05000373/LER-2017-002, Regarding Secondary Containment Inoperable Due to Interlock Doors Open
| ML17076A183 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 03/17/2017 |
| From: | Vinyard H Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA17-017 LER 17-002-00 | |
| Download: ML17076A183 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 3732017002R00 - NRC Website | |
text
Exelon Generation LaSalle County Station 2601 North 21*
1 Road Marseilles, IL 61341 815-415-2000 Telephone www.exeloncorp.com 10 CFR 50.73 RA17-017 March 17, 2017 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
LaSalle County Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-11 and NPF-18 NRG Docket Nos. 50-373 and 50-374 Licensee Event Report 2017-002-00, Secondary Containment Inoperable Due to Interlock Doors Open In accordance with 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D), Exelon Generation Company, LLC (EGG) is submitting Licensee Event Report (LER)
Number 2017-002-00 for LaSalle County Station, Units 1 and 2.
There are no regulatory commitments in this letter. Should you have any questions concerning this report, please contact Mr. Guy V. Ford, Jr., Regulatory Assurance Manager, at (815) 415-2800.
Harold T. Vinyard Plant Manager LaSalle County Station
Enclosure:
Licensee Event Report cc:
Regional Administrator - NRG Region Ill NRG Senior Resident Inspector - LaSalle County Station
NRCFORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (06-2016)
Estimated burden per response to comply with this mandatory collection 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.
l~~
LICENSEE EVENT REPORT (LER)
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections
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j Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail (See Page 2 for required number of digits/characters for each block) to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (315().0104), Office of Management and Budge~ Washington, DC 20503. If a (See NUREG-1022, R.3 for instruction and guidance for completing this fonn means used to impose an information collection does not display a cu11entiy valid OMB control htt12:{lwww.n(c.gov/reading-rmldoc-colleQtiQns/nuregs/s!i!ff/sr1 Q22/r3l) number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE LaSalle County Station, Unit 1 05000373 1 OF 4
- 4. TITLE Secondary Containment Inoperable Due to Interlock Doors Open
- 5. EVENT DATE
- 6. LEA NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR LaSalle Country Station, Unit 2 05000374 FACILITY NAME DOCKET NUMBER 01 18 2017 2017 - 002
- - 00 03 17 2017 NA NA
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201 (b}
D 20.2203(a)(3}(i)
D 50. 73(a)(2)(ii)(A)
D 50. 73(a)(2)(viii)(A)
D 20.2201 (d)
D 20.2203(a)(3)(ii)
D 50. 73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 1 D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.13(a)(2)(m>
D 50.73(a)(2)(ix)(A)
D 20.2203<a><2>
D 50.36(c)(1 )(i)(A)
D 50.73(a)(2}(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50. 73(a)(2)(v)(A)
D 13.11(a)(4)
D 20.2203<a><2><m>
D 50.36(c)(2)
D 50. 73(a)(2)(v)(B)
D 13.11ca><5>
D 20.2203(a)(2)(iv)
D 5o.46(a)(3)(ii) 181 50. 73(a)(2)(v)(C)
D 13.11ca><1>
100 D 20.2203(a}(2)(v)
D 50.73(a)(2)(i)(A) 181 50.73(a)(2)(v)(D)
D 13.n(a)(2)(i)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.77(a)(2)(ii)
D 5o.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in The safety significance of this event was minimal, since the reactor building to outside differential pressure remained negative throughout the period that the secondary containment was inoperable. The secondary containment was inoperable for approximately five seconds, which was significantly less than the four-hour Completion Time to restore secondary containment to operable status allowed by TS 3.6.4.1 Required Action A.1.
00 The function of the secondary containment is to contain, dilute, and hold up fission products that may leak from the primary containment following a Design Basis Accident (DBA). A technical evaluation determined that the inadvertent simultaneous opening of secondary containment doors for less than 30 seconds are bounded by the existing drawdown analysis and dose calculations and will not result in a failure of a safety system function needed to control the release of radioactive material to the environment. The time that both doors were simultaneously opened for this event was approximately five seconds, which is bounded by the technical evaluation (reference Engineering Change (EC) 396711, "Safety System Functional Analysis for Unit 1
& 2 Secondary Containment Air-lock Doors.")
This event did not result in the reactor enclosure differential pressure dropping below the design bases set point of -0.25 inches vacuum water gauge. Both the inner and outer doors were promptly closed by station personnel, which ended the event. This event did not involve any kind of door or air-lock material condition preventing door closure. Additionally, both the inner and outer doors were closed by normal expected means and were capable of remaining closed as designed.
The computed dose for EC 396711 was based on the door opening during the 780 second time period prior to Standby Gas Treatment (SBGT) system drawdown and filtration. This discounts the initial 120 seconds of an event where no release takes place, in accordance with calculation L-003068, "Re-Analysis of Loss of Coolant Accident (LOCA) Using Alternative Source Terms."
The approximate five second opening of the secondary containment doors is bounded by calculation L-003068. Should an event occur, in which both secondary containment doors were open simultaneously for 30 seconds or less, it would result in a potential dose increase of approximately 3.85 percent. The 3.85 percent decrease in margin is inconsequential in comparison to the 1 O CFR 100 regulatory limits.
