundant main circuit breakers. Also. the susceptibilityv of non-Class I1:" loads etrergized fromi redundant Class IE power sources to design basis event (e.g., seismic events) could similarly'
Section 3 of IEEE Std. 384-1992 references several industry codes and standards.
threaten the redundant main circuit breakers. 7Tipping of the mttain circcuit breakers wouhld cause f/ie loss of elercgen'c, pow'er to redundant "divisionss" of equip- ni'nf. It is rec-ognized that proper breaker or fiise coordination would preclude such an event. However, because the main breakers are in series with the fault and could experience monmentaryv currents above their setpoints, it is pnrdent to preclude the use of inter- rupqting devices actuated onl' by fault current as acceptable devices for isolating non-Class A1 circuits from Class IE or A ssociated circuits.


Breakers that trip on receipt of a signal other than one derived from the flhult crurrentt or its effects (e.g.. an accident sigital) are acceptable since the downstream circuits would already be isolated from their respective power sources under accident conditions and could pose nro threat to these sources.
If a referenced standard has been separately incorporated into the NRCs regulations, licensees and applicants must comply with the standard as set forth in the regulation.


2. Section 3, Raceway: Interlocked armor enclosing cable should not be construed as a "raceway".
If a referenced standard has been endorsed by the NRC staff in a regulatory guide, the standard constitutes an acceptable method of meeting a regulatory requirement as described in the regulatory guide.  If a referenced standard has been neither incorporated into the NRCs regulations nor endorsed in a regulatory guide, licensees and applicants may consider and use the information in the referenced standard, if appropriately justified, consistent with regulatory practice.
Basis: There is no precedent or other ktrown valid reason for consideritig such cable to be a "raceway"
77Tis regulatory position is consistent with current industry practice includinig the provisions of the National Electric Code.


3. Section 4.3 should be supplemented as follows: "In general, locating redundant circuits and equipment in separate safety class structures affords a greater degree of assurance that a single event will not affect redundant systems. This method of separation should be used whenever practicable and where its use does not conflict with other safety objectives."
1.75-5  
4. Associated circuits installed in accordance with Section 4.5(1) should be subject to all requirements placed on Class IE circuits such as cable derating, environmental qualification, flame retardance, splicing restrictions, and raceway fill unless it can be demonstiated that the absence of such requirements could not significantly reduce the availability c,f the Class IE circuits.


1.75-2
==D. IMPLEMENTATION==
The purpose of this section is to provide information to applicants and licensees regarding the NRC staffs plans for using this guide.  No backfitting is intended or approved in connection with the issuance of this guide.


Basis: This is a logical extension of the standard s provisions. The specified minimum acceptable separation distances for raceways carrying Class IE circuits are predicated on assumptions related to flame r?,tardawce, cable derating. etc. The placement of cables of lesser qualification in these raceways would nullify these assumptions.
Except in cases in which an applicant or licensee proposes or has previously established an acceptable alternative method for complying with specified portions of the NRCs regulations, the methods described in this guide will be used in the evaluation of (1) submittals in connection with applications for construction permits, design certifications, operating licenses, and combined licenses for application of independence criteria to safety systems, and (2) submittals from operating reactor licensees who voluntarily propose to initiate system modifications if there is a clear nexus between the proposed modifications and this guidance with respect to the requirements for physical independence of the circuits and electrical equipment that comprise or are associated with safety systems.


===5.  The ===
REGULATORY ANALYSIS
"Note"
A separate regulatory analysis was not prepared for this regulatory guide.  The regulatory analysis prepared for Draft Regulatory Guide DG-1129, Criteria for Independence of Electrical Safety Systems, dated December 2003, also provides the regulatory basis for this regulatory guide. The NRC issued DG-1129 to solicit public comment concerning the draft of this third revision of Regulatory Guide 1.75.
following Section
4.5 should be supplemented as follows: "This exemption is limited and does not extend to other requirements such as those of General Design Criterion 17."
6. Analyses performed in accordance with Sections
4.5(3), 4.6.2, and 5.1.1.2 should be submitted as part of the Safety Analysis Report and should identify those circuits installed in accordance with these sections.
 
Basis: Extension of Regulatory Guide 1. 70 to provide the information needed in order for the staff to independently verify conformance to the standard.
 
