ML20095B638

Final Deficiency Rept,Item 75 Re Calibr Problems W/Rosemount Trip Units.Initially Reported on 820720.Trip Unit Potentiometers Made W/Silver Contacts Replaced,Recalibr & Installed

ML20095B638
Person / Time
Site:	Fermi
Issue date:	08/09/1984
From:	Jens W DETROIT EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
75, EF2-69664, NUDOCS 8408220193
Download: ML20095B638 (2)

Text

- -

.[*

l Wayne M. Jens Vice Presideo' z Nuclear Operations if Ferms2 6400 Nc4th Dee Highway

. Newport, %chigan 48166 August 9, 1984 (313) 586-41 9 EF2-69664 Mr. James G. Keppler

. Regional Administrator Region III:

U. S. Nuclear Regulatory Commission 799 Roosevelt Road

. Glen Ellyn, Illinois 60137

Dear Mr. Keppler:

Re ference : - (1) Fermi 2 NRC Docket No. 50-341 (2) Letter, D. A. Wells to J. G. Keppler, August 18, 1982, EF2-59386 (3) Letter, D. A. Wells to J. G. Keppis ,

April 15, 1983, EF2-62625

Subject:

Final Report of 10CFR50.55(e) Item 7 5 "Rosemount Trip Units" This is Detroit Edison's-final report concerning calibration problems associated with Rosemount, model 510. DU , . trip units. This item was originally reported as a potential deficiency on July -2 0,1982. Additional information was provided11n References (2) and (3).

Description-of Deficiency During calibration of Rosemount model 510 DU trip units, a high percentage of the units exhibited erratic operation and could not be calibrated. Subsequent investigation concluded that this erratic operation was caused by oxidation of the silver plated contacts'of the trip setpoint potentiometer.

Analysis of Safety Implications The-Rosemount trip units are used for the Emergency Core Cooling Systems and the' Reactor Protection System Limiting Safety System Settings. Erratic operation of these units could have adversely affected the function of these systems.

DOC O!oohh{3

. POR '

f 0 t _J

u

, A" Mr . J ame s G . Keppler

' August 9, .198 4 EF2-69664 Page'2 Corrective Action-

~ The following actions have been completed to correct the problems and prevent recurrence:

o. All Rosemount trip unit potentiometers, manufactured with silver contacts, have been replaced. The replacement potentiometers are of similar type

~

(supplied by Bourns Inc.)1eith gold plated contacts.

Gold plated contacts are not susceptible to oxidation.

o- The trip units have been recalibrated-and subsequent preoperational testing of this instrumentation is presently in progress. No additional problems have

-been encountered to date.

o The trip unit cabinets are installed in their permanent plant location and will be under an established calibration surveillance program in accordance with-Technical Specifications, upon completion of pre-operational testing.

This item is considered an isolated incident because of the unique combination of contributive causes of construction environment and the selection of silver for contact plating.

This is Detroit Edison's final report on this item. If you-5 have questions concerning this matter, please contact Mr. Lewis P. Bregni, (313) 586-5083.

Sincerely, cc: Mr. P. M. Byron

[,

Mr. R. C. DeYoung Mr. R. C. Knop t

, w ,ve- ,, ,-- -- -,,e,,- en e- n- ---r , ~ - , - -,-,,a > e -