05000335/LER-2014-001, Regarding Internal RAB Flooding During Heavy Rain Due to Degraded Conduits Lacking Internal Flood Barriers
| ML14087A011 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 03/10/2014 |
| From: | Jensen J Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2012-066 LER 14-001-00 | |
| Download: ML14087A011 (4) | |
| 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) |
| 3352014001R00 - NRC Website | |
text
FFPL.
March 10, 2014 L-2012-066 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Re:
St. Lucie Unit 1 Docket No. 50-335 Reportable Event: 2014-001 Date of Event: January 9, 2014 Internal RAB Flooding During Heavy Rain Due to Degraded Conduits Lacking Internal Flood Barriers The attached Licensee Event Report 2014-001 is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.
Respectfully, Site Vice President St. Lucie Plant JJ/KWF Attachment Florida Power & Light Company 6501 S. Ocean Drive, Jensen Beach, FL 34957
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 (02-2014)
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.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections
- LICENSEE EVENT REPORT (LER)
Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by LI E
E T Rinternet 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 for each block) 20503. It a means used to impose an information collection does not display a cun-ently valid OMB digits/characters control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the intormation collechon.
- 3. PAGE St. Lucie Unit 1 05000335 1 OF
- 4. TITLE Internal RAB Flooding During Heavy Rain Due to Degraded Conduits Lacking Internal Flood Barriers
- 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 FACILITY NAME DOCKET NUMBER 1
9 2014 2014-001 0
3 10 2014 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D1 20.2201(b)
F1 20.2203(a)(3)(i)
D 50.73(a)(2)(i)(C)
D 50.73(a)(2)(vii)
[] 20.2201(d)
F] 20.2203(a)(3)(ii)
[]
50.73(a)(2)(ii)(A)
[]
50.73(a)(2)(viii)(A)
D 20.2203(a)(1)
[
20.2203(a)(4) 50.73(a)(2)(ii)(B)
D 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)
- 10. POWER LEVEL F1 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
[]
50.73(a)(2)(iv)(A)
F1 50.73(a)(2)(x)
ED 20.2203(a)(2)(iii)
[
50.36(c)(2)
[]
50.73(a)(2)(v)(A)
D 73.71(a)(4)
El 20.2203(a)(2)(iv)
[
50.46(a)(3)(ii)
D 50.73(a)(2)(v)(B)
D 73.71(a)(5) 100 E] 20.2203(a)(2)(v)
[
50.73(a)(2)(i)(A)
[
50.73(a)(2)(v)(C)
[
OTHER r5 5Specify in Abstract below or in
______________ 20.2203(a)(2)(vi) 50.73(a)(2)(t)(B)
- 5)
Description of the Event On January 9, 2014, St. Lucie Unit 1 was in Mode 1 operation at 100 percent reactor power. The St. Lucie site was experiencing heavy rainfall. In the early afternoon the site storm drain system was challenged as the storm water basins started to back up.
At -1610 hours, operators reported that water was backing up through the -0.5 feet elevation floor drains in the reactor auxiliary building (RAB) and into the emergency core cooling system (ECCS) pump room sumps at the -10.0 feet elevation. The water was observed entering the RAB through an electrical junction box which was below the elevation for which the RAB flood protection was designed.
At -1620 hours, the control room received the B Safeguards Pump Room Sump Level High/High-High alarms.
At -1628 hours the operators entered procedure 1-AOP-24.01, "RAB Flooding," and immediately closed the ECCS sump isolation valves to preclude flooding of the ECCS pump room. However, the water level in the RAB
- - 0.5 feet elevation continued to rise.
At -1635 hours, after deliberation between the field operators and the Control Room, the operators decided to control the RAB flooding by cycling the ECCS sump isolation valves to allow batch removal of RAB water via the ECCS sump pumps.
At -1732 hours, a higher capacity temporary pump at the yard sump was used to reduce the rate of water entry into the RAB.
