ML20212D864

Summary of 861209 Meeting W/Util Re Plant Emergency Electrical Power Sys.Fsar Commitment Re Emergency Diesel Generators revised.Marked-up Draft Rept Re Ac Standby Power Sys Encl

ML20212D864
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/24/1986
From:	Heitner K Office of Nuclear Reactor Regulation
To:	Berkow H Office of Nuclear Reactor Regulation
References
CON-FIN-D-6023 TAC-59801, NUDOCS 8701050094
Download: ML20212D864 (30)

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~,, UNITED STATES 8

8 c NUCLEAR REGULATORY COMMISSION

& .I WASHINGTON, D. C. 20555

\ ..... p8 December 24, 1986 Docket No. 50-267 MEMORANDUM FOR: Herbert N. Berkow, Director Standardization and Special Projects Directo ate Division of PWR Licensing-B THRU: 0. D. T. Lynch, Jr., Section Leader Standardization and Special (

Projects Directorate Division of PWR Licensing-B FROM: Kenneth L. Heitner, Project Manager Standardization and Special -

Projects Directorate Division of PWR Licensing-B (

SUMMARY

OF MEETING WITH PUBLIC SERVICE COMPANY OF COLORADO (PSC) TO DISCUSS FORT ST. VRAIN (FSV) EMERGENCY ELECTRICAL POWER SYSTEM - DECEMBER 9, 1986

Reference:

NRC letter dated November 12, 1986 (K. L. Heitner to R. O. Williams, Jr., PSC) on Fort St. Vrain's Emergency Electrical Power System Design.

This meeting was held on December 9, 1986, in order to further discuss Fort St. Vrain's Emergency Electrical Power System. The discussion was based on the staff's recent evaluation of this system, referenced above. Specifically, the meeting agenda involved reviewing the referenced letter, and discussion of alternatives for interim and long-term solutions to the problems outlined

- therein. Attendees at this meeting are listed in Enclosure 1.

At the beginning of the meeting the PSC staff summarized the progress made on changes proposed and agreed to in our previous meeting on this subject on August 14, 1986. These changes included the following:

Removal of common start circuit contacts from relays DEV-86 RT and DEV-86 ETI between the redundant emergency diesel generators (EDGs):

This change was completed.

Implementation of a temporary modification to the DC power supplies for the degraded grid voltage and undervoltage protection system:

This change was in progress and would be completed by December 19, 1986.

PSC also noted that a separate Licensee Event Report would be submitted concerning the exhaust temperature detectors on the emergency diesel engines.

1 8701050094 861224 PDR ADOCK 05000267 4 P PDR

-2 Electrical Independence

! Electrical independence between the control circuits of the two EDGs and their respective output circuit breakers was discussed. PSC noted that they had revised their FSAR commitment (Section 8.1) concerning the EDGs to read as follows:

"The onsite electrical system (emergency standby generatorv) are so designed that they are independent of each other to the extent that no single failure will interfere with the proper operation of the redundant counterpart."

i: The staff stated that they would review these changes to the FSAR. Discussion continued on the capability of the EDG control system to perform its functions after a single failure. Several single failure sequences were reviewed to understand their impact on both automatic and manual operation of the EDG

control system. PSC concluded that they could demonstrate that no credible

single failure could affect the capability to connect manually at least one EDG to its essential bus. Additionally, they would demonstrate that the EDGs

could not accidentally be paralleled as a result of a single failure. The

, staff found this to be consistent with their request in the referenced

letter. PSC further stated that they believed that the EDG's would be able to operate automatically if a single failure occurred. The staff noted that automatic operation was desirable, but that manual operation remained acceptable because of the relatively longer time available at FSV to begin decay heat removal. Typically, decay heat removal can begin 1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after the reactor is shut down from full power.

Automatic Throw-Over (ATO) of DC Control Power Supplies for 480 Volt Switchaear PSC reviewed the design history of the 480 volt switchgear. The switchgear

installed originally was designed with the control power having a manual throw-over capability so it could be powered from either of the redundant DC buses.