7. Non-Class IE instrumentation and control circuits should not be exempted from the provisions of Section
4.6.2.
 
Basis: There is no firm technical basis for an unrestricted exemption of these circuits. Exetnptions should be justified by analysis.
 
8. Section 5.1.1.1 should not be construed to imply that adequate separation of redundant circuits can be achieved within a confined space such as a cable tunnel that is effectively unventilated.
 
9. Section 5.1.1.3 should be supplemented as follows:
"(4) Cable splices in raceways should be prohibited."
Basis: Splices have been identified as the initiating cause of several fires in raceways. Even where the separation distance is adequate to prevent a fire in the raceways of one division from affecting cables in a redundant division, all practicable means should be used to prevent the occurrence of a fire. This position against splices in raceways is therefore prudent. Splices are nrot, by themselves, unacceptable. If they exist, the resulting design should be justified by analyses. The analyses should be submitted as part of the Safety Analysis Report.
 
10. Section 5.1.2, the phrase -at a sufficient number of points" should be understood to mean at intervals not to exceed 5 ft throughout the entire cable length. Also the preferred method of marking cable is color coding.
 
Basis: 7This is a logical extension of the standard's provisions. A
5 ft maximum marking distance is considered necessary to facilitate visual verification that the cable installation is in conformance with separation criteria.
 
I1. Section 5.1.2 should be supplemented as follows:
"The method of identification used should be simple and should preclude the need to consult any reference material to distinguish between Class IE and Non-Class IE circuits, between Non-Class IF circuits associated with different redundant Class-IE systenms, and between redundant Class IE systems.'
12. Pending issuance of other acceptable criteria, those portions of Section
5.1.3 (exclusive of the NOTE
following the second paragraph) that permvi the routing of power cables through the cable spreading area(s) and.
 
by implication, the control room. should not he construed as accepiwble. Also. Section 5.1.3 should be supplemented as follows:
"WWhere feasible, redundant cable spreading areas should be utilized.-
Basis: This is a pnident specific interpretation o" thc standard's provisions in thi absncee *j sPcciic guidan.wc.
 
The Regulator'
staff recognizes that vibset,qent investigation may, prove that this approach is too conservative, however, in the absence of supporti,:e evidence to the contrarY, this cotisern'ative apprroach is desirable.
 
The use of redundant cable sprcading art-as is a logical extension of the standard's pr.'f)isions (relf Scction
5.1.1.1).
13, No significance should be attached to the different tray widths illustrated in Figure 2.
 
14. Section 5.2.1 should be supplemented as follows:
"And should have independent air supplies."
15. Where ventilation is required, the separate safety class structures required by Section 5.3.1 should he served by independent ventilation systems.
 
16. The first paragraph of Section 5.7 should be augmented as follows: "The separation requirements .of
5.6 apply to instrumentation cabinets."
 
==D. IMPLEMENTATION==
The purpose of this section is to provide information to applicants and licensees regarding the Regulatory staffs plans for utilizing this regulatory guidu.


This guide reflects current regulatory practice.
A copy of the regulatory analysis for DG-1129 is available for inspection and copying for a fee at the NRCs Public Document Room (PDR), which is located at 11555 Rockville Pike, Rockville, Maryland; the PDRs mailing address is USNRC PDR, Washington, DC 20555-0001.  The PDR can also be reached by telephone at (301) 415-4737 or (800) 397-4205, by fax at (301) 415-3548, and by email to PDR@nrc.gov.  Copies are also available at current rates from the U.S. Government Printing Office at P.O. Box 37082, Washington, DC 20402-9328 or by telephone at (202) 512-1800.  In addition, copies are available at current rates from the National Technical Information Service at 5285 Port Royal Road, Springfield, VA 22161, on the Internet at http://www.ntis.gov, or by telephone at (703) 487-4650.


Therefore, except in those cases in which the applicant proposes an acceptable alternative method for comn- plying with specified portions of the Commission's regulations, this guide will be used by the Regulatory staff in evaluating all construction permit applications for which the issue date of the Safety Evaluation Report is February I, 1974, or after.
In addition, the regulatory analysis is available electronically as a part of Draft Regulatory Guide DG-1129 through the NRCs Agencywide Documents Access and Management System (ADAMS)
at http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML040020126.  Note, however, that the NRC has temporarily suspended public access to ADAMS so that the agency can complete security reviews of publicly available documents and remove potentially sensitive information.


