ML20151K090

Safety Evaluation Supporting Util Proposed Implementation of ATWS Rule Pending Resolution of Tech Spec Issue

ML20151K090
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Site:	Summer
Issue date:	07/28/1988
From:	Office of Nuclear Reactor Regulation
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.#o o%%,, UNITED STATES l' '% NUCLEAR REGULATORY COMMIS$10N

! W ASHING TON. O. C. 20066

%. g SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i SOUTH CAR 0LihA E'.ECTRIC & GAS COMPANY l

SOUTH CAROLINA PUBLIC SERVICE AUTHORITY VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1 00CKET NO. 50-395

1.0 INTRODUCTION

On July 26, 1984, the Code of Fedtral Regulations (CFR) was amended to l include Section 10 CFR 50.62, "Requirerents for Reduction of Risk fres i Anticipated Transients Without Scram (ATWS) Events for Light-Water-Cooled Nuclear Power Plants" (known as the ATWS Rule). The requirements of Section 10 CFR 50.62 apply to all commercial light-water-cooled nuclear 1

power plants.

An ATWS is an anticipated operational occurrence (such as loss of feed-water, loss of condenser vacuum, or loss of offsite pcwer) that is accom-panied by a failure of the Reactor Trip System (RTS) to shut down the reactor. The ATWS Rule requires specific improvements in the design and operation of commercial nuclear power facilities to reduce the probability of failure to shut oewn the reactor following anticipated transients and

) to mitigate the consequences of an ATWS event.

Paragraph (c)(1) of 10 CFR 50.62 specifies the basic ATWS mitigation 4

system requirements for Westingnouse platts. Equipment, diverse from the 3 RTS, is required to initiate the auxiliary feecwater (AFW) system and a turbine trip for ATWS events. In response to paragraph (c)(1), the

Westinghouse Owners Group (WOG) developed a set of conceptual ATWS mitt-gating system actuation circuitry (AMSAC) designs generic to Westinghouse

' plants. WOG issued Westinghouse Topical Report WCAP-10858, "AMSAC Generic Design Package," which provided information on the various Westinghouse t designs.

The staff reviewed WCAP-10859 and issuto a safety evaluation of the subject topical report on July 7,1986 (Ref.1). In this safety evalue-j tion, the staff concluded that the generic designs presented in WCAP 10858 adequately met the requirements of In CFR 50.62. Tne approved version of the W*\P is labeled WCAP-10858 P.A.

During the course of the staff's review of the proposed AMSAC design, tne kCG issued Addendum 1 to WCAP-10858-P-A by letter dated February 26, 1987 (Ref. 2). This Addendum changed the setpoint of the C-20 AHSAC permissive signal from 7Cf, reactor pcwer to 401 pcwer. On August 3,1987, the WOG issued Revision 1 to WCAP-10858-P-A (Ref. 3), wnich incorporated Addendum 1 changes and provided details en enanges associated with a new variable 8800030121 000729 DR ADOCK 050 5

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timer and the C-20 time delay. For those plants selecting eitner the feedwater flow or the feedwater purp/ valve status logic option, a variable delay timer is to be incorporated into the AMSAC actuation logics. The variable time celay will be inverse to reactor power and will approximate the time that the steam generator takes to boil down to the Icw-low level setonint upon a loss of main feedwater (MFW) from any given reactor power level between 40% and 1001 power. The time delay on the C-20 permissive signal for all logics will be lengthened to incorporate the maximum tire that the steam generator takes to boil down to the low-Icw level setpoint upon a loss of MFW with the reactor operating at 401 power. The staff considers the Revision 1 changes to be acceptable.

Paragraph (c)(6) of the ATWS Rule requires that detailed information to demonstrate compliance with the requirements be submitted to the Director, Office of Nuclear Reactor Regulation (NRR). In accordance with paragraph (c)(6)oftheATWSRule,SouthCarolinaElectric&GasCorpany(SCE8G)

(licenseel provided information by lettcr dated March 24, 1988 (Ref. 4).

The letter forwarded the detailed design description of the ATWS miti-gating system actuation circuitry proposed for installation at the Virgil C. Summer Nuclear Station Unit 1.

The staff held a conference call with the licensee on April 20, 1988, to discuss their AMSAC design. As a result of the conference call, the licensee responded to the staff concerns by letter dated May 4, 1988 (Ref. 5).

2.0. REVIEW CRITERIA The systems and equipment required by 10 CFR 50.62 do not have to meet all of the stringent requirements normally applied to safety related equip-rent. However, the equiprent required by the ATWS Rule should be of sufficient quality and reliability to atrform its intended function while minimizirig the potential for transients that may challenge the safety systems, e.g., inadvertent scrams.

