ML092940701

Slides for October 22, 2009, Public Meeting, Buried Piping Experience

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 Exe Its n.

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

. - - - - __ ",11 __

ExeICYri.O 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 SusceptibtlityFlow Chari 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

• NDE Piping Prep, UT, RT

• 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 Exe10 ri.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