05000271/LER-2012-001, Potential to Flood Switchgear Room Due to Missing Conduit Flood Seal

Potential to Flood Switchgear Room Due to Missing Conduit Flood Seal

ML12212A136
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	07/23/2012
From:	Wamser C Entergy Nuclear Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
BVY 12-045 LER 12-001-00
Download: ML12212A136 (6)

LER-2012-001, Potential to Flood Switchgear Room Due to Missing Conduit Flood Seal

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
2712012001R00 - NRC Website

text

Entergy Entergy Nuclear Operations, Inc.

Vermont Yankee 320 Governor Hunt Rd.

Vernon, VT 05354 Tel 802 257 7711 Christopher J. Wamser Site Vice President BVY 12-045 July 23, 2012 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUBJECT:

Licensee Event Report 05000271/2012-001-00, Potential to Flood Switchgear Room Due to Missing Conduit Flood Seal Vermont Yankee Nuclear Power Station Docket No. 50-271 License No. DPR-28

Dear Sir or Madam:

As defined by 10CFR50.73.(a)(2)(ii)(B) and 10CFR50.73(a)(2)(v)(A - D) we are submitting the attached Licensee Event Report, LER 05000271/2012-001 -00.

There are no new regulatory commitments contained within this correspondence.

Should you have any questions concerning this letter, please contact Mr. Robert J. Wanczyk at (802) 451-3166.

Sincerely, [CJW/plc]

Attachment:

cc list:

LER 05000271/2012-001-00, Potential to Flood Switchgear Room Due to Missing Conduit Flood Seal (next page)

BVY 12-045 / page 2 of 2 cc:

Mr. William M. Dean Region 1 Administrator U.S. Nuclear Regulatory Commission 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 Mr. Richard V. Guzman, Project Manager Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 08C2A Washington, DC 20555 USNRC Resident Inspector Vermont Yankee Nuclear Power Station 320 Governor Hunt Road Vernon, VT 05354 Ms. Elizabeth Miller Commissioner VT Department of Public Service 112 State Street, Drawer 20 Montpelier, VT 05620-2601

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, and a person is not required to respond to, the information collection.

3. PAGE Vermont Yankee Nuclear Power Station 05000271 1 of 4

4. TITLE Potential to Flood Switchgear Rooms Due to Missing Conduit Flood Seal

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED SEQUENTIAL REVISION FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NUMBER MONTH DAY YEAR N/A FACILITY NAME DOCKET NUMBER 05 24 2012 2012 001 00 07 23 2012 N/A

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) ol 20.2201(b) 0 20.2203(a)(3)(i) 0l 50.73(a)(2)(i)(C)

[I 50.73(a)(2)(vii)

N 0l 20.2201(d)

El 20.2203(a)(3)(ii) 0l 50.73(a)(2)(ii)(A)

[I 50.73(a)(2)(viii)(A)

[o 20.2203(a)(1)

El 20.2203(a)(4) 0D 50.73(a)(2)(ii)(B)

[I 50.73(a)(2)(viii)(B)

EO 20.2203(a)(2)(i)

El 50.36(c)(1)(i)(A)

[I 50.73(a)(2)(iii)

[I 50.73(a)(2)(ix)(A)

10. POWER LEVEL [E

20.2203(a)(2)(ii)

El 50.36(c)(1)(ii)(A)

[I 50.73(a)(2)(iv)(A)

[I 50.73(a)(2)(x) 100 [E 20.2203(a)(2)(iii)

El 50.36(c)(2) 0 50.73(a)(2)(v)(A)

[1 73.71 (a)(4)

El 20.2203(a)(2)(iv)

El 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B)

Q 73.71 (a)(5) 0l 20.2203(a)(2)(v)

El 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C)

II OTHER jl 20.2203(a)(2)(vi)

El 50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D)

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)

Michael Gosekamp, General Manager Plant Operations (802) 257-7711REPORTABLE REPORTABLE TO

CAUSE

SYSTEM COMPONENT MANUFACTURER TO EPIX

CAUSE

SYSTEM COMPONENT MANUFACTURER EPIX

14. SUPPLEMENTAL REPORT EXPECTED

15. EXPECTED MONTH DAY YEAR SUBMISSION 0@ YES (If Yes, complete EXPECTED SUBMISSION DATE).

El NO DATE 09 14 2012 ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On May 24, 2012, with the plant at 100 percent power, Vermont Yankee (VY) discovered the potential for water intrusion into the Vital Switchgear Rooms via an underground spare conduit that was found to be missing its flood seal. The missing flood seal compromised the interior flood design controls for the Switchgear Rooms.

Were flooding of the Switchgear Rooms to occur, the operability of switchgear providing electrical power to Division I and II Engineered Safety Feature systems and Emergency Core Cooling Systems could be affected.

This could threaten the capability to shut down the reactor and maintain it in a safe shutdown condition. The cause of the event is still under investigation and will be reported in a supplemental report. The condition was corrected by installing a new flood seal, thus removing the potential flood path. Plant procedure requires inspection of the Switchgear Rooms during a flood event and includes actions that would have mitigated any flooding; therefore this event did not pose a threat to public health and safety.

NRC FORM 366 (10-2010)

,41.

(If more space is required, use additional copies of NRC Form (366A)

Description of Event

On May 16, 2012, with the plant at 100 percent power, while performing periodic manhole flood seal inspections, Vermont Yankee (VY) found a spare 4" conduit (EIIS=CND) in manhole MH-P3 that was missing a flood seal. A new seal was installed on the same day. On May 24, 2012, with the plant at 100 percent power, VY determined that the missing conduit flood seal resulted in a condition that had the potential to flood the Vital Switchgear (EIIS=EK) Rooms should water enter the manhole and conduit. Flooding could affect the operability of safety class switchgear located in this room. The electrical switchgear and distribution equipment located in the rooms power both Division I and Division II Engineered Safety Feature systems and Emergency Core Cooling Systems.

