05000220/LER-2015-002

LER-2015-002, Secondary Containment Inoperable Due to Simultaneous Opening of Airlock Doors

Nine Mile Point Unit 1
Event date:	3-3-2015
Report date:	4-21-2015
Reporting criterion:	10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
2202015002R00 - NRC Website

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202,: (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

A. PRE-EVENT PLANT CONDITIONS:

Prior to the event, Nine Mile Point Nuclear Station Unit 1 (NMP1) was operating at 93.5% power.

B. EVENT:

On Wednesday March 3, 2015 at approximately 0837 hours0.00969 days <br />0.233 hours <br />0.00138 weeks <br />3.184785e-4 months <br />, both Unit 1 Reactor Building Airlock Doors on the 340 foot elevation (Door-056 and Door-057) were opened simultaneously, resulting in a momentary loss of Secondary Containment Operability. Upon identification the doors were immediately closed and operability was restored. NMP1 was operating at 93.5% power in end of cycle coastdown. The incident occurred as personnel traversed through the airlock. From review of the Badge Access Transaction Report in addition to personnel statements from the prompt investigation, the following scenario had occurred resulting in the event:

At 0837 hours0.00969 days <br />0.233 hours <br />0.00138 weeks <br />3.184785e-4 months <br />, two workers were entering from the Turbine Building side to the Refuel Floor via door D-056. One worker was entering from the Refuel Floor side to the Turbine Building via door D-057. The single worker from the Refuel floor stepped into the airlock, and was preparing to turn and close his door when he heard the click of the other door and the other two workers opened and quickly closed their door. These actions resulted in the simultaneous opening of both secondary containment doors. This concurrent opening of both airlock doors resulted in a breach of the secondary containment. One of the doors was immediately closed re-establishing secondary containment integrity.

Operations review determined that the simultaneous opening of both secondary containment airlock doors constituted a momentary loss of secondary containment per Technical Specification 3.4.3 and NUREG 1022, Revision 3.

Review of the Reactor Building differential pressure as recorded by the plant process computer for the time period of the event indicated that the actual differential pressure remained negative and was unaffected by the brief simultaneous opening of the airlock doors.

This event has been documented in the plant's corrective action program as IR 2462596.

TO THE EVENT:

No other systems, structures, or components contributed to this event.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

The dates, times and major occurrences for this event are as follows:

March 3, 2015 0837 Two workers were entering from the Turbine Building side to the Refuel Floor via door D-056.

One worker was entering from the Refuel Floor side to the Turbine Building via door D-057.

Secondary containment was breached when both doors opened simultaneously.

Both doors were immediately closed Entered TS action statement 3.4.3, Condition C and exited.

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

No other systems or secondary functions were affected beyond the systems discussed in Section I.B.

F. METHOD OF DISCOVERY:

This event was discovered by station personnel reporting the issue.

G. MAJOR OPERATOR ACTION:

NMP1 entered TS action statement 3.4.3, and exited it when the doors were shut.

H. SAFETY SYSTEM RESPONSES:

The duration of this event was approximately 5 seconds. Review of the Reactor Building differential pressure as recorded by the plant process computer for the time period of the event indicated that the actual differential pressure remained negative and was unaffected by the brief simultaneous opening of the airlock doors. Operators entered the applicable TS action statement then exited it soon afterwards. The event concluded when one of the airlock doors was shut.

II. CAUSE OF EVENT:

Clear and well-advertised barriers for passage through the air lock doors were not followed.

The single worker entering from the Refuel Floor side had opened his door without pausing for the required 5 seconds or verifying the monitor. Contrary to site expectations and administrative postings on the door, the worker on the Reactor Building side did not pause for five seconds and did not observe the monitor to determine if individuals were entering the airlock from the opposing side. Had the worker utilized the redundant barriers afforded him, in addition to human performance verification tools, he likely would have observed the two workers preparing to enter the airlock from the Turbine Building side. The view of the opposing door D-057 on the Turbine building side is limited due to camera location and resultant view therefore requiring more reliance on a worker pausing in order to be properly observed. It is concluded therefore, that the rather rapid approach and entry from the Reactor Building side caught the TB team unexpectedly resulting in the simultaneous opening.

ANALYSIS OF THE EVENT:

Simultaneous opening of both reactor building airlock doors is reportable under 10 CFR 50.72(b)(3)(v)(C) and 10 CFR 50.73(a)(2)(v)(C). It is defined under paragraph 10 CFR 50.73(a)(2)(v)(C) as any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. Secondary Containment differential pressure was unaffected by this event.

One of the accesses to the NMP1 Reactor Building is through the airlock doors D-056 and D-057. In response to the event, the station entered the action statement for TS 3.4.3 then promptly exited it when the airlock doors were shut. Computer data identified that secondary containment differential pressure was unaffected by this event. Secondary containment structural integrity, the ability to automatically isolate the non-safety related Reactor Building ventilation system, and the Reactor Building Emergency Ventilation System availability were not impacted. It is concluded that the safety significance of this event is low and the event did not pose a threat to the health and safety of the public or plant personnel. This event does not affect the NRC Regulatory Oversight Process Indicators.

IV. CORRECTIVE ACTIONS:

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL

STATUS:

The RB 340 foot elevation airlock doors were shut.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

Disciplinary action was administered for the individual entering the airlock from the Reactor Building side.

A. FAILED COMPONENTS:

There were no other failed components that contributed to this event.

B. PREVIOUS LERs ON SIMILAR EVENTS:

NMP1 LER 2014-004, August 13, 2014.

NMP1 LER 2014-005, October 16, 2014.

NMP1 LER 2014-006, October 20, 2014.

NMP1 LER 2015-001, February 11, 2015.

(NMP1) Reactor Building was breached when workers opened both inner and outer airlock doors simultaneously while passing through. The integrity of the airlock was re-established approximately 5 seconds when one of the doors was closed and latched. Secondary Containment differential pressure was unaffected by these events.

The three LERs in 2014 occurred at the main airlock into the RB 261 foot elevation. The two LERs in 2015 have been for simultaneous opening of the airlock doors on the RB 340 foot elevation.

C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION

COMPONENT

IEEE 803 FUNCTION IEEE 805 SYSTEM

IDENTIFIER IDENTIFICATION

Reactor Building (BWR) N/A NG Reactor Building Ventilation System PDIC VA Airlock Door DR NG

D. SPECIAL COMMENTS:

None