05000336/LER-2012-001, Regarding Historical Gaps in High Energy Line Break Barrier
| ML12228A387 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/01/2012 |
| From: | Scace S Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 12-436 LER 12-001-00 | |
| Download: ML12228A387 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 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 |
| 3362012001R00 - NRC Website | |
text
Dominion Dominion Nuclear Connecticut, Inc.
Millstone Power Station Rope Ferry Road Waterford, CT 06385 AUG 0 12012 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Serial No.
MPS Lic/TGC Docket No.
License No.12-436 RO 50-336 DPR-65 DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 2 LICENSEE EVENT REPORT 2012-001-00 HISTORICAL GAPS IN HIGH ENERGY LINE BREAK BARRIER This letter forwards Licensee Event Report (LER) 2012-001-00 documenting a condition discovered at Millstone Power Station Unit 2 on June 7, 2012. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plant's technical specifications.
If you have any questions or require additional information, please contact Mr. William D. Bartron at (860) 444-4301.
Sincerely, Sepnen
' cace Site Vice President - Millstone Attachments: 1 Commitments made in this letter: None
Serial No.12-436 Docket No. 50-336 Licensee Event Report 2012-001 -00 Page 2 of 2 cc:
U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 J. S. Kim Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 C2A Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No.12-436 Docket No. 50-336 Licensee Event Report 2012-001-00 ATTACHMENT LICENSEE EVENT REPORT 2012-001-00 MILLSTONE POWER STATION UNIT 2 DOMINION NUCLEAR CONNECTICUT, INC.
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10/2010)
, the NRC may not conduct or sponsor, digits/characters for each block) and a person is not required to respond to, the information collection.
- 3. PAGE Millstone Power Station - Unit 2 05000336 1 OF 3
- 4. TITLE Historical Gaps in High Energy Line Break Barrier
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR 05000 NUMBER NO.
I FACILITY NAME DOCKET NUMBER 06 07 2012 2012 - 001 - 00 08 01 2012 05000
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR j:'(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)
N 50.73(a)(2)(x)
- 10. POWER LEVEL 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) 100 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
OTHER 20.2203(a)(2)(vi)
X 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)
Specify in Abstract below or in
- 1.
Event Description
At 19:30 on June 7, 2012, with Millstone Power Station Unit 2 (MPS2) operating at 100 percent power in Mode 1, it was determined that a series of gaps in a high energy line break (HELB) barrier rendered equipment in the west 480VAC switchgear room inoperable. The Shift Manager entered Technical Specification (TS) 3.8.2.1 Action, TS 3.8.2.1A Action "c" and TS 3.3.3.5 Action "a" at 19:30 on June 7, 2012. The openings were sealed and the equipment restored to operable status at 16:05 on June 8, 2012.
The openings in the HELB barrier were identified during maintenance activities to support a plant modification, when maintenance personnel identified a series of gaps in a wall that separates the MPS2 turbine building from the west 480VAC switchgear room. The west 480VAC switchgear room contains 480 volt emergency load center 22E [EC]. TS 3.8.2.1 "A.C. Distribution - Operating" applies in Modes 1, 2, 3, and 4 and requires certain electrical busses to be operable. With less than the complement of A.C. busses operable, TS 3.8.2.1 Action requires restoration of the bus to operable status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> or be in cold shutdown within the next 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
The gaps in the HELB barrier also affected the operability of Inverter 5 and Inverter 6 [EE]. TS 3.8.2.1A "A.C.
Distribution - Operating" applies in Modes 1, 2 and 3 and requires Inverters 5 and 6 to be operable. Action "c" stipulates with Inverters 5 and 6 inoperable or unavailable for automatic transfer via static switches VS1 and VS2 to power busses VA-10 and VA-20, respectively, restore the inverters to operable status or restore their automatic transfer capability within 7 days.
The remote shutdown instrumentation panel (C-21) [PL] is also located in the west 480VAC switchgear room. TS 3,3.3.5 "Remote Shutdown Instrumentation" applies in Modes 1, 2 and 3 and requires remote shutdown instrumentation channels to be operable. TS 3.3.3.5 Action "a" stipulates with the number of operable remote shutdown monitoring instrumentation channels less than required by TS Table 3.3-9, restore the inoperable channel to operable status within 7 days.
This condition is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) "any operation or condition prohibited by the plant's technical specifications". At the time of discovery, appropriate and timely actions were taken that met the TS action requirements. There is evidence that this condition has existed since initial construction. Since the HELB barrier required to maintain operability of bus 22E, Inverters 5 and 6, and remote shutdown panel C-21 was non-functional for an extended period, the Actions for TS 3.8.2.1, TS 3.7.2.1A and TS 3.3.3.5 were historically not met.
- 2.
Cause
This is a historical condition dating back to original construction. The gaps were located high in an overhead in the wall to ceiling interface of Q-decking at the north wall of the west 480VAC switchgear room, not visible during normal plant observation. The gaps were discovered because scaffolding had been erected to support an independent plant modification in an area not typically accessible. The apparent cause, dating back to original construction, is that no construction details were developed for sealing Q-decking when the ribbing is perpendicular to the top of the wall.
- 3.
Assessment of Safety Consequences
As a design feature, the HELB barrier is in place to limit the effects of a steam environment created by a HELB in the turbine building. The gaps in the barrier associated with the west 480VAC switchgear room area were located high in the overhead and partially obstructed by building steel. The specific HELB gaps were 91 unsealed openings in the Q-deck (ceiling structure), with a total gap area of approximately 3 square feet.
There were no adverse consequences to the health and safety of the public or the plant and its personnel resulting from the gaps in the HELB barrier.
1
This report assumes the steam from a high energy line break in the turbine building would have affected the operability of safety related equipment in the west 480VAC switchgear room. When necessary, MPS2 has operated in the past with normal ventilation to either the west or east 480VAC switchgear rooms out of service and compensatory cooling established. More detailed, formal engineering analysis is being conducted to determine the extent of the actual safety impact. Therefore, a supplement to this LER will be submitted upon completion of that more detailed engineering analysis.
- 4.
Corrective Action
The gaps were sealed. Plant walk-downs were conducted to assess the extent of condition and whether any similar conditions existed. Additional gaps in the same wall did not affect safety related equipment. No other gaps were identified.
Additional corrective actions are being taken in accordance with the station's corrective action program.
- 5.
Previous Occurrences
There are no previous occurrences identified.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
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