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In 1983-84, this switchgear was upgraded, and the ATO feature was installed as l

part of the standard configuration for the new switchgear. PSC noted that ATO consisted of two separate contactors, one in each of the two redundant DC supply circuits to the switchgear. These separate contactors were electrically interlocked. Additionally, the power supply circuit from each DC bus was protected by two independent circuit breakers. PSC believed that multiple

(. failures would be required to result in the loss of both DC buses as a result l of a single fault in the switchgear system.

! The staff stated that they still remained concerned about the ATO. The staff indicated that there were two acceptable alternatives for the ATO system.

i These are:

- The ATO could be converted to manual operation by placing the

l. circuit breakers at the switchgear under administrative control. As l such, each switchgear cabinet would be manually connected to only l one DC bus. In the event of a failure of the source of control power the operators would manually transfer the switchgear to the other DC bus.

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Alternatively, the ATO feature could be retained if the protective circuit breakers were tested periodically and properly coordinated to assure their performance.

The staff stated that either of these approaches was acceptable as an interim solution to the problems in the existing ATO system. The long-term acceptability of the existing ATO system would be related to how DC power would eventually be supplied to the 480 volt switchgear.

Undervoltage and Degraded Grid Voltage Protection PSC stated that their long-term preference was to provide a third source of DC power from the "C" battery. This would involve adding a DC distribution panel for the "C" battery, and supplying the auxiliary relays for the third set of undervoltage and degraded grid voltage relays from this distribution panel.

Thus, a single failure of a DC bus, would not compromise the undervoltage or degraded grid voltage protection of the emergency electric power system.

Furthermore, PSC stated that they were evaluating if sufficient "C" battery capacity was also available to supply the 480 volt switchgear. In that case, each of the three sets of switchgear could be powered from 2 different DC buses through the ATO for each switchgear panel. Thus, the operability of at least one DC and one AC bus was assured. The staff stated that this approach was acceptable in principle and should result in an improved emergency electrical power system.

I Schedules Schedules for fonnal submittal of PSC's proposals were discussed. It was agreed between PSC and the staff that, the following actions be taken:

PSC would submit to the staff a basis for accepting the EDG control system. This would be a single failure analysis for the

! - existing, not fully independent, EDG control system that supports the PSC comitment's as contained in the FSAP,.

- PSC would also formally propose implementation of a program to address the staff's concerns about the ATO. This interim program would be implemented fully by plant restart, reflecting the discussions above.

- PSC also would commit formally to the installation of a third DC bus as outlined above. The PSC proposal also would contain a schedule for submittal of the detailed design of this system in approximately 6 months; and completion by FSV's fourth refueling with NRC review by early 1988.

All of the above would be submitted for staff review and approval no later than January 10, 1987.

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d PSC also provided comments to the staff concerning the draft Technical Evaluation Report enclosed with the referenced letter. PSC's comments are summarized in a markup of this draft report, which is provided as Enclosure 2.

Kenneth L. Heitner, Project Manager Standardization and Special Projects Directorate Division of PWR Licensing-B Office of Nuclear Reactor Regulation i

Enclosures:

As stated cc w/ enclosures:

See next page 1

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Mr. R. O. Williams Public Service Company of Colorado Fort St. Vrain cc:

Mr. D. W. Warembourg, Manager Albert J. Hazle, Director Nuclear Engineering Division Radiation Control Division Public Service Company Department of Health of Colorado 4210 East lith Avenue P. O. Box 840 Denver, Colorado 80220 Denver, Colorado 80201 Mr. David Alberstein, 14/159A Mr. J. W. Gahm, hanager GA Technologies, Inc. Nuclear Production Division Post Office Box 85608 Public Service Company of Colorado San Diego, California 92138 16805 Weld County Road 19-1/2 Platteville, Colorado 80651 Mr. H. L. Brey, Manager Nuclear Licensing and Fuel Division Mr. P. F. Tomlinson, Manager Public Service Company of Colorado Quality Assurance Division P. O. Box 840 Public Service Company of Colorado Denver, Colorado 80201 16805 Weld County Road 19-1/2 Platteville, Colorado 80651 Senior Resident Inspector U.S. Nuclear Regulatory Commission Mr. R. F. Walker P. 0. Box 840 Public Service Company of Colorado Platteville, Colorado 80651 Post Office Box 840 Denver, Colorado 92138 Kelley, Stansfield & 0'Donnell Public Service Company Building Commitment Control Program

