ML20210F476

Part 21 Rept Re Problem in Torque Switches Supplied W/ Limitorque Operators Installed at Facility.Initially Reported on 870129.Limitorque Did Not Supply Adequate Instructions to Maintain Torque Switches Balance

ML20210F476
Person / Time
Site:	Davis Besse
Issue date:	02/03/1987
From:	Williams J TOLEDO EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-87, REF-PT21-87-028-000 1-706, PT21-87-028-000, PT21-87-28, NUDOCS 8702110083
Download: ML20210F476 (3)

Text

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TOLEDO

%mm EDISON Docket No. 50-346 JOE VVILUAMS. JR.

Serur Ves Presdert,-Nudear (419]249-2300 License No. NPF-3 (4191249-s223 Serial No. 1-706 February 3, 1987 United States Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555 Gentlemen:

This letter confirms our conversation with Messrs. P. Byron and P. Wohld of your staff on January 29, 1987. Toledo Edison is reporting a problem that was found in the torque switches supplied with Limitorque operators installed at Davis-Besse Nuclear Power Station, Unit No. 1. This condition is being reported under the requirements of 10CFR21.

The concern is that Limitorque did not supply adequate instructions to maintain the torque switches " balanced" so that the torque at torque switch trip is equal for both valve opening and valve closing. With the torque switch unbalanced, the torque switch can trip before the valve operator can produce sufficient torque, or thrust, to operate the valve against its design differential pressure.

Specifically, on January 26, 1987, in the review of the data for Toledo Edison's answer to IE Bulletin 85-03, it was determined that prior to June 9, 1985, (torque) thrust measured for the main steam to auxiliary feed pump turbine #1 containment isolation valves (MS106 and MS106A) was insufficient to close against the design differential pressure of 1100 psig. The low closing thrust for these two valves has been determined to be a result of the operators having an unbalanced torque switch. The settings on the torque switches were correct.

Imbalance, prior to developing a method of measuring thrust, was not considered as a significant parameter. The use of equipment to measure the thrust now allows this imbalance to be measured and evaluated. Based on IE Bulletin 85-03 testing, calculations indicate that MS106 would have fully closed against a maximum 468 psid pressure and MS106A would have fully closed against a maximum 901 psid pressure. These pressures are below the design differential pressure of 1100 psig. A mechanical device has been developed to measure and adjust torque switch balance without having to use thrust measuring test equipment, and has been demonstrated by testing these type of switches.

8702110083 870203 PDR ADOCK 05000346 S PDR THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENL'E TOLEDO. OHIO 43652

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a- Docket No. 50-346 License No. NPF-3 Serial No. 1-706 Page 2 Limitorque was informed by phone by Toledo Edison of this problem on January 27, 1987.

Prior to implementation of the Motor Operated Valve Reliability Improve-ment Testing Program, Davis-Besse had several unexplained torque switch tripping problems which were solved by replacing the torque switch.

These could likely have been the result of unbalanced torque switches.

Toledo Edison's Motor Operated Valve Reliability Improvement Program confirmed proper operation of all torque switches prior to the restart following the June 9, 1985, shutdown.

Very truly yours,

-: ( / _

PC:DJS:plf cc: DB-1 NRC Resident Inspector J. G. Keppler, Regional Administrator (2 copies)

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III. BASIC PRINCIPLE OF OPERATION Balance is determined by the relative position of the torque switch tripper arms. t L. Switch Assembly \ _

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Motor Train h Splined Shaft Oy '

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