ML18038B635
| ML18038B635 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/05/1996 |
| From: | Salas P TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-95-002, IEB-95-2, TAC-M93876, TAC-M93877, TAC-M93878, NUDOCS 9603110652 | |
| Download: ML18038B635 (20) | |
Text
CATEGORY j.
REGULATOR INFORMATION DISTRIBUTION
.STEM (RIDS)
ACCESSION 'NBR:9603110652 DOC.DATE: 96/03/05 NOTARIZED:
NO FACIJ.':50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 50-?96 B'rowns Ferry Nuclear Power Station, Unit 3, Tennessee AUTH.NAME AUTHOR AFFILIATION SALAS,P'.
Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Provides supplemental info in response to NRC Bulletin 95-002, "Unexpected Clogging of RHR Pump Strainer While Operating in Suppression Pool Cooling Mode."
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TITLE: NRC Bulletin 95-02 Unexpected Clogging of RHR Pump Strainer NOTES:
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Tennessee Valley Authority. Post Office Box 2000, Decatur. Alabama 36609 March 5, 1996 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of Tennessee Valley Authority Docket Nos.
50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) UNITS 2 AND 3 SUPPLEMENTAL INFORMATZON FOR NRC BULLETIN 95-02~
UNEXPECTED CLOGGING OF A RESIDUAL HEAT REMOVAL (RHR)
PUMP STRAINER WHILE OPERATING IN SUPPRESSION POOL COOLING MODE (TAC M93876~
93877~
M93878)
This letter provides supplemental information in response to NRC Bulletin 95-02, which was verbally requested by the NRC Staff in a February 29, 1996 teleconference with TVA.
As demonstrated by the information contained in the enclosure to this letter, the Emergency Core Cooling System (ECCS) pump runs during the current Unit 2 Cycle 8 are similar to the pump flows and system alignments that would be present during operations in the suppression pool cooling mode after an abnormal event or transient.
These pump flows, system alignments, pool turnovers, and run times are also comparable to what would be provided in a confirmatory test to evaluate the potential for debris entrainment on the suction strainers.,
Similar pump flows, system alignments, pool turnovers,'nd run times are expected during the current Unit 3 Cycle 7.
These pump runs are adequate to suspend and collect fibrous debris such that its presence in the pool will be evident during strainer inspection.
Experience with actual fibrous debris in the pool has shown that similar pump operation and subsequent strainer inspection will reveal the presence of fibrous material.
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U.S. Nuclear Regulatory Commission Page 2
March 5, 1996 TVA has committed to perform an as-found inspection of the suppression pool, including the ECCS.suction strainers, during the Unit 2 Cycle 8 outage, which is currently scheduled to begin on March 22,
- 1996, and during the Unit 3 Cycle 7 outage, which is currently scheduled to begin on February 21, 1997.
TVA plans to perform an engineering evaluation of the as-found condition and determine the need and scope of suppression, pool cleaning, including any necessary confirmatory ECCS pump runs and subsequent suction strainer inspections.
Experience has shown that the presence of fibrous material in the pool is readily detected by inspection of the ECCS strainers after a typical operating cycle.
This inspection, evaluation,
.and any necessary corrective actions will ensure that ECCS system operability is not lost due to debris blockage of the suction screens while a long term program is being developed.
There are no new commitments contained in this letter. If you have any questions, please contact me at (205) 729-2636.
Sincerely Pedro Salas Enclosure
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U.S. Nuclear Regulatory Commission Page 3
March 5, 1996 cc (Enclosure):
Stewart D. Ebneter Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. Mark S. Lesser, Branch Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia
- 30323, NRC Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road
- Athens, Alabama 35611 Mr. J.
F. Williams, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852
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ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNITS 2 AND 3 NRC BULLETIN 95-02'NEXPECTED CLOGGING OF A RESIDUAL HEAT REMOVAL (RHR)
PUMP STRAINER 'WHILE OPERATING IN THE SUPPRESSION POOL COOLING MODE This enclosure provides TVA's reply to the NRC questions discussed in the February 29I 1996).
TVA/NRC teleconference.
BACKGROUND The pressure suppression chamber is a steel pressure vessel in the shape of a torus below and encircling the drywell, with a centerline diameter of approximately 111 feet and a
cross-sectional diameter of 31 feet.
The Emergency Core Cooling Systems (ECCS) at BFN, [I.E., RHR, High Pressure Coolant Injection (HPCI), Core Spray (CS),
and Reactor Core Isolation Cooling (RCIC)] are supplied from a common 30-inch diameter ring header that circumscribes the suppression chamber (Figure 1).
Four tees connect the suction header to the suppression chamber.
Four strainers (with approximately 1/8 inch holes) are provided on the connecting lines between the suction header.
During ECCS pump operation in the suppression pool cooling mode, pump suction is supplied through the four strainers.
The strainers and the pipes connecting the torus to the ring header are sized such that at least one of the four strainers can be completely blocked during a postulated accident.
SPECIFIC NRC UESTIONS AND TVA S REPLY The licensee has concluded that a pump test to verify operability is not necessary for BFN Unit 2 based on pump operating experience during the operating cycle.
The licensee also stated that the torus was cleaned and desludged during the last refueling outage.
The staff needs to understand whether or not the licensee's operating experience provides an equivalent level of assurance (as the requested pump test) that the torus water is free of significant quantities of debris which could clog strainers.
A pump test which causes significant turbulence in the torus appears to be the best method for determining if there is debris which could clog the pump suction strainers in the torus.
With this in mind, the staff has the following questions on TVA's response to 'NRCB 95-02 for Browns Ferry Unit 2:
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NRC Re uest la The licensee stated that during the on going operating cycle, the RHR and CS pumps system were operated for periods of time in excess of 178 hours0.00206 days <br />0.0494 hours <br />2.943122e-4 weeks <br />6.7729e-5 months <br /> of operation.
