ML20195C668
| ML20195C668 | |
| Person / Time | |
|---|---|
| Issue date: | 01/31/1975 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20195C592 | List: |
| References | |
| FOIA-86-270 REGGD-01.075, REGGD-1.075, NUDOCS 8605300425 | |
| Download: ML20195C668 (3) | |
Text
Revision 1
. o,U.S, fdUCLEAR REGULATCRY C"iMMi^SION JanuaWS
.n O -REGULATORY GU DE REGULATORY GUIDE 1.75 PHYSICAL INDEPENDENCE OF ELECTRIC SYSTEMS A. INTRODUCTION auxiliary or supporting systems that must be operable for the protection system and the systemsit actuates to Section 50.55a, " Codes and Standards," of 10 CFR perform their safety.related functions. This guide applies Part 50, "Ucensing of Production and Utihzation to ali types or nuclear power plants.
Facilities," requires in paragraph (h) that protection systems meet the requirements set forth in the Institute B. DISCUSSION of Electrical and Electronics Engineers Standard,
" Criteria for Protection Systems for Nuclear Power Draft IEEE Standard, " Criteria for Separation of Generating Stations,"(IEEE 279)' . Section 4.6 of IEEE Class IE Equipment and Circuits," dated July 20,1973, Std 2791971 (also designated ANSI N42.71972) was prepared by Ad floc Subcommittee 6 of the Nuclear requires, in part, that channels that provide signals for Power Engineering Committee (NPEC) of the Institute the same protective function be independent and of Electr_ical and Electronics Engineers. The draft was physically separated. General Design Criterion 3, " Fire ' subsequently modified by NPEC in August 1973 Protection," of Appendix A, " General Design Criteria incident to the normal process of developing its
~ for Nuclear Power Plants," to 10 CFR Part 50 requires, technical content. The modified draft standard provided in part, that structures, systems, and components criteria for the separation of redundant Class IE important to safety be designed and located to equipment and circuits inralled at nuclear power plants.
minimize, consistent with other safety requirements, the Inasmuch as there was an urgent need for explicit probability and effect of fires. General Design Criterion guidance in the area of physicalindependence of electric 17, " Electric Power Systems," requires,in part, that the systems and in view of the considerable guidance already onsite electric power supplies, including the batteries, available from the modified IEEE draft standard, the and the onsite electric distribution system have Regulatory staff prepared a document entitled,"Appen-sufficient independence to perform their safety func- dix 1 to Regulatory Guide 1.75-PhysicalIndependence tions assuming a single failure. General Design Criterion of Electric Systems." This Appendix, which was 21, " Protection System Reliability and Testability," _ essentially the modified IEEE draft standard further requires, in part, that independence designed into modified to (a) address acceptably those portions of the protection systems be sufficient to ensure that no single standard on which there was not complete agreement, failure results in loss of the protection function. This (b) describe logical extensions of the standard's guide describes a method acceptable to the Regulatory provisions that wers acceptable to the Regulatory staff, staff of complying with IEEE Std 2791971 and Criteria and (c) provide clarification where necessary, was 3,17, and 21 of Appendix A to 10 CFR Part 50 with endorsed by the February 1974 version of this guide.
respect to the physicalindependence of the circuits and Subsequent to the issuance of the February 1974 electric equipment comprising or associated with the version of this guide, the modified IEEE draft standard Class IE power system, the protection system, systems upon which the guide and its Appendix were based actuated or controlled by the protection system, and evolved,in the normal course of standard development, into IEEE Std 384-1974, "lEEE Trial.Use Standard Criteria for Separation of Class IE Equipment and
' Copies may be obtained from the Institute of Electrical and Circuits," (also designated ANSI N41.14). IEEE Std Electronics Engineers, United Ertgince:ing Center,345 East 47th 3841974 has undergone balloting within Ad floc Street, New York, New York 10017. Subcommittee 6 and NPEC and was approved by the UstJAC REGULATORY CUIDES Copees of publ4shed guides may be obtaened by request endecating the divisions dessted to the U $ Nuctear Regulatory Commession. Washengton. D C. 20%&.