EC 396711 also evaluated the pressure impact on the secondary containment and the ability of the SBGT system to achieve the TS required negative pressure. The results of the evaluation show SBGT would restore secondary containment pressure within three minutes which is well below the 15 minute maximum drawdown time required by TS.
Based on the short duration of door opening (approximately five seconds), no material condition preventing door closure or maintaining the doors closed, and attendance by knowledgeable personnel who closed the doors immediately, the secondary containment safety function was maintained.
CORRECTIVE ACTIONS
The defective circuit board with a degraded relay, which had been in-service since February 2016, was replaced with an interim circuit board that had been manufactured with a newer version of the original relay. This circuit board had been previously obtained from the vendor as a contingency for use in the event of a door failure. Operability of the secondary containment was restored on January 19, 2017, at 1325 CST, upon completion of a satisfactory test of the interlock doors. Station personnel were unable to reproduce the failure on the removed card.
A set of final upgraded circuit boards with more robust relays was manufactured, bench-tested by the manufacturer, and "burned in" for 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> to ensure functionality, before they were delivered the site for use as the final corrective action repairs. The site performed additional bench-testing of the delivered cards before installation in the plant. The affected interlock doors, as well as the remaining sets of high-traffic interlock doors, were upgraded with the new-style circuit board.
PREVIOUS OCCURRENCES
SEQUENTIAL NUMBER 002 REV NO.
00 The interlock that failed was scheduled to have the circuit card replaced the week following this event as an action created from a previous failure. Corrective actions from previous events had been ongoing to upgrade interlock door circuit cards with ones that had improved relays. These corrective actions were the result of causal investigations with previous events as follows.
LER 2016-001-00:
On February 17, 2016, Unit 2 was in Mode 1 at 100 percent power and Unit 1 was in Mode 5 tor a refueling outage with no fuel movements or operation with the potential to drain the reactor vessel (OPDRV) in progress. At 1035 hours0.012 days <br />0.288 hours <br />0.00171 weeks <br />3.938175e-4 months <br /> CST, both air-lock doors of the Unit 2 Chemistry Lab corridor to Unit 2 reactor building were open at the same time for approximately five seconds.
The cause was failure of the relays on the door controller circuit card. The controller circuit card was replaced, which restored the interlock functionality. Corrective actions included determination of the cause of vendor quality issues with the controller circuit card relays and procurement of a more reliable controller circuit card following cause identification of the relay failures from vendor analysis.
LER 2015-003-00:
On February 17, 2015, Unit 1 was in Mode 1 at 100 percent power and Unit 2 was in Mode 5 for a refueling outage with no fuel movements in progress. Activities involving OPDRVs were in progress in the secondary containment on Unit 2. At 1145 hours0.0133 days <br />0.318 hours <br />0.00189 weeks <br />4.356725e-4 months <br /> CST, it was reported that both air-lock doors between the Unit 1 diesel generator corridor and the Unit 1 reactor building were open at the same time for approximately five to ten seconds. The cause was a failure of a controller circuit card in the door interlock logic. The circuit card was replaced, which restored the interlock functionality. Corrective actions included a cause determination tor the premature controller circuit card failures and replacing the card with more reliable models.
LER 2015-001-00:
On December 12, 2014, both Units 1 and 2 were in Mode 1 at 100 percent power with no fuel movements in progress. At 1324 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.03782e-4 months <br /> CST, it was reported that both air-lock doors between the Unit 2 diesel generator corridor and the Unit 2 reactor building were open at the same time for approximately ten seconds. The cause was a degradation of the door closure mechanism, and the contributing cause was a less than robust design of the door interlock assembly. Corrective actions from the previous occurrences to identify, procure and install a more robust interlock assembly design were in progress at the time of the event.
Additional corrective actions, including periodic preventative maintenance to inspect, tighten, and replace fasteners as necessary, were in place but did not preclude this event. This event did not involve a door controller circuitry reliability issue.
LER 2014-001-00:
On February 18, 2014, Unit 1 was in Mode 5 with fuel moves in progress during a refueling outage, and Unit 2 was in Mode 1 at 100 percent power. At 1820 hours0.0211 days <br />0.506 hours <br />0.00301 weeks <br />6.9251e-4 months <br /> CST, it was reported that both air-lock doors between the Unit 2 diesel generator corridor and the Unit 2 reactor building were open at the same time tor approximately three seconds. The cause of the event was degradation of the door closure mechanism and door frame seal. A contributing cause was a less than robust design of the door interlock assembly. Corrective actions from the previous occurrences to identify, procure and install a more robust interlock assembly design were still in progress at the time of the event. Additional corrective actions included creating a periodic preventative maintenance task to inspect, tighten, and replace fasteners as necessary. This event did not involve a door controller circuitry reliability issue.
COMPONENT FAILURE DATA
Manufacturer: Security Door Controls (SOC)
Device: UR2-4 Controller Card Component ID: 1695558 Page _4_ of _4_