05000331/LER-1981-020-01, /01T-0:on 810527,primary Containment Integrity Breached When Inner & Outer Airlock Doors Were Open Simultaneously While H/P Technician Exited Drywell.Cause Unknown

/01T-0:on 810527,primary Containment Integrity Breached When Inner & Outer Airlock Doors Were Open Simultaneously While H/P Technician Exited Drywell.Cause Unknown

ML20004F148
Person / Time
Site:	Duane Arnold
Issue date:	06/10/1981
From:	Rager M IES UTILITIES INC., (FORMERLY IOWA ELECTRIC LIGHT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20004F145	List: 05000331/LER-1981-020, Forwards LER 81-020/01T-0 05000331/LER-1981-020-01, /01T-0:on 810527,primary Containment Integrity Breached When Inner & Outer Airlock Doors Were Open Simultaneously While H/P Technician Exited Drywell.Cause Unknown
References
LER-81-020-01T, LER-81-20-1T, NUDOCS 8106160559
Download: ML20004F148 (3)

LER-1981-020, /01T-0:on 810527,primary Containment Integrity Breached When Inner & Outer Airlock Doors Were Open Simultaneously While H/P Technician Exited Drywell.Cause Unknown

Event date:
Report date:
3311981020R01 - NRC Website

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DUANE AidCLD ENERGY CENTER Iowa Electric Light and Power Company Licensee Event Report - Supplemental Data Docket No. 050-0331 Licensee Event Report Date: June 10, 1981 81-20 Reportable Occurrence No:

Event Description

During reactor startup on May 27, 1981 following a refueling outage, ~ primary containment integrity was breached when both the inner and outer airlock doors were momentarily open simultaneously. A Health Physics Technician had entered the drywell to start an air sampler. Upon exiting the drywell the technician closed the inner door completely with the handwheel and " bumped" the handwheel to verify closure. The handwheel pointer also indicated closed.

He then opened the outer door and stepped out of the airlock. The interlock mechanism for the outer door, which was subsequently found to operate properly, would have prevented the opening of' the outer door if the inner door had not been closed. As he was closing the outer door, the inner door opened for unknown reasons. The inner door's interlock mechanism should have prevented any movement of the inner door's locking mechanism once the outer door had been opened. The interlock mechanism for the inner door was found

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inoperable during subsequent investigations. Air had begun to rush into the airlock as the inner door opened. This air movement was caused by the slightly negative pressure maintained in the drywell. The H.P. Technician immediately closed the

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outer door and then cycled the inner door's handwheel back to the closed position.

The drywell was subsequently entered by a maintenance supervisor to inspect the inner door's locking mechanism. The, inner door latching mechanism, which was in the closed position, was holding the door open approximately 3 inches.

No problems were found with the inner door's locking mechanism aside from the interlock mechanism problem. The inner door was shut and airlock exited without further problems.

Subsequently an H.P. Technician again entered the drywell to retrieve the air sampler and he experienced no problems with the airlock. Operations _ personnel chained and locked the handwheels on the outside of the airlock to ensure primary containment integrity was maintained.

Technical Specification 3.7.A.2 requires primary containment integrity be maintained whenever the reactor is critical or when coolant temperature exceeds 212 degrees F.

No releases to the environment occurred as a result of this event. No previous similar occurrences have been reported.

Cause Description An examination of the inner door's locking mechanism by maintenance personnel could detennine no definitive cause for the failure of the inner door to stay closed.

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DUANE ARNOLD ENERGY CENTE't Iowa Electric Light and Power Ccmpany Licensee Event Report - Supplemental Data Docket No. 050-0331 Licensee Event Report Date:

June 10, 1981 Reportable Occurrence No:

81-20 (Continued)

However, the inner door's interlock mechanism which should have prevented the inner door from opening once the outer door was open, was found inoperable.

Further investi-gation revealed that the rod which should have prevented the inner door handwheel from cperating while the outer door was open, was bent.

Corrective Action

The bent rod in the inner door's interlock mechanism was straightened and returned to service. The chain which holds the door in the closed position while the latching mechanism is rotated into place, was tightened. This will provide assurance in the future that the door is being secured in the fully closed position.

All DAEC personnel have been instructed that all primary containment entries shall require the independent verification by one individual from the DAEC Operations Department and one other person that at least one door in the primary containment airlock remains closed at all times whenever the ' primary containment is required.

In addition, following each personnel entry and subsequent exit, both primary contain-

. ment airlock doors shall be chained closed and padlocked.

This ins.truction will remain effective until a design review of the airlock system can be completed to evaluate ~if any equipment modifications are appropriate to preclude the occurrence of similar events.

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