ML20084K046

AO 50-237/1974-53:on 741021,insp of Berger-Paterson Shock Suppressors Revealed Four Snubbers Low on Oil & Two Inoperable.Probably Caused by Seal Deterioration.Snubbers Will Be Replaced

ML20084K046
Person / Time
Site:	Dresden
Issue date:	10/31/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
NUDOCS 8305190130
Download: ML20084K046 (3)

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Adctress Reply to: Pos: Office Box 767 Chicago lilinois 60690 BBS Ltr.#790-74 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 October 31, 1974 Mr. James G. Keppler, Regional Director Directorate of Regulatory Operations-Region III U. S. Atomic Energy Co::aission 799 Roosevelt Road Glen Ellyn, Illinois 60137

SUBJECT:

REPORT OF AE!OFlGL OCCURRENCE PER SECTION 6.6.B 0F THE TECS1ICAL SPECIFICATICUS.

INSFECTION OF EERG M-PATERSON SHOCK SUPPP.ESSORS.

References:

1) Regulatory Guide 1.16 Rev.1 Appendix A

2) Notification of Region III of AEC Regulatory Operations Telephone: Mr. P. Johnson, 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> on October 22, 1974 Telegram: Mr. J. Keppler, 1615 hours0.0187 days <br />0.449 hours <br />0.00267 weeks <br />6.145075e-4 months <br /> on October 22, 1974 Report Number: 50-237/1974-53 .

Report; Date: October 31, 1974 7, ' ~ " l N '\ ,

hl Occurrence Date: October 21, 1974 l

Facility: Dresden Nuclear Power Station, Morris, Illinois Jlk .~ b.'l gr y jR IDENTIFICATION OF OCCURRENCE .

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On October 21, 1974, an inspection was made of the thirty-one (31) anubbers contained in the drywell. The inspection of the Bergen Paterson shock suppressors revealed that four (4) of the snubbers were low on oil with two (2) of then being considered inoperable.

Following is a list of the findings on the failed and low level drywell snubbers giving the actual piston extension, fluid level indicated position and seal material contained within Failed & Low Level Snubbers As Found Condition

, Snubber _ Actual Piston Fluid Level . >

_I.D. No. Rod Extension Indicated Position Seal Material 5 3 25" 5.75 (low) PU 6 3.00" 4.0 (low) LP 15 4.25" 6" (failed) ~ PU 17 4.0 6." (failed) PU E-P - Ethyleno Propylene Scal 'atcrial PU - Polyurethane ScallMaterial Ljd" p 0305190130 741031 .s.138.J .

PDR ADOCK 05000237 3, . s PDR COPY SENT REGION- >

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Mr. Jam a G. K'; er '

October 31, 1974 DESIGNATION OF APPARENT CAUSE OF CCCURRENCE (Equipment Failure)

The mode of leakage of oil from snubber E5 is unknown at this time but with the polyurethane scal material, it is probable that the seals are deteriorating.

In reviewing the low oil level of snubber #6, it appears that when it was rebuilt in into September with othylene propylene and reinstalled, the as left oil level was close to what Dresden considers as a low oil level. This low oil level is determined by comparing the piston extension to the accumu-lator indicator measurement. When the accumulator measurement is one (1) inch greater than what is measured on the piston extension, then this is considered a low oil level condition. Uith this condition, however, therc is sufficient oil to provide the design loading for this snubber.

With regard to the two snubbers #15 and 17, these contained the polyurethane seal material. The snubbers were subsequently disassembled and the seal material was found to be dried, cracked and flattened out. The mode of failure is attributed directly to this seal deterioration. Tha seals in these two snubbers have been in service for almost a year's time with no s16nificant oil leakage until now.

ANAIXSIS OP OCCURRENCE O L In evaluating the safety implication of the inoperable snubber conditions, the health and safety of the public was not in jermardy. Had a pipe ruptu"e occurred as a result of an earthquake, the cmergency core cooling systems and primary containment were availabic to provide adequate core cooling and subsequently containment within the d o ell.

CORRECTIVE ACTION C The initial corrective action was to refill snubber numbers 5 and 6 and replace numbers 15 and 17 with snubbers containing othylene propylene seal material. .

In addition, all snubbers containing the polyurethane seal material and other snubbers that exhibited oil leakage subsequent to their installation will be replaced with new design snubbers or rebuilt snubbers containing the ethylene propylene seal material.

These snubbers will be replaced during the upcoming refueling outage scheduled for November 8, 1974.

Following is the results of the as left condition of the failed and low level drywell snubbers:

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• O l Mr. James 0. Keppler ->- October 31, 1974

- Snubber Actual Piston Fluid Level I,D. No. Rod Extension Indicated Position Seal Material 5 3 75" 3 0" PU 6 3 75" 3 0" E-P 15 3 5" 3 0" . E-P 17 4.75" 4.5" E-P FAILURE DATA Prior to June 1974, all snubber failures were related to the usage of the polyurethane scal material. In June 1974, a snubber inspection was conducted on the drywell snubbers and revealed that eight (8) snubbers were considered inoperable. Six (6) of the ci6ht (8) failed snubbers contained all ethylene propylene seals with the remaining two containing the polyurothane seal material. The mode of failure of the othyleno propylene snubbers could not be determined at that timo. However, on Auaust 24, 1974, three snubbers were removed due to notable oil leaka6e. Upon the disassembly, it was found that the accumulator piston seal cup of one snubber was installed in reverse

~ which provided a leakage path. In another, it was found that an O' ring in the shaft seal was partially removed from the seal consequently prc1Sicing another leakage path. However, in the third snubber, it was found that the C,' shaft seal had axial scratches which were providing another leakage path.

These scratches appeared to be produced by the stpel filings in the snubber oil which was a result of sovere binding between die main piston head and cylinder. This binding and constant vibration removed metal from both the cylinder and the head and deposited ir;the snubber oil.

Sincerely, y,. ,

C .

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/ l .,'Stephenson D/ ft!Vf P G.

Superintendent BBS:RIN:do S

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