Tank

Operations

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Double-Shell

Tank Corrosion

Chemistry

Control &

Monitoring

May 30, 2013

Tank

Operations

Contract

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Double-Shell Tank Chemistry Control

Key Elements of Tank Corrosion Control and Monitoring

Predictive Elements Chemistry Control (Hydroxide/Nitrite)

Hydroxide Depletion

Waste Compatibility Assessments

Laboratory Testing

Monitoring and Evaluation Corrosion Probe Monitoring

Ultrasonic Testing

Visual Inspections

Overall DST Integrity Program Schedule

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Waste Chemistry Corrosion Control

Objective: Limit corrosion inside the DSTs

Maintain established pH and nitrite (NO2-) concentration to

limit pitting corrosion and prevent cracking corrosion

Refine pH and NO2- ranges using corrosion testing program

with guidance from the Expert Panel Oversight Committee

DSTs are controlled to requirements defined in OSD-151-T-00007, Operating Specifications for the Double-Shell Tanks

Why is it Important to Establish the Minimum Essential Corrosion

Protection Needed to Preserve the DSTs?

Every 1,000 gallons of 50% NaOH added to a DST for pH corrosion

control increases the Na inventory by 1.65 MTs, extending the WTP

mission between and 1 days depending on feed envelope. In 4

years during the FY2000 2005 period, 288 MTs of Na were added to the DSTs for pH control, extending the WTP mission by ~ 144 days.

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Waste Chemistry Corrosion Control

(as described in OSD-151-T-00007)

Why are Hydroxide (OH-) and Nitrite (NO2) Important for DST

Chemistry Corrosion Control?

Pitting and stress cracking are the principal forms of corrosion attacking

the carbon steel DSTs. OH- additions increase the pH, preventing

pitting; and NO2- additions prevent initiation of nitrate-induced stress

cracking corrosion.

Double-Shell Tank Waste Corrosion Chemistry Controls

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OSD-151-T-00007 Limits Vary with

Temperature

Limits change based on waste temperature

At low waste temperatures, no concern of SSC, protection from pitting based on modest [OH-]

concentration

At high waste temperatures, greater need for higher [NO2

-] concentrations to prevent cracking

Minimum pH requirements of 12 (0.010M [OH-])

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Implementation of OSD Chemistry Control

Conduct periodic sampling of the waste in DSTs to determine the [NO2

-], [NO3-], and [OH-] concentrations, and to verify that measured

concentrations are within the limits

Establish and maintain a database to track the [NO2-], [NO3

-], and

[OH-] concentrations in each DST

Prior to waste transfers, the final states of the shipping and receiving DSTs are evaluated for compliance with the waste chemistry limits (Waste Compatibility Program)

Waste samples are analyzed per the requirements of a Tank Sampling and Analysis Plan (TSAP) and when results are not in

compliance with the TSAP:

Out-of-specification chemistry must restored within 30 days or an Operating Specification Recovery Action Plan prepared to restore [NO2],

[NO3-], and [OH-] concentrations within established limits

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Basis for Periodic Sampling

Sampling requirements identified in annual update to RPP-7795 Chemistry Control Technical Basis

RPP-7795 identifies which DSTs are approaching limits with prediction of when they should be sampled

Default sample interval is once/five years; up to ten years allowed if model determines longer interval is justified

Tanks containing highly-concentrated liquids, such as double-shell slurry (typically Waste Group A tanks), show chemical stability and a

longer interval may be justified

The database is RPP-13639 Caustic Limits Report, updated every year, and just recently issued

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Corrosion Chemistry In-Tank Changes

Hydroxide depletion occurs by

CO2 absorption at supernatant surfaces

Oxidation of organic species

Reaction with aluminum solids

Mechanistic Hydroxide Demand Model and empirical Hobbs model require ventilation air flows to estimate

absorption of CO2 by waste

Flows for most tanks are individually controlled

Aging waste tanks (AY & AZ Tank Farms) have shared primary ventilation system

SST Waste Retrieval

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Chemistry Control During Retrieval

SST solids are expected to have some hydroxide depletion during retrieval during to:

Aluminum dissolution

Carbonate/Bicarbonate and Phosphate/Biphosphate buffering

The body of corrosion testing indicates little risk of corrosion at the high [NO2