The follcwing review criteria were used to evaluate the licenste's sub-mittels:

l 1. The ATWS Rule 10 CFR 50.62.

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2. "Considerations Regarding Systems and Equipeent Criteria." published I in the Federal Register, Volute 49, No. 124 dated June 26, 1984 1

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3. Generic Letter 85-06, "Quality Assurance Guidance for ATWS Equipment inat is hot Saf:rty Related."

4 Safety Evaluation of WCAP-10858 (Ref. 1).

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5. WCAP-10858-P-A. Revision 1 (Ref. 3),

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i l C i l 3.0 0!SCUS$!0N AND EVALVATION si l 4

To determine that conditions indicative of an ATWS event are present, the _

licensee nas elected to implement the WCAP-10858-P A AMSAC design associ.  !

ated with monitoring the steam generator water level and activating the l AMSAC hhen the water level is belcw the Ich-low setpoint. Also, the 1 Itcensee will implement the new time delay (as described in the introduc-l tion section) associated with the C-20 permissive consistent with the i requirements of Revision 1 to the WCAP.

I Many details and interfaces associated with the implementation of the I final AMSAC design are of a plant-specific nature, in its safety evalua.  !

tion of WCAP-10858, the staff identified 14 key elements that require i resolution for each plant design. The following paragraphs provide e '

} discussion on the licensee's compliance with respect to each of the

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plant specific elements. [

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1. Diversity  ?

The plant design should include adequate diversity between the AMSAC  ;

equipment and the existing Reactor Protection System (RPS) equipment.  !

! Reasonable equipment diversity, to the extent practicable, is  !

] required to minimize the potential for common-cause failures.

l i The licensee has orovided information to confirm that tne AMSAC logic i circuits will be otverse from the RPS in the areas of design, equip. '

ment, and manufacturer. Where similar types cf components are used. .

suen as relays, the AMSAC will utilize an cutput relay of a different make and manufacturer than those used in the RPS.

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i 2. Logic Power Supplies i

L l Logic power supplies need not be Class 1E. but must be capable of l

perforaing safety functions upon a loss of offsite pcwer. The logic  ;

! ' power must come from a power source tnat is independent from the RPS [

q power supplies. l 1

L i The licensee has provided information verifying tnat the logic power  !

l supplies selected for the Summer Station AMSAC logic circuits will f provide the maximum available independence from the RPS power  !

I. supplies. The AMSAC will be powered frem nonsafety-related pcmer  !'

supplies which will be independent of the RPS ana capable of opera-

, ting upon a loss of offsite power.

3. Safety-Related Interiace

. Tne implementation of the ATWS Rule shall te such that the existing RPS continues to meet all applicable safety criteria.

] The proposed Summer Statien AMSAC design interfaces at its input with j the existing Class 1E circuits of the steam generator level instru-j eentation and turbire first-stage icpulse pressure instrumentation.

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r At its output, the AMSAC will interface with the Class 1E circuits of r the AFW pumps. Connections with the AFW control circuits will be  :

made downstream of approved Class 1E isolation devices. The licensee t has confirmed to the staff that the existing safety-related criteria that are in effect at tne Summer Station, as described in its FSAR Section 7.1, will continue to be met af ter the implementation of ,

AMSAC (i.e., the RPS will cont,inue to perform its safety functions i without interference from AMSAC). Refer to item 9 for further  !

discussion on this issue. j i

4. Quality Assurance l

1 The licensee is required to provide information regarding compliance  !

with Generic Letter (CL) 85 06, "Quality Assurance for ATWS Equipment r That is Not Safety Related." , j l

The criteria of the f4RC quality assurance guidance (GL 85-06) were (

reviewed by the licensee. The licensee stated that the quality l assurance practicts at the Summer Station, as applicable to  ;

consafety related AMSAC equipment, comply with the guidance of i GL 85-06.  !

5. Maintenance Bypasses  !

Information showing hcw maintenance at power is accomplished should be provided. Also, maintenance bypass indications should be incor-  !

porated into the continuous indication of bypass status in the l contrel room.

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The licensee provided information showing how maintenance is to be  !

accomplished at power. The staff was informed that maintenance at power will be performed by inhibiting the operation of AMSAC's output relays, which will block the output signal and, thut, prevent it from  !

reaching the final actuation devices. The continuous indication of  !

bypass status will be provided in the main control room through the I use of status lights and annrnciation. It is the staff's understand- l ing that the licensee will conduct a human-factors review of the subject indication consistent witn the plant's control room design process.

6. Operating Bypasses The operating byphsses sneuld be indicated continuously in the control roce. The independence of the C 20 permissive signal sh.ould be addressed.