During subsequent examination, the missing flood seal was found in the bottom of manhole MH-P3.

This event is reported in accordance with 10CFR50.73.(a)(2)(ii)(B) as an event or condition that resulted in the plant being in an unanalyzed condition that significantly degraded plant safety and 10CFR50.73(a)(2)(v)(A-D) as an event or condition that could have prevented the fulfillment of a safety function.

Cause of Event

The cause of the event is still under investigation and will be reported in a supplemental report.

Analysis of Event

The entrances to the VY administration (EIIS=MA) and Turbine Buildings (EIIS=NM) are located at the 252.5 feet elevation. VY Updated Final Safety Analysis Report (UFSAR) Table 2.4-9 shows that the maximum VY flood level expected would reach a maximum elevation of 252.5 feet, at a time of 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> into the flood. VY UFSAR Section 2.4.3.4 states, "Since the entrances to all of these structures are at elevation 252.5 feet MSL, they are at maximum flood stage and thus, are protected against the maximum probable flood." However, UFSAR Section 2.4.3.4 also states, "A potential avenue of water intrusion into the Switchgear Rooms, Elevation 248.5 feet MSL exists through underground conduits routed from manholes and handholes to the Switchgear Room floor. Should water enter these manholes, the underground conduits could provide a path for water to enter the Switchgear Room manholes. If the water level gets high enough, flooding in the Switchgear Rooms and lower levels of the administration and Turbine Building could occur. This flooding could affect the operability of safety class switchgear." The spare conduit with the missing flood seal created a potential flow path from an exterior manhole to the Switchgear Rooms via manhole MH-P3, located in the yard adjacent to the station startup transformers, and manhole MH-P2, located in the Switchgear Rooms.

Following the VY Individual Plant Examination External Events review all conduits running into the Switchgear Room manholes connected to yard manholes were sealed to limit any leakage into the room during site flooding conditions. In conjunction with the conduit sealing, sufficient portable pumping capacity was provided on-site to remove any water which may enter the Switchgear Room manholes. Additionally, the site flood procedure was revised to direct plant personnel to remove this water in the event of flooding and to open Switchgear Room doors to provide a flow path for water out of the room if ponding cannot be prevented.

Should the postulated flooding event occur, the plant would be shutdown when the flood level reaches the 237 foot elevation, which is approximately 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> into the event. This shutdown is required before the intake structure becomes submerged by the flood water. As the level continues to rise and enter manhole MH-P3, water would begin flowing through the unsealed conduit connecting these structures to the west Switchgear Room, with (If more space is required, use additional copies of NRC Form (366A) the water levels in the unsealed conduit matching the flood level. The cover on manhole MH-P3 would act to restrict the flow of flood water into the manhole from above. Per UFSAR Table 2.4-9, the water level reaches elevation 247.2 feet 84 hours9.722222e-4 days <br />0.0233 hours <br />1.388889e-4 weeks <br />3.1962e-5 months <br /> into the event, and remains above this level for approximately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

During the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period in which the flood water level is above elevation 247.2 feet, the Switchgear Room water level would seek external flood level. Unabated, the water level could reach a level of 4 feet within the room.

However, by procedure, water would be pumped out of manhole MH-P2 with up to two sump pumps rated at 100 gallons per minute each and would flow out of the Switchgear Room doors and into the lower levels of the Turbine Building. The Turbine Building contains no safety system equipment which would be jeopardized by this water intrusion; therefore this drain path would lessen the severity of the maximum postulated flood upon Switchgear Room water introduction.

VY has a preventive maintenance task to perform visual inspections of manhole flood seals every 18 months. The conduit with the missing seal was previously inspected on November 2, 2010 and the flood seal was found to be in place.

Safety Significance

Plant procedure requires a plant shutdown be initiated if water levels indicate an imminent flooding condition which may cause river level to exceed 230 feet, which is 18.5 feet below the level of the Switchgear Rooms. Plant shutdown would have to be complete by the time the flood stage reaches 237 feet due to inundation of the circulating water pump motors. The procedure also requires that additional actions be implemented if a flood occurs, including using a sump pump to remove water from switchgear manholes should in-leakage occur and opening Switchgear Room doors to provide a path for water to flow out of the room if ponding cannot be prevented. To date the maximum river level that has occurred at the site was elevation 231.4 feet. Because the probability of a maximum flood is extremely low, the highest level achieved during a previous high water condition was 17.1 feet below the elevation of concern and the prescribed procedural actions in the event of flooding, this event is not considered to have resulted in an increased threat to public health and safety.

Corrective Actions

Completed Actions

1) Repairs were made by procuring and installing a new flood seal so that the flow path has been plugged.

2) The flood seal integrity for all the spare conduits that interface with the Switchgear Rooms was checked and found acceptable.

Planned Actions

1) Complete investigation and causal evaluation.

2)

Replace all screw type flood seals in spare conduits with an Engineering approved substitute.

3)

Revise surveillance procedure to verify seal tightness through physical inspection.

(If more space is required, use additional copies of NRC Form (366A)

Previous Similar Events

In 1997, VY reported the potential for water intrusion into the Vital Switchgear Rooms via underground conduits during Maximum Postulated Flood Conditions due to a design vulnerability that resulted in conduit seals not being installed (LER 97-002-01, dated 05/29/1997).

No previous similar events have been reported in the last 5 years.