ML18029A151
| ML18029A151 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 10/05/1984 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| TAC-54150, NUDOCS 8410100452 | |
| Download: ML18029A151 (10) | |
Text
REGULATORY DEFORMATION DISTRIBUTION S EM (RIDS)
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ACCESSION NBR;8410100452 DOC ~ DATE: 84/10/05, NOTARIZED: YES FAG IL:,50"260 Browns Ferry Nuclear Power Stationi Unit 2i Tennessee 50-296 Browns Ferry Nuclear Power Stations Unit 3< Tennessee AUTH INANE AUTHOR AFFILIATION MILLSELBM~
Tennessee Yalley Authority RECIP ~ NAME RECIPIENT AFFILIATION DENTONEH,RE Office of Nuclear Reactor Regulationi Director DOCKET' 025e'.
05000260 05000296
SUBJECT:
Forwards responses to GE Svc, Info Ltr 002 re wetwell/Drywall inerting.Operating instructions for containment inerting sys 8 primary containment sys revised.
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TENNESSEE VALLEYAUTHORITY CHATTANOOGA. TENNESSEE 37401 400 Chestnut Street Tower II October 5, 1984 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Dear Mr. Denton:
In the Matter of the Tennessee Valley Authority Docket Nos. 50-259 50-260 50-296 By my letter to you dated September 14,
- 1984, we provided general information regarding implementation of General Electric Service Information Letter (SIL) 402 at the Browns Ferry Nuclear Plant.
As committed to in that letter, we are submitting as an enclosure a more detailed discussion of the SIL 402 implementation.
If you have any questions, please get in touch with us through the Browns Ferry Project Manager.
Very truly yours, TENNESSEE VALLEY AUTHORITY
~'r sr Subscribed and sworn to before me this ~
day of L. M. Mills, anager Nuclear Licensing 1984.
Notar'y Publ c My Commission Expires Enclosure cc (Enclosur e):
U.S. Nuclear Regulatory Commission Region II ATTN:
James P. O'Reilly, Regional Administrator 101 Marietta Street, NW, Suite 2900
- Atlanta, Geor gia 30323 Mr. R. J. Clark Browns Ferry Project Manager U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue
- DOCK 05000259 P
PDR An Equal Opportunity Employer
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ENCLOSURE IMPLEMENTATION OF GENERAL ELECTRIC SERVICE INFORMATION LETTER 402 nWETWELL/DRYWELL INERTING<r BROWNS FERRY NUCLEAR PLANT SIL 402 ITEM 1
Evaluate Inertin S stem Desi n Evaluate the design of the nitrogen inerting system.
Investigate the potential for introducing cold (less than 40 F) nitrogen and the orientation of the nitrogen port relative to the vent header, downcomers, or other equipment in the wetwell and drywell which may be in the path of the injected nitrogen.
Assure that the temperature monitoring devices, the low temperature shutoff valve, and overall system design are adequate to prevent.the injection of cold nitrogen into the containment.
TVA RESPONSE We have reviewed the system design of the Browns Ferry containment inerting system.
The current system design has multiple controls and indications which are sufficient to prevent cold nitrogen (450 F) from flowing into the primary containment.
During purging operations, nitrogen flow and temperature is monitored in the control room to maintain 5 50 F nitrogen temperature.
If nitrogen temperature decreases to $ 50 F, the low temperature shutoff valve will close and prevent injecting cold nitrogen into the primary containment.
During makeup operations, the makeup vaporizer electric heater will energize if nitrogen temperature decreases to C70 F and the low temperature shutoff valve will close if nitrogen temperature decreases to (50oF.
The continued use of these low temperature setpoints will preclude any low temperature problems.
It should be noted that the configuration of the nitrogen injection piping into the wetwell at Browns Ferry is different from the configuration at Hatch Nuclear Plant as shown in figures 1 and 2.
As such, the liquid nitrogen and/or cold gases would not impinge directly on any downcomer or the vent header.
SIL 402 ITEM 2 Evaluate Incr tin S stem 0 eration Review the operating experience of the inerting system to assure that the vaporizer, the low temperature shutoff valve and the temperature indicators have functioned properly.
Evaluate the plant calibration, maintenance and operating procedures for the inerting system.
