05000325/LER-2014-003, Regarding Secondary Containment Loss of Safety Function Due to Airlock Door Interlock Design
| ML14142A006 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/09/2014 |
| From: | Hamrick G Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BSEP 14-0051 LER 14-003-00 | |
| Download: ML14142A006 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3252014003R00 - NRC Website | |
text
DUK George T. Hamrick Vice President Brunswick Nuclear Plant P.O. Box 10429 Southport, NC 28461 o: 910.457.3698 MAY 0 9 2014 10 CFR 50.73 Serial: BSEP 14-0051 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Brunswick Steam Electric Plant, Unit No. 1 Renewed Facility Operating License No. DPR-71 Docket No. 50-325 Licensee Event Report 1-2014-003 In accordance with the Code of Federal Regulations, Title 10, Part 50.73, Duke Energy Progress, Inc., submits the enclosed Licensee Event Report (LER). This report fulfills the requirement for a written report within sixty (60) days of a reportable occurrence.
Please refer any questions regarding this submittal to Mr. Lee Grzeck, Manager - Regulatory Affairs, at (910) 457-2487.
Sincerely, George T. Hamrick MAT/mat
Enclosure:
Licensee Event Report CQ
U.S. Nuclear Regulatory Commission Page 2 of 2 cc (with enclosure):
U. S. Nuclear Regulatory Commission, Region II ATTN: Mr. Victor M. McCree, Regional Administrator 245 Peachtree Center Ave, NE, Suite 1200 Atlanta, GA 30303-1257 U. S. Nuclear Regulatory Commission ATTN: Ms. Michelle P. Catts, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 U. S. Nuclear Regulatory Commission ATTN: Mr. Siva P. Lingam (Mail Stop OWFN 8G9A) (Electronic Copy Only) 11555 Rockville Pike Rockville, MD 20852-2738 Chair - North Carolina Utilities Commission P.O. Box 29510 Raleigh, NC 27626-0510
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 0113112017 (02-2014)
(02,-20114)
Estimated burden per response to comply with this mandatory collecton request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
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 RBranch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by REPORT internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of 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 digits/characters for each block) control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Brunswick Steam Electric Plant (BSEP), Unit 1 05000325 1 OF 4
- 4. TITLE Secondary Containment Loss of Safety Function Due to Airlock Door Interlock Design
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONT A
YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FAITYNM OKIUBE YEAR NUMBER NO.
MONTH DAY'YEAR 05000 FACILITY NAME DOCKET NUMBER S2014 003
- - 00 1 05 09 2014 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[1 20.2201(b)
[I 20.2203(a)(3)(i) 50.73(a)(2)(i)(C)
D 50.73(a)(2)(vii)
[1 20.2201(d)
El 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A)
[
50.73(a)(2)(viii)(A)
[1 20.2203(a)(1)
D 20.2203(a)(4)
E 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
Ej 20.2203(a)(2)(i)
E 50.36(c)(1)(i)(A) 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[D 50.36(c)(1)(ii)(A)
Ej 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
[E 50.73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
[_ 50.73(a)(2)(v)(B) 1] 73.71 (a)(5) 00 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C)
El OTHER l 20.2203(a)(2)(vi)
[]
50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify inAbstract belowor in
[
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Back-ground Initial Conditions At the time of these events, Unit 1 was in Mode 5 at zero percent of rated thermal power (RTP). There were no other structures, systems or components out of service that contributed to this event. Operations with the Potential to Drain the Reactor Vessel (OPDRVs) were in progress, and secondary containment was credited as operable.
Reportability Criteria Two conditions are being reported in accordance with 10 CFR 50.73(a)(2)(v)(C), as conditions that could have prevented fulfillment of a safety function needed to control the release of radioactive material.
During the first, secondary containment [NG] was considered inoperable per Technical Specification (TS) requirements for approximately one minute on March 13, 2014, when both the inner and outer secondary containment airlock doors (i.e., doors 1-RB1-DR-EL050-303 and 1-RB1-DR-EL050-304), on the 50 foot elevation of the reactor building, had been simultaneously opened. The NRC was initially notified of this event on March 13, 2014 (i.e., Event Number 49910), in accordance with 10 CFR 50.72(b)(3)(v)(C).
During the second, secondary containment was considered inoperable per TS requirements for approximately 10 seconds on March 17, 2014, when both the inner and outer secondary containment airlock doors (i.e., 1-RB1-DR-EL020-203 and 1-RB1-DR-EL020-204), on the 20 foot elevation of the reactor building, had been simultaneously opened. The NRC was initially notified of this event on March 17, 2014 (i.e., Event Number 49921), in accordance with 10 CFR 50.72(b)(3)(v)(C).