The licensee has provided information stating tnat an AMSAC operating b) pass (C-20) will be used to enable the operators to bring the plant up in power during startup and to avoio spurious AMSAC actuations at power levels below 40s reactor ocwer (the C-20 arming setpoint).

Above 40% reactor power, the C-20 will automatically are the AMSAC Icgics. The C 20 permissive signal will originate from existing

first stage turbine impulse chatber pressure sensors and upon a turbine trip (loss of the C 20), the permissive signal will be mainteitted by a timer f or a period of time consistent with Revision 1

to WCAP-10858-P-A. The licensee has determined that this time delay

, will be sufficient to ensure that AMSAC will parform its functicn in

the event o' a turbine trip ( Dss of ined AT'eS). The C-20 permissive dgnal wi',1 be taken downstream from qualified isolators shd will not interfera with the RPS. The operating bypass will be indtcated continuously in the control room via annunciation and status lights It is the staff's understanding that, whenever it dis &teles the AMSAC.

the licensee will conduct a human-factors review of the subject indication consistent with the plant's control room design process.

7. Means for Bypassing ine means for bypassing shall be accomplished by using a permanently installed, human-factored, bypass switen or similar device. Dis-l allowed methous for bypassing centioned in the guidance snould not be utilized.

The licensee's response stated that a permanently installed control switch will be used for the bypass function. The disallowed methods for bypassing, such as lif ting leads, pulling fuses, blocking relays, l and tripping breakers will not be used. The bypass switch will be located on the AMSAC Test / Maintenance panel, it is the staff's understanding that the licensee will conduct a human-fact. ors review of the AMSAC bypass controls consistent with the j plant's detailed control room design process.

8. Manual Initiation Manual initiation capability of the AMSAC mitigation function at the system level must be provided.

In the plant-specific submittal, the licensee discussed how manual turbine trip and auxiliary fcedwater actuation are accomplished by the operator. In summary, the operator can use existing manual J

controls to perform a turbine trip and to start auxiliary feedwar.er

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flow should it be necessary. Inus, no additional manual inittstion capability will be required as a result of installing the AMSAC equipeent.

9. Electrical Incependence From Existing Reactor Protection System i Independence is required from the sensor output to the final actua-tion device, at knich point nonsafety-related circuits must be isolated from safety-related circuits by qualified Class 1E isolators.

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1 6-The licensee discussed how alectrical independence is to be achieved.

The proposto design requires isolatico between t,he non-Class 1E ANSAC and the Class IE circuits asercia ed with the steam generator (SG) tevel, the turbine first stage 15culse chamber cre;sure sionals, and the AFW pumps. The licensee has informec the staff that the required isolation will be achieved using alectrical isolation devices that l have been qualified and tested to Class 1E electrical equiprent requirements. In addition, th= isolaters were testfG 6s described in Appendix A to the safety evaluation (Ref.1).

10. Physical Separation From Existing Reactor Protectier. System The implementation of the ATWS mitigating system mast be suco that the separation criteria applied to the existing RPS are not violated.

Tne 11cer.5c6 stated that the AMSAC circuitry will be pnysically separated from the RPS circuitry. The licensee has furtner statto tnat the cable routing will be independent of protection system cable routing and that the ATWS equipmer,t cabinets will be located so tcat there will be nc interaction wita the protection system cabinets. .

The licensee als9 stated that the RPS design will continue (subse- ,

quent to the trolementation of AHSAC) to meet the separatier. criteria originally established for the Summer Station during initial plant licensing.

11. Environmental Qualification 3

The plant-specific submittal shoulo address the environmental quali-fication of ATWS equipment for anticipnted onerational occurrences.

Tne licensee stated that AMSAC attigation equipment will be located in areas of the plar.t that are censidered to be a mild environoent. ,

The licensee also stated that the equipeent will be enytronmentsily qualified for ant *cipated operational occurrences that might occur associated witn tae respective equipment locatier.s. ,

l 12. Testability at Power  !

I heasures to test the ATWS ritigatirg system tefore installatio. . as  ;

well as periodically, are to be establisned. Testir.g of tha system may oe performed with the system in the bypass mod . Testing from the input sensor through to the final actuatior revice should be pe.-forcej with t'.it plant shut dcwn.

The 11ceniet stated that a corplete end-to-end test of the AMSAC syssemp including the AMSAC cutputs tnrouch to the final antuation r devices, vill be rerforned during each refueling cutage. Witn the  ;

pla.it at sewer, tre system can be tested with the AMSAC output actuation devices oypassed. The testing cF 3bility cens4sts of a ,

series or overlopping tests. These tests will verify analog channel accuracy, se tpoint (bistable trip) accurac:<, cr. incidence logic cperation, and operatien ard accuracy of all tirers. Tne at-pcwer '

legiu tests 'till be performed at least every 62 days.