Assure that cold nitrogen injection would be detected and prevented.
TVA RESPONSE We have reviewed the operating experience of the containment inerting system at Browns Ferry.
Our review indicates that the vaporizers, system
- controls, and temperature indicator s have been functioning properly.
We have r eviewed the maintenance history from January 1,
1984 to present.
The only maintenance item found that could affect the low temperatur e controls for the inerting system was that the purge line low temperature shutoff valve calibration'as checked on February 17, 1984.
The temperature controller and the low temperature shutoff valve have been added to the system instrument and maintenance instruction to ensure that the temperature controller receives required periodic calibration or maintenance.
To further ensure proper operation of the inerting system, we have revised the Operating Instructions (OI) for the Containment Inerting System (OI 76) and Primary Containment System (OI 64).
OI 76 ensures that cold nitrogen
(<50 F) will not be injected into the primary containment during purging operations.
OI 64 now monitors run time of the drywell Delta P air compressor to detect possible cracking of internal containment piping.
SIL 402 ITEM 3 Test for Dr well/Wetwell B ass Leaka e
Perform a bypass leakage test as. soon as convenient to confirm the integrity of the vent system.
This test should be conducted during plant operation following normal plant procedures.
If no procedures exist, the fol'lowing is a general guide for preparing your procedure:
pressur ize the drywell to approximtely 0.75 psi above the wetwell pressure, maintain this dr ywell pressure and measur e the pressure buildup in the wetwell.
Any bypass leak area can then be calculated (and is limited by Technical Specifications on many plants) from the wetwell pr essur e and the drywell-wetwell pressure differ ence.
This will provide an indication that the vent system integrity is intact and that no gr oss failure exists.
TVA RESPONSE A drywell/wetwell bypass leakage test was performed on Browns Ferry unit 1 and unit 2 to ensure the integrity of the vent system as requested by NRC IE Bulletin 84-01 for plants that were currently operating.
The results of the test indicate from the long drywell/wetwell Delta P
compressor idle times and the relatively low leakage flow rates, that there are no anomalies that are indicative of cracks in either unit 1 or unit 2 vent headers.
Based on the visual inspection (Item 5) and procedural changes (Item 2), the bypass leakage test will not be performed on unit 3, which is currently in a refueling outage.
SIL 402 ITEM 4 Ins ect Nitro en In ection Line Conduct an ultrasonic test (UT) as soon as convenient of all accessible welds in the nitrogen injection line from the last isolation valve to the wetwell and drywell penetrations.
Also UT the containment penetrations and the containment shell within 6 inches of the penetration.
UT is recommended because cracks would be most likely to initiate on the inside of the pipe or on the side of the metal in contact with cold nitrogen.
TVA RESPONSE Satisfactory operating experience, multiple controls and indications, and procedural controls make the introduction of cold nitrogen
(<50 F) unlikely in either the past or future.
Therefore, we do not plan to perform ultrasonic examinations on the nitrogen injection lines penetrating the drywell and wetwell or the containment penetrations and containment shell within six inches of the penetration.
SIL 402 ITEM 5 Ins ect Containment J
During the next planned
- outage, perform a visual inspection of the vent
- header, downcomers and other equipment in the containment which might be expected to be affected by the injection of cold nitrogen.
The vent header should be inspected on the outside and the inside.
Also inspect the containment shell or steel liner for at least 6 inches around the nitrogen penetration.
TVA RESPONSE As requested by IE Bulletin 84-01, a visual inspection was performed on unit 3, which is in a refueling outage.
No cracks were found; however, four pinholes wer e discovered in the downcomer to vent header weld in bay 6 on unit 3.
All four pinholes in this construction weld wer e porosity
- holes, which have been ground out and repaired.
For the same reasons listed in Item 4, we do not plan to perform the additional visual inspections specified in GE SIL 402 for unit 3.
We do not plan to perform any visual inspections per GE SIL 402 on units 1 and 2 based on the reasons listed in item 4.
Indicate the location of our Nitro en Inertin S seem entr Port.
Nitrogen Inerting Sys 20" entry port Vent Pipe MAINVENT VENT HEADER DEFLECTOR 7'ATWALK DOWNCOMER SRV LINE DOWNCOMER TIES QUENCHER RING GIRDER TIE DOWN
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