ML20009C532
| ML20009C532 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/16/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.E.4.1, TASK-2.K.3.13, TASK-2.K.3.15, TASK-2.K.3.25, TASK-TM NUDOCS 8107210203 | |
| Download: ML20009C532 (8) | |
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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 374o1 400 Chestnut Street Tower II fn
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Mr. Harold R. Denton, Director
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Office of Nuclear Reactor Regulation JUL o 0198)
- U.S. Nuclear Regulatory Commission g
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Washington, DC 20555 s'
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Dear Mr. Denton:
p In the Matter of the
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Docket Nos. 50-259 Ternessee Valley Authority
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50-260 50-296 Enclosed are our positions for Browns Ferry Nuclear Plant on the following NUREG-0737 items.
II.E.4.1 Dedicated Hydrogen Penetrations II.K.3 13 Separation of High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) System Initiation Levels Analysis and Implementation II.K.3.15 Modify Break Detection Logic To Prevent Spurious Isolation of High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC)
II.K.3.25 Effect of Loss of Alternative Current Power on Pump Seals We will continue to be as responsive as possible, however, we are continuing to incur difficulties regarding overall work load and qualified equipment procurement.
Very truly yours, TENNESSEE VALLEY AUTHORITY L. M.
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Nuclear Regulatico and Safety d
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- 1981, me a24ht.$Aubus-Notap Public 6f O
My Commission Expires t 9 8 1 Enclosures 8107210203 810716 PDR ADOCK 05000259 p
PDR An Equal Opportunity Employer
7 ENCLOSURE BROWNS FERRY NUCLEAR PLANT
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NUREG-0737 ITEMS i
II.E.4.1 -_ Dedicated Hydrogen Penetrations
.TVA Response:
-As committed to'in our December 23, 1980 response from L. M. Mills to H. R. Denton,-TVA has completed the full evaluation of the purge system according to NRC's October 31, 1980' clarifications of post-TMI
-requirements. This was done since Browns Ferry Nuclear Plant does not use
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- dedicated penetrations but rather shares some piping with the containment purge system.
Our review has indicated that some modifications will be required to bring the vent side of the system into strict conformance with single failure criteria.- We have analyzed the existing configuration; and, although we find -it acceptable for safety considerations, we have developed a preliminary design for making the system strictly single failure proof in accordance with the_NRC clarifications. We will notify NRC concerning Ethe modification schedule as soon as equipment procurement dates are arranged.
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II.K.3 13 -' Saparation of High Pressure Coolant Injection (HPCI) and
-Reactor Core Isolation Cooling (RCIC) System Initiation Levels Analysis and-Implementation
_TVA. Response:
As stated in our December 23, 1980.L. M. Mills to H. R. Denton letter, TVA
- committed to the auto restart of RCIC modification. We have proceeded with
. the design and procurement of qualified equipment to meet : the _ requirements of this. position. Based on.the present vendor estimate of equipment delivery dates, we can -tentatively commit to the following scheduled outages:
U 1 - March 1983 U 2 - March 1982 rU 3 September 1981 i
= II.K.3 15 - Modify Break-Detection Logic to Prevent Spurious Isolation of High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC)
'TVA Response:
This modifloation: involves adding a timer to thelbreak detection logic to prevent' spurious' isolation.,The modification-on HPCI is complete. The design'and ; procurement for the RCIC modification la proceeding; and, based upon the latest qualified equipment delivery dates, TVA has scheduled the implementation-of:these modifications during the next scheduled refueling outages as follows:
.U 1~- March 1983'
-U 2'- March 1982-U 3 September '1981 s-
II.K.3.25 - Effect of Loss of Alternative Current Power on Pump Seals TVA Summary:
Two independent systems provide cooling water to the recirculation pump seals:.(1) the reactor building closed cooling water (RBCCW) system, and
'2)- the recirculation pump seal purge portion of the control rod drive
-(CRD).
The RBCCW pumps have. automatic restart logie on loss of offsite ac power-and.are~ powered from the 480-V shutdown boards. The CRD pumps do not automatically restart, but the 1B CRD pump on units 1 and 2 and the 3B CRD pump on unit 3 have. emergency power and can be manually restarted if required.. Therefore, both systems are available to maintain the temperature of the recirculation pump seals below 2500F.
Total failure of both recirculation pump saal cooling water systems will not result in a safety problem. Even in the case of bo',h systems failing followed by extreme degradation of the pump seals, the primary coolant loss, analyzed to be less than 70 gallons a minute, 9111 be corpensated for by normal or emergency water level controls. Consequently, no hazard to the health and safety of the public will result from total loss of recirculation pump seal cooling water.
IttTRODUCTION This has been prepared in msponse to item II.K.3 25 of NUREG-0737 entitled, "Effect of Loss of Alternative Current Power on Pump Seals." This item states, "The licensees should determ Me, on a plant-specific. basis, by analysis or experiment, the consequences of loss of cooling water to the mactor meirculation pump seal coolers. The pump
' seals should be designed to withstand a complete loss of alternating current (ac) power for at least two hours. Adequacy of the design should be demonstrated." NRC has clarified the phrase " complete loss of alternat?.ng current-(ac) power" to maan only loss of offsite power.
