ML20012C631

Submits Revised Response to NRC Bulletin 88-004 Re Potential safety-related Pump loss.Motor-driven Auxiliary Feedwater Pumps Have Been Revised to Include Addl Info Describing Operations of Pumps & Description of full-flow Test Program

ML20012C631
Person / Time
Site:	Sequoyah
Issue date:	03/15/1990
From:	Wallace E TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-88-004, IEB-88-4, NUDOCS 9003220303
Download: ML20012C631 (7)

Text

w TENNETEE VALLEY AUTHORITY CH ATTANOOG A. TENNESSEE 37401 SN 1578 Lookout Place MAR 151990 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of. ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 SEQUOYAH NUCLEAR PLANT (SQN) - REVISED RESPONSE TO NRC BULLETIN 88 04 -

POTENTIAL SAFETY-RELATED PUMP LOSS

References:

1. TVA letter to NRC dated August 2, 1988, "Sequoyah Nuclear Plant (SQN) - NRC Bulletin (NRCB) 88-04, ' Potential Safety-Related Pump Loss'"

2. TVA letter to NRC dated December 22, 1989, " Tennessee Valley Authority - Sequoyot, Nuclear Plant Unit 1 - Docket No. 50-327

- facility Operating License DPR Licensee Event Report (LER) 50-327/89031" The subject bulletin requested licensees to investigate and correct, as applicable, two mintflow design concerns. The two concerns are (1) potential for deadheading or adverse pump-to-pump interaction during mlniflow operation and (2) adequacy of installed mlniflow capacity for a single pump in operation.

The purpose of the letter is to provide TVA's revised response to the subject bulletin for SQN. Recent events (Reference 2) have shown that the corrective actions identified for the residual heat removal (RHR) pumps in the original assessment (Reference 1) were not adequate to detect the onset of pump-to-pump interaction.

The original corrective action (short- and long-term) for the RHR pumps was to evaluate, during each refueling outage, the pump differential pressure data obtained during the quarterly Section XI pump tests. This evaluation averaged the data for each pump and compared the average differential pressure between the two pumps against an acceptance value of 8 pounds per square inch differential (psid) (the actual calculated allowable value is 11.1 psid). As documented in Reference 2, the frequency of evaluating the pump differential pressures (every refueling outage) wn not adequate since the averaging technique did not address real-tirne cases where the 11.1 psid criteria were not met. Actual plant testing showeJ the pressure differential was greater than 11.1 psid during plant power oM eetion, and subsequent runnirg of both RHR pumps on mlniflow proved that dr.:J! Nd!ng of one of the pumps would occoi .

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r Enclosure I contains TVA's revised response that outlines new short- and

~long-term actions that will be taken for SQN's RHR pumps, t

l In addition, TVA's original corrective actions regarding SQN's motor-driven auxiliary feedwater pumps have been revised to include (1) additional information describing the intermittent operation of these pumps, (2) a '

. description of SQN's full-flow test program, and (3) a commitment for L installing additional mlniflow capacity during the Cycle 5 refueling outage i

for each unit.

The adequacy of the mintflow lines for SQN's other safety-related pumps has been confirmed.

r The commitments associated with this submittal are stated in Enclosure 2.

Please direct questions concerning this issue to Don V. Goodin at (615) 843-7734.

Very truly yours, TENNESSEE VALLEY AUTHORITY E. G. Wallace, Manager Nuclear Licensing and Regulatory Affairs Enclosures cc: Ms. S. C. Black, Assistant Director (Enclosures) for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White il nt, North 11555 Rockvllle Pike Rockville, Maryland 20852 Mr. B. A. Wilson, Assistant Director (Enclosures)

, for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region 11 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector (Enclosures)

Sequoyah Nuclear Plant 2600 Igou ferry Road Soddy Daisy, Tennessee 37379 I

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t E ENCLOSURE 1 Tennessee'ValleyAuthority(TVA)hasreevaluatedSequoyahNuclearPlant's (SQN's) initial response to NRC Bulletin 88-04 (reference Enclosure 1 of TVA's letter to NRC dated August 2,1988, Sequoyah Nuclear Plant (SQN) - NRC Bulletin (NRCB) 88-04, ' Potential Safety-Related Pump Loss'"). As a result of this reevaluation TVA's response for SQN's residual heat removal (RHR) and L motor-driven auxiliary feedwater-(MDAFH) pumps has been revised. TVA's original' response for SQN's other safety-related pumps was confirmed and remains unchanged.