Regulatory Gu; des are issued to describe end make avadable to the public Attenteon Director of Standards Development Comments and suggestions for methods acceptable to the NRC staff of implernenteng specifee parts of the emprovements in these guedes are encouraged and should be sent to the Commiss.ons regulatsoe.s. to dehneate techneques used by the staff in Secretary of the Commession. U$ huclear R egulatory Commission.
eva?uating sp ecific problems or postulated accidents. or to provede guidance to Washington, D C 20%5. Attenteon Deckeneng and Service Section
/ apptocants Regulatory Guedes are not substitutes for regulations and compleance l with thern is not requered Methods and soluteens different from these set out in the guedes will be acceptable of they provide a basis for the findings requesete to the issuance er continuance of a perenst se lecense by the Commession The guides are issued m the fellevuong ten broad doveseens 1 p,,,, R eactoes 2 Research and Test Reactors 6 P oducts
- 7. Transportation 3 fuels sad Matenals f aceletees S Occupat.onst Health Published guides wdl be revesed penodecally, as appropriere to accommodate 4 Envoeonmental an d Seting g Antstrust Review c omments and Io reflect new informateen or empenence 5 Materials and Plant Protection 10 Ceneral 8605300425 860521 PDR FOIA GARDE 86-270 PDR -- - -
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""lEEE Standards Board on February 28,1974. His 1. Section 3, Isolation Device, should be supplemented
- resision to the guide endorses, with certain exceptions, as follows: "(Interrupting devices actuated only by fault pg g
IEEE Std 384-1974. current are not considered to be isolation devices within ! ,
The Regulatory staff does not agree with certain the context of this document.)" m provisions of the trial-use standard such as those Basis: Logical extension of the Standard's provisions.
pettaining to the definition of " raceway," the routing of The standard defines " isolation device" in terms of power cables through the cable spreading area (s) and preventing malfunctions in one section ofa circuitfrom control room, and the status of non. Class 1E circuits that caushig unacceptable influences in other sections of the are not separated from associated circuits by acceptable circuit or other circuits. Under the postulated conditions distance or barriers. This lack of agreement is reflected of a loss-of coolant accident, loss ofoffsite power, and a in Regulatory Positions C.1,2,4,6,7,9,10,and 12. cable tray fire, the proximity of circuits energizedfrom There are also several segulatory positions that are redundant Class IE power sources could lead to logical extensions of the Standard's provisions and concurrent high fault currents (e.g. short to ground) reflect current Regulatory staff renew practice. For which, in turn, threaten the redundant main circuit example, a provision of the standard which addresses the breakers. Also, the susceptibility of non-Class IEloads
" degree of separation commensurate with the damage energized from redundant Class IE power sources to potential of the hazard" does not specifically cover cable design basis crent (e.g., seismic events) could similarly tunnels which,in the event of a fire, may not effectively threaten the redundant main circuit breakers. 7)ipping separate redundant circuits or equipment. As another of the main circuit breakers would cause the loss of example, the standard requires that methods of emergency power to redundant " divisions" of equip-identification distinguish between redundant Class IE ment. It n recognised that proper breaker or fuse systems, associated circuits, and non-Class IE systems. coordination would preclude such an event. Ilowever, By implication, associated circuits assigned to different because the main breakers are in series with thefault and redundant divisions should also be identified. Ilowever, could experience momentary currents above their the provision is implicit. An explicit provision should be setpoints, it is prudent to preclude the use of inter-provided. rupting devices actuated only by fault current as Detailed bases are included hercin for those acceptable devices for isolating non-Class IE circuits regulatory positions that are significantly at variance from Class /E or A ssociated circuits.
with the standard's provisions.The remaining regulatory Breakers that trip on receipt of a signal other than positions are logical extensions, or clarifications, of the one derived from the fault curreift or its effects (e.g., an -
standard's provisions. accident signal) are acceptable since the downstream ;,
circuits wculd a! ready be iso lated from their respective ' .,J pown sources unda accident condWons and could pose C. REGULATORY POSITION no threat to these sources.
IEEE Std 384-1974 sets forth criteria for the 2. Section 3, Raceway: Interlocked armor enclosing separation of circuits and equipment that are redundant. d The determination of which circuits and equipment are cable should not be construed as a raceway".
redundant and the degree of redundancy required is Basis: There is no precedent or other known valid outside the scope of this guide and the standard. The reason for considering such cable to be a " raceway" standard also sets forth criteria relating to tests and 7his regulatory position is consistent with current ,
analyses for determining the flame-retardant character. industry practice including the provisions of the istics of proposed cable installations. The criteria are NationalElectric Code.
acceptable provided such tests and analyses are based on realistic premises and are otherwise fully applicable to 3. Section 4.3 should be supplemented as fo!!ows: "In the actual cable installations. Eeneral, locating redundant circuits and equipment in The guidance in IEEE Std 3841974,"lEEE Trial Use separate safety class structures affords a greater degree Standard Criteria for Separation of Class IE Equipment of assurance that a single event will not affect redundant and Circuits," dated March 15, 1974, is generally systems. This method of separation should be used acceptable to the Regulatory staff and provides an whenever practicable and where its use does not conflict adequate basis for complying with IEEE Std 279-1971 with other safety objectives."
