ML20063E875
| ML20063E875 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 08/25/1982 |
| From: | Oprea G HOUSTON LIGHTING & POWER CO. |
| To: | Jay Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, ST-HL-AE-876, NUDOCS 8208310063 | |
| Download: ML20063E875 (7) | |
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The Light (OE Mf Houston Lighting & Power P.O. Box 1700 Houston, Texas 77001 (713)228 9211 August 25, 1982 ST-HL-AE-876 File Number: G12.127 SFN: V-0530
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Mr. John T. Collins
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Regional Administrator, Region IV
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Nuclear Regulatory Commission i
611 Rvan Plaza Dr., Suite 1000 t
Arlin'gton, Texas 76012 M
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Dear Mr. Collins:
South Texas Project Units 1 & 2 Docket Nos. STN 50-498, STN 50-499 Interin Report Concerning the Design of the Auxiliary Feedwater Systen On July 27, 1982, pursuant to 10CFR50.55(e), Houston Lighting & Power Conpany notified your office of a potential deficiency involving the design of the Auxiliary Feedwater System (AFWS).
The concern was comprised of several itens involving improper classification of components and piping, and one unioue iten involving overpressurization of the AFWS discharge piping.
Reports for two of those items which were found to represent a potential safety hazard are attached. With regard to the concern related to the continuous drain piping in the AFWS turbine stean supply line being non-safety class, Bechtel has determined that this situation does not create a safety hazard.
Bechtel is currently evaluating the safety hazard associated with the classification of the AFWS pump recirculation lines and an interim report on this matter is attached.
A final report will be provided to your office by September 15, 1982.
If you should have any questions concerning this item, please contact Mr. flichael E. Powell at (713)877-3281.
Very ul.1 yours, 1
q Exec [utive'VicePresident W
r SSR/ng Attachment Gp 8208310063 820825 PDR ADOCK 05000498 S
Ilouston Lighting & Power Cornpany cc:
G. W. Oprea, Jr.
August 25, 1982 J. H. Goldberg ST-HL-876 J. G. Dewease File Number: G12.127 J. D. Parsons Page 2 D. G. Barker C. G. Robertson R. A. Frazar J. W. Williams R. J. Maroni J. E. Geiger H. A. Walker S. M. Dew J. T. Collins (NRC)
D. E. Sells (NRC)
W. M. Hill, Jr.
(NRC)
M. D. Schwarz (Baker & Botts)
R. Gordon Gooch (Baker & Botts)
J. R. Newman (Lowenstein, Newman, Reis, & Axelra l)
STP RMS Director, Office of Inspection & Enforcement Nuclear Regulatory Connission Washington, D. C. 20555 G. W. Muench/R. L. Range Charlas Bechhoefer, Esquire Central Power & Light Conpany Chairman, Atomic Safety & Licensing Board P. O. Box 2121 U. S. Nuclear Regulatory Connission Corpus Christi, Texas 78403 Washington, D. C.
20555 H. L. Peterson/G. Pokorny Dr. Janes C. Lamb, III City of Austin 313 Woodhaven Road P. O. Box 1088 Chapel Hill, North Carolina 27514 Austin, Texas 78767 J. B. Poston/A. vonRosenberg Mr. Ernest E. Hill City Public Service Board Lawrence Livermore Laboratory P. O. Box 1771 University of California San Antonio, Texas 78296 P. O. Box 808, L-46 Livermore, California 94550 Brian E. Berwick, Esquire Willian S. Jordan, III Assistant Attorney General Harnon & Weiss for the State of Texas 1725 I Street, N. W.
P. O. Box 12548 Suite 506 Capitol Station Washington, D. C.
Lanny Sinkin Citizens for Equitable Utilities, Inc.