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B L TVA REVISED RESPONSE v

!' 4. (a)- Summarize the Problems and Systems Affected le RHR Purapj

.SQN s two parallel RHR pumps are required to operate at mlniflow L conditions during a small-break loss of coolant accident (LOCA) or

, main steamline/ main feedwater line break event. Because the discharge k headers for the RHR pumps are connected by an open crosstle, there is c .a potential.for pump-to-pump' interaction resulting in the weaker of l-the two pumps deadheading because of pump head differences. Analysis and recent events (Licensee Event Report (LERL 50-327/89031) confirmed deadheading of a weaker pump for Unit I when both pumps operate on mtniflow.

MDAFH Pumps SQN's MDAFH pumps do not have a pump-to-pump-interaction problem; however, the mlniflow lines are not. sized for continued long-term L operation on mintflow. The pump manufacturer recommends a continuous flow through the pump of 165 gallons per minute (gpm). The MDAFH pumps are used for unit start-up to 5 percent power. During these start-up evolutions, the pumps are operated for relatively long n periods of time at flows less than 165 gpm.

4. (b) Short-Term and Long-Term Corrective Actions RHR Pumps Short-term - As a result of-recent events that confirmed that pump-to-pump interaction would occur if both RHR pumps were operated in parallel on mlniflow, SQN has implemented the following short-term corrective actions.

1 _TVA has revised SQN Emergency Instruction E-0, " Reactor Trip or Safety Injection (Revision 8)," to check if one RHR pump should be  ;

stopped following a safety injection (SI) signal, which automatically starts both RHR pumps. This revision requires one pump to be placed in standby if RCS pressurt is greater than 180 pounds per square inch gauge (psig) (both pumps operating on j

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I mlniflow following the SI signal) and adds a precautionary .  !

> statement that requires the operator to restart the pump placed in L

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standby-if the operating pump trips. A caution statement also  ;

~ requires operator-action to ensure that the RHR pumps are manually '

started if (1) RCS pressure decreases below 180 psig and 1 (2) offsite~ power is lost following an SI reset.

These procedure changes. ensure that. extended operation in-the deadheaded condition does not occur, thereby precluding pump damage.

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. 2. TVA has revised SQN System Operating Instruction (SOI) 74.1, '

i. " Residual Heat Removal System" to ensure the RHR pumps do not "

l- operate in parallel while on miniflow for greater than 10 minutes.

i' Long-Term - TVA will install check valves in SQN's RHR pump discharge .

piping (downstream of the miniflow line) to preclude.the possibility for pump-to-pump' interaction. This will allevi.te the need for one of ,

,' the pumps to be stopped, as currently required in SQN's Emergency Instruction E-0 (Item I above). Following the installation of check .;

valves in SQN's RHR system, Instructions E-0 and S01 74.1 will be  ;

e revised to remove the interim measures currently used to prevent ,

extended pump operation in the deadheaded condition. '

MDAFH Pumps TVA's review of its initial response to NRC Bulletin 88-04, regarding SQN's MDATH pumps, identified the need for a clearer description of the: intermittent operation of these pumps, a During start-up to 5 percent power operation, SQN's MDAFH pumps are L used to maintain water level in the steam generators. The t'DAfH pumps L operate on mlniflow (25 gpm) untti makeup to the steam generators is required. During the time that makeup is required, the flow through .

the pump-is allowed to increase to 175 gpm until adequate steam #

generator levels are achieved. Once steam generator level has been ,

achieved, the makeup flow is terminated, and the pump returns to the mintflow condition. Continuous operation of these pumps is necessary to support the start-up operation. The intermittent changes in flow through the pump cannot be eliminated because of the ilmitations on ,

pump motor starts. Extended operation at 25 gpm is not desirabic.

