ML20207B870
| ML20207B870 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/02/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| IEB-88-004, IEB-88-4, TAC-R00428, TAC-R00429, TAC-R428, TAC-R429, NUDOCS 8808040305 | |
| Download: ML20207B870 (6) | |
Text
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3 TENNESSEE VALLEY AUTHORITY
$N 157B Lookout Place August 2, 1988 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 i
Gentlemen:
i In the Matter of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 l
I SEQUOYAH NUCLEAR PLANT (SQN) - NRC BULLETIN (NRCB) 88-04, "POTENTIAI SAFETY-RELATED PCMP LOSS" This letter provides "NA's response to NRC questions regarding the adequacy of minificw systems for asfety-related pumps. These questions were expressed in NRCB 88-04, which was ise' sed by the NRC on May 5, 1988.
> provides the results of TVA's evaluation of the issues identified in h1CB 08-04 for SQN. A submittal date of August 15, 1988, was required to obtain and evaluate additional information on required minimum flows from the pump suppliers as required by the subject bulletin. This extension was discussed with Jack Donohew, of NRC's Office of Special Projects (NRC-OSP), on July 1, 1988.
t The commitments made in this submittal are stated in enclosure 2.
If you have any questions, please telephone D. L. Williams at (615) 632-7170.
Very truly yours.
P TENNESSEE VALLEY AUTHORITY l
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R. G diey, Dir tor Nuclear Licensi g and
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Regulatory Affairs i
Enclosures j
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See page 2 i
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G808040305 680802 PDR ADOCK 05000327
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. U.S.. Nuclear Regulatory Commission August 2,~1988 Enclosures-
'cc (Enclosurts):
Ms. S.
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Black, Assistant Director for. Projects TVA Projects Division U.S. Nuclear Regulatory-Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland.20852 Mr. F. R. McCoy, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Sequoyah Resident Inspector
~Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379
ENCLOSURE 1 SEQUOYAH NUCLEAR PLANT (SQN) UNITS 1 AND 2 NRC BULLETIN (NRCB) 88-04 POTENTfAL SAFETY-RELATED PUMP LOSS The purpose af'NRCB 88-04 was to request. Licensees to investigate rnd correct, as applicable, two'miniflow design concerns.
The first concern involves the potential for the dead-heading of one or more 'ptsps in' safety-related systems that have'a miniflow line common to two or more pumps'or other pipingL configurations that do not preclude pump-to-pump interaction during miniflow operation. The second concern is whether or not the installed miniflow capacity is adequate for even a single pump in operation.
DISCUSSION:
TVA evaluated the following SQN system pumps for these concerns as required by items 1, 2, and 3 of Actions Requested of NRCB 88-04:
- Essential. Raw Cooling Water (ERCW)
- ERCW Screenwash
' Component Cooling Water
' Motor-Driven Auxiliary Feedwater (MDAFW)
' Turbine-Driven Auxiliary Feedwater
- Safety Injection
- Centrifugal Charging.
The system-by-system evaluation included the review of design drawings, design data, surveillance test data, maintenance data, and pump. supplier information where available.
Some pump suppliers have not responded to'our request for verification of miniflow design adequacy because of the high number of similar requests from numerous other utilities as a result of NRCB 88-04.
TVA will reevaluate the affected pumps when this information is received within the next few weeks. Any reportable conditions identified will be reported in accordance with applicable regulatory requirements.
Item 4 of Actions Requested of NRCB 88-04 requests a. written response-that (a).
summarizes the problems and the systems affected,-(b) identifies the short-term and long-term modifications to plant operating procedures or hardware that have been or are being implemented to ensure safe plant operations, (c) identifies an appropriate schedule for long-term resolution of this and/or other significant problems that are identified as a result of this bulletin, and (d) provides justification for continued operation particularly with regard to General Design Criterion 35 of Appendix A to Title 10 of the Code of Federal Regulations (10 CFR 50), "Emergency Core Cooling," and 10 CFR 50.46, "Acceptance criteria for Emergency Core Cooling System for Light Water Nuclear Power Rea. tors."
TVA's response to Item 4 follows.
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' RESPONSE:
4.'
(a)' SUMHARIZE THE PROBLEMS AND SYSTEMS-AFFECTED The-SQN safety-relatad system pumpe evaluated are not adversely affected by the miniflow operating conditions identified by the bulletin with the exception'of the RHRiand the MDAFW pumps.
