ML20128C408
| ML20128C408 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 05/03/1985 |
| From: | Hufham J TENNESSEE VALLEY AUTHORITY |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21-85, REF-PT21-85-263-000 NCR-R-30, PT21-85-263, PT21-85-263-000, NUDOCS 8505280288 | |
| Download: ML20128C408 (3) | |
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.a TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 37401 400 Chestnut Street Tower II I8 'b'/g May 3, 1985 Ay *g BLRD-5043843-35
/
. BLRD-50439M3-31 1U.S. Nuclear Regulatory Camission Reglon II Attn:
Dr. J. Nelson Grace, RegLonal Administrator 101 Marietta Street, NW, kite 2900 Atlanta, Georgia 30323
Dear Dr. Grace:
BELLEFWTE NUCLEAR PLANT WITS 1 AND 2 - B&W PLANT INTERNAL BCLT FAILEES
- BLRD-5043843-35, BLRD-5043943 FINAL REPORT
- The subject deficiency was initially reported to NRC-CIE Inspector Linda Watson on May 13,1983 in accordance with 10 TR 50.55(e) as NCR R-30.
This was
' followed by our interim reports dated Jtne 13 and December 5,1983 and Atgust 29, 1984.
NG BLN NEB 8413 has also been generated to dociatent this concern. TVA intends to report on both NGs simultaneously. Encimed is our final report. We consider 10 TR Part 21 applicable to this deficiency.
If you have any questions, please get in touch wLth R. H. Shell at FTS 858-2688.
Very truly yours,
TEleiESSEE VALLEY AUrHORITY ed. W. Huf han, Manager Licensing and Regulations Enclostre cc:
Mr. James Taylor, Director (Encimtre)
Office of Inspection and Enforcement U.S. Nuclear Regulatory Canmissim Washington, D.C. 20555 Records Center (Enclosure)
Institute of Nuclear Power Operations 1100 Circle 75 Parkway, mite 1500 Atlanta, Georgia 30339 p r r-b il0ld S.ag.
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An Equal Opportunity Employer
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3 Yi ENQ.G5 URE BELLEFOITE NUCLEAR PLANT UNITS 1 AND 2 B&W PLANT INTERNAL BG.T FAILURES BLRD-50-438/83-35, BLHD-50-439/83-31 m
10 TR 50.55(e) 3 NGs R-30 AND BLN NEB 8413 5
FINAL REPORT g
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Descriotion of Deficiency f
Sh The BW Owners Group has opened issue R-30, " Internals Bolting Failures,"
d documenting a potential safety concern with B&W plants. Specifically, there have been failures of A286 bolts used in various reactor internals C
applications at Oconee 1, Rancho Seco, and Crystal River 3 B&W review of 4
the Bellefonte Nuclear Plant (BLN) reactor internals joint design indicated that stress corrosion cracking (SCC) failures of A286 bolts like those which 3
occurred at the above listed operating plants oculd also occur at BLN.
The i
following fim joints in the BLN reactor internals utilize A286 bolting i
material:
(1) plenta lug to cover, (2) vent valve to core support assenbly, (3) core support lug, (4) plenta cylinder to upper grid, and (5) coltan j
weldnent to upper grid. BW estimated peak stress levels for these joints by multiplying the sin of the preloaded and operating stresses by an estimated stress concentration factor. The resulting peak stresses for joints 1 and 2 i
are well below the actual yield stress. Joint 3 has low stress but the high 7
stress concentration factor under the bolt head results in a relatively high peak strees valae. The peak stresses for joints 4 and 5 are much greater l
than the acttnl yield stress. Hi@ stresses increase the potential for SCC.
1 The root cause of this problon was B&W's apparent failure to adequately determine stresses during the design and material selection process of the 9
BLN reactor internals bolts. After several instances of bolt failure at operating plants, BW reevaltnted the stresses on the BLN bolts and found i
that scme of the A286 bolts were overstressed. BW then recommended that the j
overstressed bolts be replaced.
f^
Safety Im lications The subject condition mi@t result in loosened or free bolts in the reactor 7
vess el. Loose or free bolts could result in reactor coolant flow-induced
?
vibrations in the plenta cylinder, coltnn weldnents, and vent assenblies
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affected.
In addition, loose parts in the reactor coolant flow stream could 4
impact the fuel assenblies and cause cladding damage. Either of these y
conditions could be adverse to the safe operation of the plant.
g S
Corrective Action All of the A286 bolts in the five BLN reactor internals joints identified 5
above are being replaced with bolts fabricated f rom Inconel X-750 HTH.
New E
locking devices are also being provided with the replacement bolts. Inconel j/
X-750 HrH has greater resistance to SCC than A286.
Even trutgh the stress levels on scue of the bolts are low enotgh that the A286 bolts may provide l
satisf actory service for the life of the plant, W A believes that replacing i
all of the A286 bolts with Inconel X-750 HTH bolts will minimize the d
potential for SCC failuren.
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Instruction 2 for replac;nent of th2 A286 bolts era given in MW field change 1
pa2kapa (FTO) 264 and 296 for unito 1 and 2, respectively. These FTs have been approved and trammitted to TVA's Office of Ccnstruction. Imtallation of the unit '1 replacement bolts is complete. All init 2 hardware is onsite.
Unit 2 installaticn should be completed by October 1,
- 1990, Sin'oe the overstressed bolts are-being replaced with bolts made from a f
-material that is stronye and more res1. tant to SCC than A286, and sinoe TV A has no other plants with B&W-supplied fl3SS,' there is no action required to prevent recurrence.
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