Citizens Concerned About Nuclear Power c/o Ms. Peggy Buchorn 5106 Casa Oro Route 1, Box 1684 San Antonio, Texas 78233 Brazoria, Texas 77422 Jay Gutierrez, Esquire Hearing Attorney Office of the Executive Legal Director U. S. Nuclear Regulatory Connission Washington, D. C.
20555 Revision Date 08-23-82
FINAi, REPORT ON THE CONDENSATE STORAGE TANK VACUUM BREAKER I.
SUMMAR,Y Only one non-safety class vacuum breaker is provided to protect the Seismic Category I, ASME Safety Class 3 condensate storage tank (CST). This vacuum breaker will be upgraded to Safety Class 3 and redundant vacuum breakers will be provided to the CST.
If the condition is not corrected, the failure of the vacuum breaker could result in an excessive vacuum condition in the CST.
The auxiliary feedwater pumps would not have sufficient NPSH, thus disabling the auxiliary feedwater system (AFWS).
Furthermore, the excessive vacuum could result in damage to the CST.
II.
DESCRIPTION OF THE DEFICIENCY During a review of the condensate storage system and the auxiliary feedwater system, it was found that a non-safety class vacuum breaker is used on the CST.
The CST is a Seismic Category I, Safety Class 3 tank which provides water storage for the auxiliary feedwater system.
The non-safety class vacuum breaker is used as a backup to the nitrogen gas system, which is a non-safety class system and therefore is assumed not to function during accident conditions.
Since the vacuum breaker serves a safety-related function, it should be classified as a safety grade device.
If the single vacuum breaker is stuck closed, excessive vacuum could be created in the CST.
Under the vacuum condition, the auxiliary feedwater pumps would not have sufficient NPSH to deliver water to the steam generators. The exc essive vacuum in the CST could result in damage to the tank and loss of some or all of the auxiliary feedwater.
III.
CORRECTIVE ACTION Two ASME Safety Class 3 vacuum breakers will be provided for the condensate storage tank to meet the single failure criteria.
IV.
RECURRENCE CONTROL No recurrence control is necessary for this item.
V.
SAFETY ANALYSIS The condensate storage tank provides sufficient water storage for the auxiliary feedwater system to remove reactor shutdown decay heat during any incident causing loss of main feedwater.
The condensate storage tank, which is a Seismic Category I, Safety Class 3 concrete structure with stainless steel liner, is an atmospheric tank protected by a non-safety class vacuum breaker.
If the singic vacuum breaker to stick in the closed position, a vacuum would be created in the tank were when water is pumped out of the tank. The available NPSH for the auxiliary feedwater pumps would be less than the required pump NPSH and degrade the
- Deficiency Evaluation Report (Vacuum Breaker)
Page 2 4
ability of the auxiliary feedwater pumps to deliver water to the steam generators. The CST concrete structure is designed for a 3 psi differential pressure to withstand an atmospheric pressure drop due to a tornado. The excessive vacuum caused by the failure of the singic vacuum breaker could result in damage to the concrete structure and loss of auxiliary feedwater inventory.
Therefore, failure of a single vacuum breaker when the AFWS is in operation could disable the AFWS, preventing it from performing its intended safety function. This is a significant deficiency in final design as approved and released for construction.
FINAL REPORT ON THE AFWS PUMP DISCHARGE PIPING I.
SUMMARY
The present design pressure for AFWS pump discharge piping is 1620 psig which is less than the shutoff head of 1710 psig for the motor driven AFWS pumps and 2700 psig for the turbine driven AFWS pump at the turbine overspeed trip (4450 rpm). The design pressure for the motor driven pump discharge piping will be changed to 1800 psig. The possibility of reducing the operating speed and overspeed trip point of the AFWS turbine to acceptable limits will be investigated.
If it is not feasible, the design pressure of the discharge piping will be changed to 2700 psig.
If the design pressure of the AFWS discharge piping is not changed, a line break of the pump discharge piping could result in loss of all the auxiliary feedwater to the steam generators.
II.
