ML092940701
| ML092940701 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 10/21/2009 |
| From: | Exelon Generation Co |
| To: | Office of Nuclear Reactor Regulation |
| Miller G, NRR/DORL, 415-2481 | |
| References | |
| Download: ML092940701 (11) | |
Text
Exelon~
Oyster Creek I Exelon Buried Piping Experience October 22, 2009 ExeItsn.
Oyster Creek I Exelon
./ Agenda
- Overview
- Oyster Creek Underground Piping Leaks
- Buried Piping Program
- Exelon Experience & Plan
- Technical Discussion of Lessons Learned for Buried Piping Experience 1
Exelon~
Overview
./ Exelon has changed approach-more proactive
./ Exelon is inspecting buried piping at all sites with a formal program consistent with industry approach
./ Long term repair/replacement projects being identified to improve the reliability of high risk piping
./ No public health or safety consequences
./ Affected public perception / confidence Exelon.
April 2009 Tritium Leak
./ Leaks in the 8-inch and 10-inch carbon steel Condensate Transfer System lines
./ 8-inch line understood to be Stainless Steel
./ 10-inch line under vacuum during power operation
./ No plant operational or nuclear safety issues associated with the leaks 2
Exelon.
April 2009 Tritium Leak
./ Causes
- Root Cause 1: "anodic dissolution" in conjunction with a susceptible material
- Root Cause 2: erroneous assumptions in program basis led to flawed tritium mitigation strategy
- Contributing Cause 1: improperly applied coatings during repairs in the early 1990s
- Contributing Cause 2: change management processes were inadequate
- Contributing Cause 3: 100% verification of piping integrity is not practical Exelon.
April 2009 Tritium Leak
./ Corrective actions to prevent recurrence
- Move affected dlrectburled piping either above ground or in monitored trenches
- Perform a thorough program assessment and update the program based on the results 3
Exelon.
August 2009 Tritium Leak
,/ Six-inch aluminum Condensate Transfer line
,/ Piping leak occurred inside the Turbine Building wall penetration
,/ Identified through Turbine Building sump pump-down rate
,/ No plant operational or nuclear safety issues associated with the leak Exelon.
August 2009 Tritium Leak
,/ Causes
- Root Cause 1: galvanic corrosion resulting from a coating breach
- Contributing Cause 1: incomplete extent of condition reviews
- Contributing Cause 2: buried piping program does not include piping internal to penetrations and the conditions of the penetrations are typically unknown 4
Exelen.
August 2009 Tritium Leak
../ Corrective actions to prevent recurrence
- Implement a risk-based strategic inspection plan including all piping traversing though piping penetrations
../ Additional corrective actions
- Institutionalize guidance to document as-left conditions following excavations
- Inspect all piping penetrations and document the as-found and as-left conditions ExeICYri.O
- __ ",11 Buried Piping Program
../ Goal: Ensure structural integrity, prevent forced outages, avoid emergent repairs, eliminate environmental impact and enable sites to implement well planned repairs in a timely manner.
../ Process is 4 steps
- 1. Pre-Assessment Analysis
- 2. Indirect Assessment
- 3. Direct Examination
- 4. Post Assessment 5
Exelon.
Exelon Buried Piping Program Approach
./ The original approach for the Exelon Buried Piping Program was to categorize the high risk piping, perform inspections, and repair/replace based on unacceptable inspection results and/or actual leakage.
./ The approach has changed to add a proactive replacement or containment strategy to the Buried Piping Program as a Strategic Capital Project Exelon.
Buried Piping Program Scope
.Il!R.IlIr.n Direct E:umlneUon ftgme 1:
Four -Step Process for the B..-ied Pipe and Raw W"l8f Piping Program 6
Step 1 Pre-Assessment Analysis
,/ Buried Pipe Governing Procedures Buried Piping Program Guide Raw Water Corrosion Program Guide Buried Piping Exam Guide Buried Piping Performance Indicators
,/ Risk {R} defined as: R =Susceptibility x Consequences o Susceptibility factors:
o Is cathodic protection applied o Leak history o Age of coating, condition of coating o Location: Under tracks, roadway, building penetration (depth) o Process fluid o Soil o Consequence Factors:
o Safety o Piping contains environmentally sensitive fluids (Rad-Waste, tritium, fuel 011) o LCO associated with the piping (SR Service Water) o Lost production required to repair (high repair cost)
Exelon.
