ML20246M746
| ML20246M746 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 07/13/1989 |
| From: | Creel G BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| REF-PT21-89, REF-PT21-89-118-000 PT21-89-118, PT21-89-118-000, NUDOCS 8907190208 | |
| Download: ML20246M746 (3) | |
Text
- - _ _ _
I BALTIMORE GAS AND ELECTRIC CHARLES CENTER. P. O. BOX 1475. BALTIMORE, MARYLAND 21203 GroRGE C. CREEL vice Paes,oest Nuctran twenov (300 260-4 e55 July 13,1989 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 10 CFR Part 21 Written Report: Steam Generator Snubber Nuts Found Not to Meet Manufacturer's Material Composition Specifications Gentlemen:
Baltimore Gas and Electric Company has discovered a condition which we believe meets the criteria of a defect in a basic component as defined in 10 CFR 21. This letter provides the information required to be reported to the NRC pursuant to 10 CFR 21. A verbal notification was made to Mr.
J.
T.
Wiggins, of Region I headquarters, at 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br />, on July 12, 1989.
Facility:
Calvert Cliffs Unit Nos. I and 2 Compo.'.ent:
Grinnell Co. T.J.10"x5" Snubber Tie Rod Nuts Firm:
Grinnell Co. (Snubber Manufacturer)
LaSalle Steel Co. (Tie Rod Nut Steel Manufacturer)
Nature of Defect:
During reassembly of a Grinnell T.J.10"x5" Steam Generator Snubber for Calvert Cliffs Unit 2, a nut sheared in half during the final torquing pass of the tie rods which hold the snubber piston and cylinder assembly togethep in the axial direction. During the final torque pass, thel first of twelve nuts in the circular pattern was torqued to 560 ft-lbs. The second nut in the torquing sequence was being torqued to 560 ft-lbs when the first nut in the sequence suddenly sheared in half and flew off in opposite directions. The first and second nuts are located 180" apart in the torquing pattern. The nut sheared, creating two semi-circular pieces.
l 89071902OG 890713 p-d
//
3G/ $
/
PDR ADOCK 05000317 I
t
J i7 DocumeniCot'nrol Desk
~
July 13,1989
- Page 2 ;
l The failed nut and nine other similar nuts from the same snubber were sent to our materials lab for analysis. The l
~ nut material was reported by Grinnell Co. to be ~ "e.t.d."
150 l
(a trade name of the LaSalle Steel Co.). Our test - results i
do not agree with the stated material properties 'of the nut.
The stated - properties correspond - to approximately 'an AISI 4140 alloy, while our test results. indicate that.the' j
failed: nut and she other nuts analyzed are approximately an
.l AISI 1140. alloy. An AISI 1140 alloy - would be less ductile and have-less tensile and. yield strength than an AISI 4140 alloy. This discrepancy. in material composition
')
results in the yield strength of the nuts being d
approximately 75,000 psi and the tensile' strength being approximately 85,000 psi, rather than 130,000 psi and 150,000 psi, as stated in manufacturer sp:cifications for-l the "e.t.d."
150 material. It was also noted that the nuts are one-inch hex flange nuts which-have thinner walls than a
'l standard one-inch nut. It is felt that the thinner walls may have also contributed to the failure.
l Safety Hazard:
Because these nuts were made of a material that is inferior in strength to that specified by the manufacturer, there was a higher probability that the nuts would have failed under
)
actual design loading conditions. The nuts also provided a i
significant safety hazard as projectiles to personnel in surrounding areas while the nuts were being torqued. The
-i snubbers have been declared inoperable for the purposes of
-l satisfying Technical Specification - requirements.
I Date Information An engineering determination of 10 CFR Part 21 deportability j
Verified:
was completed on July 12, 1989.
Number of Components:
There are a total of 32 Steam Generator Snubbers at Calvert Cliffs Units I and 2.
Each snubber contains 24 of the subject nuts for a total of 768 nuts. The subject nuts were specifically manufactured for Grinnell 10"x5" early vintage snubbers. We do not believe that this type of nut is used in other applications at Calvert Cliffs.
Corrective Actions:
We plan on replacing all of the subject "e.t.d."
150 nuts with A194Gr2H nuts. The new nuts are the same specification as is used on current vintage Grinnell 10"x5" snubbers. The nuts are currently on order and shall be replaced on all snubbers for each Unit prior to Unit restart. It should be noted
'hn.t Grinnell's current stock replacement is the A194Gr2H nut.
' Document Cotnrol Desk l 7 i
July 13,1989 Page 3 Vendor Recommendations:
Grinnell Co. has indicated that they hava had no reports of similar nut failures. They have also indicated that it is permissible to replace one nut at a time by removing the old nut, installing and torquing a new nut to proper l
final torque. Then, after all nuts on a snubber are l
replaced, verifying all nuts are at the proper torque.
Should you have any further questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours,
(
L GCC/CDS/ dim cc:
D. A. Brune, Esquire J.
E.
Silberg, Esquire R. A.Capra,NRC S. A.McNeil, NRC W. T. Russell, NRC H. Eichenholz/V. L. Pritchett, NRC T. Magette, DNR