DESCRIPTION OF DEFICIENCY During a review of the pipe material criteria and the AFWS, it was found that the AFWS pump discharge piping is designed at 1620 psig. The shutoff head of the motor driven pump is 1710 psig which is in excess of the design pressure rating of the piping. The turbine driven pump has a shutoff head of 2700 psig at the turbine overspeed trip (4450 rpm). This is far in excess of the discharge piping rating. The operation of the turbine driven pump could result in a line break and loss of auxiliary feedwater to the steam generator served by the turbine driven pump.
Since the design pressure of the cross-connecting piping is the same as the AFWS pump discharge piping, the normally closed flow control valve could be forced open and could result in the pipe rupture of the motor driven AFWS pump discharge line and loss of all the auxiliary feedwater to the associated steam generators.
III.
CORRECTIVE ACTION The design pressure of the pipe, fittings and valves of the motor driven pump discharge line and cross-connecting line will be increased to 1800 psig. The turbine manufacturer will be asked to investigate the possibility of reducing the operating speed and overspeed trip point to acceptable limits.
If it is not feasible, the design pressure of the pipe, fittings, valves, and cross-connecting valves will be increased to 2700 psig.
IV.
RECURRENCE CONTROL No recurrence control is necessary for this item.
V.
SAFETY ANALYSIS The design pressure of all the AFWS pump discharge piping and the cross-connecting piping is 1620 psig. The on-off control valve in the cross-connecting line is designed for 1620 psig and the maximum pressure of the control valve is 2124 psig.
If the turbine driven pump is operated at the turbine trip point (4450 rpm), the maximum discharge pressure will be 2700 psig. Under this condition, the turbine driven AFWS pump discharge line
Deficiency Evaluation Report I
(Discharge Piping)
Page 2 could be ruptured, and/or the normally closed control valve could be forced open and possibly result in the rupture of the motor driven AFWS pump discharge piping. Under these circumstances, the associated steam generators will not receive auxiliary feedwater.
In conjunction with an initiating event involving the unavailability of another steam generator loop (e.g.
steam generator tube rupture or steamline break) concurrent with a single failure, all steam generators could potentially lose auxiliary feedwater.
Therefore, an overpressurization of the AFWS discharge piping could disable the AFWS, preventing it from performing its intended safety function. This is a significant deficiency in final design as approved and released for construction.
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INTERIM REPORT ON Tile AFWS PUMP RECIRCULATION LINES 1.
SUMMARY
Four AFWS pump recirculation lines outside the Isoloation Valve Cubicle (IVC) connected to the condensate storage tank were identified as non-safety class piping. The failure of these lines in a seismic event could result in the loss of the auxiliary feedwater inventory when the AFWS pumps are in operation.
11.
DESCRIPTION OF DEFICIENCY
,During a review'of the AFWS, it was found '. hat the AFWS pump recirculation s
' lines outside the IVC are non-safety class piping. The rupture of the recirculation lines in a scismic event may result in the loss of the auxiliary feedwater inventory. Adequate water storage is required to be raintained in the condensate storage tank for the AFWS to remove the heat from the RCS during any transient condition. A review of the water storage requirements is being performed by Bechtel to determine if a safety hazard cotird exist.
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CORRECTIVE ACTION
,d6erechive dctions are under, consideration at this time.
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(, SAFETY ANALYSIS.
s The cerJensare storage tank iu designed to retain a sufficient quantity of water for the AFWS to remove RCS heat under transient conditions. The rupture of the recirculation lines when the AFWS pumps are in operation will result in the loss;of portions of the water inventory of the AFWS. The mininem water inventory currently described in the FSAR is based on a combins' tion of criterja. A reduction of the water inventory below the 91nimum given in the FSAR will not necessarily create a safety hazard. Thus,
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.BechtOI is reviewinn the impnct of ruptured recirculation lines on the requiredwaterinventlo,y.
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