ML20081G678

Requests Concurrence on Proposed Mod to HPCI Steam Exhaust Line Vacuum Breaker Configuration.Mod Would Significantly Improve Containment Performance by Providing More Reliable Means for Containment Isolation During Accident Conditions

ML20081G678
Person / Time
Site:	Quad Cities
Issue date:	06/10/1991
From:	Stols R COMMONWEALTH EDISON CO.
To:	Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
NUDOCS 9106130260
Download: ML20081G678 (14)

Text

.

Ccmmonwealth Edison 0

1400 opus Place O-Downers Grovo, Imnois 00515 June 10,1991 Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Document Control Desk

Subject:

Quad Cities Nuclear Power Station Units 1 and 2 Proposed Modification to the HIOh Pressure Injection Coolant (HPCI) Steam Exhaust Lino Vacuum Breaker Configuration NRC Docket Nos. 50 254 and 50 265 l

References:

(a)

H.J. Miller to Cordell Reed letter dated 1

October 26,1990 (b)

D.G. Eisenhut to D.M. Mustof letter dated June 3,1984 (c)

R. Stols to T.E. Murley letter dated March 20,1991 Dr. Murley:

On September 25,1990 members of the NRC's (including representatives from Region lll and NRR) and Commonwealth Edison's staffs conducted a meeting to discuss Quad Cities Station's actions to improve the performance of containment Reference (a)). During that isolation valves during 10 CFR 50 Appendix J testing (d modification to eliminate the meeting, Commonwealth Edison > resented a propose need to perform Type C testing o~ the High Pressure Coolant injection (HPCI) steam exhaust line check valve (230145). Commonwealth Edison Indicated that NRC concurrence on the new testing requirements for the system would be requested.

The attachment provides the description of the existing configuration and the proposed modification. Commonwealth Edison requests the NRC's review and concurrence of our testing requirement assessment for the proposed modification.

Commonwealth Edison has determined that this modification would significantly improve containment performance by providing a more reliable means for containment isolation during accident conditions, in addition, this modification would eliminate the need for accelerated testing (and potential repairs) of the HPCI steam exhaust check valve, thereby reducing the amount of occupational exposure required for the maintenance of the containment boundary. As such, Commonwealth Edison has added this modification to the installation schedule for the upcoming Unit 2 Refueling Outage which is scheduled to begin on December 28,1991.

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Dr. T.E. Murley June 10,1991 Commonwealth Edison respectfully requests that NRC concurrence be recolved no lator than September 3,1991 to accommodato tho final design of the modification.

A submittt.1 (Roforence (c)) which described the HPCI steam exhaust lino raodification was reviously provided to the Commission; however, minor changes to the conceptual dosi n have occurred. As a result, this submittal supersedos the Reference (c) sub ittal.

Please direct any questions or comments to mo at (708) 515 7283.

W:ry imly yours,,

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Rita $tols i

Licensing Administrator A.B. Davis, Ro0 on 111 Administrator l

cc:

F.A. Maura, inspector, Region lli LN. Olshan, Project Manager, NRR J.A. Kudrick, Technical Staff, NRR T.E. Taylt/r, Senior Resident inspector, Quad Cities

Attachment:

High Pressure Coolant injection (HPCI) Steam Exhaust Line Modification Figures:

HPCI Turbino Exhaust Line HPCI Sparger Conceptual Design isolation Logic for Vacuum Breaker Lino Enclosuro:

General Electric Servics Information Letter No. 30 dated October 31,1973 L

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ATTACllMENT lilGli PRESSURE COOLANT INJECllON (HPCI)

STEAM liXilAUST LINE MODIFICAllON Dackground 15,1990, Ro0 on lll issued Inspection Rr ar150 254(265)/69024 which On Juno l

summarized the results of their inspection of the Quad C,aos 10 CFR 50 Appendix J Test Program. A Notico of Violation which cited inoffectivo correctivo actions to repetitivc valvo failures wan issued. One of the valvers which was citud as a concern was the High Pressure Coo' ant injection (HPCI) steam oxhaust check valvo (230145).

The HPCI steam exhaust valve has exporlonced repeated Local Loak Rato Test (LLRT) failuros. The 230145 valvo condition datorlorates due to the unstablo steam condonsation during HPCI turbino low steam flow conditions. Provlous attempts to improvo valvo performanco consisted of rodosigning the 230145 valvo and/or chan0 n0 the saatin0 matarla!s. In responso to thohotico of Violation, Commonwealth i

Edison committod to accolorate the tost Interval for the 230145 valve to ensure that its containmont function romains offectivo. Survoillanco procedures woro revised to minimizo potential damage to the valvo during low spood turbino operation.

