ML18036B297
| ML18036B297 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/21/1993 |
| From: | Salas P TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9305250332 | |
| Download: ML18036B297 (14) | |
Text
'Tennessee Valley Authority. Post Otfice Box 2000, Decatur. Afabama 35609 10 CFR 50. 55a (g) (5) (iii)
U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter Of
)
Tennessee Valley Authority
)
Docket No. 50-260 BROWNS FERRY NUCLEAR PLANT (BFN) - UNIT 2 - NRC REQUEST FOR ADDITIONAL INFORMATION (RAI) FOR VALVE FCV 2-68-33 BONNET-TO-BODY BOLTING REQUEST FOR RELIEF
Reference:
Letter from TVA to NRC dated May 16,
- 1993, "Browns Ferry Nuclear Plant (BFN)
Unit 2 American Society of Mechanical Engineers (ASME)
Section XI Inservice System Pressure Test Program Request for Relief for Valve FCV 68-33 Bonnet-to-Body Bolting" The purpose of this letter is to provide NRC additional information regarding Request for Relief SPT-6 submitted in the reference letter.
In accordance with the provisions of 10 CFR 50.4 and 10 CFR 50.55a(g)(5)(iii),
BFN submitted the referenced letter requesting relief from IWA-5250(a)(2) of the 1986 Edition of the ASME Boiler and Pressure Code.
ASME Section XI paragraph IWA-5250(a)(2) states that if leakage occurs at a bolted connection, the bolting shall be removed, visual test VT-3 examined for corrosion, and evaluated in accordance with IWA-3100.
BFN proposed as an alternate method to perform a VT-1 examination in accordance with ASME Section XI Code requirements with the studs in place in lieu of the ASME Section XI Code required VT-3 with the studs removed.
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A teleconference wa held on May 19, 1993, with NRC and TVA personnel to discuss technical issues relative to thc reference letter.
During this discussion TVA agreed to provide additional i'nformation to support the NRC review.
The enclosure contains the requested additiona3 information.
Xf you have any questions, please
'telephone me at (205) 729-2363.
- Sincerel, Pe o Salas Manager of'ite Licensing Enclosure cc (Enclosure):
,NRC Re'ident Inspector Browns Ferry Nuclear Plant Route 12, Box 637
- Athens, Alabama 35611 Mr. Thierry M. Ross, Project Manager.
U.S. Nuclear Regulatory Commission One White F'lint,, North 3.1555 Rockville Pike Rockvi l le, Maryland 20852 U.S. Nuclear Regulatory Commission Region l1 101 Marietta Street, Nb, Suite 2900
- Atlanta, Georg.ia 30323
ii
U.S. Nuclear Regulatory Commission SW.25
)993 PS: GMM:DEM: SKH Enclosure cc (Enclo ure):
R.
R. Baron, PSB 1K-BFN D. L. Brannen, C18 ATH3-BFN M. J. Burzynski, LP 5B-C E.
R.
Cobean, Jr.,
M. Cuoco, LP SB-C R.
- Fecht, LP 58-C R.
N. Huston, Rockville Licensing Office-C T. J.
R. Mullee, BR 5D-C D.
E.
- Nunn, LP 38-C J.
A. Scalice POB 2C-BFN O. J.
Zeri ngu>>,
PAB 1E-BFN
'N: LSUBSiBOLTT.NG. D).'M
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ENCLOSURE
,Browns Ferry Nuclear Plant Unit 2
,Request for Relief SPT-6 Additional Information On May 19,
- 1993, TVA held a teleconference with NRC personnel to discuss historical inservice inspection" arid maintenance activities, performed on recirculation system cross-tie valve FCv-2-68-33.
In addition, TVA provided the following metallurgical perspective relative to,this valve.
Inservice Ins ection Histor ISI May 17,1979, Unit 2 Cycle 2:
BFN performed an ultrasonic test on the valve stem for 2-FCV-68-33.
September 16, 1982, Unit 2 Cycle 4:
BFN perf ormed a VT-1 on the bolts f:.or. valve 2-FCV-68-33.
All bolts were determined to be acceptable.
September 23,
- 1986, Unit 2 cycle 5B:
BFN performed a
VT-1 on the bolts for valve 2-FCV-68-33.
All bolts were determined to he acceptable.
April 8, 1991, Unit 2 cycle 5B:
BFN performed the 10-year Hydrostatic'test.
VT-2 identified a leak at the packing for. valve 2-FCV-68-33.
May ll,l993, Unit 2 cycle 6:
BFN performed a inservice leak test.
VT-2 identified a leak at the bonnet-to-body fox valve 2-FCV-68-33.
May 15,
- 1993, Un.it 2 cycle 6:
BFN performed a VT-1 {for the e>'posed portion only) on the 24 bolts for, va]ve 2
FCV-68-33.
Mav 19, 1993,.
Unit.
2 cycJc 6:
BFN performed a U'I'xam on all 2d bolt.no cracking was noted.