! Room 900 Coordinator l 550 15th Street Public Service Company of Colorado Denver, Colorado 80202 2420 W. 26th Ave. Suite 100-D Regional Administrator, Region IV U.S. Nuclear Regulatory Commission

611 Ryan Plaza Drive, Suite 1004 Arlington, Texas 76011 Chairman, Board of County Commissioners l of Weld County, Colorado Greeley, Colorado 80631 Regional Representative Radiation Programs Environmental Protection Agency 1 Denver Place 999 18th Street, Suite 1300 Denver, Colorado 80202-2413 l

Enclosure 1 Meeting - NRC-PSC Emergency Electrical Power System December 9, 1986 Name Organization Ken Heitner NRC/NRR/DPWRL-B Charles Hinson NRC/NRR/DPWRL-B John Reesy Public Service Company of Colorado Robert Schenderlein Public Service Company of Colorado James Selan Public Service Company of Colordo Jeff Johns Public Service Company of Colorado I. Ahmed NRC J. Calvo NRC/NRR/DPWRL-B H. Berkow NRC/NRR/DPWRL-B

0. Lynch NRC/NRR/DPWRL-B 3

.'. Enclosure 2 EGG-NTA-A u g u s t 7.,/ 9 1 4 m <

sus a med <L < l a6 WsW Co m m en ki- & <c m f5C n Ll\ 8G REVIEW OF THE FORT ST. VRAIN ONSITE AC " STANDBY" POWER SYSTEM WITH REGARDS TO COMPLIANCE TO THE SINGLE FAILURE CRITERION AND THE SER DOCKET NO. 50-267 TAC NO. 59801

! INEL Reviewers - J. F. Jacobsen/A. E. Nolan NRC LEAD Reviewer - I. Ahmed INEL PROGRAM Manager - C.1. Nalezny NRC FSV Project MANAGER - K. Heitner NRC Program Manager - M. Carrington Idaho National Engineering Laboratory EG&G Idaho, Inc.

Prepared for the U. S. Nuclear Regulatory Commission Washington, D.C. 20555 l Under DOE Contract No. DE-AC07-761031570

! FIN No. D6023 i

CONTENTS Acknowledgments............................................... 11 Abstract...................................................... iii Summary.......................................................

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1. INTRODUCTION........................................... 1

2. DESIGN BASE CRITERIA.................................... 2

3. EVALUATION.............................................. 3 i

3.1 System Description................................. 3 3.2 Event Analysis..................................... 5 3.3 Licensee Response to NRC Concerns.................. 6 3.4 Additional Examples of Single Mode Failures........ 9 t

4. CONCLUSIONS............................................. 10

5. REFERENCES.............................................. 12 9

APPENDIX A...................................................... A-1 i

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i ACKNOWLEDGMENTS The author would like to acknowledge D. J. Henderson for his assistance in analyzing emergency diesel generator systems, A. D.

Hill for his assistance in functional operation of electrical distributioh equipment, and B. L. Collins and R. E. Polk for their technical assistance throughout the review.

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ABSTRACT This report was prepared for the U.S. Nuclear Regulatory Comission (NRC) to assist them in evaluating the Fort St. Vrain (FSV) Nuclear Power Generating Station onsite AC " standby" power system for compliance with 10 CFR 50, Appendix A, General Design Criteria 17 (Single Failure Criteria).

This report also evaluates the Public Service Company of Co?orado (PSC) response to concerns expressed by the NRC in their Safety Evaluation Report (SER), which evaluates the December 18, 1984, failure of the onsite AC " standby" power system (Licensee Event Report [LER] ASedeM).

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SUfMARY in bt

, a a h> a k-The Fort St. Vrain onsite AC " standby" power system failed during Mt a semi-annual loss-of-offsite-power and turbine trip surye111ance Fed test on December 18, 1984.Subsequer g T w h .i', to mthis o 3- A wthe event, . ,-Nuclear

> y r Fem-wa r c.ourq 1

• Regulatory Ccmission (NRC) asked EG&G Idaho to review the responses

k. luer of the licensee for compliance to the single failure criteria and for o F tue 5rriem compliance to the Safety Evaluation Report (SER) issued by the NRC. ~ .om pach, EG8G Idaho has reviewed the Licensee Event Report (LER), supporting documentation,electricaldiagrams[FSAR,andcorrespondence submitted by the licensee to the NRC in connection with this event.

