IR 05000029/1980003
| ML19312E874 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 04/25/1980 |
| From: | Foley T, Martin T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML19312E873 | List: |
| References | |
| 50-029-80-03, 50-29-80-3, NUDOCS 8006180057 | |
| Download: ML19312E874 (8) | |
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U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT Region I 0-29/80-03 Report No.
Docket No.
License No. D R-3 Priority Category
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Licensee: _jankee Atomic Electric Company
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25 Research Drive Westborough, Massachusetts 01581
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Facility Name:
Yankee Nuclear Power Station (Yankee Rowe)"
Inspection at:
Rowe, Massachusetts
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Inspection con uct d:- February 15-19, 1980 Inspectors:
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d$ h Y.~F'oley,ReaporInfector O date s10ned ~
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date signed Approved by: [
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T. T. Martin,[3, RO&NS Branchhief[ Reactor P/ojects date ' signed Section No.
Inspection Summary:
Inspection on February 15-19,1980 (Report No. 50-29/80-03)
Areas Inspected: Special, unannounced inspection by a regional based inspector of the circumstances surrounding the failure of Yankee Rowe's Low Pressure Turbine.
The inspection involved 33 inspector-hours onsite by one region-based inspector.
Resul ts: No items of noncompliance were identified.
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Region I Form 12
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(Rev. April 77)
8006180057
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DETAILS
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1. -PeRons Contacted
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Yankee Atomic Electric Company Personnel a.
H. Autio, Plant Superintendent D. Army, Technical Assistant L. French, Engineering Assistant J. Kay, Licensing Engineer P. Laird, Maintenance Supervisor J. Shippee, I&C Supervisor
- N. St. Laurent, Assistant Plant Superintendent
- J. Staub, Technical Assistant to the Plant Superintendent b.
Westinghouse Electric Corporation Personnel C. Florin, Service Engineer S. Furey, Service Engineer Dr. L. Kramer, Materials Engineer E. Shields, Service Engineer c.
NRC Consultants Dr. A. Goldberg, Lawrence Livermore Laboratories Dr. R. Streit, Lawrence Livermore Laboratories Dr. J. Weeks, Brookhaven National Laboratories d.
NRC Personnel V. Noonan, Chief. Engineering Branch, D0R C. Sellars, Senior Materials Engineer, D0R
- denotes those present at the exit interview.
2.
Scope of the Inspection This inspection was of the circumstances surrounding the failure of the Yankee Rowe Low Pressure Turbine during plant startup on February 14, 1980 and to examine the extent of the damage caused by the turbine failure.
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3.
Document Review The inspector reviewed portions of the following documents inorder to determine the sequence and circumstances surrounding the event:
OP-2102 Rev. 6 Turbine Startup
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OP-2100 Rev. 23 Plant Startup from Cold Shutdown
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Shift Supervisor's Log for February 13-15, 1980
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Memorandum From T. Danek to File dated February 14, 1980 " Turbine
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S tartup" Memorandum From T. Danek to H. Autio, dated August 7,1979 " Turbine
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Vibration During Load Reduction" Westinghouse Power Generation Service Division Job Report No.
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BST-92065 dated September 10,1979 " Investigation of vibration excursion on #4 bearing" Westinghouse Power Generation Service Division Job Report No.
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BST-92953 dated February 27,1976 " Work scheduled for this outage" Westinghouse Steam Service Inspection Report Serial No. 13-1851
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and 1852 dated October 20, 1975 Westinghouse Maintenance Contract Log Book 408 Job Report No.
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BST-92132 dated February 14, 1980.
NRC IE Information Notice 79-37, dated December 28,1979 " Cracking
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in Low Pressure Turbine Discs" The following strip chart recorder data was reviewed:
Turbine Speed for February 14, 1980.
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Shaft vibration for February 14, 1980 and August 9,1979.
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Cylinder Expansion for February 14, 1980.
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Feed Flow, Steam Flow, Feed Pressure, Steam Pressure " totalizer
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charts" for February 14, 1980 and November 5, 1979.
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4.
Description of Events and Circumstances a.
Description of the Event Yankee Rowe had been shutdown since January 19, 1980, to install Short Term Lessons Learned Category A items.
On February 14, sufficient steam to rotate the turbine to synchronus speed (provide 1980, the unit was returning to approximately 5-7% power to 1,800 RPM). All turbine testing was completed showing all conditions to be normal. The turbine was brought to 1,800 RPM and conditions were achieved to synchronize the generator and load the turbine.
Prior to synchronizing a loud noise was heard from the L.P.
turbine accompanied by excessive vibration.
The turbine tripped automatically and coasted to a stop in 25 minutes. Attempts to rotate the turbine on the turning gear failed.
The licensee's representatives removed an inspection cover and observed sheared blades and portions of disc material. The licensee's representative then notified Westinghouse and the NRC.
b.
Circumstances Surrounding the Event The following events took place at the times indicated prior to and after the incident on February 14, 1980:
Commenced turbine throttle and control valve 0830 hours0.00961 days <br />0.231 hours <br />0.00137 weeks <br />3.15815e-4 months <br />
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exercise.
Turbine Rolling 50 to 150 RPM (off of the Turning 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br />
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Gear)
Valve Closure Time Test of control and throttle 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br />
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test valves Turbine at 500 RPM conducted the Turbine Auxiliary 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br />
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Governor test Conducted the oil over speed test 1125 hours0.013 days <br />0.313 hours <br />0.00186 weeks <br />4.280625e-4 months <br />
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Turbine at 1,800 RPM under the control of the 1133 hours0.0131 days <br />0.315 hours <br />0.00187 weeks <br />4.311065e-4 months <br />
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governor with both throttles wide open, turned the turbine control over to the Control Room for phasing onto the high' lines.