At -1803 hours, an Unusual Event (UE) was declared as the significant rainfall exceeded the site's storm drain system capacity.
The UE was terminated at -0001 hours on January 10, 2014, after the significant rains subsided and the storm drain were observed draining site water accumulation.
All safety related accident mitigation and safe shutdown equipment remained operable prior to, during, and after the event.
Cause of the Event
The cause of the RAB flooding was due to' legacy installation issues with two non-safety electrical conduits [EIIS:CND] in the ECCS pipe tunnel that lacked the required internal flood barriers. Degradation of the conduits provided a water entry path into the R.AB. The extent of condition identified four more conduits with the same legacy installation issue, for a total of six conduits without internal flood seals. Qualified flood seals have now been installed where these conduits terminate in the building in order to restore the RAB to a waterproofed condition. The Organizational and Programmatic portion of the root cause evaluation is on-going at the time the LER was submitted. This LER will be supplemented once the evaluation is completed, approximately 60 days from the date of this LER.
The direct cause of the storm water basin back up that allowed the ECCS pipe tunnel to flood was blockage of the piping that connects east storm water basin to the overflow basin. The blockage that contributed to the storm drain system flow restriction has been removed.
Analysis of the Event
This condition is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(B) as an event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety. Although this event did not result in any loss of function, postulated external flooding events could result in RAB water levels exceeding the analyzed RAB internal flooding event, as a result of the discovery of these missing conduit seals. This is contrary to design as it is assumed that design features seal the RAB below the +17.2 feet elevation from water sources external to the RAB.
The site is comprised of an east and a west drainage system that outflows to the east and west storm water basins, which in turn flow to the southwest overflow basin and to the southeast overflow basin through a 36-inch interconnection. The southeast overflow basin has a high level outflow valve that can be opened during excessive rainfall events. Due to flow blockage from the east storm water basin to the overflow basins, the severe rainfall caused the water level of the east storm water basin to rise above its banks and flood the plant area west of the G1 and G2 warehouses. Once the water level exceeded the elevation of the Unit 1 component cooling water (CCW) building floor (elevation +12 feet) the building no longer drained and allowed the backflow to flood the adjacent ECCS pipe tunnel and yard sump. The degraded conduit within the ECCS pipe tunnel, along with the lack of internal conduit flood barriers in the RAB side, provided a direct path for water to enter the RAB.
The water intrusion into the RAB continued until the storm drain blockage was corrected and the remaining volume of water in the ECCS pipe tunnel drained into the building. Operators took action to remove the flood water, by cycling the ECCS room sump isolation valves in order to utilize the installed sump pumps.
As previously noted, during this event there was no loss of safety related accident mitigation or safe shutdown equipment. Florida Power & Light (FPL) is currently evaluating various external flooding scenarios to determine if any postulated conditions could have resulted in, the loss of safety related accident mitigation or safe shutdown equipment. Once this evaluation is complete, FPL will provide a supplement to this LER.
Safety Significance
The safety significance of the RAB flood protection bypass provided by the degraded conduits is currently being assessed by FPL, and will be provided in a supplement to this LER.
Corrective Actions
- 1. All conduits identified as lacking internal flood barriers during the extent of condition reviews were provided with qualified seals.
Failed Component(s)
Various non-safety conduits
Similar Events
On December 27, 2012, FPL reported degraded penetration seals within electrical manways that bypassed St.
Lucie Unit 1 RAB external flood protection features in LER 50-335/2012-010. This original construction legacy issue was discovered during the Fukushima 50.54(f) flooding walkdowns that were performed as part of the NRC-approved NEI walkdown scope. Unit 2 was also identified to have unsealed conduit penetrations, but was not included in that LER as a flooding evaluation performed at the time concluded Unit 2 was bounded by its internal flooding analysis. Once complete, the insights developed from the detailed St. Lucie flooding models being developed for the recent event will be applied to the 2012 LER condition. If any conditions are identified that exceed previous analysis results, those conditions will be reevaluated for impact on equipment operability and reportability.