ML20090E482

AO 50-237/75-46:on 750929,reactor Scrammed on High Drywell Pressure During Drywell Inerting Process.Caused by Operator Valving Error,Allowing Nitrogen Flow to Bypass Inerting Pressure Control Valve Into Drywell.Operators Cautioned

ML20090E482
Person / Time
Site:	Dresden
Issue date:	10/09/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
11937, 673-75, AO-50-237-75-46, NUDOCS 8303310700
Download: ML20090E482 (2)

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Com ealth Edison V e

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L/ AddGss R;' ply t;: Post Office Box 767 Chicago, Ill i nois 60690

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P2S Ltr. #673-75 Dresden Nuclear Power Station T J,,,'x R. R #1 ,

Morris, Illinois 60450 October 9, 1975

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Mr. James G. Keppler, Regional Director -

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Directorate of Regulator / Operatien-Region TII \ '- Q. , ,:;y+< '< j,

- 'i U. S.1:uclear Ra,c.nlatory Cc=icsion V ,

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SUBJE,T: RZTORT CF 5:'CR'GL OCCURRENC2 PER SECTION 6.6.A 0F TRE TECENICAL SPECIFICI. TICS U'1IT-2 R:.I.CTCn SCRAM CN LRY'<?ILL OVER-PRESSURI7lTICN Referencoc: 1) Regulatory Guide 1.16 Rev. 1 1.ppendix A

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2) Notification of Regien III of U. S. Nuc1 car Regulatory Co=issien Telephone: P. Johnson, 1150 hours0.0133 days <br />0.319 hours <br />0.0019 weeks <br />4.37575e-4 months <br /> on September 29, 1975 Telegrem: J. Keppler, 1310 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.98455e-4 months <br /> on September 29, 1975

3) Drawing Number M-25 Report Number: 5c-237/75-46 Report Date: October 9, 1975 -

Occurrence Date: September 29, 1975 Facility: Dresden Nucicar' Power Station, Morric, Illinois

• IDE::"'IFICATION CF CCCUF2E!CE The Unit-2 rcactor scra =ed on high drywell pressure during the drywell inerting process.

CONDITICNS FRICR TO CCCt'RRE:!CE Unit-2 was in the run mode at a power level of 1055 Et and 303 We.

DESCRIPI'ICN OF OCCURRFl!CE During the process of inerting the primary contairment atmosphere, the pressure in the containment reached the high drywell precsure scram setpoint, and the reactor scra m ed at 0524 hours0.00606 days <br />0.146 hours <br />8.664021e-4 weeks <br />1.99382e-4 months <br /> en September 29, 1975 83033'10700 75iOO9 -

PDR ADOCK 05000237 COPY SENT REGION 'llf#~, -

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U) g y ff. 9a*m:s G. Yapplsr Octob:r 9, 1975 DESIGNATION OF APPAREyf CAUSE OF OCCURRENCE (Operator Eiror)

.The drywell over-pressurization apparently resulted from a valving error which.

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occurred during clearing of the previous weekend outage. Manual valve 8502-501

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was partially opened, allowing nitrogen flow to bypass the inerting pressure control valve and pass directly into the drywell.

ANALYSIS OF OCCURRH:CE This occurrence did not threaten the safety of plant personnel or the general public. Upen sensing hich drywell prcncurc, the unit scra=ed satisfactorily, with all Enercency Core Cooling Systc= (IICS) equipment functioning as required. .

CORRECTIVE ACTIC'! .

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After receiving the high drywell pressure alarm, the NSO immediately verified the inerting pressure centrol valve ,to be closed. A chift foreman and operator were dispatched to the torus area to check valving and found manual bypass 8502-501 to be partially open. The valve was imediately closed. -

A sample of the drywell atmosphere was obtained for analysis. No unusual activity was noted, and the drywell was vented to the Standby Gas Treatment System.

All E=crgency Core Cooling syste s were returned.to the normal modo, with the exception of liPCI which failed to trip (see report no. $0-237/75-45).

A task force was asse= bled to study the problem and take corrective action.

The follcwing corrective actions were completed:

1) A lock and chain were installed to lock the manual-bypass valve in the closed position.

2) Procedures were revised to clarify valve checklists; the valve checklist was revised to include locking manual bypass valve.

3) To avoid operator confusion, correct vslve tago-ins was verified to correspond to valve checklist.

4) 4localleak-ratetestwasperformedonthevo5umeboundedbyvalves A0-2-1601-21, -22, -55, -56, and manual bypass 2-8502-501, with satisfactory results.

Operators were cautioned to verify proper valve numbers when taking valves out of service as well as when clearing outages. A-locked-valve checklist for Unit-2 is being prepared to ensure that errors of this nature do not recur.

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/ B.Superintendent B. Stephenson ,

DES:JSK:smp File /NRC u