ML20093K500
| ML20093K500 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 07/09/1984 |
| From: | Jens W DETROIT EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| 107, EF2-69271, NUDOCS 8407310102 | |
| Download: ML20093K500 (3) | |
Text
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- !:grk' H. Jens e
V(e Prew9nt Nx$ ear Operkuons Fem 2 em,a n.mn o.., %.m July 9, 1984 EF2-69271 Mr. James G.
Keppler Regional Administrator Region III U.
S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137
Dear Mr. Keppler:
Reference:
(1) Fermi 2 NRC Docket No. 50-341 (2) Letter D.
A. Wells to J.
G.
- Keppler, December 22, 1983, EF2-66490
Subject:
Final Report of 10CFR50.55(e) Item 107
" Mechanical Problems with RHR Pumps" This is Detroit Edison's final report concerning mechanical problems with the RHR pumps.
Item 107 was originally reported as a potential deficiency on November 21, 1983, and subsequently documented in Reference (2).
Description of the Deficiency An examination of the RHR pump B internals was conducted to determine if the pump was the source of debris (set screws) found in a check valve downstream of the pump.
This examination revealed problems with the pump, and the pump internals were sent to the manufacturer for evaluation.
The manufacturer, Byron-Jackson, informed Detroit Edison that the amount of wear on the pump hydrostatic bearings was excessive considering the amount of time the pumps had operated.
Subsequent investigation by Detroit Edison revealed that RHR pumps "B"
and "D" had the following mechanical problems:
1.
Liquid penetrant tests revealed impellers with linear indications (cracks);
2.
hissing set screws from the wear rings in the pump bowls; 3.
Excessive wear on the wear rings and the hydrostatic bearings.
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s Mr. James G.
Keppler July 9, 1984 EF2-69271 Page 2 Analysis of Safety Implications The RilR pumps could experience reduced longevity and pre-mature failure.
A common mode failure could occur resulting in all four pumps.becoming simultaneously unavailable, thereby, negating accident and long-term cooling capability.
Ilowever, such a simultaneous pump failure without some prior surveillance indication or with a total loss of performance capability is highly unlikely for all RilR pumps.
Specific consequences are as follows:
1.
The extension of the crack to the point of impeller failure could cause pump failure.
2.
Loose set screws could pass through the impeller and lodge in valve seat areas or jam in a check valve hinge and cause a valve not to close.
(A loose parts analysis performed by General Electric determined that there are no safety implications for set screws entering into the vessel.)
3.
The loosened wear ring could cause a pump to jam.
Corrective Action The following corrective actions were initiated as a result of a joint evaluation conducted by General Electric and Byron-Jackson, and concurred with by Detroit Edison:
1.
Metallurgical examination revealed that the cracks were original casting flaws which did not propagate as a result of pump operation.
The cracks were subsequently weld repaired.
2.
Vibration of the puup assembly loosened the set screws.
Replacement set screws have been installed and tack welded.
3.
Ineffective hydrostatic bearing design, coupled with pump assembly vibration, caused the damage to the bearings.
Grooves behind the bearing surfaces have been removed to improve performance.
A harder material than the original has been used in the wear rings to improve wearability and stability.
4.
The following corrective actions were taken to reduce the pump assembly vibration:
i o
e.r
-o-Mr. James G..Keppler July 9, ' 198 4
.EF2-69271 Page 3 The pump nozzle to pipi,ng' interface has been a.
-braced; b.-
Multiple breakdown orifices have been installed to reduce flow induced vibration.
A ten-day test run, including ~ vibration analysis,-was conducted and verified the adequacy of-the corrective actions.
This is Detrol't Edison's final report' on this item..If you have questions concerning this matter, please contact Mr. Lewis P. Bregni, (313) 586-5083.
l Sincerely, i
/
l A
cc:
Mr.
P. M. Byron Mr.
R. C. DeYoung Mr.
R.
C. Knop