05000390/LER-2012-002, Regarding Unanalyzed Condition Affecting Probable Maximum Flood (PMF) Level
| ML12241A315 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 08/28/2012 |
| From: | Grissette D Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LER 12-002-00 | |
| Download: ML12241A315 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3902012002R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 August 28,2012 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
10 cFR 50.73 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390 Licensee Event Report 39012012-002, Unanalyzed Gondition Affecting Probable Maximum Flood Level This submittal provides Licensee Event Report (LER) 39012012-02. This LER provides details concerning an unanalyzed condition affecting the probable maximum flood level for Watts Bar Nuclear Plant. The condition is reported as an LER in accordance with 1 0 cFR 50.73(a)(2)(iiXB).
There are no regulatory commitments in this letter. Please direct any questions concerning this matter to Donna Guinn, WBN Site Licensing Manager, at (423) 365-158e.
Respectfully,
. E. Grissette Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Page 2
U.S. Nuclear Regulatory Commission Page 2 August 28,2012 Enclosure cc (Enclosure):
NRC Regional Administrator - Region ll NRC Senior Resident Inspector - Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION 110-2010)
LTGENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
APPROVED BY OMB: NO. 3150-0104 EXPIRES. 10t311201s
, the NRC may not conduct or sponsor, and a person is not required to respond to, the i nformation col lection.
- 1. FACILITY NAME Watts Bar Nuclear Plant (WBN) Unit 1
- 2. DOCKET NUMBER 05000390 5
1
- 3. PAGE OF
- 4. TITLE Unanalyzed Condition Affecting Probable Maximum Flood (PMF) Level
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.
MONTH DAY YEAR FACILITY NAME N/A DOCKET NUMBER 06 29 2012 2012 r 002 r 0
08 28 2012 FACILITY NAME N/A DOCKET NUMBER
- 9. OPERATING MODE 1
I 20.2201(b) tl 20.2201(d) tl 20.2203(aX1) tr 20.2203(aX2Xi) n 20.2203(aX2Xii)
! 20.2203(aX2Xiii) tr 20.2203(aX2)(iv) tr 20.2203(aX2Xv) tl 20.2203(aX2Xvi) tl s0.73(aX2XiXc) n 50.73(aX2XiiXA)
X 50.73(aX2XiiXB) tr 50.73(ax2xiii) tr 50.73(aX2XivXA) tr 50.73(aX2XvXA) n 50.73(aX2XvXB) tr 50.73(aX2XvXc) tr 50.73(aX2XvXD)
! s0.73(aX2Xvii) tr 50.73(aX2XviiiXA) tr 50.73(aX2XviiiXB) tr 50.73(aX2Xix)(A) tr s0.73(aX2Xx) n n.71(aX4) tr r3.r1(aXs) tr orHER Specify in Abstract below or in Date February 1,2012 Event While conducting preliminary hydrologic analysis for the proposed TVA Clinch River site, topographical areas upstream of the Watts Bar Dam were identified that are potential overflow/rim leakage areas during a PMF event. These areas were not discovered during previous hydrology analyses. No immediate/interim actions for impacted safety related equipment were required.
Updated PMF calculation changed the WBN design basis PMF to Elevation 739.2ft. This would result in a design basis flood level of 741.7 ft MSL exterior of the IPS on the Intake Channel side. Because the interior of the IPS is hydraulically connected to the exterior of the IPS on this side of the structure, the water could enter the interior of the IPS on Elevation 741 ft, travel over concrete door thresholds located at Elevation 741.5 ft and potentially affect safety related ERCW and HPFP equipment located on Elevation 722 ft of the lPS. Earlier preliminary calculations had indicated that the WBN PMF elevation could be increased to 739.2ft MSL and affect IPS equipment, and sandbags were already staged at the IPS to protect equipment during a PMF event.
An application to revise the WBN Unit 1 UFSAR regarding changes to hydrologic analysis was submitted for NRC review.
c.June 29,2012 July 19, 2012
Other Systems or Secondary Functions Affected
No other systems or secondary functions were affected by this event.
Method of Discovery
While conducting preliminary hydrologic analysis for the proposed TVA Clinch River site, topographical areas upstream of the Watts Bar Dam were identified that are potential overfloWrim leakage areas during a PMF event. This resulted in issuance of an updated calculation titled "PMF Determination for Tennessee River Watershed."
F.
Operator Actions
WBN operations procedures were revised to incorporate contingency measures to protect ERCW and HPFP equipment located on ElevationT22 ft of the lPS.
D.
E.
ilr.
G.
Safety System Responses No safety system activation occurred.
CAUSE OF EVENT
The apparent cause for the PMF flood level increasing to Elevation 739.2 ft is due to the use of geographical information system (GlS) technology to more accurately map topographical areas upstream of Watts Bar dam, as well as the use of updated hydrological modeling software.
These technological advances in geographical mapping and computer modeling provide a more conservative determination of flood levels and were not available during the original licensing of WBN Unit 1.
ANALYSIS OF THE EVENT
On June 29,2012, TVA approved an updated calculation titled "PMF Determination for Tennessee Valley Watershed" that increased the WBN design basis PMF level to Elevation739.2ft MSL.
WBN is required to be able to place and maintain the plant in a safe shutdown condition up to the design basis flood level. Earlier preliminary calculations had indicated an increase in PMF elevation, and contingency measures to protect the TBBP motors, and ERCW and HPFP equipment located in the IPS had already been put in place. No actualflooding occurred; however, because of the unanalyzed condition, the potential existed for WBN to exceed its design basis PMF and adversely affect plant safety.
ASSESSMENT OF SAFETY CONSEQUENCES
Based on the above "Analysis of the Event," this event did not adversely affect the health and safety of plant personnel or the general public.
CORRECTIVE ACTIONS
A.
lmmediate and Interim Actions WBN entered the information into the Corrective Action Program as Problem Evaluation Report 573093. Prior to official issue of the updated PMF calculation, sandbags were staged at the IPS to protect ERCW and HPFP equipment during a PMF event.
Procedures for flood mode preparation were revised to include contingency measures for protection of ERCW and HPFP equipment located on ElevationT22 ft of the lPS.
B.
Corrective Actions
The corrective actions are being managed by the WBN Corrective Action Program.
Corrective ac'tions include issuance of a procedure to inspect compensatory measures for flood protection semiannually until permanent plant modifications are installed. The TBBP temporary flood barrier will be installed around the TBBPs. Permanent plant modifications will be installed to provide a flood protection barrier for the TBBPs and affected IPS equipment.
tv.
V.
vt.
VII. ADDITIONAL INFORMATION
A.
Failed Components No failed components have been identified.
B.
Previous LERs on Similar Events A review of reportable events within the last three years did not identify any previous
similar events
C.
Additional Information
No additional information available.
D.
Safety System Functional Failure This event did not result in a safety system functional failure in accordance with 10 CFR 50.73(a)(2)(v) and NEI 99-02.
E.
Loss of Normal Heat Removal Consideration None
VIII. COMMITMENTS
None.