1.75.3}}
Please check the NRCs Web site for updates concerning the resumption of public access to ADAMS.}}


{{RG-Nav}}
{{RG-Nav}}

Revision as of 23:13, 15 January 2025

Criteria for Independence of Electrical Safety Systems, Rev. 3
ML043630448
Person / Time
Issue date: 02/07/2005
From: Aggarwal S
Materials Engineering Branch
To:
References
DG-1129 RG-1.075, Rev 3
Download: ML043630448 (5)
v • d • e


1 Standards promulgated by the Institute of Electrical and Electronics Engineers (IEEE) may be purchased from the IEEE Service Center,

445 Hoes Lane, Piscataway, NJ 08854 (800-678-4333).

The U.S. Nuclear Regulatory Commission (NRC) issues regulatory guides to describe and make available to the public methods that the NRC staff considers acceptable for use in implementing specific parts of the agencys regulations, techniques that the staff uses in evaluating specific problems or postulated accidents, and data that the staff need in reviewing applications for permits and licenses. Regulatory guides are not substitutes for regulations, and compliance with them is not required. Methods and solutions that differ from those set forth in regulatory guides will be deemed acceptable if they provide a basis for the findings required for the issuance or continuance of a permit or license by the Commission.

This guide was issued after consideration of comments received from the public. The NRC staff encourages and welcomes comments and suggestions in connection with improvements to published regulatory guides, as well as items for inclusion in regulatory guides that are currently being developed. The NRC staff will revise existing guides, as appropriate, to accommodate comments and to reflect new information or experience. Written comments may be submitted to the Rules and Directives Branch, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.

Regulatory guides are issued in 10 broad divisions: 1, Power Reactors; 2, Research and Test Reactors; 3, Fuels and Materials Facilities; 4, Environmental and Siting;

5, Materials and Plant Protection; 6, Products; 7, Transportation; 8, Occupational Health; 9, Antitrust and Financial Review; and 10, General.

Requests for single copies of draft or active regulatory guides (which may be reproduced) should be made to the U.S. Nuclear Regulatory Commission, Washington, DC

20555, Attention: Reproduction and Distribution Services Section, or by fax to (301) 415-2289; or by email to Distribution@nrc.gov. Electronic copies of this guide and other recently issued guides are available through the NRCs public Web site under the Regulatory Guides document collection of the NRCs Electronic Reading Room at http://www.nrc.gov/reading-rm/doc-collections/

and through the NRCs Agencywide Documents Access and Management System (ADAMS)

at http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML043630448. Note, however, that the NRC has temporarily suspended public access to ADAMS so that the agency can complete security reviews of publicly available documents and remove potentially sensitive information. Please check the NRCs Web site for updates concerning the resumption of public access to ADAMS.

U.S. NUCLEAR REGULATORY COMMISSION

Revision 3 February 2005 REGULATORY GUIDE

OFFICE OF NUCLEAR REGULATORY RESEARCH

REGULATORY GUIDE 1.75 (Draft was issued as DG-1129, dated December 2003)

CRITERIA FOR

INDEPENDENCE OF ELECTRICAL SAFETY SYSTEMS

A. INTRODUCTION

Section 50.55a, Codes and Standards, of 10 CFR Part 50, Domestic Licensing of Production and Utilization Facilities, requires in 10 CFR 50.55a(h) that protection systems for plants with construction permits issued after January 1, 1971, but before May 13, 1999, must meet the requirements stated in either IEEE Std. 279, Criteria for Protection Systems for Nuclear Power Generating Stations,1 or IEEE Std. 603-1991, Criteria for Safety Systems for Nuclear Power Generating Stations.1 For nuclear power plants with construction permits issued before January 1, 1971, protection systems must be consistent with their licensing basis or may meet the requirements of IEEE Std. 603-1991. The safety systems for plants with construction permits issued after May 13,

1999, must meet the requirements of IEEE Std. 603-1991.

Section 4.6 of IEEE Std. 279-1971 requires, in part, that channels that provide signals for the same protective function must be independent and physically separated. Section 5.6.1 of IEEE Std. 603-1991 states, Redundant portions of a safety system provided for a safety function shall be independent of, and physically separated from, each other to the degree necessary to retain the capability of accomplishing the safety function during and following any design basis event requiring that safety function. General Design Criterion (GDC) 17, Electric Power Systems, in Appendix A to 10 CFR Part 50 requires, in part, that electric power

1.75-2 from the transmission network to the onsite electric distribution system shall be supplied by two physically independent circuits that are designed and located so as to minimize to the extent practical the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions. GDC 21, Protection System Reliability and Testability, requires, in part, that redundancy and independence designed into the protection system shall be sufficient to assure that no single failure results in a loss of the protection function. GDC 22, Protection System Independence, requires that the effects of natural phenomena, and of normal operating, maintenance, testing, and postulated accident conditions on redundant channels do not result in loss of the protection function.