Short-Term - TVA had previously implemented a program to periodically I test SQN's MDAfH pumps under full-flow conditions. This ongoing test program began during the Unit 2 Cycle 3 refueling outage and was designed to detect and trend any pump degradation. This testing is in -

addition to the quarterly American Society of Mechanical Engineers (ASME) Section XI miniflow tests for pump operability. {

Long-Term - TVA has conducted a design study to evaluate the addition L

of a bypass line in parallel with the min 1 flow recirculation piping -

that would allow SQN's MDAFW pumps to operate at a higher flow rate -

. during low steam generator flow conditions. As a result of this  :

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evaluation,- TVA has included as a commitment under Item 4(c) below a modification to install additional miniflow capacity during the

~ Cycle 5 refueling outage for each unit.  ;

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H . r 4.'(c) : Schedule for Lono-Term Resolution RHR Pumps '

. .TVA will install check valves in the RHR discharge piping downstream  ;

of the mintflow lines. Installation will.be. complete prior to 1 y start-up from the Cycle 5 refueling outage for each unit. t MDAfW Pumps  !

.. 3 il TVA will install additional mlniflow capacity for SQN's MDAfW pumps. .t

' Installation will be complete prior to start-up from the Cycle 5 refueling outage for each unit.

4. (d) Justification for Continued Operation RHR Pumps j A TVA calculation (SQN-74-D053 HCG-ML-071988) shows that the RHR pumps -i

'will operate for'approximately 11 minutes at a deadhead condition .

before pump damage will occur. Step 15 of Emergency Instruction E-0  ;

p was revised to check if one'RHR pump should be stopped following a  ;

j safety injection signal. This ensures that the pumps will not run in parallel longer than 11 minutes-after an Si initiates start of both pumps. This step in the procedure will be performed well before the ,

11 minutes. Also the 501-74.1 has been revised to ensure that the RHR  ;

pumps are not run in parallel on mintflow for greater than 10 minutes.

l MDAFW Pumps  !

E Performance of the ASME Section XI tests Indicates that these pumps can continue to m at design requirements. .

r r TVA recently replaced the rotating elements on.SQN's Unit 2 MDAfW L pumps. The 2A-A clement was replaced in January 1988 during SQN's ,

extended shutdown. The 2B-B element was replaced during the Unit 2 Cycle 3 refueling outage (between January and April 1989). In r addition, full-flow testing of both Unit 2 MDAfW pumps was performed i during start-up from the Unit 2 Cycle 3 refueling outage. This full-flow surveillance test showed that the pumps' performance i exceeded the design requirements.

During'the upcoming Unit 1 Cycle 4 refueling outage (currently projected to begin March 15, 1990), TVA will disassemble and inspect +

SQN';; 1 A-A MDAFW pump for damage and degradation. As part of SQN's  ;

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. ongoing fulliflow test: program,:TVA will conduct full-flow testing.'of=the 'j Unit 1 MDAfW pumps:to ensure these pumps meet or-exceed their design , j requtrements. This: testing will be completed during start-up from the Unit-1  ;

Cycle:4' refueling ~ outage. The above~ actions provide added assurance for~the-safe operation:of SQN's. AFW pumps.  !

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" h(gt ENCLOSURE 2 ,

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, TVA Commitments  ;

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1. TVAwill.installcheckLvalvesinSequoyahNuclearPlant's(SQN's) residual heat removal (RHR) discharge piping downstream.of the mlniflow lines. .

Installation will be complete no later than start-up from the Cycle S '

refueling outage for each unit. 3

2. Following the installation of check valves in SQN's RHR system, SQN .

' Emergency Instruction E-0 and SQN. System Operating Instruction (SOI) 74.1

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will be revised to remove the short-term interim measures currently used to prevent pump-to-pump interactions. This revision will be complete c -prior to start-up from the Cycle 5 refueling outage for each unit.-

U 3. TVA will lnstall: additional miniflow capacity for SQN's motor-driven auxiliary feedwater (MDAFW) pumps. Installation will be complete prior.to start-up from the Cycle'5 refueling outage for-each unit, u .

4. TVA will disassemble and inspect SQN's'lA-A MDAfW pump internais for

. damage and degradation. This inspection will be completed prior to e start-up from the Unit 1 Cycle 4 refueling outage.

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5. TVA will conduct full-flow testing of SQN's Unit.1 MDAfW pumps-to ensure

-these pumps-meet or exceed thelr. design requirements. This. testing will be completed during start-up from the Unit 1 Cycle 4 refueling outage.

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