05000352/LER-2014-001, Regarding Inoperable Reactor Enclosure Secondary Containment Integrity Due to Open Airlock

Regarding Inoperable Reactor Enclosure Secondary Containment Integrity Due to Open Airlock

ML14008A007
Person / Time
Site:	Limerick
Issue date:	01/08/2014
From:	Dougherty T Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LG-14-010 LER 14-001-00
Download: ML14008A007 (4)

LER-2014-001, Regarding Inoperable Reactor Enclosure Secondary Containment Integrity Due to Open Airlock

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3522014001R00 - NRC Website

text

10CFR50.73 LG-14-010 January 8, 2014 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Unit 1 Facility Operating License No. NPF-39 NRC Docket No. 50-352

Subject:

LER 2014-001-00, Condition That Could Have Prevented Fulfillment of the Reactor Enclosure Secondary Containment Integrity Safety Function This Licensee Event Report (LER) addresses a condition that could have prevented fulfillment of the reactor enclosure secondary containment integrity safety function. Both airlock doors on one reactor enclosure airlock were briefly opened simultaneously due to the airlock design.

This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(v)(C).

There are no commitments contained in this letter.

If you have any questions, please contact Robert B. Dickinson at (610) 718-3400.

Respectfully, Original signed by Thomas J. Dougherty Vice President - Limerick Generating Station Exelon Generation Company, LLC cc: Administrator Region I, USNRC USNRC Senior Resident Inspector, LGS

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013

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

1. FACILITY NAME Limerick Generating Station, Unit 1

2. DOCKET NUMBER 05000352

3. PAGE 1 OF 3

4. TITLE Inoperable Reactor Enclosure Secondary Containment Integrity Due to Open Airlock

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.

MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 05000 10 30 2013 2014 - 001 - 00 01 08 2014 FACILITY NAME DOCKET NUMBER 05000

9. OPERATING MODE 1

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)

OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)

Specify in Abstract below or in LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

Analysis of the Event

There was no actual safety consequence associated with this event.

The potential safety consequences of this event were minimal. Both doors on the airlock were open simultaneously for less than 10 seconds.

To prevent an unplanned breach of secondary containment each reactor enclosure airlock is equipped with door open indicating lights which are used to locally verify the door status. If both doors are opened simultaneously a local alarm is actuated. If both doors remain open for greater than 10 seconds an alarm is actuated in the main control room and operators are dispatched to verify the airlock doors are closed.

UFSAR 6.2.3.2.1 describes the secondary containment design. The reactor enclosure secondary containment (Zones I and II) are designed to limit the inleakage to 200% of their zone free volume per day, and the refueling area secondary containment (Zone III) is designed to limit the inleakage to 50% of its zone free volume per day. These inleakage rates are based on a negative interior pressure of 0.25 in wg, while operating the standby gas treatment system (SGTS). Following a LOCA the affected zone is maintained at this negative pressure by operation of the SGTS.

Cause of the Event

This event was caused by a weakness in the design of the reactor enclosure airlocks since there is no mechanical interlock and the door open indicating light does not prevent simultaneous opening of both airlock doors.

Corrective Action Planned A modification is being evaluated for the airlock doors.

Previous Similar Occurrences Unit 2 LER 2013-003 was submitted due to a reactor enclosure airlock breach caused by a weakness in the airlock design. Unit 2 LER 2013-002 was submitted due to a reactor enclosure airlock breach caused by an non-functional airlock door open indicating light not providing the correct door status.