05000315/LER-1998-046, :on 981103,determined That Afs Was Unable to Meet Design Flow Requirements During Special Test.Caused by Failure to Consider All Aspects of Sys Operation in Design of Suction Basket Strainers.Sys Will Be Redesigned

:on 981103,determined That Afs Was Unable to Meet Design Flow Requirements During Special Test.Caused by Failure to Consider All Aspects of Sys Operation in Design of Suction Basket Strainers.Sys Will Be Redesigned

ML17335A377
Person / Time
Site:	Cook
Issue date:	12/03/1998
From:	Gebbie J INDIANA MICHIGAN POWER CO.
To:
Shared Package
ML17335A376	List: 05000315/LER-1998-046, :on 981103,determined That Afs Was Unable to Meet Design Flow Requirements During Special Test.Caused by Failure to Consider All Aspects of Sys Operation in Design of Suction Basket Strainers.Sys Will Be Redesigned
References
LER-98-046, LER-98-46, NUDOCS 9812090137
Download: ML17335A377 (6)

LER-1998-046, on 981103,determined That Afs Was Unable to Meet Design Flow Requirements During Special Test.Caused by Failure to Consider All Aspects of Sys Operation in Design of Suction Basket Strainers.Sys Will Be Redesigned

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
3151998046R00 - NRC Website

text

NRC Form 366 U.S. NUCLEAR REGUIATORYCOMMISSION (6-1996)

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

APPROVED BY OMB NO. 31504104 EXPIRES 06/3012001 ESTSIATED SORDEN PER RESPONSE TO ~Y WITH TISS MANDATORY INFORMATIONCOllECRON RECIJEST'. 50.0 HRS. REPORTED lESSONS lEARNED ARE NCORPCRATED erTO THE UCENNNO PROCESS AND FED SACK TO eeVSTRY. FORWARD COMMENTS RECARDSIO SIJRDEN ESTSIATE TO THE INFORMATIONANO RECORDS MANACEMENTSRANCN IT@ FSTI. U.S. NIJCIEAR RECIRATCRY COMASSSIOM.

WASHINGTON. DC 205550001.

AIKI TO THE P~ REDvcTlcer PRoJEGT 151500IOIL CFFIOE CF MANAGEMENTAND SUDCET, WASISNSTON. DC 20505 FACIUTYNAME 11)

TITLEle)

Cook Nuclear Plant Unit 1 OOCKETNUMBER(2) 05000-315 PAGE IS) 1 of4 AuxiliaryFeedwater System Unable to Meet Design Flow Requirements During Special Test EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIESINVOLVED(6)

MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REVISION NUMBER MONTH DAY A IU DC Cook - Unit 2 A ILIlY NUMB 05000-316 03 98 98 046 00 12 03 98 OPERATING MODE (9)

POWER LEVEL(10) 00 20.2201 (b) 20.2203(a)(1) 20.2203(a)(2)(i) 20.2203(a)(2)(v) 20.2203(a)(3)(i) 20.2203(a)(3)(ii) 50.73(a)(2)(i) 50.73(a)(2)(ii) 50.73(a)(2)(iii)

THIS REPORT IS SUBMITTEDPURSUANT TO THE REQUIREMENTS OF 10 CFR g: (Check one or more) (11) 50.73(a)(2)(viii) 50.73(a)(2)(x) 73.71 20.2203(a)(2)(ii) 20.2203(a)(2)(iii) 20.2203(a)(2)(iv) 20.2203(a)(4) 50.36(c)(1) 50.36(c)(2)

LICENSEE CONTACT FOR THIS LER (12) 50.73(a)(2)(iv) 50.73(a)(2)(v) 50.73(a)(2)(vii)

OTHER Specitr h Abelreol below or nNRCFonn28SA NAME TELEPHONE NUMBER (SKSJde Area Code)

Mr. Joel Gebbie, Safety Related Mechanical Engineering Supervisor 616/465-5901, x1543 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX SUPPLEMENTAL REPORT EXPECTED 14 YES (ItYes, corn lete EXPECTED SUBMISSION DATE X

NO EXPECTED'UBMISSION DATE 15 MONTH OAY Abstract (Limitto 1400 spaces, l.e., approximately 15 single-spaced typewritten lines) (16)

On November 3, 1998, with Unit 1 in Mode 5, a special test was conducted on the Unit 1 West Motor Driven Auxiliary Feedwater (MDAFW)Pump to determine the potential effect on suction strainer loading when Essential Service Water (ESW) is used as the suction source. The 1 West MDAFWpump had been specifically chosen as having the highest risk for strainer plugging.

Approximately 60 seconds into the test the differential pressure across the strainer exceeded the maximum allowed, flow dropped below the design flowvalue, and the test was terminated.