In Septembor,1990 Commonwealth Edison conceptualized a modification to enhance the current design of the HPCI exhaust r.ystem and also to creato a now containmont boundary such that the 230145 valvo can be removed from the 10 CFR 50 Appendix J Program. This pro 30 sed modification was discussed with members of the NRC staff (including Ro0lon 11 and NRR representativos). The proposed modification provides the following benefits:

1.

Adds the ability to isolate the vacuum breaker line, thereby avoiding the potential for a contalnment atmosphoro leakage path throu0 the HPCI h

turbino exhaust; 2.

Improves the reliability of the vacuum breaker with a one out-of two twico check valvo configuration; 3.

Providos improved access for maintenanco, since the vacuum breaker is located external to the torus; and, 4.

Improves the steam condensation stability through the use of a spar 0er which is designed to provide for more stablo condensation over a wide rango of steam flows, thereby minimizing the cyclical" chugging" load en the 230145 valvo.

Commonwealth Edison Indicated that the NRC confirmation of the now testin0 toquirements would be requested.

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ATTACHMENT (continued)

Existing Configumtion The existing configuration of the HPCI steam exhaust line is provided in Figure

1. The HPCI turbino exnaust line runs from the e@aust of the HPCI turbine through the Residual Heat Removal (RHR) corner room, penetrates the torus and discharges below the torus water level. The line contains two large turbine exhaust check valves (230145 and 210174), which are designed to prevent water from backing up into the turbine, inside ihe torus, a vacuum breaker line which is equipped with two small check valves ties into the HPCI turbine exhaust line downstream of the turbine exhaust check valves. During normal HPCI operation, this vacuum breaker relieves the vacuum which is created by steam condensin0 n the exhaust line downstream of the check i

valves.

The vacuum breaker line inside the torus provides a path for communication between the inside and outside containment atmospheres. The large HPCI steam exhaust check valves are, therefore, required to prevent post accident containment atmosphere from escaping.10 CFR 50 Appendix J, Section ll.H requires localleak rate testing (Type C)insting of the containment isolation valves.

The HPCI 23014 and 23015 valves (HPCI steam supply) Isolate on a Group IV isolation signal. These signals are: high HPCI steam flow; high HPCI room temperature;or low reactor pressure. The basis for HPCIisolation during high steam flow or high room temperature is to assure system isolation in the event of a HPCI line break. High pressure steam is required for the operation of the HPCI system. The steam supply valves isolate when HPCI is no longer capable of performing its design function.

Proposed Modification The proposed modification (Figure 1) eliminates the unisolatable air path between the inside and outside containment atmosphotos through the removal of the vacuum breaker and addresses the cause of the 230145 valve deterioration.

The existing vacuum breaker line, which is located inside the torus, will be removed. The HPCI exhaust line terminates below the minimum water level of the suppression pool and, therefore, will not communicato directly with the containment atmosphere. The suppression poolinventory provides ari effective water seal during the post accident period Verification that sparger holes in the exhaust line will be submersed following accident conditions has been performed.

Removal of the existing air leakage pathway between the torus atmosphere and the HPCI exhatat line eliminates the vacuum breaker protection. In order to protect the HPCI turbine exheiust line from unstable steam condensation (chugging) and water hammer damage, ta well as to provide a vacuum relief function, an exhaust line sparger and a new veuum breaker configuration is proposed. The new 4 inch vacuum iine will be an isolatabl6 air leakage pathway between the ccatainment air space and the HPCI exhaust line and is located external to the torus (Reference Figure 1).

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ATTACllMENT (continued)

Proposed Modification (continued)

The line will contain two motor operated Date valves; four,4 inch check valves in a one out of two twice arrangemont; two 4 inch blockinD Dato valves for testing; and localleak rato test (LLRT)inp linos with 3/4 inch globo sockolot valves. The outboard valvoc will bo poworod from the 250VDC Division 11 power soutco. Tho inboard valvo will be fod from the 480 VAC Division 11 aower source. The valvos can be operated through remote or manual operation in tio unlikely event of the f ailure of the automatic isolation featuro. The valves will be procured to safety related and to environmental qualification standards.

The sparger will be installed on the end of the HPCI turbine exhaust line inside of the torus and is designed to promoto more stablo steam condensation. The first row of holes on the sparger will be located at or below tho existing HPCI exhaust line submergence (Rotorence Fi uro 2). The valves and piping will be qualiflod for all 0

applicable loads, includin0 selsmic and Mark I containment considerations.

The logic for the vacuum broahor isolation valves has been developed in accordance with the recommendations containod in General Electric Servico information Letter 30 (Enclosuro 1) and is consistent with the design of later operating plants (e.g., LaSalle RCIC system). The vacuum breaker line isolation valves will

.solate on bl h drywell pressure concurrent with low reactor pressuro. The containment 0

isolation valves will be normally open to assure the operational readiness of HPCI. As such, the vacuum breaker line will be isolated during conditions indicative of a lar00 break inside of the drywell concurrent with low reactor pressure conditions such that HPCI can no lon0er perform its function. The logic for the closure of each valve is one-out of two taken twice arrangement (Reference Figure 3). The inolation signal is featured with a seal in signal such that the signal must be roset and manual action must be implemented to open the valves following isolation. The isolation signal to each valve is provided from separato control divisions such that no single physical f ailure could prevent isolation.

