ML20137Z972
| ML20137Z972 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 11/22/1985 |
| From: | Hufman J TENNESSEE VALLEY AUTHORITY |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21-85, REF-PT21-85-504-000, REF-PT21-C NCR-4030, PT21-85-504, PT21-85-504-000, NUDOCS 8512110471 | |
| Download: ML20137Z972 (2) | |
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TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 374o1 SN 157B Lookout Place
'db YNN be 1, 1 85 BLRD-50-438/85-11 BLRD-50-439/85-11 U.S. Nuclear Res;ulatory Cornmission Region II Attn:
Dr. J. Nelson Crace, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Dear Dr. Grace:
BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 - CRACKED CYLINDER BLOCK ON TDI DIESEL CENERATORS - BLRD-50-438/85-11 AND BLRD-50-439/85-ll - REVISED FINAL REPORT The subject deficiency was initially reported to NRC-OIE Inspector Al Ignatonis on March 18, 1985 in accordance with 10 CFR 50.55(e) as NCR 4030.
This was followed by our first interim report dated April 12, 1985.
Our final report was submitted on July 9, 1985. Enclosed is our revised final report. We consider 10 CFR Part 21 applicable j
to this deficiency.
If you have any questions, please get in touch with R. H. Shell at FTS 858-2688.
Very truly yours, TENNESSEE VALLEY AUTHORITY f
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. W. Huf am, ' Manager i ensing and sk Protection Enclosure Mr. James Taylor Director (Enclosure) ec:
Office of Inspection and Enforcement U.S. Nuclear Regulatory Cotumission Washington, D.C.
20555 Records Center (Enclosure)
Institute of Nuclear Power Operations 1100 Circle 75 Parkway, Suite 1500 Atlanta, Georgia 30339 8512110471 851122 PDR ADOCK 05000438 S
PDR An Equal Opportunity Employer p
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k ENCLOSURE BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 CRACKED CYLINDER BLOCK ON TDI DIESEL GENERATORS BLRD-50-438/85-11 AND BLRD-50-439/85-11 NCR 4030 10 CFR 50.55(e)
- REVISED FINAL REPORT
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Description of Deficiency Upon the recommendation of the TDI Diesel Generator Owners Group, TVA implemented an extensive inspection and mainterance program that revealed cracks in components which would not ordinarily require inspection. Diesel generator 1B contained two cracks in the cylinder block extending 1-1/2 inches up the lip of the cylinder liner landing surface and 5/8-inch across the top of the block.
4 The exact cause of the cylinder block cracks cannot be determined. Trace casting contaminants leading to degenerate graphite structure and reduced fatigue resistance properties have been identified by the TDI Diesel Generator Owners Group as the most likely root cause of block cracking in TDI engines.
However, since the cracked block at Bellefonte Nuclear Plant (BLN) exhibited only a relatively minor amount of degenerate graphite structure and had cracks l
only in the area of one cylinder, we feel this is not the cause of cylinder block cracking. The cylinder block cracking is probably due to the very small cylinder liner to block clearance and a galled wrist pin and piston skirt assembly.
Safety Implications l
This type of cylinder block cracking has been analyzed by Failure Analysis Associates for the TDI Diesel Generator Owners Group and is considered to be a i
ligament crack. Extensive operating experience at other plants demonstrates that ligament cracks arrest at the cylinder liner landing and have no effect i
on engine operation because the cracks are fully contained between the liner and the block material beyond the cylinder head stud holes. Based on this, the condition is not considered to be detrimental to the safe operation of the plant.
Corrective Actions corrective actions are not required to be taken since the cylinder block cracking is not detrimental to the diesel engine and the cracks are not expected to propogate.
TVA and Transamerica Delaval have implemented the following actions to prevent the recurrence of future cracking in the diesel engine cylinder blocks:
1.
TVA has increased the clearance between the cylinder block and liner to l.
reduce stress in the cylinder block on the unit 1 BLN diesel generator
' engines. This action to prevent recurrence will-be completed on the unit l
2 diesel generator engines by one (1) year before fuel load of unit 2.
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.2-2.
TVA has replaced the galled piston skirt assembly and wrist pin in the affected cylinder.
3.
TVA will incorporate an inspection program in site procedures to monitor the existing cracks and will inspect for additional cracks during routine maintenance. These procedures will be in effect by one (1) year before fuel load of unit 1.
4.
TDI has incorporated production changes to decrease stress in the cylinder block. These changes were to increase the cylinder block to liner clearance and increase the depth of cylinder stud bosses and the depth of stud hole threads.
5.
TDI has incorporated product enhancements to increase the cylinder block top thickness and improve material from the original class 40 to class 45 cast iron. These changes will increase the allowable stress of the cylinder block,
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