ML20084D053

AO 50-237/75-40:on 750611,five Arrays Exhibited 5% Scram Times Exceeding Tech Specs Limits During 2x2 Array Test. Caused by High Regulated Pressure in Scram Valve Air Header. Regulator Reset to Correct Pressure

ML20084D053
Person / Time
Site:	Dresden
Issue date:	06/20/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
380-75, 8884, AO-50-237-75-40, NUDOCS 8304080458
Download: ML20084D053 (5)

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4 il BBS Ltr. #380-75 Dresden Nuclear Power Station R. R. #1 11 orris, Illinois 60450 June 20, 1975 Mr. James G. Keppler, Regional Director Directorate of Regulatory Operation-Region III ,

U. S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137 5UBJECT: REPO:tT OF ABNOPJt\L OCCURRENCE PER SECTION 6.6. A 0F THE TECFNICAL SPECIFICATIONS 25 ROD SC?J01 TEST

References:

1) Regulatory Guide 1.16 Rev.1 Appendix A

2) Notification of Region III of 1[. S. Nuclear Regulatory Co:=ission Telephone: Mr. Knopf, 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on June 12, 1975 Telegram: Mr. Koppler, 1245 hours0.0144 days <br />0.346 hours <br />0.00206 weeks <br />4.737225e-4 months <br /> on June 13, 1975 Report Number: 50-237/75-40 Report Date: June 20, 1975 Occurrence Date: June 11, 1975 Pccility: Dresden Nuclear Power Station, Morris, Illinois IDENTIFICATION OF OCCt"tRENCE On June 11, 1975 at 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br />,schile performing 2 x 2 array tests following a scheduled 25 rod scram test, five arrays exhibited 57. scram times exceeding the Technical Specification limits in Section 3.3.C.1.

CONDITIONS PRIOR TO OCCURRENCE Unit-2 was operating at a power level of 1333 }r.!t and 355 }r.ic.

DESCRIPTION OF OCCURRENCE The 2 x 2 array scram tests were being performed to determine the cause of long 57. scram times on four control rod drives (H-7, G-10, K-7, F-13) which occurred during the 25 rod scram tests. Five 2 x 2 arrays showed excessive

57. scram times.

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Mr. James G. Keppler Juna 20, 1975 O s (

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DESIGNATION OF APPAREt.T CAUSE OF OCCURREt:CE (Operator Error)

The cauce of the slow 57. scram times was determined to be a high regulated pressure in the scram valve air header of approximately 88 psig. Normal scram valve air header pressure should be approximately 75 psig.

The tuo regulators which supply air to the header were found to be out of adjustment. This maladjustment caused oscillations of the header pressure as incoming instrument air pressure equalized, accounting for the inconsistent data. The high/ low scram header pressure switch was improperly calibrated; consequently, the operating personnel vere not alerted to an abnormal pressure condition. The higher pressure in the header increased the opening time of the scram air valves.

ANA1.YSIS OF OCCURRENCE Althpugh the above mentioned drives could not meet the 5% scram times, all other times were within the Technical Specification limits. In addition, upon sub-sequent retesting, all the drives ucre within the Technical Specification limits for 5" times.

Given these circumstances , it was concluded that the reactor uns operating safely uith sufficient scram time capability to shut down in case of a tran-sient. The safety and health of plant personnel.and the public were in no uay jeopardized by this occurrence.

CO.1RECTIVE ACTION Initial action was to rctest the four drives which exhibited slow 5% timec.

This rctest yicided timcs within the Tcchnical Spccificatica limits (sec en-closed data sheet). To determine the reason for the slo.; initirl tinsn, c.

test 3 as rua to measure the tira fror drop out of the scram air pilet valve to the novemaat of the scram valves theuselves. The tes t' v,s des igned to e hr..

deterioration of diaphra;;ms on the scrcn pilot air v.:1ves t.hich ceuld cause e slow initial bleed off of air pressure and a conscquent loa.; ecrem tit.e f or M.

travel.

This test indicated times well within the specificatica of 270 millisccands.

Further scram tests were performed on 2 x 2 arrays surrounding the feur sly.

drives. These times ucre also slou (see attached sheet). This problem wr.s finally traced to high pressure in the scran valve air header. The scram valve air header regulators were reset to the correct pressure of 75 psig.

' lith the header pressure corrected, all four drives performed oatisfactorily.

The scram valve air header pressure suitch uns also recalibra ted, with provi-sions for more frequent calibrations in the future. A procedural change has been initiated, requiring scram testing personnel to verify proper header pressure before testing. These corrective actions will be performed by July 15, 1975.

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Mr. James G. Keppler ,,. June 20, 1975 e

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F/.II.T.'R!: DATA Unit-3 control rod drives exhibited slow 5'/. and 207. times on March 2,1975 (Report 1;o. 75-13). This deficiency was attributed to worn seals.

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C0" TROL ROD DRIVE SCRAM TEST DATA SHEET

57. 107, 207. 507. 907, 1007.

25 Rod Scran Test 6-10-75 Average Times .3S .54 .00 1.65 2.82 3. l; 2 25 Rod Scram Test 6-10-75 Average Times After Retest of K-7, F-13, H-7,'G-10 .357 .51 .77 1.61 2.79 3.39 Retest of Six Drives (K-7) .31 .45 .71 1.55 2.70 3.29 After Scrna Valve Air (F-13) .33 .48 .76 1.65 2.06 3.47

!!ccder Pressurc /.djust- (H-7) .33 .43 .75 1.62 2.80 3.47 ment (G-10) .34 .47 . .72 1.52 2.58 3.13 (H-9) .33 .48 .75 1.59 2.77 3,40 (G-8) .32 .45 .70 1.53 2.59 3.19 Technieni Specification Limits .375 ---

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