This regulatory guide describes a method acceptable to the NRC staff for complying with the NRCs regulations with respect to the physical independence requirements of the circuits and electric equipment that comprise or are associated with safety systems.

This regulatory guide contains information collections that are covered by the requirements of 10 CFR Part 50, which the Office of Management and Budget (OMB) approved under OMB control number 3150-0011. The NRC may neither conduct nor sponsor, and a person is not required to respond to, an information collection request or requirement unless the requesting document displays a currently valid OMB control number.

2 Standards promulgated by the IEEE may be purchased from the IEEE Service Center, 445 Hoes Lane, Piscataway, NJ 08854.

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B. DISCUSSION

IEEE Std. 384-1992, Standard Criteria for Independence of Class 1E Equipment and Circuits,2 was prepared by Working Group SC 6.5 of IEEE Nuclear Power Engineering Committee and was approved by the Standards Board on June 18, 1992. This standard provides criteria and requirements for establishing and maintaining the independence of safety-related equipment and circuits, and auxiliary supporting features by physical separation and electrical isolation. Based on the results of separation testing completed by the nuclear industry on internally generated electrical faults, the following significant changes were incorporated in IEEE Std. 384-1992: (1) separation distance criteria were reduced for certain configurations identified in IEEE Std. 384-1981, and (2) separation distance criteria were added for configurations that were not previously addressed. These configurations include cable trays and conduits, cable trays and cable in free air, and conduits and cable in free air. The underlying separation criteria are that (1) physical separation and (2) electrical isolation must be provided to maintain the independence of safety-related circuits and equipment so that the safety functions required during and following any design-basis event can be accomplished .

Section 5.6(3) of IEEE Std. 384-1992 provides general criteria for independence between safety- related and non-safety-related circuits. When minimum separation cannot be met, it allows an analysis of non-safety-related circuits to demonstrate that the safety-related circuits are not degraded below an acceptable level. If the analysis is successful, the non-safety-related circuits can remain as non-safety- related circuits. However, Section 5.5.2(3) contradicts Section 5.6(3) by stating that the analyzed circuits are still called associated circuits following an analysis or test demonstrating that the safety-related cables are not degraded below an acceptable level. The staff position is that (1) non-safety-related circuits that are not separated from safety-related circuits through the minimum separation or barriers, must be treated as associated circuits, and (2) the cables that are associated because they are powered from a safety- related source serving non-safety-related loads or share the safety signal must also be treated as associated circuits. Both of these groups of associated circuits should not ever become associated with a redundant division through its proximity or shared signal to preserve the independence.

The term associated circuits has a different connotation in this regulatory guide than it does for fire protection (Appendix R to 10 CFR Part 50). This regulatory guide defines associated circuits as non-safety-related circuits that are not physically separated or not electrically isolated from safety- related circuits by acceptable separation distance, safety class structures, barriers, or isolation devices.

The associated circuits in Appendix R include both safety-related and non-safety-related circuits because they involve alternative and redundant safe shutdown equipment. Post-fire safe-shutdown capability is distinctly different from, and credits operability of different equipment than the safety- related equipment required for emergency shutdown of a nuclear power plant. Regulatory Guide 1.189, Fire Protection for Operating Nuclear Power Plants, provides additional guidance concerning the fire protection area.

IEEE Std. 384-1992 includes an informative appendix that provides background information about the cable testing program that various public utilities conducted to support the criteria for reduced separation distance. In particular, the appendix states and the NRC staff agrees that the use of cable wrapping is an acceptable method to reduce separation distances, but each wrapping system should be analyzed or tested on a case-by-case basis. This method will be subject to approval by the NRC staff.

