ML20101B575
| ML20101B575 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/28/1984 |
| From: | Counsil W, Sears C NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| F0232A, F232A, SD-22, NUDOCS 8412200390 | |
| Download: ML20101B575 (3) | |
Text
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General Offices
- Selden Street. Berlin, Connecticut sY sYuNcowan P.O. box 270 wucma mesa wa co"""
HARTFORD, CONNECTICUT 06141-0270 L
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(203) 665-5000 November 28,1984 Docket No. 50-423 F0232A Dr. Thomas E. Murley Regional Administrator Region i U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406
References:
(1)
W. G. Counsil letter to R. C.
Haynes, B10539, dated August 20,1982.
(2) IE Information Notice 82-56, " Robertshaw Thermostatic Flow Control Valves," dated December 30,1982.
Dear Dr. Murley:
Millstone Nuclear Power Station, Unit No. 3 Reporting of Potential Significant Deficiencies in Design and Construction:
Robertshaw Thermostatic Control Valves in the Diesel Generator Cooling System (SD-22)
In a June 28, 1982 telephone conversation between your Mr. T. Elsasser and our Mr. S. Orefice, Northeast Nuclear Energy Company (NNECO) reported a potential significant deficiency in the design and construction of Millstone Unit No. 3 as required by 10CFR50.55(e).
The potential significant deficiency involved the potential failure of Robertshaw thermostatic control valves in the emergency diesel generator cooling system. Failure of these valves could result in extreme engine overcooling which could damage the diesel engines. This condition is further detailed below.
Each of the Millstone Unit 3 diesel generators has one, five inch Robertshaw Model 1285 thermostatic control valve in its intercooling water system.
Functionally, the valve responds to coolant temperature at its inlet and either diverts the coolant around the intercooler heat exchanger or, when the coolant is at its operating temperature, allows it to flow through the intercooler heat exchanger. Reference (2) further details two specific concerns which provide a basis for the potential failure of Robertshaw Model 1284 and 1285 thermostatic flow control valves. Of particular concern is the potential back off or complete I
disengagement of the valve stem nut on the lower over-run assembly and the swelling or contamination of an "O" ring assembly.
The back off or disengagement of the valve stem nut affects the temperature setpoint and could 8412200390 841128 PDR ADOCK 05000423 S
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4 2-result in running a diesel engine with excessively low coolant temperatures.
Swelling or contamination of an "O" ring assembly could restrict or prevent movement of the valve plug resulting in the valve plug remaining in its bypass position and the diesel not being adequately cooled. Either of these conditions can result in degraded diesel generator performance.
Upon disassembly and inspection, it was discovered that the valve stem nut for one of the valves,3EGS*TCV44A, had become completely disengaged. We have concluded that the design method for securing the valve stem nut 'on the threaded stem was inadequate. Hence, we consider this to be a significant deficiency since the misoperation of the valves could have adversely affected the capability of the diesel generators to perform their design function.
t Corrective action included the replacement of the lower over-run assemblies and the removal of the "O" rings from the valves. On the replacement assemblies, the valve stem nut is now secured with a cotter pin. Parts and procedures were i
procured from Colt (the diesel vendor) and Robertshaw (the valve manufacturer).
Although it is uncertain whether or not the nut disengaged during shipment or factory testing, the nut was never found. Assuming the nut was in place when the diesel was built, discussions with Colt and our analysis indicate that the nut is probably lodged in the shell side of the intercooler heat exchanger.
Our analysis considered the size of the nut, the tortuous path to the outlet of the i
heat exchanger, and the low flow velocity in the heat exchanger and concluded i
that this condition is acceptable. Colt concurs with this decision. In addition, if there were any problems associated with this condition, they would be
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discovered during the Millstone Unit No. 3 startup testing program.
1 We consider this to be our final report closing out SD-22. We trust that the above information satisfactorily responds to your concerns.
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Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY ua.4.(bd j
W. G. Counsil
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Senior Vice President By: C. F. Sears Vice President I
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Mr. R. C. DeYoung, Director Division of Inspection and Enforcement U. S. Nuclear Regulatory Commission Phillips Building 7920 Ncrfolk Avenue
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