FIgUre4B.
Buried Pipe SusceptibtlityFlowChari 7
Exel~m, Step 2 Indirect Assessment Met Inspection Purpose Key Conditions Method Under Shielded NeM Cased Parallel Stray Deep Under pevcd corrosion River/
piping pipe-Current HighAC roads activity were-line voll Close lute-val Assess 3
3 2
3 2
2 2
2 Survey(CIS) effectiveness ofCP system Electro-magnetic Locate coating 2
3 2
3 2
2 2
3 defects Pearson Locale coating 3
3 3
3 3
2 2
2 defects CUITaltVoltage Locate coating 3
3 3
3 1,2 1,2 2
1,2 GraWml(ACVG defects DCVG)
C*Sc<ln (AC)
Locale coaling 2
3 2
3 1,2 1,2 2
3 CICOS detects Torsional Guided Wall thickness 4,6 4,6 3,6 4,6 4,6 4,6 4,6 4,6 Wave survey RemoteField Pinillg& Wall 4,5 4,5 4,5 4,5 4,5 4,5 4,5 4,5 Eddy Current thickness (RFEC) 1 =Applicable: capable of locating small holidays in coatlng (Isolated and < 11n2),and conditiona that do not cause CP fluctuations 2 =Applicable: capable of detecting large (isolated or continuous) coaUng ho~daY6 3 =Not applicable to this method without additional considerations.
4 = Wall thickness survey G-wave and RFEC only.
5 =RFEC requires access to (pitch), pipe Internal, and needs an exit point. Tool must traverse the length of pipe inspected. Pipe may need to be taken out of service.
6 =The G-wave signal becomes more attenuated ee overburden becomes greater; therefore, the effectiveness decreases.
Step 3 Direct Assessmel,ts
./ Buried Piping: External Corrosion
- Excavations have significant impact on plant operations
- Coating evaluation
- NDE: Piping Prep, UT, Pit depth, extent
./ Raw Water: Internal Corrosion
- Plant OE; external corrosion above ground interfaces
./ Contingencies required to be in place
- Pre-assessment corrosion (flaw) handbook
- Parts / materials 8
Exelori.7 Step 4 Post Assessment
./ Corrosion Rate is the key
./ Remaining Life
./ Time to next inspection
./ Effectiveness of inspection methods
./ Update the Database & Program documents
./ Repair/Replace Recommendations Exe10ri.8 Exelon Experience 2009
./ Experience in proactively identifying degraded piping using indirect assessment methods.
./ Failures related to:
- Age of piping
- Coating condition
- Initial construction backfill conditions
- Effectiveness of cathodic protection
./ Development & application of new NDE techniques and associated limitations
./ Repair technologies
- Cured in place
- Carbon fiber wrap
- Traditional methods 9
Short and Long Term Plans
./ Short Term (<3 years):
- Continue with program of indirect assessment and follow-up direct assessment as degraded segments are identified
- Optimize Cathodic Protection Systems
- Mitigation of known buried piping system vulnerabilities
- Initiate use of high density polyethylene (HDPE) on buried piping for long term corrosion prevention
- Plan for proactive replacemenUmitigation of high risk buried piping segments
./ Long Term (>3 years):
- New Technology Inspection Applications to complete initial indirect assessment of high risk buried piping
- Incorporate use of high density polyethylene (HDPE) on Buried ASME Class 3 piping for long term corrosion prevention and to minimize risk
- Plan for large scale repairs/replacements projects with corrosion resistant materials and to improve operational flexibility ExeIOtf.O Challenges/Barriers/Gaps
./ Original Design Practices
- Building construction over piping, inaccessible piping
- Poor original cathodic protection design
- Piping not designed for current inspection methods
- No access to piping internals
- Concrete encased
- Piping depth up to 35 feet
- Insulated flanges
./ Importance of Cathodic Protection not fully recognized
./ Contingencies for Buried Piping Work
- Applying new inspection technologies (non-code) to effectively inspect buried piping
- Challenge for timely repair of degraded piping 10
Summary
./ Exelon has changed approach-more proactive
./ Exelon is inspecting buried piping at all sites with a formal program consistent with industry approach
./ Inspections of buried inaccessible piping is a challenge and new technology is being developed
./ Approval of corrosion resistant material for repairs and replacements needed for long term plans
./ Long term repair/replacement projects being identified to improve the reliability of high risk piping 11