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C. REGULATORY POSITION

Conformance with the requirements of IEEE Std. 384-1992, Standard Criteria for Independence of Class 1E Equipment and Circuits, provides a method that the NRC staff considers acceptable for satisfying the agencys regulatory requirements concerning physical independence of the circuits and electrical equipment that comprise or are associated with safety systems, subject to the following:

(1)

Sections 7.1.2.1, 7.1.2.4, and 7.2.2.3 of IEEE Std. 384-1992 should be supplemented as follows:

The breaker or fuse that is automatically opened by fault current may be used as an isolation device, provided that (a) the fault current under bolted and arcing fault conditions (assuming multiple faults of all non-safety-related loads and load current of all safety-related circuits) will cause the nearest circuit breaker or fuse to interrupt the fault current prior to initiation of a trip of any upstream protection device, and (b) periodic testing of circuit breakers (visual inspection of fuses and fuse holders) during every refueling must demonstrate that the overall coordination scheme under multiple faults of non-safety-related loads remains within the limits specified in the design criteria for the nuclear power plant.

(2)

The summary results of the analysis performed to meet the requirements of IEEE Std. 384-1992, for example, to comply with Sections 5.5.2, 5.6, 6.1, etc.,

should be included in the final safety analysis report for the nuclear power plant.

(3)

Section 6.1.1.2 of IEEE Std. 384-1992 should be supplemented as follows:

Cable splices in raceways should generally be avoided to the extent that it is practical to do so.

(4)

Section 5.6(3) of IEEE Std. 384-1992 should not be construed as allowing less than minimum separation of non-safety-related circuits from safety-related circuits to be justified by analyses without treatment of the affected non-safety-related circuits as associated circuits.

(5)

Section 3 of IEEE Std. 384-1992 references several industry codes and standards.

If a referenced standard has been separately incorporated into the NRCs regulations, licensees and applicants must comply with the standard as set forth in the regulation.

If a referenced standard has been endorsed by the NRC staff in a regulatory guide, the standard constitutes an acceptable method of meeting a regulatory requirement as described in the regulatory guide. If a referenced standard has been neither incorporated into the NRCs regulations nor endorsed in a regulatory guide, licensees and applicants may consider and use the information in the referenced standard, if appropriately justified, consistent with regulatory practice.

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D. IMPLEMENTATION

The purpose of this section is to provide information to applicants and licensees regarding the NRC staffs plans for using this guide. No backfitting is intended or approved in connection with the issuance of this guide.

Except in cases in which an applicant or licensee proposes or has previously established an acceptable alternative method for complying with specified portions of the NRCs regulations, the methods described in this guide will be used in the evaluation of (1) submittals in connection with applications for construction permits, design certifications, operating licenses, and combined licenses for application of independence criteria to safety systems, and (2) submittals from operating reactor licensees who voluntarily propose to initiate system modifications if there is a clear nexus between the proposed modifications and this guidance with respect to the requirements for physical independence of the circuits and electrical equipment that comprise or are associated with safety systems.

REGULATORY ANALYSIS

A separate regulatory analysis was not prepared for this regulatory guide. The regulatory analysis prepared for Draft Regulatory Guide DG-1129, Criteria for Independence of Electrical Safety Systems, dated December 2003, also provides the regulatory basis for this regulatory guide. The NRC issued DG-1129 to solicit public comment concerning the draft of this third revision of Regulatory Guide 1.75.

A copy of the regulatory analysis for DG-1129 is available for inspection and copying for a fee at the NRCs Public Document Room (PDR), which is located at 11555 Rockville Pike, Rockville, Maryland; the PDRs mailing address is USNRC PDR, Washington, DC 20555-0001. The PDR can also be reached by telephone at (301) 415-4737 or (800) 397-4205, by fax at (301) 415-3548, and by email to PDR@nrc.gov. Copies are also available at current rates from the U.S. Government Printing Office at P.O. Box 37082, Washington, DC 20402-9328 or by telephone at (202) 512-1800. In addition, copies are available at current rates from the National Technical Information Service at 5285 Port Royal Road, Springfield, VA 22161, on the Internet at http://www.ntis.gov, or by telephone at (703) 487-4650.

In addition, the regulatory analysis is available electronically as a part of Draft Regulatory Guide DG-1129 through the NRCs Agencywide Documents Access and Management System (ADAMS)

at http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML040020126. Note, however, that the NRC has temporarily suspended public access to ADAMS so that the agency can complete security reviews of publicly available documents and remove potentially sensitive information.

Please check the NRCs Web site for updates concerning the resumption of public access to ADAMS.


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