The review determined that the proposed modifications to the system by Public Service Company of Colorado (PSC) did not resolve the concerns as pointed out in the SER. The diesel engines and their i e j associated generator output breakers remain.dsusceptible to a single 3

failure that will result in the loss of all " standby" power.

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en - . h d :- a sa s< y <.d < u ru PS'c hur o f t w c.~.- F-T A R 4 o -t u e. f ollou n3 :

"The onsite electrical system (emergency standby generators) are so designed that they are independent of each other to the extent that no single failure will interfere with the proper operation of the redundant counterpart." ,

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1. INTRODUCTION On December 18, 1984, the Fort St. Vrain Nuclear Power Generating s., % c Station (FSV) experienced a tetel failure 6 he onsite AC " standby" u h ,. k

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power system during a semi-annual test of the system.1 As a result of this failure and of other NRC concerns about the independeace of redundant power sources in the " standby" system, the NRC' evaluated the FSV emergency electrical systems. The results of this evaluation were contained in a Safety Evaluation (SE), which was transmitted to the licensee on July 10, 1985.2 The SE addressed two safety-related concerns, raised the question of possible '

nonconformance to the FSAR, and concluded that the plant could be operated, relying on manual controls, for an interim period while actions to correct the safety-related concerns were being pursued, i

The licensee responded by letter, dated September 13, 1985,5 which

transmitted the Proto-Power Corporation's evaluation of the FSV's m onsite " standby" power system and their recomendaticns.

The NRC then contracted EG&G Idaho to: 1) review the emergency diesel generator (EDG) system for compliance to the single failure criteria;

2) review FSV's proposed resolution to ths NRC's concerns, as raised in the SER;.and, 3) evaluate the independence of redundant " standby"

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power sources.

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2. DESIGN BASE CRITERIA The following design base criteria were applied in the evaluation of the Fort St. Vrain " standby" AC power system:

1. General Design Criterion 17 (GDC), " Electrical Power Systems," of 10 CFR 50 Appendix A, " General Design Criteria for Nuclear Power Plants."

2. IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."

3. IEEE Standard 308-1974, "IEEE Standard Criteria for Class 1E Power Systems for Nuclear Power Generating Stations."

4. IEEE Standard 384-1981, "IEEE Standard Criteria for Independence of Class 1E Equipment and Circuits."

5. IEEE Standard 352-1975, "!EEE Et:nd:rd Criterie fer Cle;; IE >

Pewer Sy:t;;; fer Nuci..i Pe er Cenerating Stetien;gf.

6. IEEE Standard 379-1977, "IEEE Standard Application of the Single Failure Criterion to the Nuclear Power Generating Station Class 1E Systems."

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3. EVALUATION ,

3.1 System Description As shown in Figure 1, the FSV onsite AC power system consists of two 1210 kW emergency generators (each driven by two diesel engines),

output breakers', redundant primary buses (No. 1 and No. 3), and a smaller swing bus (No. 2). The buses are common to both the offsite power source and the emergency diesel generators (EDG).

I I - , e , ,3 , oy The swing busjautomatically connects to the first primary bus eg an dieset 9 , ., ~ +v < -.% v& sy +5mh.

The results of the reliability calculations in the Fort St. Vrain FSAR are based on an operational " standby" system with a two-out-of-four failure. PSC has stated that a two-out-of-four 5

diesel engine failure cannot disable the " standby" power system.

However, our analysis shows that a two-out-of four failure can cause g tw=_ -% 6. -oJ < .5 s ,- -

a tete-1 failure pf " standby" power.

3.3 Licensee Response to NRC Concerns 4

In response to the concerns expressed by the NRC in the SER, PSC contracted the Proto-Power Corporation to conduct an overall i

evaluation of the FSV onsite " standby" power system. This study evaluated the 480 VAC essential bus tie breaker control scheme. The

1. a., .- o J f ~ m study included the 480V essential bus undervoltage relays 4 s:n :,re,'the 480V switchgear bus supply breakers, the 480V essential bus tie breakers, the diesel generator circuit breakers, the load sequencer, timers T1 and T2, and the diesel engine start /run circuitry.6 i

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As a result of their evaluation, Proto-Power Corporation recomended that PSC rewire certain terminal blocks to provide e physical separation of the essential circuits. This recomendation is

, superficial at best, as it does not achieve the independence between the two redundant systems. The relays and their contacts still interact with the two redundant systems, and the potential for esamon-

f. - . ., + w e- aubat A % J e.

mon failures remains.

