ML20084R488

AO 50-249/75-16:on 750316,during Control Rod Drive Scram Testing Surveillance,Control Rod Drive Scram Times Failed to Meet Limiting Condition for Operation Per Tech Specs.Caused by Deterioration of Drive Seals.Control Rod Drive Retested

ML20084R488
Person / Time
Site:	Dresden
Issue date:	03/27/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084R493	List: ML20084R488 ML20084R498
References
196-75, AO-50-249-75-16, RO-50-249-75-16, NUDOCS 8306150138
Download: ML20084R488 (3)

Text

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((' 3 Onel abonal Plaza, Ch cago. Iltnois Address Hoply to: Post Office Box 767 Nj,.

%r Cnicago, litinois 60690 BBS Ltr. #196-75 Dresden Nuclear Power Station R. R. #1 g ,'

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Morris, Illinois 60450 k, N'3' March 27, 1975 .

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s s ., _,.! q L [U,,93 ,l 'N' . !.i j Hr. James G. Koppler, Regional Director > 5  !

Directorate of Regulatorf Operationn-Region III Y U. S. Nuclear Regulatory Co: mission ,Qf^

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799 Roosevelt Road Olen Ellyn, Illinoin 60137 N' {.;

SUBJECT:

REPORT OF AE'!OP2!AL OCCURREEE PER SECTION 6.6.A 0F THE TECHNICAL SPECIFICATIC'I UNIT 3 EXCESSIVE CCNTROL RCD SCRAM TD'ES

References:

1. Regulatory Guide 1.16 Rev. 1 Appendix A

2. Notification of Region III of U. S. Nuclear Regulatory Co::rniscion Telephono: Mr. P. Johnson, 1455 hours0.0168 days <br />0.404 hours <br />0.00241 weeks <br />5.536275e-4 months <br /> on March 17, 1975 Telegram Mr. J. G. Keppler, 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br /> on March 17, 1975 Report Nuinber: 50-249/1975-16 Report Dato March 27, 1975 Occurrence Datos March 16, 1975 Fao111ty: Dresden Nuclear Power Station, Morris, Illinoie. 60450 IDE!TIFICATION OP OCCURRE!CE Unit 3 control rod drive ceram times failed to moet a limiting conditicr. for oporation as defined in section 3 3.C.1 of the Technical Specification.

CONDITIONS PRIOR TO OCCURRE!CE Prior to the occurrence, the unit was operating at 1285 megawatts thermal with the unit in the "Run" mode. Electrical load was at a ctoady state condition o a: of 250 megawatts electric.

Neo c8 DESCRIPTION OF OCCURRD!CE COPY 3ENr REGION >

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-o On March 16, 1975 the two week 25 control rod drivo scram testing survoillance was in progress. Upon completion of tecting it tin dotermined that drive ~J9

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had execeded tho 25 drive averaco for t,ho 90fo insertion timo by greater thany' .2.

p 0 75 seco. The *icht drives around J-9 were then scram tested.\0f thcoe c o:

eso eiSht drivos, J-8 and K-10 had a 903 insertion time which exceededsthe limit f[ I

-can.tn of 0 7) seca greater than tho average of the 25 control rods. It wasx then ~

nococaary to ceram tuo more driven to complete the eight driven around 3437

Mr. James G. K;ppler March 47 75 J-8, and four more drives to complete the eight drives around K-10.

Drive K-8 was not tested at this time since it was previously declared to be inoperable and was inserted to position "00". Drive J-9 at this time was also -

declared to be inoperable, but because it was at position "48" it was decided to test it and apply all limiting conditions to the results. To insure that 25 operable drives were tested, drive J-9 was replaced by drive P-10 to calculate the average insertion times.

The results of the scram test showed that the limits for the average scram insertion times for the three fastest drives of all groups of four control rods in a two by two array could not be met. Two by two arrays around drive J-8 failed the 5%, 20%, and 50% scram limits, around drives H 8 and K-10

! failed the 5% and 20% limit, and around drives I,-9, L-11 and J-11 failed the 1 5% scram limit. A total of eight drives, with the addition of J-9 and K-8, resulted in the long two by two array scram times.

DESIGNATION OF APPMIET2 CAUSE OF OCCURRENCE (Equipnent Failure) l The cause of the failures appears to be due to deterioration of the drive seals. The deterioration of the drive seals has been noted in the past and is being closely monitored. Additionally, the scram pilot solenoid valves were replaced on drive J-9 after recorder traces revealed clou opiata travel of the scram valves. When an inspection was made, it was found that the pilot valve "O" rings were hardened which possibly prevented proper valve operation.

None of the other drives exhibited this problem.

ANALYSIS OF OCCURRD3CE The safety of the plant and public was not in jeopardy during the period of slow scram insertion times. If a-scram had occurred all control rods would have fully inserted. Slow scram times, below 905 insertion, will have a neglibile effect on transients since the unit was operating at less than 50%

power significantly below the limiting scram reactivity curve. In addition, following the discovery of slow scram times, a retest of the drives was performed. During the second scram test of the drives on March 16, 1975

( all of the drives improved such that all Technical Specification limits were met.

CORRECTIVE ACTION The innediate corrective action taken was to retest the same 39 control rod drives. During the retest all drives improved and all technical specification limits were met.

The drive J-9 acram pilot solenoid valves were replaced and its precharge pressure increased to the e h allowed by procedure. When drive J-9 was scram tested on March 21, 1975 its scram time was well within Technical l

Specification limits. To determine if increased precharge pressure decreased the scram insertion time, drives K-10, J-8, H-8, L-9, L-11, J-11, and K-8.

were tested on March 23 and 24, 1975 at 400 W e. The results of the scram test e

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}- March 27, 1975 revealed that all drives were still within technical specification limits with a negligible improvement in the initial scram insertion times.

To incure that the control rod drives remain within Technicals pecification limits the eight slow drives will be scram tosted once each week until the unit outage scheduled for April 1975

_PAILURE DATA The control rod drives have experienced tuo types of problems in the past.

1) Uncoupling at position 48, caused by the innor filter and 2) seal wear, causing slow scram times. The most recent exccasive scram times were reported to the 11RC, Region III, by letter dated Parch 12, 1975 The reporting of this abnomal occurrence was extended, per station request to the Region III offico en March 25, 1975, to include additional infomation on the inspection of drive J-9 pilot valves. The results of that inspection ,

are included in this report. I g LB. B. Stephenson

't Superintendent

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