-] concentration and low supernatant temperature (< 40oC [104oF]),

even with some [OH-] depletion

Approach to SST Retrieval

Start with the DST supernatant within corrosion chemistry limits

Sample DST supernatant at an appropriate point during retrieval (usually ~50% completion)

Be prepared to respond with [OH-] addition at an appropriate time, supported with more specific information from samples

Resample after [OH-] has been added and/or retrieval has been completed to verify tank has been returned to specification

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Laboratory Testing

Provides the basis for specification changes and to understanding of corrosion propensity for any off-normal

conditions discovered

Includes testing for pitting propensity by Cyclic Potentiodynamic Polarization (CPP) and cracking by Slow Strain Rate Testing

(SSR)

222-S Laboratory for CPP tests on actual tank waste samples

Det Norske Veritas Laboratory (DNV) and Savannah River National Laboratory (SRNL) for more extensive testing with waste simulants

Special test plan under development to evaluate vapor-space corrosion

Understand effect of ammonia as inhibitor

All work guided by Expert Panel (EPOC)

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In-Tank Corrosion Monitoring

Five tanks currently fitted with corrosion monitoring systems and corrosion coupons

Waste corrosion potentials have been stable

Coupons removed from the tanks have shown little sign of corrosion (

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Primary Tank Wall Ultrasonic Inspection

Inspections conducted on a eight to ten year cycle

Two 24-inch risers used to gain access to the annulus

Walls cleaned as necessary

Inspections performed:

Four 15-inch wide full height wall inspections

Examine 20 feet of vertical and horizontal welds

Criteria: 20% wall loss, 50% through wall pitting, and critical crack lengths

All DSTs have completed a minimum of one UT cycle; 60% two or more UT cycles; 10% three UT cycles through FY 2012

Force Institute PSP-4 Plus Digital System on AWD-5 Crawler

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Primary Tank and Annulus Video Inspections

Video inspections performed on a five to seven year interval

Inspect all four quadrants

Re-inspect areas of interest identified in the Tank Integrity Inspection Guide [Archived Inspection database]

Water intrusion inspection done every two years in each tank farm

Annulus Extent of Condition Inspections completed to establish visual baseline for DSTs with construction histories similar to tank AY-102

Examined between ten to twelve risers

Created >95% visual reference for annulus floor and portion of primary tank visible from inspection risers

Radiation-hardened, Pan, Tilt, Zoom Auto-focus Inspection Cameras

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Double-Shell Tank Integrity Program Schedule

Expert

Panels

Field Work

Ultrasonic Testing

Visual Inspections

Technology

Ultrasonic Testing

Visual Inspection

Chemistry Optimization

Probe Design

1997 1998 2001 2002 2004 2006 1999 2000 2003 2005 2007

BNL-52527

Tank Structural Integrity Panel

PNNL-13571

DST Life Extension

1996 2008

First Round of UT for 28 DSTs

BNL-52361

Structural Analysis Guideline Panel

RPP-RPT-22162

Waste Chemistry Optimization

RPP-19438

Waste Level Rise

RPP-31129

Vapor Space

Corrosion

Activities

Forensic First

AN-107 Probe

Forensic Second

AN-107 Probe

First Generation

Electro-Chemical Noise Probes

Electro-Chemical

Noise Probes

Multi-Function

Corrosion Probes

Analog Ultrasonic

Testing

Digital Ultrasonic

Testing

Knuckle Ultrasonic

Testing

Potential Measurement

Corrosion Probes

Tank Specific

Testing

Bounding Chemistry

Analysis

Limited Access Analog Cameras Digital Cameras

Second Round of

UT for 6 DSTs

Continued UT of DSTs

2009 2010 2011

Forensic AY-101 Probe

Forensic AN-102 Probe

Vapor Space, Liquid Air Interface, and Pit Corrosion

Expert Panel Oversight Committee

2013 2012 2014 2015 2016

Stress Corrosion Cracking

Replaceable Corrosion

Monitoring Probes

Integrity

Assessments RPP-28538 Double-Shell Tank

Integrity Assessment,

HFFACO, Milestone M-48-14 Update RPP-28538

Tank AY-102 Leak / DST

Extent of Condition