What was the maximum period of time the pumps were operated for during any one pump operation during the last cycle?
What was'he maximum flow rate to/from the suppression pool during these pump operations?
Did the licensee operate more than one pump at a time in torus cooling or test modes?
If so, how long?
What was the combined flow rate?
TVA Re 1
To Re uest ia The intent of TVA's response to Bulletin 95-02, Item 2 is to inspect the strainers for accumulated debris after operating ECCS pumps for a significant period'f time while the pumps are aligned to the suppression pool.
A tabl'e is provided that shows examples of ECCS pump runs during the current Cycle 8 on BFN Unit 2.
These pump flows and system alignments are similar to those that would be present during operations in the suppression pool cooling mode after an abnormal event or transient.
These pump flows, system alignments, pool turnovers, and run times are also comparable to what would be provided in a.confirmatory test to evaluate the potential for debris entrainment on the suction strainers.
Similar pump run times and system.alignments are expected during the current Unit 3.Cycle 7.
These pump runs meet the intent of Bulletin 95-02, Request 2, for performing a test.
NRC Re uest ib What was the pool turnover time at the maximum flowrate to/from the suppression pool?
TVA Re 1
To Re uest ib The approximate number of pool turnovers and flow rates associated with each pump run are provided in the table.
NRC Re uest ic What. is the configuration of the torus cooling,and test flow return lines relative to the suction strainers?
Specifically, would, the water be well mixed when operating in torus cooling or pump test modes?
Would the pool water be sufficiently turbulent to suspend the materials which may be lying on the pool floor?
Does the licensee have any evi'dence that operation of the pumps as they did during the last cycle would suspend materials on the torus floor (e.g.,water samples or visual experience).
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TVA Re 1
To Re uest 1c Each CS or RHR loop,was operated taking suction through the four common ECCS strainers and returning to the torus at one of four return lines as shown in Figure 2.
Operation of ECCS in this configuration takes suction through all four strainers and agitates the water in the torus bay where the particular loop discharges.
These configurations have RHR system alignments and flows that are comparable to what would be provided in a confirmatory test of operations in the suppression pool cooling mode.
The run durations and flows are adequate to suspend and collect fibrous debris such that its presence in the pool will be evident during strainer inspection.
Experience with actual fibrous debris in the pool has shown that similar pump operation and subsequent, strainer inspection will reveal the presence of fibrous material.
NRC Re uest 2
The response discusses implementation. of a suppression pool cleaning program based of plant specific industry information.
The ongoing Boiling Water Reactor Owners'roup (BWROG) work will provide an analysis method which will help the licensee determine an appropriate cleaning frequency.
What criteria will the licensee use to determine adequate pool cleanliness, or how will that criteria be developed?
Does the licensee intend to establish a program to inspect the strainers and torus on a regular basis to ensure the adequacy of their torus cleaning program during outages between scheduled cleanings?
TVA Re 1
To Re uest 2
TVA's long term program and associated criteria for pool cleaning are under development in conjunction with industry efforts. It is anticipated that analytical margin for strainer blockage, industry experience with debris found in pools, and success of Foreign Material Exclusion (FME) programs will be inputs to criteria development.
In addition to developing a long term cleaning program, our letter of November 15, 1995 committed to visually inspect ECCS strainers each refueling outage.
TVA plans to video-tape the as-found conditions and review the tape to determine general cleanliness.
General water clarity, broad areas of debris on the pool bottom that could obscure fibrous material and debris that have the potential to transport to the strainers are key elements of the cleanliness evaluation.
Isolated items of debris such as small pieces of tape or string would not be considered significant.
Experience has shown that the presence of fibrous material in the pool is readily detected by inspection of the ECCS strainers after a typical operating cycle.
This inspection, evaluation, and any necessary corrective actions will ensure that ECCS system operability is not lost due to debris blockage of the suction screens while a long term program is being developed.
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TABLE UNIT 2 CYCLE 8, ECCS PUMP'UNS DATE 12-5-94 2A PUMPS CS FLOW (GPM) 9000
, DURATION (MIN) 366 POOL TURNOVERS 3.43 12-6-94 12.-30-94 2-23-95 4-13-95 9-8-95 12-'2-95
.2-23-96 2C 2A
& C, 2C 2B D'B D'A
& C 2A
& C
,2A 2C 2B 2D 9000 12000 9000 3125 3125 12000 3125 3125 12000 12000 12000 359 27 345 20'8 188 25 23 196 198 134 3.36 0.34 3'. 25
- 0. 07 0.06 2.35
- 0. 08 0.
08'.
4'5 2'8 1.68 E-4
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FIGURE 1
CROSS-SECTION OF THE SUPPRESSION CHAMBER VENT HERDER VAC'UM BRE."".i<ER 4 TORUS DRYHELL
~BELLOHS MAIN VENT.
CAT'rlfiLK MAINSTEAM RELIEF VALVELINE POOL SURFACE
~EL ~37 '-0
~ECCS HEADER DOHi~~OMER DOHNCQMER TIFBAR VENT HEROER SUPPORT iggER SCAB PLATE TIE OOHN EL 51S '-0 T-QUENCHER E-5
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FIGURE 2
PLAN VIEW OF THE SUPPRESSION CHAMBER C.S.
TEST RETURN OR PUMPS A
dc C
C.S TEST RETURN OR PUMPS 8 4 0 1804 e<
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Sp~
g9, cC pe 4.
RMR TEST RETURN FOR PUMPS A
8c C 904 614 2704 cD 644 RMR TEST RETUF FOR PUMPS 8
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