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1135 hours0.0131 days <br />0.315 hours <br />0.00188 weeks <br />4.318675e-4 months <br /> a loud bang was heard from the Low Pressure
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Turbine accompanied by a turbine trip, high vibration and rubbing noise.
The Pan Alarms readings approximately 5 minutes after the turbine shutdown were as follows:
Stm. Gens. Hi/Lo Lev.
No. 3 F.W. Htr. Hi/Lo Lev.
No.1 F.W. Htr. Hi/Lo Lev.
C. W. Vac. Prim. Tk. Hi/Lo Lev.
C. A.C. Hi Temp. Lo 011 Lev. Trip No.
Right Separator Hi Level Turb. Trip Lo Brg. Oil Pressure Thrust Bearing Pre-Trip Turb. Trip Lo Vacuum Turb. Sep. Drain Rec. Hi/Lo Lev.
Turb. Vibration Hydrogen Panel Brg. Oil Hdr. Press. Low Left Separator Hi Lev.
No.1 Nozzle Low Press.
Cire. Water AT & Temp. Hi.
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1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> Reactor Plant was placed
" Hot Standby" and cooling down.
Prior to the turbine trip and while the turbine was coming up to 1,800 RPM the following conditions were observed to be normal:
Turbine eccentricity
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Turbine vibration
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Cylinder expansion
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Bearing oil temperatures
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Steam Generator water levels within the Narrow Range indication
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5.
Turbine History
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The Yankee Rowe Low Pressure Turbine (L.P. Turbine) is a 145 M4 9 stage tandem-compound double exhaust turbine.
The turbtne was partially assembled in the field, and placed into comercial operation in 1961.
During the initial period of operation a steam up lift problem and a Control Valve problem occurred, which were resolved by design changes.
The last major overhaul of the LP Turbine occurred in October 1975 at which time the LP Turbine was completely inspected and the LP Spindle was grit blasted and non-destructively examined by Boston Power Generation Service Department. During this inspection cracks were noted in the stellite strips in the last row of the Governor End of the LP Spindle.
Cracked blade lashing lugs and cracked stellite strips in the last row of the L-2 row, the L-3 row and L-4 row of the 6enerator End were also noted. All cracked stellite strips were replaced.
Both cracked blade lashing lugs were repair welded and passed dye penetrant examination.
It was stated in the Power Generation Service Dtvision Report Job No.
BST-92953 dated February 27, 1976 that the condition of the last rows of the LP spindle blading is satisfactory for service until the next scheduled LP Turbine inspection.
It was also recomended that during the next scheduled outage of the LP Turbine, the blade roots of Rows 8 and 9c should be welded.
bspection of the upper half of the steam deflector plate revealed approximately 200 crack indications which were rotary filed out and dye penetrant examined.
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On August 3,1979, during a load reduction from approximately 180 MWE the plant experienced a turbine vibration panalarm at approximately 166 MWE. The instrument readings were verified to be correct.
Yankee Rowe's maintenance and instrument technicians investigated the vibration by taking local vibration readings at various points on the turbine-generator bearings.
It was determined that excessive vibration occurred at bearings number 3 and 4 between 165 and 150 MWE.
On September 7,1979 Westinghouse Power Generation Service Division performed an investigation of the vibration excursion on #4 bearing.
The excessive vibration did not reoccur during this investigation.
Yankee Atomic Electric Co. was advised to install a micro-balancer adapter before startup, and was provided a sketch for making one.
The adapter was fabricated and installed.
6.
Post-Event Examination On February 15, 1980 the licensee and Westinghouse representatives commenced disassembling the LP Turbine.
Removal of the inner casing and debris located inside the inner casing revealed severe damage to the LP Turbine and associated components as follows:
inner cylinder (casing):
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All stationary blades were crushed or damaged. A crack was formed in at least one steam extraction port.
Support strength members were sheared off or bent, and the lower half of the casing appeared to be warped.
turbine discs:
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The two inner most discs, each containing the first (2) stages of turbine blades had been separated from the spindle.
One disc, on
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turbine blades:
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The first four stages (rows of blades) were sheared / separated from the discs. The fifth and sixth stages were severely damaged.
The seventh through ninth stages sustained little or no damage.
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associated components:
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The steam deflector plate was mangled and torn from its supporting structure.
It should be noted that despite the extensive damage inside the inner casing, neither the inner casing or the outer casing was penetrated.
There were however, minor cracks around the center dowel pin in the outer casing.
7.
Mechanism of Failure The exact cause of turbine failure has not been determined at this time. Westinghouse Corporation is presently investigating the mechanisa of failure, and samples of the failed discs are in process of being obtained for analysis by Lawrence Livermore Laboratories and Brookhaven National Laboratories (NRC consultants).
By visually examining the failed discs bores the inspector observed extensive cracking in the Generator end disc bore and no cracks in the Governor end disc bore. -There were no cracks visually noted at any keyway on either disc. At this time the failure appears to be caused by the Generator end disc experiencing metal fatigue and stress corrosion, which fragmented and impacted upon the Governor end disc fracturing it and causing the subsequent damage described above.
8.
Exit Interview The inspector met with the licensee's representatives (denoted in paragraph 1) at the conclusion of the inspection to discuss the scope and findings of the inspection as detailed in this report.
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