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l l i The bypass of the AMSAC output actuation dtvices will be accomplished i tarceqh a permanently installer bypass switch which negates tne need t to istt laats, pull fuses, trip breakers, or physically block relays.  !

I Status outputs to tha main control board. Indicating that a generil l l warningconditionexistswithAMSAC,willbeinitiatedwhenthe Plant procedures will be used to test system s outpats are bypassed. [

l the AMSAC circutt.*y ano outputs. These procedures will ensure tnat  ;

l AM3AC is returned to service when testing is complete.  !

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l It is tne staff's understanding that the licensee will conduct a '

l human-f actors review of the controls and indications used for testing i

purposes that is consistent with the plant's cetailed control roca ,

design process, j l j l 13. Completion of Hitigative Action l l T The licensee is required to verify that (1) the protective action,  !

once initiated, goes to completion and (2) the subsequent return to L l operation reqatres deliberate operator action. l l l The licensee reipanded tnat the syster design will be such that AMSAC t i is consistent with the circuitry of the auxili4ry feedwater and i turbine trip centrol systems, as well as the blowdown and sampling I systems. Once initiated, the design will ensure that protective l action goes to ccerpletion. Deliberate operator action will be l l required to return the final actuition devices to normal operation l I

ind to recover from the AMSAC actuation. l 14 Tecnnical Specifications l The plant-specific submittal should address Technical Specification (

I requirements for AMSAC. '

The licensee responded that no Technical Specification action 1; l proposed with respect to tne AMSAC. The licensee stated that the I systes does not meet NRC criteria for inclusion in the Technical  !

Specifications. The surveillance interval and actions required to i service the AMSAC will be administratively controlled using stat. ion [

l procedures.  !

The equipment required by tha ATW5 Rule to reduce the risk associated j with an ATWS event must be d. signed to perform its functions in a  :

reliable manner. A mothed acceptable to the staff for demonstrating i

, that the equipeent satisfies the reliability requirements of the ATh$ [

l Rule is to provise lietting conditions for operation and surveillante l l requirer 4nts in tne Technical Specifications. I l

l In its Interte Commissicn Policy Statecent of Tecnnical Specif testion l l Improvementsfor*uclearPcwerPlants(52FederalRegister3788,  !

l Fatsruary 6,1987), tna Cocsission established a specific set of l l objective criteria for detern ning which regulatory requirements and l l l ,

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l operating restrictions should be included in Technical Specifica-  :

tions. The staff is presently reviewing ATWS requirements to  ;

criteria in this Policy Statement to determine whether and to what j extent Technical Specifications are appropriate. Accordingly, this aspect of the staff teview remains open pending completion of, and  ;

subject to the results of, the staf."s further review. The staff t will provide guidance regarding the Technical Specification require.

ments for AMSAC at a later date. (

4.0 CONCLUSION

l The staff concludes, based on the above discussion and subject to final  ;

resolution of the Technical Specification issue, that the AMSAC design ,

proposed by South Carolina Electric & Gas Company for the Virgil C. Summer  !

Nuclear Station, Unit 1, is acceptatle and is in compliance with the ATWS  :

Rule,10 CFR 50.62, paragraph (c)(1). The staff's conclusion is further subject to the successfu completion of certain noted numan-factors engineering reviews. Until staff review is completed regarding the use of '

Technical Specifications for ATWS requirements, the Itcensee should l continue with the scheduled installaticn and implementation (planned  !

operation) of the ATWS design utilizing administratively controlled procedures.

Principal Contributor: R. Stevens Dated: July 28, 1988 i f

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REFERENCES

1. Letter, C E. Rossi (hRC) to L. D. Butterfield (WOG), "Acceptance for Referencing of Licensing Topical Report," July 7,1986.

2. Letter, R. A. Newton (WOG) to J. Lyons (NRC), "Westinghouse Owners Group Addendum 1 to WCAP-10858 9-A and WCAP-11233 A: AMSAC Generic Design Package," February 26, 1987.

3. Letter, R. A. Newton (WOG) to J. Lyons (NRC), "Westinghouse Owners Group Transmittal of Topical Report WCAP-10858 P-A, Revision 1 AMSAC Ceneric Design Package," August 3, 1987.

4 Letter. O. A. Nauman (SCE&E) to U. S. NRC, "Implcrentation of ATWS Rule (10 CFR 50.62)," March 2t, 1988.

5. Letter, D. A. Nauman (SCE&G) to U.S. NRC, "Implerentation of ATWh

• Rule (10 CFR 60.62), Supplemental Information," May 4,1988.

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