ML20085B288

Ao:On 720829 & 30,during Trip Testing Four Control Rods Failed to Drop.Caused by Degradation of Lubrication on Spline Surfaces.Temporary Test Program & Relubrication Procedure Initiated

ML20085B288
Person / Time
Site:	Palisades
Issue date:	09/08/1972
From:	Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085B259	List: ML20085B254 ML20085B263 ML20085B278 ML20085B288
References
NUDOCS 8307080078
Download: ML20085B288 (3)

Text

r -

r

% A ff. V N ud (/d. _s j SEPf f fg7

~

,[^ ', ConSumBIS

i. H Power i-s_ c'

%.w Company a v d General Offices: 212 West Mechigan Avenue, Jacu t,on, Michigan 49201. Area Code 517 788-0550 September 8,1972 Mr. John F. O' Leary, Director Re: Docket No 50-255 Directorate of Licensing License DPR-20 United States Atomic Energy Commission Washington, DC 20545

Dear Mr. O' Leary:

Late in the evening of August 29 and the morning of August 30, 1972, four control rods (No 8, No 20, No 33 and No 37) failed to drop during routine control rod drive mechanism (CRDM) trip testing. This trip testing was being conducted prior to returning the Palisades Plant to ser-vice following a scheduled four-day outage. Three (No 8, No 33 and No 37) of the four CRDM motor packages (includes the clutch mechanism) were subsequently replaced with spare units and an extensive test program was conducted on the fourth (No 20) to deteemine the cause of the failure.

The clutch mechanism of one of the removed motor packages was disassembled and inspected. This inspection revealed nothing that would cause the clutch halves to fail to separate, although some personnel felt that there might be a slight wear pattern in the baked on lubri-cant on the clutch spline. The other two motor packages were not dis-assembled prior to shipment to the NSSS vendor for further detailed examination and testing.

Further detailed trip testing was conducted on the No 20 CRDM motor package. Trips were initiated from varying elevations. Trip time traces were obtained. The clutch was visually verified to be en-gaged when it was de-energized. It was verified, based on this testing, that the cause of the failure to trip was due to the clutch halves 7

failing to separate.

hll It appeared that these malfunctions were similar to that g experienced with CRIN No 5 on June 2,1972 and reported by our letter dated June 12, 1972. This clutch assembly was inspected and tested in M detail by the NSSS vendor with no conclusive results obtained. It was ~

trip tested over 150 times and the failure could not be repeated. The p inspection revealed a slight brass coloring of the lubricated spline J surface, possibly due to ratcheting of the clutch halves, but the con-

M l dition of the lubricant appeared to be favorable.

sVkd 8307080078 721220 gDRADOCK 05000255 PDR I I o '1 IlI COPY SENT REGIU

r O

Mr. John F. O' Leary, Director O 2 Re: Docket No 50-255 License DPR-20 September 8, 1972 Review of the clutch design yielded two possible failure mech-anisms. One was associated with removal of the shim which maintained a 15 mil gap between the clutch halves. Thfs shim had been removed during 1971 to correct a rod dropping occurrence experienced during Ithe zero power physics tests. The second was the possibility of a lubrication breakdown on the clutch spline.

L The No 20 motor package was removed, the shim installed and the motor package reinstalled. Trip testing was resumed. The No 20 clutch mechanism was trip tested 63 times. The CRDM failed to trip nine times.

The No 20 motor package was again removed and the clutch spline was lubricated with a dry molybdenum disulfide powder lubricant.

This is the same type of lubrication that is baked on the spline by the NSSS vendor. The motor package was reinstalled and trip tested 60 more times. The trip traces revealed all trip times to be normal. The motor package was again removed and the shim was removed from the clutch mechanism. The motor package was reinstalled and trip tested another 25 times. Again, the trip traces revealed all trip times to be normal.

Based on the above described testing, it was concluded that I

failures to trip of the four CRDMs were caused by degradation of the

-), '

lubrication on the spline surfaces. The Palisades Safety Audit and Review Board concluded that a high degree of reliability could be as-cribed to the CRIES and the plant be returned to service if:

1. A lubrication procedure was developed and all clutch splines were relubricated in an identical manner.

2. The motor package that was originally installed on CRDM No 20 be relubricated and reinstalled in a position in which the effect of its being routinely tripped would minimize power perturbations.

3 All CRDMs be trip tested prior to the initial return of the plant to service.

h. The CRDM on which the No 20 motor package was installed be trip tested daily during plant operation.

5 All other CRDMs be trip tested weekly during plant opera-tion.

This solution and testing program was considered temporary.

It will remain in effect until a modification can be developed and tested for the clutch mechanism which embodies a more positive means of separating the clutch halves. At this time several possible modi-fications are being evaluated by the NSSS vendor and the tentative schedule for completion of this evaluation, testing and installation at the plant is approximately two months.

b

., I Mr.JohnF.O'Le9, Director O 3 l

Re: Docket No 50-255 l License DPR-20 '!

September 8, 1972 l The plant was returned to service under the conditions pre-scribed above by the Safety Audit and Review Board on Sunday, September 3, 1972. All trip testing performed since this return to service has been nomal.

We will keep your representatives informed as to the progress with respect to proposed modifications. These modifications will be reviewed prior to installation at the plant and reported in accordance with the provisions 10 CFR 50 59 and the Technical Specifications.

Yours very truly, Ralph B. Sewell (Signed)

RBS/sm Ralph B. Sewell Nuclear Licensing CC: BHGrier Administrator IJSAEC i

I j

- . _ . -. . . . . - . - . . . - -- .- -..- . _.. - - - .- - .- - ... - . -.