ML20028H004
| ML20028H004 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 10/01/1990 |
| From: | Wallace E TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9010050144 | |
| Download: ML20028H004 (5) | |
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TENNESSEE-VALLEY. AUTHORITY m,..
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f, U. S. Nuclear Regulatory Commission
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ATTN:l-Document Control Department Washingi.on, ~ D.C.. 20555 Gentlemen:
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In'the Matter of
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Docket'No. 50-260 Tennessee Valley' Authority
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BROWNS FERRY NUCLEAR PLANT (BFN) - ASME SECTION XI REPAIR AND REPLACEMENT PROGRAM - UNIT 2 - REQUEST FOR RELIEF Enclosed for~your consideration is a Request for Relief (RFR)'from the code m
requirement of performing a radiographic examination of a base metal repsir to the unit 2 recirculation system ring header piping. The radiographic examination is' impractical to perform at this time because it would require
' the: draining. of the -reactor vessel and its associated recirculation system
- piping:-in order to obtain code acceptable results in'the repaired area.
The proposed alternative examinations will provide assurance of the piping
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. integrity..
.Please process this.RFR on an expedited basis. This matter has been r
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.previously discussed with D. H. Moran and other members of your staff.
If you-have.any questions, please telephone Patrick P. Carier, BFN, at
- (205) 729-3570.-
i Very truly yours, t
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TENNESSEE VALLEY AUTHORITY b. G. Wallace, Manager j
E Nuclear Licensing and Regulatory Affairs.
Enclosure
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9010050144 901001-POR: ADOCK 05000260 P
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..U.S* Nuclear Regulatory Commission 00T H gg h
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Ms.' S.' O. Black, Deputy Director Project Directorate 11-4 U.S. Nuclear Regulatory Commission i
One White-Flint, North
-11555 Rockville Pike, Rockville,-Maryland 20852 s
NRC Resident Inspector-browns Ferry Nuclear Plant i
Route 12 Box 637 Athens, Alabama 35699-2000 Thierry M. Ross, Project Manager U. S. Nuclear Regulatory Commission One White-Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr.'B. A.' Wilson, Project Chief U.S. Nuclear Regulatory Commission y
Region II 101 Marietta. Street, NW, Suite 2900
. Atlanta, Georgia ~30323-k
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-ENCLOSURE REQUEST FOR RELIEF.
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. UNIT:
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SYSTEM Recirculation'(System No. 68)
TVA DRAWING 47W817-1 COMEONENT 22-inch piping, 1.02-inch wall; ASTM A-358 (material class 1), type 304SS TVA CLASS A
E BACKGROUND A surface indication was detected by liquid Penetrant (PT) examination of a weld removal area on the recirculation system piping during modifications to the system supports. This indication was removed by grinding and subsequently, welding was required-to restore the piping to acceptable conditions. The indication was in an area where a component support attachment had been removed.
Location of the base metal repair (BMR) is at approximately 357' azimuth, Rad 16' 11", 1-7/8" above vendor weld seam # GR-2-52-LS as identified on ISI Drawing # ISI-0270-0 Rev.00.
The area of the.
BMR is approximately 2" X~2" with'an' excavation depth of.280".
The site Welding QC. Group discovered the indication
.in the removal area of an integral attachment.
Six pipe lug attachments were removed in this area as-part of a support modification required by Engineering Design. The modification required that more attachments be welded at-other locations around the circumference of the pipe at the same azimuth.
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The indication was discovered during a liquid Penetrant (PT) examination :af ter removal nf. the previous attachments and their attachment welds.
The indication was described as an approximately 1/2-inch star crater crack. As the indication was removed by grinding andLsubsequent PT inspections performed to verify removal, the indication evolved into a linear intermittent-type indication.
Porosity was observed during one point of removal along with the linear indication.
Although indications were observed where other attachments were removed at this support location, they were wcld indications within the attachment weld. These indications required no base metal grinding for removal except the expected " clean-up" depth.
Inc:- were no other repairs to the base material as a result of indications in weld removal areas at this support location.