RER Pumps
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The two parallel RHR pumps wil1 be operated at miniflow conditions during a.small-break loss'of' coolant accident (LOCA) or main steam line/ main feedwater line break. event..Because the discharge headers for the.RHR pumps are connected by an open cross-tie, there-is a potential for pump-to-pump interaction resulting in the weaker.of the two pumps dead-heading because of pump head differences. Analysis indicates dead-heading of a weaker pump could occur if-both pumps operate in miniflow and the head differential between the pumps exceeds 11 pounds per square inch'(psi).
MDAFW Pumps The MDAFW pumps at SQN are used for unit startup up to 5-percent power.
Low flows can be required for extended periods during this mode of operation, resulting in the potential for pump damage.
One of the SQN unit 1 MDAFW pumps has previously been rebuilt to overcome head / flow' deficiencies that were attributed to; impeller cavitation damage as.a result of extensive miniflow operation.
4 (b) SHORT-TERM AND LONG-TERM CORRECTIVE ACTIONS
-RHR Pumps Short-term - A routine surveillance test procedure that is used to monitor the pump performance will be revised by October 30. 1988, to require evaluation of the pump differential pressure data during each refueling outage. This will ensure'that. unacceptable pump-to-pump interaction is not occurring by evaluating the results of the test data obtained during routine tests conducted since the previous refueling outage.
TVA considers this action to be adequate for both short-term and long-term resolution.
However, hardware modifications (e.g., check valves added to the discharge piping for each RHR pump) are being evaluated for economic consideration.
If system modifications are implemented, an updated response to this bulletin will be provided.
MDAFW Pumps A precaution har b'en added to the auxiliary feedwater system operating instre<_t.on S02-3.2 to ensure the MDAFW pumps are operated in an intermittent-flow mode to deliver a minimum flow of at least 75 gallons per minutt (gal / min) to each steam generator as required during the startup to 5-percent power mode of operation.
This will increase minimum flow through the pump from 25 gal / min to 175 gal / min and avoid the potentially damaging operating condition. -
TVA considers these actions to be adequate for both short-term and long-term resolution.
However, hardware modifications are being evaluated for economic consideration. These include:
(1) an alternate reans of supplying flow to the steam generators during startup to eliminate the need to use the MDAFW pumps for this purpose, (2) an additional bypass. valve installed in-parallel with the miniflow recirculation orifice to allow the MDAFW pumps to operate at a higher flow rate during low steam generator flow conditions, and (3) an electronic governing system for the main feedwater pump turbines to allow greater turndown capability and eliminate the need to use the MDAFW pumps during startup.
If system modifications <are implemented, an updated response to this bulletin will be provided.
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- 4. (c) SCHEDULE FOR LONG-TERM RESOLUTION l
l The procedural modifications identified for both the RHR and MDAFW pumps as short-term resolution are considered adequate for long-term resolution. The RHR test procedure will be. revised by October 30, 1985. The MDAFW procedure _ modification has been completed.
- 4. (d) JUSTIFICATION FOR CONTINUED OPERATION RHR Pumps The pump supplier has stated that the pump can operate at a minimum flow of 100 gal / min for at least 20 minutes eithout impairing the pump's ability to perform its safety function.
The results of recent surveillance tests indicate that the differential between the RHR pumps is less than 11 psi.
Therefore, at least 100 gal / min flow through the weaker pump is assured.
This establishes a minimum time l
of 20 minutes for the pumps to begin full injection flow or for operator action to place them in standby mode.
Emergency Instructions l
E-0 and E-1 provide operator actions to shut down the RHR pumps after a safety injection signal is received if the reactor coolant system pressure is greater than 180 psi and is stable or increasing (i.e.,
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indication.of a small-break LOCA).
Based on operator experience, 20 minutes is considered a reasonable response time for this action because this and all preceding actions are performed in the control room.
MDAFV Pumps The precaution incorporated into the AFW pumps' operating instructions provides adequate assurance that damage to pumps from miniflow during startup will be avoided. Also, results of surveillance and postmodification testing performed before mode 1, on the SQN unit 2 MDAFW pumps, provide added assurance of safe operation.
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ENCLOSURE 2-SEQUOYAH NUCLEAR PLANT'(SQN)
NRC BULLETIN -(NRCB) 88-04 POTENTIAL SAFETY-RELATED' PUMP LOSS LIST OF COMMITMENTS j
.A routine' surveillance test procedure that is used to monitor the pump performance will be revised by October 30, 1988, to require' evaluation of the pump differential' pressure dhta during each refueling outage. This will ensure that;unaccepta ae pump-to-pump interaction is not occurring by evaluating the results of the-test data obtained during routine tests conducted since the previous refueling' outage.
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