With both doors open, Surveillance Requirement 3.6.4.1.2 of Technical Specification (TS) 3.6.4.1, Secondary Containment, was not met, rendering secondary containment inoperable. In accordance with the guidance of NUREG-1022, Event Reporting Guidelines 10 CFR 50.72 and 50.73, Revision 3, TS inoperability of a structure, system, or component with no redundant equipment in the same system operable constitutes an event that could have prevented the fulfillment of a safety function.
These conditions are also being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as operation which was prohibited by the plant's TSs. With secondary containment inoperable, Required Action C.2 of TS 3.6.4.1 requires the initiation of action to suspend OPDRVs. As a result of the short duration of the secondary containment inoperability, this Required Action could not be completed.
Event Description
At 0937 Eastern Daylight Time (EDT) on March 13, 2014, Operations was informed that both the inner and outer secondary containment airlock doors, on the 50 foot elevation of the reactor building, had been simultaneously opened for approximately one minute. This event occurred while an employee was exiting secondary containment at the same time an employee was entering secondary containment. Upon recognition of the condition, the employees took action to secure both doors.
Subsequently, on March 17, 2014, at 0750 EDT, Operations was informed that both the inner and outer secondary containment airlock doors, on the 20 foot elevation of the Unit 1 reactor building, had been simultaneously opened for approximately 10 seconds. This event occurred while an employee was exiting secondary containment immediately after another employee had previously entered. Upon recognition of the condition, the employees took action to secure both doors. At the time this condition occurred, OPDRVs were in progress and secondary containment was credited as operable.
Event Cause
The root cause of these events is that the design of the secondary containment airlock door interlocks is not robust enough to prevent inoperability of secondary containment.
Statements from personnel involved in the events and maintenance technicians who investigated afterwards clearly demonstrate that the interlock was physically actuating both during and after the events.
The interlock systems have known physical vulnerabilities and require maintenance of moving parts to guarantee proper function. It is possible for the door position switch or plunger to stick in intermittent cases, particularly if the door is experiencing heavy use during an outage. The interlock system, when actuating properly, ultimately relies on the door to be in the fully closed and latched position in order for the plunger to be effective. The door may go out of alignment periodically due to heavy use, may not completely close under a high differential pressure, or may not be challenged by personnel, any of which potentially renders the plunger ineffective.
Safety Assessment
The safety significance of these events was minimal. The principal functions of secondary containment are to minimize ground level release of airborne radioactive materials and to provide the means for a filtered and controlled elevated release of the reactor building atmosphere if an accident should occur. The safety objective of secondary containment is to limit the release of radioactivity to the environs after an accident so that the resulting exposures are kept to a practical minimum and are within 10 CFR 50.67 and 10 CFR 100 values. The durations of a potential for release to have occurred during these two events via the open airlock doors was approximately one minute, and approximately 10 seconds, respectively.
Throughout these events, secondary containment negative pressure was maintained and no release occurred.
Corrective Actions
Any changes to the corrective actions noted below will be made in accordance with the site's corrective action program.
The following corrective actions have been completed.
In each event, the secondary containment airlock doors were closed to re-establish secondary containment.
Video monitoring equipment was installed for Units 1 and 2 at the 20 foot personnel airlock doors to be used for ingress and egress. The 50 foot personnel airlock doors for both Unit 1 and Unit 2 were identified as emergency use only. These actions will remain in place until the newly designed interlocks for the airlock doors have been installed.
The following corrective action to prevent recurrence (CAPR) is planned.
Design and implement a new interlock for the Unit 1 and 2 secondary containment personnel airlock doors.
Previous Similar Events
A review of LERs for the past three years identified the following previous similar occurrences.
LER 2-2013-005, dated December 19, 2013, reported a loss of secondary containment integrity due to gaps in the Unit 2 secondary containment airlock door seals. Corrective actions included translating design basis requirements for secondary containment into acceptance criteria for the Unit 1 and Unit 2 secondary containment pressure boundary doors, as well as completing procedure revisions to incorporate the acceptance criteria. Since the causes of the events were different, the actions from LER 2-2013-005 could not have reasonably been expected to prevent the condition reported in LER 1-2014-003.
LER 2-2014-001, dated May 2, 2014, reported that both the inner and outer secondary containment airlock doors, on the 50 foot elevation of the reactor building, had been simultaneously opened for approximately one to two minutes on March 5, 2014. The root cause and corrective actions for the event reported in LER 2-2014-001 are the same as for this LER (i.e., LER 1-2014-003). However, due to the short duration between these events, corrective actions to prevent recurrence had not been implemented. As such, they could not have prevented the condition reported in LER 1-2014-003.
Commitments
No regulatory commitments are contained in this report.