The AFWsystem was declared inoperable, and an ENS notification was made at 1649 hours0.0191 days <br />0.458 hours <br />0.00273 weeks <br />6.274445e-4 months <br /> EST in accordan'ce with 10 CFR 50,72(b)(2)(i), for a degraded condition found while shutdown.

This LER is therefore submitted in accordance with 10 CFR 50.7(a)(2)(ii).

The root cause of this condition is a failure to consider all aspects of system operation in the design of the suction basket strainers.

The system willbe redesigned to perform its design function while taking suction from the ESW system.

Broad scope preventive actions are being performed under the Engineering Issues Review to assess the scope and quality of actions being taken to address system, structure, and component performance including operability, design and licensing basis issues.

The safety significance of this condition was evaluated considering the result-of both the initial test and a second test.

Based on a postulated short duration low flowcondition, and the AFWdesign utilizing the Condensate Storage Tank as primary suction source with ESW as a backup, it was determined that the condition did not pose a threat to the health or safety of the public.

" ~aag090i37 98i2033i PDR ADOCK 050003i5 SU.S. NUCLEAR REGULATORYCOMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITYNAME(1)

Cook Nuclear Plant Unit 1 DOCKET NUMBER(2) 05000-315 YEAR SEQUENTIAL NUMBER REVISION

. NUMBER LER NUMBER(6)

'AGE(3) 2 of 4 98 046 00 TEXT (I/mole space Is requimd, use additional copies ofNRC Form (366A) (17)

Conditions Prior to Event

Unit 1 was in Mode 5, Cold Shutdown Unit 2 was in Mode 5, Cold Shutdown Descrl tlon of Event On September 21, 1998, a Safety System Function Inspection (SSFI) self-assessment of the AuxiliaryFeedwater (AFW) system began, using SSFI techniques in accordance with NRC Inspection Procedure 93801, "Safety System Functional Inspection". The inspection team utilized a vertical slice review in the functional areas of engineering design and configuration control, operations, maintenance, surveillance and testing, and quality assurance and corrective actions.

The self-assessment conciuded on October 23, 1998.

During the SSFI, itwas noted that the AFWsystem had not been evaluated for operation using the Essential Service Water System (ESW) as the suction source.

ESW is Lake Michigan water, which contains some amount of sand, silt, and debris.

Certain design basis scenarios require switchover of the AFWsystem water supply from the Condensate Storage Tank (CST) to ESW. The original specification for the AFWpump suction strainers did not identify the ESW system as a supply source.

The suction strainers were specified for the clean water normally supplied by the CST, therefore, the concern arose as to whether or not the strainers would become loaded with sand, silt, and other debris more quickly than a fouled strainer basket could be cleaned and returned to service.

As a result of this concern, a special test was written to determine the loading rate of a suction strainer basket while aligned to ESW. The test was run on November 3,1998, and an initial ESW flow rate of approximately 560 gallons per minute (gpm) was established through the strainer for the Unit 1 West motor driven AFWpump. After60 to 80 seconds the silt and debris which was resident in the ESW line loaded the strainer, causing the differential pressure across the basket strainer to exceed 10 psid. Due to the high differential pressure, the test was terminated.

During the 60 to 80 seconds of the test, the ESW flow rate decreased from its maximum value of 560 gpm to approximately 400 gpm. As the design flow rate for ESW to the AFWsystem is 450 gpm, the AFWsystem was declared inoperable.

After the test was terminated, the strainer basket was removed and inspected to determine the nature and quantity of debris.

Several live zebra mussels were found in the basket, along with a quantity of crushed zebra mussel shells, and sand.

Cause of Event

The root cause of this condition is a failure to consider all aspects of system operation in the design.

The original design of the suction basket strainers did not take into account that the backup source ofwater for the pumps was lake water.

Documentation from 1970 shows that the original purchase order for the Motor Driven Auxiliary Feedwater (MDAFW)pump directed the supplier to provide a suction strainer sized for condensate.

There is no indication that the strainers could potentially be required to operate utilizing lake water as a suction source.

Contributing to this condition is the design configuration of the ESW supply lines to the AFW pumps.

These lines, especially to the West MDAFWpump, were installed such that debris tends to collect in them. The lines for the East MDAFWpump and the Turbine Driven AFW (TDAFW)pumps tap offthe side of the main 20 inch ESW header.

These 2 pumps comprised the original AFWdesign. The West MDAFWpump, which was added to the units in 1978, ties into the ESW system at an elbow where the 20 inch ESW header turns upward. The ESW supply line extends downward from the elbow, and is therefore an ideal debris trap.U.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITYNAME(1)

Cook Nuclear Plant Unit 1 DOCKET NUMBER(2) 05000-315 98 LER NUMBER (6)

SEQUENTIAL NUMBER 046 REVISION NUMBER 00 PAGE (3) 3 of 4 TEXT (Ifmom space is nrqui ed, use additional copies ofNRC Form (366A) (17)

Anal sls of Event This condition was determined to be reportable in accordance with 10 CFR 50.72(b)(2)(i), as a condition which was found while the reactor was shut down, which ifit had been found while the reactor was operating, would have resulted in the nuclear power plant being in an unanalyzed condition. An ENS notification was made on November 3, 1998, at 1649 hours0.0191 days <br />0.458 hours <br />0.00273 weeks <br />6.274445e-4 months <br /> EST in accordance with 10 CFR 50.72(b)(2)(i), for a degraded condition found while shutdown.