Investigation Of loss.of offsite ac power indicates that there will be no
- effect on the cooling water except for a 40-second loss of flow between the time the RBCCW pumps lose normal power and the "A" RBCCW pump restarts on
-emergency power.
The.. investigation has also led to the-conclusion that
- the loss of pump seal cooling is not a safety problem, but may require seal repairs prior to msuming operation.
This evaluation presents a description of the seal cooling systems, an evaluation of seal performance under loss of offsite ac power conditions, and the msults of a seal leakage analysis for extremely deteriorated seals.
GEtERAL DESCRIPTIO_?]
- The BWR recirculation pump design incorpor ates a dual mechanical shaft seal assembly to control leakage around the rotating shaft of the recirculation-pump. Each assembly consists of two seals built into a cartridge that can be re'placed without removing the motor from the pump. Each individual seal in the cartridge is designed for full pump design pressure and can
- adequately limit' leakage in the event that the other seal should fail.
During normal operation, the mairculation pump seals require forced cooling due to the temperature of the primary reactor water and due to the friction heat generated in the sealing surfaces. For most BWR's, two systems accomplish this forced cooling: the RSCCW system and the seal purge system. Cooling water, provided by the RBCCW system, flows through a heat exchanger around the seal assembly. This RBCCW flow cools primary reactor water which flows to the lower seal ce-ity, thereby maintaining the seals at the correct operating temperature. The seal purge system injects clean, cool water for the CRD system into the lower seal cavity. This seal purge flow also provides efficient cooling for the seals.
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On loss'of offaite ac power, the RBCCW pumps will trip. If no accident signal is present, the "A" and "B" RBCCW pumps: restart' immediately on emergency power and continue to supply cooling water to the pump seal heat "exchangers. In the event of a coincident accident s'ignal, the "A" RBCCW pump.will automatically restart after 40 seconds. If'the "A" RBCCW pump fails to start; the '.'B" RBCCW pump will automatically start 3 seconds after -
the "A"--RBCCW pump fails to start. Therefore, RBCCW pumps will provide cooling water to essential loads, including recirculation pump seal heat exchangers,. preventing any damage to the recirculation pump seals on loss of offsite ac power. The control-rod drive.(CRD) system pumps can also be l powered from emergency buses and provide additional protection to the pump seals.
SEAL-PERFORMANCE AND EVAL 1ATION
.Under normal corditions'with the primary reactor system at or near rated temperature'and pressure and the recirculation pumps either operating or secured, both'RBCCW and seal purge are operating. These two systems maintain the. seal temperatures at approximately 1200F.
Recirculation pump vendor: test data shows that the pump seals may begin to deteriorate when seal temperature exceeds 250 F.
If an event occurs
~where both closed cooling water to the pump seal heat exchanger and control rod drive seal purge flow are totally lost, the recirculation pump' seals will heat up.
This will occur whether or.not the pump is running. Vendor test data, taken while operating at approximately 5300F/1040 psia, indicates.that the seals will heat up, reaching 2500F approximately 7
. minutes after a total-loss of cooling. Similar test data indicates that if either one of the seal cooling systems is in operation, the seal temperatures remain well below 2500F and no seal deterioration occurs.
-If both closed cooling water and seal purge are totally lost and if the seal temperatures exceed 2500F,~ seal deterioration may occur resulting in primary coolant leakage to the drywell~. An analysis of fluid loss through a degraded seal modeled the fluid leakage path as a series of fluid volumes with interconnecting junctions each having appropriate initial conditions (l). The model assumed gross degradation of the mechanical-seals. Gross failure of these seals encompasses warpage, fractures, and grooving of the seal faces due to excessive thermal gradients and dirt.
I NE00-24083, " Recirculation Pump Shaft Seal Leakage Analysis," November 978.
(Licensing Topical Report)
m The results of this seal.leakags analysis show that, even with gross degradation of the seals,_the leakage would be less than 70 gpm. This-amount.of leakage is within the capacity of normal or redundant emergency vessel water level control systems. A leakage of 70 gpm is equivalent to a liquid leak of 0.001'ft2 flow cross sectional area. Even if the seals on both recirculation pumps fail, the effects of such leakage do not influence
= the results of loss-of-coolant accident analy ses.
It is emphasized that the: seal leakage analysis is extremely conservative, and a leakage rate of 70 gpm is not expected upon seal failure.
OPERATIONAL CONSIDERATIONS If an event occurred which led to seal degradation and subsequent leakage, the operator could isolate the pump by closing both the recirculation suction and. discharge valves. Following an event'where the seal temperatures exceeded 2500F, the utility would have - to determine whether to directly return to power operation or to-replace the pump seals.
Factors influencing this decision would include the seal's operating history, the amount of time without cooling, and peak seal temperature. It is stressed that, even if the scal is grossly degraded, no safety problem will exist because the maximum leakage is small.
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CONCLUJT"NS Two systems provide coolin; to the recirculation pump seals. If either one of these systems is operating, recirculation pump operation without the second cooling system may continue with no harm to the seals. If both seal cooling systems are inoperable, the pump seals will overheat approximately 7 minutes after the total loss of cooling and seal deterioration may begin.
Based on fluid loss analysis of extremely degraded seals, the leakage is less than To gpm. This amount of leakage will not lead to a safety concern
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but may degrade the seals such that they would have to be repaired prior to resuming operation. Consequently, no change in design is necessary.
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