ML083380490
| ML083380490 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 10/14/2008 |
| From: | Entergy Nuclear Operations |
| To: | NRC Region 1 |
| Jackson D RGN-I/DRP/PB2/610-337-5306 | |
| Shared Package | |
| ML083380467 | List: |
| References | |
| Download: ML083380490 (80) | |
Text
Vermont Yankee Cooling Tower Update October 14, 2008 ML083380490
Agenda
Introductions
Basic Plant Overview
Cooling Tower Overview
- Normal Cooling Function
- Safety Function
Cooling Tower Events
- Three Events
- August 2007
- July 2008
- September 2008
- Event Causes and Corrective Actions
- Event Summary
Long Range Planning
Introductions
Introductions
Ted Sullivan, Entergy Site Vice President
Chris Wamser, Gen. Manager Plant Operations
John Dreyfuss, Director, Nuclear Safety Assurance
Norm Rademacher, Director of Engineering
Basic Plant Operation
River Tower Tower Condenser
Functions of the Cooling Towers
Cooling Tower Functions Normal Cooling Function Safety Function
Cooling Function
Cooling Function Purpose Modes of Operation Design Overview Design Features
Cooling Function - Purpose Cool River Water prior to return to Connecticut River Maintain Environmental Conditions for river NPDES Thermal Discharge Permit
Cooling Water Modes of Operation
Cooling Water Modes Open Closed
Intake Discharge Cooling Towers C
o n
d Open Cycle Towers River
Intake Discharge Cooling Towers C
o n
d Closed Cycle Towers River
Modes of Operation - Summary Cooling Tower operation is dictated by River Conditions
- Season
- River Flow
- River Temperature
Cooling Tower Design
Cooling Tower Design go to page 21
AIR FLOW WATER VAPOR HEAT REJECTED go to page 25
Back to pg. 21
Back to pg. 21
Cooling Tower Design Features
Design Features Two 500 Long Towers
- Tower 1 (East)
- Tower 2 (West) 11 Cells per Tower Each Cell has one fan and motor Water distribution system go to page 28
Design Features -
Water Distribution Two Distribution Headers per Tower 90,000 GPM each Multiple Sections, Bell and Spigot Joint Design Pipe Size Varies: 60 to 24 Water Deck / Distribution Valves Fill Material go to page 32
Back to pg. 28
Back to pg. 28
Design Features -
Structural Support Loads:
3/4 Water (primary) 3/4 Fan/motor (secondary)
Saddle Configuration - HOLDS UP PIPE Columns - support water and fans Joints go to page 35
Back to pg. 32
Safety Function
Safety Function Safety Related Cell 2-1 Seismic Qualification Cell 2-2 Alternate Cooling - Loss of Intake Independent from normal Cooling Function
Photo Safety-related Seismic Design
Safety Related Cell CT2-1 Provides Backup Source of Cooling Plant Condenser Discharge to River Safety Equipment Cooled Shutdown Cooling System Backup Electricity Generators Spent Fuel Pool
Independent Safety Piping
Cooling Tower Events
Cooling Tower Events August 2007: Cell 2-4 Failure July 2008: Support Saddle Failures September 2008: Distribution Header Leak
Cell 2-4 Failure August 2007
Cell 2-4 Failure Causes of Event Corrective Actions
Cell 2-4 Failure -
Cause of Event Two support columns failed Failure of B Columns caused Distribution Header to sag
- Loosened slip joints and caused large leaks Additional water increased weight on remaining support columns Other Support columns overloaded and failed Resulted in a partial collapse go to page 47
C
C B
C B
A S
C B
A
C B
A
C B
A B Column Failure Point
Cell 2-4 Failure - Causal Investigation Root Cause:
Support columns failed due to overload condition Other Causes:
3/4 Inadequate Inspection Methods of Wood Structure 3/4 Inadequate Preventative Maintenance Contributing Cause: Design of Fill Material
Cell 2-4 Failure -
Corrective Actions Rebuilt Cell 2-4 Completed Extent of Condition Inspections and Repairs Fully Revised Inspection Procedures and Acceptance Criteria Established 2008 Cooling Tower Project Plan
Cell 2-4 Failure -
Corrective Actions Phase 1 of Long Range Plan - Completed May 2008 1/3 Replacement - (Bay 4)
New Structural Member Material: Fiberglass Reinforced Plastic (FRP)
New Fill Material Extent of Condition Repairs Used External/Fleet Technical Expertise Long Range Plan go to page 63
2008 Cooling Tower Project (Phase 1)
Fire Wall Typical Cooling Tower Cell Fire Wall Plenum Area Walkway Distribution Header Bay 1 Bay 2 Bay 3 Bay 4 Bay 5 Bay 6 Bay 7 A
B C
S A
B C
S
57
28
July 2008 Event
July 2008 Event Field Observation Leak in Distribution Header (Cell 1-1 East, ~60 gpm)
Broken/Degraded Saddles (4 in tower 1, 2 in tower 2)
Cause of Event Wooden Saddle to FRP Connection Identified by VY Design Engineering prior to placing tower in service Incorrect Technical Assessment by Engineering/Vendor Limited to FRP/Wood Saddles go to page 67
Back to pg. 64
July 2008 Event Corrective Actions Full extent of condition walkdowns Repaired all saddles/connections Revised design documentation
September 2008 Event
Distribution Header Leak -
Initial Actions
Operations Field Observations:
Potential depression in fan deck Leak in distribution header piping
Cooling water to towers promptly secured
Remained at 100% plant power output for ~ 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />
Lowered power to 55% due to river flow
Distribution Header Leak -
Inspections
Walkdowns performed using revised inspection procedures
Leak NOT caused by structural problem
Cause: Packing leak attributed to start/stop of cooling water pumps (not uncommon)
Additional inspections - 8 degraded columns:
- 1 Level 1 - replace; unrelated to leak
- 3 Level 2 adjacent to Level 1 - replace
- 4 Level 2 - address next maintenance window go to page 72
Inspection Acceptance Criteria Level 1: Replace immediately Level 2:
9 If adjacent to Level 1, replace immediately 9 Otherwise, replace next maintenance period Level 3: Inspect/monitor
Distribution Header Leak -
Corrective Actions Leak repaired Replaced support columns
Cooling Tower Event Summary
Cooling Tower Event Summary
Safety function not affected
Maintained compliance with federal/state discharge permit
No impact from power uprate
Revised Inspection procedures/organizational sensitivity effective
Substantial investment in reliability improvements
Long Range Plan
Long Range Plan Phased approach based on maintenance availability 3/4 Phase 1: Bay 4 Complete 3/4 Phase 2: Bay 2 Spring 2009 3/4 Phase 3: Bay 6 Spring 2010 Other inspections/repairs based on revised methods/procedures
Phase 1 Bay 1 Bay 2 Bay 3 Bay 4 Bay 5 Bay 6 Fire Wall Bay 4 C & B Supports Water pipe header / water deck Typical Cooling Tower Cell Bay 7 Fire Wall
Bay 1 Bay 2 Bay 3 Bay 4 Bay 5 Bay 6 Bay 7 Fire wall Bay 2 C & B Supports Water pipe header / water deck Typical Cooling Tower Cell Phase 2 Fire wall
Water pipe header / water deck Typical Cooling Tower Cell Phase 3 Bay 1 Bay 2 Bay 3 Bay 4 Bay 5 Bay 6 Bay 7 Bay 6 C & B Supports Fire wall Fire wall