This LER is therefore submitted in accordance with 10 CFR 50.73(a)(2)(ii).

The AFWsystem provides water to the steam generators when main feedwater is unavailable because of a loss of main feedwater, unit trip, feedwater or steam line break, loss of off-site power, or small break Loss of Coolant Accident (SBLOCA). This water removes core residual heat to prevent the release of primary water through the pressurizer safety or powerwperated relief valves and allows the plant to cool down to the point at which Residual Heat Removal (RHR) can be placed in service.

Each unit is equipped with one turbine driven AFWpump and two motor driven AFWpumps.

Each pump is equipped with a suction strainer with two baskets.

For each unit, the TDAFP serves all four steam generators and each MDAFWpump serves two steam generators.

The steam to the AFWpump turbine is supplied from two of the steam generators.

The pieferred source of water for the AFWsystem is the non-safety related CST. Each unit's CST is cross-tied by a normally closed air operated valve to provide condensate to the opposite unit's AFW. Ifboth CSTs are unavailable, water is supplied from Lake Michigan via the safety related ESW system, which is connected upstream of the AFWpump suction strainers.

A minimum of 175,000 gallons is required to maintain the unit at hot shutdown for nine hours.

On November 4, 1998, a second strainer test was performed using the same special test procedure, and the suction line for the same MDAFWpump. ESW flowwas again established through the suction basket strainer, however, since the debris had been flushed out during the initial test, the flowrate and strainer differential pressurize stabilized at 500 gpm and 0.7 psid, respectively.

The test flowwas maintained for 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, during which the flow rate and differential pressure remained relatively constant.

The results showed that without debris in the suction line, the AFWsystem would meet its design flow requirements while taking suction from the ESW system.

The only debris removed from the suction line was the debris that had collected in the strainer during the first test. The results of the two tests showed that once the strainer had removed the initial surge of debris from the stagnant suction line, shifting to the spare strainer basket would have enabled the MDAFWpump to meet its design flow requirements while taking suction from the ESW system.

The initial debris load could be removed from the first strainer basket so that it could be placed back in service ifthe second strainer basket became fouled. Since the suction line that was tested was the one most susceptible to debris accumulation, there is reasonable assurance that the performance of the other two suction lines would be equal or better for each unit.

Based on the results of the tests, it is postulated that ifthe AFWsystem had been required to mitigate an accident, within a short period of time the accumulated debris in the ESW lines would have loaded the suction strainer basket, bringing in the differential pressure annunciator in the Control Room. An operator would have been sent to switch strainers, placing the clean basket strainer in service in accordance with approved plant procedures.

For approximately 10 minutes, the AFW pumps would have provided flowto the steam generators at a lower flow rate than the design of 450 gpm. After the clean strainer basket is placed in service, the flow rate would have increase to some value greater than the design value. Thus, it is anticipated that had the AFWsystem been required to operate to mitigate the consequences of an accident, the system may have operated at a lower than design flow rate for a short period of time.

NRCSORM 366A, U.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXTCONTINUATION FACILITYNAME(1)

.Cook Nuclear Plant Unit t DOCKETNUMBER(2) 05000-3(5 YEAR 98 LER NUMBER(6)

SEQUENTIAL NUMBER 046 REVISION NUMBER 00 PAGE (3) 4of4 TEXT (Ifmoro spaceis required, use additional copies ofNRC Form (366A) (17)

Based on the short duration of the identified low flow condition, in combination with the AFW design to take primary suction from the CST and use ESW as a backup suction source, it has been concluded that the condition did not pose a threat to the health or safety of the public.

Corrective Actions

An expedited request for modification was approved to correct this design problem. The request stated that the AFW system must be modified to ensure that is it is capable of maintaining its design flow rate while taking suction from the ESW system.

Although more than one potential modification was identified in the request, it is not known at this time precisely how the problem willbe resolved.

This has been identified as a restart issue.

The Engineering Issues Review Group was chartered to provide an independent review of the actions being taken to bound and address identified engineering issues.

The group willassess the scope and quality of actions being taken to address system, structure, and component performance including operability, design and licensing basis issues.

The group willalso specifically review the results of the AFWSSFI to ensure that the lessons (earned from this inspection have been identified and factored into the restart strategies and other corrective actions taken to address engineering issues.

Previous Similar Events

315/98-029-00 II