ML20132G110
| ML20132G110 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 09/13/1985 |
| From: | Van Brunt E ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | Kirsch D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| REF-PT21-85, REF-PT21-85-434-000 ANPP-3341-TDS, ANPP-33461-TDS, DER-85-24, PT21-85-434, PT21-85-434-000, NUDOCS 8510010472 | |
| Download: ML20132G110 (7) | |
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' o fECEIVED Imc Arizona Nuclear Power Proje{tg gp g pg g q
P O. BOX $2034 e PHOENIX. ARl2ONA 85072-2034 Septenber13, iib' ANPP-33461-TDS/TPS U. S. Nuclear Regulatory Comission Region V 1450 Maria Lane - Suite 210 Walnut Creek, California 94596-5368 Attention: Mr. D. F. Kirsch, Acting Director Division of Reactor Safety & Projects
Subject:
Final Report - DER 85-24 A 50.55(e) Reportable Condition Relating To Broken Diesel Generator Ibrbocharger Bolts File: 85-019-026; D.4.33.2
Reference:
A) Telephone conversation between R. C. Sorensen and T. P. Siegfried on June 6, 1985 B) ANPP-32974, dated July 10, 1985 (Interim Report)
C) ANPP-33205, dated August 15,1985 (Time Extension)
Dear Sir:
Attached is our final written report of the Reportable deficiency under 10CFR50.55(e), referenced above. The 10CFR21 evaluation is also included in this report.
Very truly yours, M
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i E. E. Van Brunt, Jr.
Executive Vice President Project Director EEVB/TPS/nj Attachment cc: See Page Two 8510010472 850913 PDR ADOCK 05000528 S
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- ANPP-33461-TDS/TPS September. 13, 1985 Mr. D. F. Kirsch DER 85-24 Page Two cc:
Richard DeYoung, Director Office of Inspection and Enforcement U. S. Nuclear Regulatory Cannission Washington, D. C.
20555 J. G. Haynes D. B. Karner W. E. Ide D. B. Fasnacht A. C. Rogers L. A. Souza T. D. Shriver D. E. Fowler C. N. Russo J. R. Byntrn J. M. Allen D. Canady A. C. Gehr G. A. Hierzer W. G. Bingham R. L. Patterson R. W. Welcher H. D. Foster D. R. Hawkinson-R. P. Zinmerman M. L. Clyde B. T. Parker T. J. Blocxn J. D. Houchen D. N. Stover J.' E. Kirby l
Records Center Institute of Nuclear Power Operations 1100 Circle 75 Parkway, Suite 1500 Atlanta, Georgia 30339
FINAL REPORT - DER 85-24 DEFICIENCY EVALUATION 50.55(e)
ARIZONA NUCIZAR POWER PROJECT (ANPP)
PVNGS UNITS 1, 2, 3 I.
Description of Deficiency Workers observed that the head of a turbocharger support bolt had been sheared off on the Unit 2 Train B diesel generator. A check of the Unit 2 Train A diesel revealed that two' bolts had vibrated loose and backed out of the holes. Ioose bolts were also discovered in both trains in Unit 1 when examined, fractures were found. The bolts in Unit 1 have been replaced with A-193, Grade B7 full thread studs and A-194, Grade 2H nuts ~under Work Authorizations 87104 and 87109.
Evaluation The diesel generator (D/G) provides energency power to equipment required for safe plant shutdown in the event of loss of preferred power. Two D/G sets (Train A, Train B) are provided per plant. The turbocharger is located at the forward end of each diesel engine.
Engine exhaust gases drive a turbine which'in turn drives an air compressor that draws combustion air in, compresses it, and forces the air into the combustion cylinders.
The turbocharger is mounted on a support bracket which is attached to the engine by eight 5/8" x 11 x 1%" bolts in the vertical plane and six 5/8" x 11 x lt" bolts in the horizontal plane (see attached drawing, item 2). The bolt material is SAE J429, Grade 5.
NCR SM-5849 stato. that bolts in the vertical. support member on both trains of the Unit 1 and 2 diesels have either been sheared off or vibrated loose and fallen out.
The vertical bolts in quest. ion (eight bolts, three of which have failed on each unit) are installed'for seismic reasons only. Cooper Energy Services ~ (CES), the vendor, has reviewed the seismic study conducted on the turbocharger support bracket and determined that six bolts out of the eight bolt pattern.could fail before seismic integrity would be compromised.(Reference 1).
However, the eight bolts are of the same material and stressed in the-same manner, therefore, the eight' bolts may all be subject to failure which will comprcunise diesel generator operability.
The root cause of the bolt failure is attributed t'o fatigue due to engine vibration as discussed in Reference 2 (attached). The low pre-
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stress specified for the bolts provided clanping forces which were insuf--
ficient to prevent bolt fatigue failure due to vibratory loads.
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Final Report DER 85-24 Page Two II. Analysis of Safety Implications Based on the above evaluation, it is concluded that the condition is Reportable under 10CFR50.55(e) and 10CFR21, since it is a generic design defect, which if left uncorrected would constitute a significant safety hazard. This report addresses the reporting requirements of 10CFR21.21(b)(3) with the exception of subpart (vi), regarding the number and location of such components supplied to other facilities.