and the Commission's General Criteria 3,17, and 21 of Appendix A to 10 CFR Part 50 with respect to the 4. Associated circuits installed in accordance with physical independence of the circuits and electric Section 4.5(1) should be subject to all requirements equipment comprising or associated with tia Class IE placed on Class IE circuits such as cable derating, power system, the protection system, systems actuated- environmental qualification, flame retardance, splicing or controlled by the protection system,and auxiliary or restrictions, and raceway fill unless it can be supporting systems that rnust be operable for the demonstiated that the absence of such requirements -
protection system and the systems it actuates to perform could not significarttly reduce the availability of the their safety-related functions, subject to the following: Class IE circuits. s m, ,
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Basis- This is a logical extension of the standard's 11. Section 5.l.2 should be supplemented as follows:
. , ' provisions The specified mininium acceptable separation "he method of identification used should be simple distances for raceways carrying Class IE circuits are and should preclude the need to consult any reference
(, predicated on assumptions related to flame retardance, matenal to distinguish between Class IE and Non. Class cable derating, etc. The placement of cables of lesser IE circuits, between Non. Class IE circuits associated qualiAcation in these racew.tys would nullify these with different redundant Class.IE systems,and between i assumptions. redundant Class IE systems."
- 5. De " Note" fol!cwing Section 4.5 should be 12. Pending issuance of other acceptable criteria, those supplemented as follows: "This exemption is limited and portions of Section 5.1.3 (exclusive of the NOTE does not extend to other requirements such as those of following the second paragraph) that permit the routing Genesa! Design Criterion 17." of power cables through the cable spreading area (s)and, by implication, the control room, should not be
- 6. Analyses perfor ned in accordance with Sections construed as acceptable. Also, Section 5.1.3 should be 4.5(3),4.6.2, and 5.Lt.2 shoul:1 be submitted as part of supplemented as follows: "Where feasible, redundant the Safety Analysis Report and shoWd identify those cable spreading areas should be utihzed."
circuits installed in accordance sith these sections. Basis: This is a prudent specific interpretation of the Basis: Extenstors ofRegulatory Guide 1. 70 to provide standard's provisions in the absence of specificguidance.
the information needed in order for the staff to The Regulatory staff recogni:es that subsequent independently verify c:mformance to the standard. Investigation may prove that this approach is too conservative; however, in the absence of supporting
- 7. NonDass IE insuumentation and control circuits evidence to the contrary, this conservative approach is should not be exempted frem the provisions of Section desira'ble.
4.6.2. The use ofredundant cable spreading areas is a logical Basis: There is na finn technical basis for an extension of the standard's provisions (ref Section unrestricted exemption of these circuits. Exemptions 5.1.1.1).
should bejustified by analysit
- 13. No significance should be attached to the different
- 8. Section 5.1.1.1 should not be construed to imply that tray widthsillustratedin Figure 2.
adequate separation of sedundant circuits can be 7 achieved within a confined space such as a cable tunnel 14. Section 5.2.1 should te supplemented as follows:
that is effectively unventilated. "And should have independent air supplies."
- 9. Section 5.1.1.3 should be supplemented as follows: 15. Where ventilation is required, the separate safety
"(4) Cable splices in raceways should b prohibited." class structures required by Section 5.3.1 should be Basis: Splices have been iden:llied as the initizting served by independent ventilation systems.
cause of several fires in raceways Even where the separation distance is adequate to prevent a fire in **se 16. The first paragraph of Section 5.7 should be raceways of one divmon from affecting ables in a augmented as follows:"The separation requirements of '
redundant division, cli practicable mwns should be usa! 5.6 apply toinstrumentation cabinets."
to prevent the occurrence ofafire. 77aspo:ition against splices in raceways is therefore prudent. Splices are not, by themselves, unacceptable. If they exist, the resultin8 D. IMPLEMENTATION design should be justified by analyses. The analyses should be submitted as part of the Safety Analysis Report. "Ihe purpose of this section is to provide information to applicants and licensees regarding the Regulatory
- 10. Section 5.1.2, the phrase "at a sufficient number of staff's plans for utilizing this regulatory guide.
-3 points"should be understood to mean at intervsis not to This guide reflects current regulatory practice.
exceed 5 ft throughout the entire cable length. Also the Therefore, except in those cases in which the applicant preferred method of marking cable is color coding. proposes an acceptable alternative method for com-Basis: 7his is a logical ertension of the standard's plying with specified portions of the Commission's provisions. A 5 ft merimum marking distance is regulations, this guide will be used by the Regulatory considered necessary to facilitate visual verification that staff in evaluating all construction permit applications the cable installation is in coy ~ mee with separation for which the issue date of the Safety Evaluation Report criteria. is February 1,1974, or after.
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