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In addition to recomending the rewiring of the terminal blocks, the Proto-Power report disclosed a potential failure associated with '

I the synchronizing (sync) switch with respect to a degraded bus condition. Under normal operating conditions, when the voltage of (

the on-line bus drops to the 77.5% level, the associated output breaker is tripped and the associate'd tie breaker is closed to transfer the previously degraded bus to another operating bus.

i The' report pointed out that if the sync switch is failed, or if the operator neglected to return the sync switch to the "0FF" position, the degraded bus associated output breaker would be inhibited from tripping, and the possibility would exist for paralleling the degraded bus to a normal operating bus by closing the associated tie i

breaker.

l As a result, Proto-Power recomended that a normally closed contact on the output breaker be wired in series with the applicable contact that closes the associated tie breaker. This modification will l

• prevent the associated tie breaker from being closed if the i

associated output breaker has not been opened.

The sync switch is used only during . load testing to sync the diesel generator frequency and phase with off-site power. The sync switch at FSV is of the maintained-contact typie, as e;; ::d t: thR

( v retur,. i.v vii, or normai, position whh:trirusuaHy-used@

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PSC stated that, in addition to the recommendations made'by the Proto-Power Corporation, other analyses performed on the " standby" system showed that automatic closure of each EDG output breaker is provided for through two diverse paths. Therefore, the automatic operation of a redundant power supply (EDG) is assured.

This statement is essentially in error, since " diverse" means to have different forms or components. The paths for the closure of each EDG output' breaker are idential in their design, function, and components, and both paths are subjected to the potential for comon mode failures. Qe Proto-Power recomendation did not remove the w cece , tn o components sFa that arecom comon~

to the

.w o J c, two b pat [Ilet=+ M He-e st p ,-o b e b . t i kg c.o m p o a c h tr ir c.sn r's1e cd low.

3.3.1 Analysis of the Licensee's Response An analysis of the licensee response determined the following:

1. The rewiring of certain terminal blocks achieves only 9 physical separation of the wiring of redundant i

circuits and does nothing to create electrical independence of the redundant circuits. No functional l

changes to the existing circuits were made. ud

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2. The rewiring of the sync switch removed the potential for paralleling a degraded bus to an operating bus.

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3. In spite of the claim of here being two d verse paths to provide for the utomatic closure the EDG sup breakers,[the nalysis shows tha he breakers 11 not ,

close i either of the gener ors does not ve both d) sel engines connected running).

3.4 Additional Examples of Sinale Mode Failures From the sc'ematic h diagrams provided by the licensee, it appears f a b-+H e a u% u We. son %l s gs km ,

thatsystemindependencehasbeencompr{sedmanytimes. For example, on PSC drawing E-1203, page P-1601, the plant design allows for the following devices to be supplied from both redundant instrument buses ESSB1LO and ESS82LO, and CR-9200-A and CR-9200-B, contacts from breakers 252DG1A and 252DG1B; TIMERS T1 AND T2; CR-9240, CR-9228, CR-9215, and TR-9212. On print E-1203, page p-1600, CR-922B, CR-9201, CR-9202, TR-9205, TR-9206, CR-9205, CR9206, T1, T2, 286G1A, and 286G1B also appear to compromise the independence of the 4

redundant systems.

e Page P-30 of E-1203 indicates that auxiliary relay DEV86RT, through its contacts, initiates the start /run logic of all four diesel engines. The single failure of this control relay could prevent all four diesel engines from being started automatically and, in the case of a credible desigr basis event, the relay could prevent the diesel engines from being started manually. (T%s *g n'f *#

kur S.abregueatly been c e.~we d )

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4. CONCLUSIONS The review of the Fort St. Vrain documents and drawings revealed the following deficiencies in the onsite AC " standby" system.