The now vacuum breaker isolation valves will be required to have no greator than a 50 second closure time. The most severe radiological release results from fuel damage due to a loss of reactor level which is accompanied by a loss of reactor pressure. Since HPCI vacuum breaker isolation valvas would close under low pressure conditions (concurrent with high drywell pressure), the vacuum breaker isolation valves would be closed prior to fuel damage. As such, the closure time was determined based on the ability of the valve to close and assures that any potential radiological release is below reOulatory and Technical Specification limits.

10 CFR 50 Appendix J Testing Requirements l

The Station's Appendix J Test Program will be modified to eliminate the HPCI steam exhaust check valve (230145). In accordance with the NRC's position contained in reference (a), the exhaust line terminates below the minimum suppression pool level and, therefore, is provided an effective water seal during post accident conditions. Verification of suppression poolinventory and sparger submergence following post accident conditions has been performed. The HPCI stearn exhaust vacuum breaker isolation valves will bn added to the program and tested in accordance with the requirements for Typo C testing.

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lei:ter SERVICES October 31e 1973 SIL th. 30 im in uic 1 Catepry P Pp(1/RCIC TURB!WI IXRAU$7 LINE VAC{LH BRCAKCR$

Surveillance testine er the HPC1/RCIC systme at mary operating bas has disclosed an undes: table exhaust line vacuum condition that causes rare cr trore of the fo11catrG adverse effectst 1.

Pressure instability in the exhaust line.

2.

Cyc1tng.snd slamire of the exhaust line check valves.

3.

Pips and torus vibr6 tion.

4.

Water slug carryover.

5.

Post shatdosn vibration caused by stessi collapse.

Investigatiens into this phenmenon during the course of pre op activities at Brwns Ferry 1 and Peach Gotton 2 beve concluded that HPC1/RCIC systens can tenefit significantly by the installation of visuum breakers on t*e turbine exhaust lines. Testa conducted at Brwns ferry snd Peach Bottom confirved that the installation of vacuutr brenkers improves low lead optri-tion and provides acceptable turbine shutdown condittuns by minim 12ing pressure fluctuations. Also, the installation of these vacuum brtike's will prevent water fror) rising in the turbine exhaust 11ne during i pis.

tulated LOCA when the torus would becoine pressurized.

The miniinum views breaker site recosteerded is 2 inches for HPCI turbine exhaust, and its inches for RCIC turbine exhaust. The vacuum breaker oe:4 valves should Este a pressure drop of less than 0.6 psi to assure adeusui vacuum breaker capability.

Figures 14 2 (attached) provide schematics of the.ttfamtrdtj instal' ttiM.

bote that Figure 1 applies to plants having HPCI systems whereas figure ;!

is applicable to HPC1/RCIC systns.

b yeeremty et repesientetion emp ensed or kerate is enese ein respot to the toewency, tornpleierseas et ose41rses of 161s tilctmetlos Q+n+ ret fleet le Comporty eenvents no respoesit#lty fet habitity or domste whloh t'isy result from the use of t'ils Infor ns'h.ei, NU%t AR ENtitGY olVislCN e niNH sE RVICEs e s AN JOSE C ALif CRNIA Q[y[R Al h ((ECT RlC e

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51L Ho. 30 Page 2 Note also that both vacuum breaker configurations include provisions far positive isolation of the suopression pool air space. This provisien is l

in compliert:s with AtC criteria that check valves not be used for lonq tem isolation.

The positive isolation should to automatically initia:ed by a contifhaTTon of low reactor pressure and high drywell pressure. T ie existing low reactor pressure switches may"Te used, combined with exis t.

ing "t pilg" high drywell pressure switches. Electricti separation should be meintained to the redundant isolation switches.

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Retrate manual switches in the control room are not re utred local swi;chus are considered adequate. However, control room indtestin 1Ights shou'd be provided, plus an alam annuncitting 'YACVUM BREAKER !$0 T!0N VALVES lt07 FULt.Y OPEM.'

l If additional help in implee>enting tills recomended installktion is detirec.

d Seneral Electric would be pleased to provide a quotation for supplomonia) i engineertr.) or installation assistance.

Prepared byl V. 6. Greyhet Approved byl 3 Akb Issued by:

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D.' t. Br1(enbau h, manager a

Perfervance EY4 untion and Perfor1 nance Analysis and Irtproverrent Service,Connunications Product Referencel E41 - HPCI 5 stem ES) - RCIC $ tai 4

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