05000263/LER-2013-008-01, Regarding Both Secondary Containment Access Doors Briefly Opened Simultaneously

Regarding Both Secondary Containment Access Doors Briefly Opened Simultaneously

ML14072A170
Person / Time
Site:	Monticello
Issue date:	03/12/2014
From:	Fili K Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-MT-14-019 LER 13-008-01
Download: ML14072A170 (4)

LER-2013-008, Regarding Both Secondary Containment Access Doors Briefly Opened Simultaneously

Event date:
Report date:
2632013008R01 - NRC Website

text

Xcel Energy@

March 12, 2014 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket 50-263 Renewed Facility Operating License No. DPR-22 Monticello Nuclear Generating Plant 2807 W County Road 75 Monticello, MN 55362 L-MT-14-019 10 CFR 50.73 Revision 1 to LER 2013-008, "Both Secondary Containment Access Doors Briefly Opened Simultaneously" After submittal of Licensee Event Report (LER) 2013-008, "Both Secondary Containment Access Doors Briefly Opened Simultaneously," the NRC questioned whether the LER was implying that the primary method for maintaining airlock integrity utilized airlock door windows.

This is in conflict with the Monticello Nuclear Generating Plant Updated Safety Analysis Report.

Therefore, a revision to the LER was developed. Revision 1 of LER 2013-008 is attached.

Summary of Commitments This letter contains no new commitments and no revisions to existing commitments.

Karen D. Fili Site Vice President, Monticello Nuclear Generating Plant Northern States Power Company-Minnesota Enclosure cc:

Regional Administrator, Region Ill, USNRC Project Manager, Monticello Nuclear Generating Plant, USNRC Resident Inspector, Monticello Nuclear Generating Plant, USNRC

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 (02-2014)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

YEAR 2013

6. LER NUMBER I

SEQUENTIAL I NUMBER 008 REV NO.

01 2

3. PAGE OF 3

On September 18, 2013, while performing the secondary containment (SCT) [JM] airlock [AL] door [DR]

interlock [IEL] surveillance test, the interlock to the main plenum room did not prevent the opening of both doors to the plenum room airlock (DOOR-85 and DOOR-86). With the outer door to the main plenum room open, the inner door was able to be opened. The plenum airlock doors were then closed. The operator attempted a second time to verify interlock functionality. This time the inner door was opened, and again the interlock did not prevent the opening of the outer door. The plenum airlock doors were immediately closed. The total time both doors were opened is estimated to be less than ten (1 0) seconds.

With both doors open, Technical Specification (TS) surveillance requirement (SR) 3.6.4.1.3 was not met and secondary containment was declared inoperable. Secondary containment was declared operable after independently verifying that at least one SCT access door was closed. There were no radiological releases associated with this event.

The safety related function of the airlock doors is to maintain SCT boundary.

EVENT ANALYSIS

This event is reportable in accordance with 10 CFR 50. 73(a)(2)(v) as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to:

(C) Control the release of radioactive material; (D) Mitigate the consequences of an accident.

SAFETY SIGNIFICANCE

The safety significance of this event is minor. From a risk perspective the Large Early Release Fraction (LERF) exposure was less than one minute, and is bounded by the safety analysis which assumes a five minute positive pressure period. From a high energy line break (HELB) perspective, the short duration that the HELB door was open is within the normal egress allowance provided in plant procedures for HELB doors.

CAUSE

In this event the surveillance test procedure being performed is used to verify the functionality and operability of Appendix R Fire/HELB Doors. This procedure did not have detailed instructions compared to the procedure that is used to provide a functional check and visual inspection of SCT airlock doors. The procedure for verifying SCT airlock doors has steps to verify the associated indicating light is on or audible indication exists (to verify that the interlock relay is energized) prior to challenging the closed door. The Appendix R/HELB Doors procedure simply states to challenge the doors without validating that the interlock is functioning by observing the status of the indicating light or audible indication.

Therefore, the Equipment Cause Evaluation (ECE) performed for the event determined the following cause for the event:

Both DOOR-85 and DOOR-86 were simultaneously opened during testing because the surveillance procedure lacked specific direction for the user to obtain visual or audible confirmation that the interlock energized prior to challenging the closed door. In addition the failure of the interlock mechanism contributed to the ability to open both doors simultaneously.

CORRECTIVE ACTION

Corrective actions identified in the ECE include the following to correct the identified cause:

Immediately verified both airlock doors were closed.

The door interlock was repaired.

Station airlock interlock testing procedures will be revised to provide specific instructions to not challenge the opposite door if there is no indication that the interlock activation is present when a door is open.

PREVIOUS SIMILAR EVENTS

On June 3, 2010, DOOR-72 and DOOR-82 for Airlock 413 (985' Pump Room) were inadvertently opened simultaneously, breaching the SCT boundary. Personnel immediately identified the situation and closed both doors within four to five seconds (estimated). The cause of the event was the design of the interlock between the doors in the 985' Pump Room. The interlock design allows simultaneous entry under specific timing conditions (i.e., the doors are opened at exactly the same time-otherwise, the interlock prevents one door from opening if the other is open). This event was reported in LER 2010-002-02. A similar event involving these same doors occurred on August 5, 2010 and is reported under LER 2010-003-01.

On November 4, 2010, DOOR-62 and DOOR-63 for Airlock 124 were inadvertently opened simultaneously, breaching the SCT boundary. This occurred when personnel attempted to enter the airlock from SCT before the outboard door fully closed. The local alarm sounded for approximately one to two seconds, and the plant employees noticed DOOR-62 was not fully closed. Plant personnel immediately closed the doors and notified the Control Room that SCT was momentarily breached (for approximately 5 seconds). The apparent cause for Airlock 124 breach was intermittent failure of the magnetic bond sensor due to a lack of periodic maintenance. This event was reported in LER 2010-004.

ADDITIONAL INFORMATION

Energy industry identification system (EllS) codes are identified in the text within brackets [xx].