1. As discussed in section 3.2, the present breaker control circuit design may prevent the automatic energizing of the 480V essential buses.

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.} 2. As discussed in section 3.3, PSC has not complied with l IP" 4

the NRC concerns. The potential for a single failurey disabling the " standby" power system still exists. mo , '"de E

. Independence between the two emergency diesel generator power systems has not been achieved.

As stated earlier, the proposed modifications I. (re-wiring of the terminal blocks) do not eliminate the j ,

potential for a single failure disabling the standby -

I* power system, and do not provide the required independence between the redundant power systems.

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3. As discussed in section 3.4, there are a number of control interconnections between the redundant generators and circuit breakers that may allow a single -

failure to result in the loss of both " standby" power systems.

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e It is recommended that the licensea perform a detailed single failure analysis and propose any necessary corrections in the design to the NP.C for review and concurrence. .

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! "The onsite electrical system (emergency standby generators) are so designed that they are independent of each other to the extent that no l single failure will interfere with the proper operation of the redundant j counterpart."

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5. REFERENCE DOCUMENTS l

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1. Licer.see Event Report, Fort St. Vrain Unit No.1, Docket No.

50-267, " Failure of Diesel Generator to Close-In During Loss of Outside Power Test," December 18, 1984.

2. NRC letter, E. H. Johnson to 0. R. Lee, with enclosed Safety Evaluation of Emergency Electrical Power System, July 10, 1985.

3. Fort St. Vrain, Final Safety Analysis Report, Updated FSAR, Revision 2,Section VIII. s

4. Fort St. Vrain Unit No. 1 Schematic Diagram, Drawing No. E-1203.

5. PSC letter, D. W. Warembourg to D. R. Hunter, P-85318, September 13, 1985.

6. Proto-Power Corporation, " Truth-Analysis / Action-Reaction Review of 480V Essential Bus Tie Breaker Control Scheme,"

• t August 1985.

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APPENDIX A FAULT TREE ANALYSIS OF DIESEL AND Lb?,0 BREAKER -

SEQUENCING LOGIC .

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APPENDIX A FAULT TREE ANALYSIS OF DIESEL AND LOAD BREAKER SEQUENCING, LOGIC A fault tree analysis was performed on the diesel engines and output breaker sequencing logic based on control diagram E1203, page P-1601. The analysis was performed using the methodology presented in IEEE Standard 352-1975.

The analysis, as presented in Figures A-1 through A-3, shows that the events leading to failure of the essential buses are as follows: l i

1. Loss of all power sources. '

! 2. Loss of the output breakers from the emergency diesel generators.

l On generator IA, for example, breaker 252DG1A will not be closed if relays CR-9203 and TR-9201 have not been energized. Relay CR-9203 will not be energized if any of the following occurs: The contacts of IRSX1A or CR-9201 are open; P1 or P2 is open; timer circuits are open; the centacts of TR-9212, TR-9211, or 286G1B are open.

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Since the contacts of all these relays are in series, either contactsCR-9252-AorCR-9252fBcanbeopenandrelayIRSX1Awill not be energized. Relays CR-9252-A and CR-9252-B are energized only when both engine 1A and engine 18 are running. Therefore, in order u A., k. lly to 'close DG output breaker 252DG1A, both engines (1A and 18) must be running. This same logic condition exists on generator 1B (breaker 2520G1B) and on engines 1C and ID.

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M Decembsr 24, 1986 PSC also provided comments to the staff concerning the draft Technical Evaluation Report enclosed with the referenced letter. PSC's comments are summarized in a markup of this draft report, which is provided as Enclosure 2.

original signed by Kenneth L. Heitner, Project Manager Standardization and Special Projects Directorate l

Division of PWR Licensing-B Office of Nuclear Reactor Regulation

Enclosures:

DISTRIBUTION:

As stated [ Docket . File j ACRS (10)

NRC ~ PDR~~ ~~ PNoonan cc w/ enclosures: Local PDR 0 Lynch See next page PBSS Reading NRC Participants JPartlow IAhmed, PEICSB HBerkow JCalvo, PEICSB KHeitner CMiller, PEICSB CHinson 0GC-BETH EJordan BGrimes (O

PBSS PBSS Ifst PEICSB PEICSB o a KHeitner:cw Olync IAhme CMiller

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