ML19340E368

From kanterella
Jump to navigation Jump to search
Responds to IE Bulletin 80-19 Re Failures of Mercury Wetted Matrix Relays.Tabulated History of Matrix Relay Failures Encl.Requests Exemption from Requirement Ordering Replacement of Relays
ML19340E368
Person / Time
Site: Fort Calhoun Omaha Public Power District icon.png
Issue date: 10/21/1980
From: William Jones
OMAHA PUBLIC POWER DISTRICT
To: Seyfrit K
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
IEB-80-19, TAC-42508, NUDOCS 8101140182
Download: ML19340E368 (3)


Text

e .

CENTRAL FILES

' r4.

PDR:HQ

,LPDR

, NSIC Omaha Public Power District STATE 1623 HARNEY CMAMA. NESRASKA 68102 TELEPHONE 536 4000 AREA CODE 402 October 21, 1980 m

E s:

=e 1.n Mr. K. V. Seyfrit', Director g" _ b g

U. S. Nuclear Regulatory Commission 'j C Office of Inspection and Enforcement 5 .. . , %g Region IV M r

611 Ryan Plaza Drive C Suite 1000 Arlington, Texas 76011

Reference:

Docket No. 50-285

Dear Mr. Seyfrit:

Omaha Public Power District received IE Bulletin 80-19, dated July 31, 1980, regarding failures of RPS mercury wetted matrix relays.

The District has completed its evaluation of the matrix relay failures at Fort Calhoun, in response to Item 3 of the bulletin. Attached is a tabulated history, to date, of tge relay failures and a calculation of the failure frequency, 4.3 x 10- failures per hour. Based on this and a number of similar failures at the other CE NSSS stations, as reported in CE Availability Data Program Information Report on Mercury Wetted Matrix Relays, the District inte-ds to replace all mercury wetted re-lays. The relays which will replace the existing ones will be a dry contact type design with the addition of an interposing relay for cur-rent capacity to pick up the clutch power supply contactors. This design should increase the reliability of the reactor protection system.

The relays will be purchased in the near future, and it is anticipated that, after receipt, they will be installed during the next refueling outage or sooner, should plant conditions permit.

The District requests exception to the requirement of Item 2 of the bulletin to replace failed mercury wetted relays with new relays. New mercury wetted relays are no longer available from the manufacturer; therefore, the supply is limited. The dry contacts cannot be used without the interposing relay for current capacity to the clutch con-tactors, as discussed above. The District's experience with the mercury wetted relays has shown that the apparent relay failure mode has been a buildup of mercury across the contacts. This buildup has always been cleared in the past by tapping the relay. Accordingly, the District proposes as an interim measure, upon " failure" the relays will be re-paired by tapping and demonstration of operability. If this does not clear the problem, the relay will then be replaced. In addition, the District has increasec relay testing frequency as required by the bulletin.

l

@10114 0 \gs l

Q

r Mr. K. V. Seyfrit October 21, 1980 Page Two As further justification, the reactor protective system provides a multiple trip path scheme which exceeds single failure criteria.

Therefore, the District believes the proposed measures will assure continued safe operation of the plant.

Sincerely,

, ,~~' .

.s 1-W. C. Jones Division Manager Production Operations WCJ/KJM/TLP:jmm Attachment pc: Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission Washington, D. C. 20555 LeBoeuf, Lamb, Leiby & MacRae 1333 New Hampshire Avenue, N. W.

Washington, D. C. 20036

RELAY FAILURE 5 Matrix Failures Annunciation Failures 4/6/79 9/4/80 5/7/79 9/25/80 5/15/80 Hours of Operation approximately through 10/1/80 46,144 + 100(24) = 48,544 hours0.0063 days <br />0.151 hours <br />8.994709e-4 weeks <br />2.06992e-4 months <br /> Failures per relay hour (24 total relays installed)

~

1/48,544 x 24-/ 5 = 4.3 x 10-6 Failure Rate Estimate 10-8 to 10-6 " Wash 1400" for relays

-i

.