7 l<
e P g3 2 Cf 3 CONCLUSION:
The probable cause of the indication is that it resulted l
f rom a t evious welding operation.
It may have occurred during W1 ding of the previous attachments, or it may have been. previously repaired area, considering the depth of L.4 removal area. This conclusion is based on the fact that the type of indication observed is indicative of welding (i.e., star crater crack and porosity) and also it was in the area of a previous i
weld. No other indications propagating into the base material have been discovered in this support location.
Therefore, this indication is considered to be an isolated case.
IMFilACTICAL ASME Section XI, 1980 Edition, through the EXAMINATION Winter 1981 Addenda, IWA-4120, requires that repairs REQUIREMENT be performed in accordance with the Owner's Design I
Specification and Construction Code. The original General Electric Company design specification 21A2100AE i
requires radiography of all pressure retaining full penetration groove welds.
In addition, later editions and addenda of ASME Section III, require radiography based on the depth of the repair.
BASIS FOR RELIEF Radiography is not practical for in-service conditions f
at the repair area. The reactor pressure vessel Ond associated recirculation system is filled with water.
It is impractical to drain the vessel to perform the radiography.
It is also not feasible to obtain a Code-acceptable radiograph when using gamma rays to L
penetrate the epproximate 1-inch pipe wall thickness and the volume of water within the 22-inch diameter pipe.
4 Ultrasonic examinations were performed on the base metal repair are at weld identification area R-2-004-023-R1.
A stralgt Seam technique was employed.
Also',
additiont.1 ultrasonic mmim.ons were performed using the 'IVA approved pwesure NUT 28 Rev.2, with TCR 90-41,
" Ultrasonic Examinatiu of Weld Overlay Piping."
For weld bond and weld metal integrity, both dual element straight and high angle dual element refracted longitudinal creeping wave transducers were used to perform the examination of the weld repair. This examination method was developed to find intergranular stress-corrosion cracking (IGSCC) in overlay weld repairs and is considerably more sensitive than normal weld repair examination techniques.
Exarinations were performed by Level Il and Level III certified personnel, and no recordable indications were found.
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A scheduled 10-year hydrostatic test of the recirculation system and this repair area is to be performed prior to restart of the unit. This test will be performed at a test pressure of 1104 t o 1158 psig and a temperature of 182'F to 207'F.
The proposed alternative ultrasonic examination and hydrostatic test, coupled with the required sutface exams, will provide assurance of the integrity )f the pressure boundary to a degree equivalent to that provided by a radiographic examination.
HARDSHIP OF DRAINING There are two issues which contribute to the REACTOR VESSEL AND impracticality of draining the reactor vessel and o
RECIRCULATION LINES associated recirculation piping:
TO PERFORM RADIOGRAPHY 1.
1.
ALARA impact associated with the assembly (and subsequent disassembly) of the unit two reactor vessel for drain down are expected to be approximately two (2) REM. Radiological impacts associated with these evolutions are increased surface contamination levels and increased risks h
of airborne contamination due to drying of highly contaminated surfaces inside the reactor cavity and vessel.
In addition, increased radiation exposures rates can be expected inside the unit two drywell. The increase in exposure rates are expected to be significant above the 584' elevation and access to these areas would be restricted. The increase on the 584' elevation and below is expected to be approximately 20 percent. At the present time work activities in the drywell are accruing approximately 10 REM per week. The increase in ace Plated exposure realized would obviously and on the duration of the drain down but, assunJ < a drain down period of two weeks would result in an approximate four (4) REM increase in exposure.
The total exposure increase resulting from drain down and continued drywell work is projected to be approximately six (6) REM.
2.
Work associated with the drain down of the unit 2 vessel would divert resources from other ongoing unit 2 restart scheduled activities.
The resources required to drain the vessel, process the water through the radwaste system, delay scheduled work, combined with an adverse ALARA impact make draining the vessel impractical when an equivalent method of nondestructive examination exists to evaluate the repair area.
ALTERNATIVE The weld repair was ultrasonically examined.
EXAMINATION Also, a system hydrostatic test will be performed in accordance with ASME Sectica XI, IWA-5000, f