A copy of this evaluation will be sent to CES for their information.
III. Corrective Action The existing SAE Grade 5 bolts are to be replaced with longer ASTM A-193, Grade B7 full threaded studs and A-194, Grade 2H nuts. ' The torque value is to be increased to 110 ft/lbs., which will increase the pre-stress and eliminate vibratory loads. DCPs 20M and 30M-DG-049 have been issued to perform this work on Units 2 and 3.
Bechtel cal-culation 13-CC-ZQ-M01 verifies that 110 ft/lbs. is adequate for this application and has been' confirmed by ANPP surveillance procedure 73TI-lDG01. Unit 1 has been corrected under Work Authorizations 87104 and 87109. Work on Units 2 and 3 to be completed prior to fuel load.
CES has been informed of the change in fasteners and material (Ref-erences 1 and 3). They approved the use of Grade B7 studs as long as they are of equal or greater strength than Grade 5.
Grade B7 studs have a yield strength of 105 KSI while Grade 5 has a yield strength of 92 KSI.
Studs of Grade B7 are suitable for high temperature use.
IV. References 1.
Cooper Energy Services letter, CES No. 493, June 27, 1985, MIC 245674.
2.
APS Memo PVNGS-WS-M85, May 21,1985 3.
Telex BT/CES-E-6923, August 26, 1985
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5 Arizona Nuclear Power Project PVNGS-WMS-M85-018
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Name/ Ext /Sta. D. E. Sachs/6557/6077 CATE:
May 21, 1985
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Name/Exusta.W. E Simko/6555/6077
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Failure of Unit 1 Diesel Generator
SUBJECT:
Turbocharger Mounting Bolts (EER-85-DG-028) i File: 85-157-419 on 5/15/85, several of the subject fractured bolts were visually examined and hardness tests were performed. This was done i=. order to determine why
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the bolts failed.
The bolts were 5/C" dia.,11 threads per inch (UNC). II:" long SAE grade 5.
Two cf the bolts had fractured in the coot of the first thread, very close to the underside of the bolt head. Two other bolts had fractured approxi-
'mately 3/4" from the underside of the heads.
l the bolts cet the required values of Rockwell i
The hardness test; revealed that Actual hardness was RC 27-28.
"C" 23-32.
- Rather, None of the fractured surf aces revealed signs -of brittle fracture.
- Further, they had a very smooth appearance typical of f atigue cracking.
evidence of fatigue crack arrest lines (beach marks) were observed on the At least 75% of the frac-f two bolts that had cracked close to the heads.
tured area was fatigue cracked, with the remainder typical of a ductile The cracking pattern is typical of a lov nominal strass' with medium-to-high stress concentration, when ce= pared with drawings of fatigue overload.
The high fracture appearance in the A=erican Society for Metals Handbook.
stress concentration is caused by the threads.
I The reco= mended fix for this problem is to take the usual steps to reduce or eliminate fatigue cracking conditions, without introdu f
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i factors.
modification to the RCP diffuser bolt problect of 1983.
Specifically, the following should be done:
Upgrade the material from SAE grade 5 to AST'i A-193 grade B7 or SAE 1.
grade 8.
a,j Use studs instead of bolts to assure full thread engagement of the 2.
engine's cast iron threads.
c The present length of 11:"
Increase the length of the studs or bolts.The plate which is clamped by 3.
is rather short for a 5/8" dia. bolt.
- j the bolts to the' engine is approximately 5/8" thick, which is also
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Page 2
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Memo to L.G. Papworth p{LM{
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rather short for the maintenance of preload when using a 5/8" dia. bolt.
This distance should be doubled or tripled.
4.
Increase the torque value to at least 110 ft. Ib. from the original 50 ft. lb.
The original preload was only approximately 26 ksi, or 297. of the SAE grade 5 min. yield strength of 85 ksi.
This value is very low, and it allows the stress on the bolt to vary considerably.
It is the variance of the stress that results d5 i ! ~
in fatigue fractures, rather than the maintenance of a relatively T:Rj high uniform stress via high prelcad. A torque of 110 ft. lbs. will
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result in a preload stress of approximately 58 ksi if the threads 7
are lubricated.
This is 55% of the min. yield strength of B7 material, and 48% if SAE grade 8 is used.
As of now, the actual preload required to prevent any of the bolts from loosening is unknown. The bolts will therefore require periodic checking on a frequent basis (after.several hours of running, then after several days) until it can be determined that they remain tight. The tightening torque can be increased considerably (to 200 ft. Ib.) if loss of bolt preload is experienced at the 110 ft. Ib., level.
The source of the changing stresses-on the bolts are believed to be from
- engine vibrations, rather than from differential thermal expansion.
The use of the hbove recom=endations is expected to prevent future bolt / stud cracking.
WMS/DBH/ DES /ds cc:
J. R. Bynum 6125 O. J. Zeringue 6130 R. K. Nelson 6310 J. E. Kirby 6249 A. C. Rogers 4054 P.,,L. Brand.jes.... 6234.
R. Kandals Bechtel J. W. Tills 6310 J. V. Crews 6296 C. P. McNemar 6296 R. P. Indap 6296 R. A. Kropp 6077 C. D. Mackaman 6077 N
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