Maintenance Hister BFN has reviewed the maintenance for va'i've 7.-FCV-G8-33 from 1984 to present.
')'his review did not identify any maintenance records requiring repair. to FCV-2-68-33 due to bonnet-to-body leaks prior to the leaks discovered in May 3.993.
BFN.has concluded that the valve studs have not been removed since initial installation.
Qt
ENcLOSURE {continued)
Page 2
Hetallur ical roe ective Request for Relief SPT-6 recommended a VT-l inspect:ion because the valve studs cannot. be fully removed without:
causing damage to both the studs and valve body,.
According
'to the vendor (Anchor,Darling) the studs were coated with castor oil as a thread lubricant during original manufacture.
After six cycles of operation the vendor anticipates thread seizing and galling.,
and recommond against: attempting t:o remove.the studs.
The accessible area will provide adequat:e information for establishing the joi.nt integrity and structural condition of the studs.
The st;uds are all threaded ASTM A5<0 C23 which is similar to AISl 4340 material.
The va]ve body (CFSM) is mounted at an acute angle and approximat;< ly four linear inches of t:hread are accessib'le.
Correct.,ive actions will require drillin<3 an overbore hole which would reduce ligament. spacing on the valve.
The remaining 1in< ar areas are engaged in the valve body and nuts and wa(.-hers.
These area - wi11 not fail t:he acceptance criteria of Section Xi because (l) the acute mounted valve will not al].ow moisture to collect on the exposed
- threads, therefore, no corrosion should occur..
Since there i.
a 2A thread fit, there is no path for wat<.r entrainment.
The studs are alloyed with beneficial nickel,
- chromium, and molybdenum.
The corrosion rate of carbon steel would be less than two mi,l, per year in a similar application.
(7.)
Any deformed threads may be verified vi.ually, the joi.nt also will be deformed.
(3)
The studs were examined us.i.ng ultrasonics to detect any form of cracking.
(4,)
The vendor has determined that..two studs may fai3 during operation without; loss of joint integrity.
Xt is concluded t-.hat the alternative examination hould'rovide adequate information for the physical,. condition of the studs and joint.
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ENCLOSURE (Continued)
IX-.
The following information was requested by NRC at the conclusion of the May 19, 1993 teleconference.
1.
What is the hardness of 'the studs?
On May 19,
- 1993, BFN performed
.a hardness test on the studs.
Accessibility difficulties vere encountered vith six of the studs.
The results (Hardness Rockwell C) for the remaining 18 studs range from 21 to 35 HRC.
2.
Here the 24 bol'ts lubricated prior to being torqued?
The bolts did not receive any additional penetration oi3 other than used to soak the bolts
- over, a 24-hour period prior to the attempt to remove them.
The pc.netratinq oil used on the bolts was Sprayon 203 manufactured by Sherwin-Williams.
The oil was sprayc..d on the top of the nuts and on the exposed thread between the bonnet and valve body.
!3FN attempted to remove si x of: the bo)t nut-with a torque value of approximately 2000 ft-lbs, only two of, the six nuts were loosened.
During thc.
re-tightening process a diametrical torquing pattern was used with an initial torque value of'pproximatel'y 1500 ft-lbs, increasing to a maximum of. approximate: ly 2200 ft-lbs.
This value is below the recommended vendor torque value of 2300 ft-lbs.
Industry standards I'or.
1-3/4 aj]oy bolts has an allowable torque value of 3000 it-lbs.
3.
What did the vendor (Anchor-Darling) mean when they stated tha".
a 3oss of two bolts wou3d maintain valve integrity (i.~.,
a loss of two bolts would not hold thc.
joint or a loss of two bo]ts the valve would not leak)?
The valve desi.gn included the potential los, of one single stud. at any stud 3ocation and the loss of two
.studs if the corresponding stud locations were 180 degrees apart (i.e
, stud locations basically acro"-='-
from each other, not side-by-side or close to each other).
Thi.
means that, assuming the va]ve was funct,ional and'eak free 'before the stud loss, the valve was,designed to remain functional. and l.eak.free after.
the stud lo.,ses described above.
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8GG'd IHlGA ENCLOSURE (Continued)
Page 4
A loss of studs at two locati'ons next, t:o each other.
or.
in close proximity to each other described is outside the design basis of the valve.
Therefore, valve function cannot be assured under t:his condition.
- However, given the inherent, safety factor. associated with standard class valves, anchor darling feels t:hat this condition will allow some bonnet rotation which will eventually lead to joint deformati'on and body-to-bonnet joint. leakage.
O'.
What are BFN's plans for off-loading the reactor core during the next refueling?
BFN currently does not plan. to off-1'oad t.he core during the next outage.
5,.
How many studs do you need to maintain structura,l integrity of the joint?
The valve was designed for accept. able operation nf 22 of the 24 stud. in place.
The two studs lost; must be 3:SO degrees apart (basically across from each other).
Two lost studs in close proximit:y or three or,more lost studs are conditions outside the desi,gn basis of the valve.
Va.lve function cannot be assured under.
these conditions.
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