DNV GL © 2014 SAFER, SMARTER, GREENER DNV GL © 2014

Sandeep Chawla and Narasi Sridhar

Modeling of Hanford Double-Shell Tank Waste Simulants

1

OLI Simulation Conference 2014

21-22 October, 2014, Florham Park, NJ

DNV GL © 2014

Background

Hanford Site in southeastern Washington State

– Storage of 55 million gallons of radioactive and chemically hazardous wastes

– From weapons production in WWII and Cold War

Waste stored in 177 underground carbon steel storage tanks

– 149 single shell tanks – SSTs (0.55 to 1M gallon capacity)

– Constructed 1943-1964

– 28 double shell tanks – DSTs (1M gallon capacity)

– Constructed 1968-1986

2

Background information: J. A. Beavers et al., “SCC of Carbon Steel in Nitrate Based

Hanford Waste Simulants,” presentation at CORROSION 2014, San Antonio, TX, March

2014.

DNV GL © 2014

Background

US DOE, Office of River Protection responsible

Current plan

– Transfer wastes from SSTs to DSTs over next 25 years

– Retrieve wastes from DSTs

– Vitrify into glass logs for repository storage

– Close tanks by 2048

Great emphasis on maintaining integrity of both types of tanks

Management of DSTs important for transfer of wastes from SSTs

3

DNV GL © 2014

Background

Nitric acid was neutralized with sodium hydroxide and sodium carbonate

– Primarily nitrate based alkaline wastes

– Some carbonate based wastes

Tanks have three phases

– Supernatant liquid

– Saltcake layer consisting of precipitated salts

– Sludge consisting of metal oxides with an interstitial liquid

4

DNV GL © 2014

Waste leakage

67 SSTs are considered possible leakers

– 750,000 gallons of waste leaked into soils

– Waste discharge to SSTs stopped in 1980

– Pumpable liquid transferred to DSTs

– Saltcake and sludge being transferred to DSTs

Cause of leaks not established

– SCC likely cause for some tanks

– High nitrate concentrations

– Elevated temperature

– Lack of stress relief of weld

5

DNV GL © 2014

Chemistry limits for corrosion control

Research at SRNL and Hanford

established safe waste chemistry

limits for preventing pitting corrosion

and SCC

– Nitrate concentration determines

whether pitting or SCC is concern

– Maintain adequate levels of

hydroxide and nitrite, which are

inhibitors

– Increase inhibitor concentrations

to offset increasing nitrate

concentration from waste transfers

6

B. J. Wiersma and K. H. Subramanian, “Corrosion Control Measures for Liquid Radioactive Waste Storage Tanks at the Savannah River Site,” SRNL-STI-2012-00745, Savannah River National Laboratory, 2012.

DNV GL © 2014

Double Shell Tank DST-AY-102

Tank AY-102

First double-shell radioactive waste storage tank constructed at Hanford

1 million gallon capacity

Completed in 1970, commissioned in 1971

Currently stores hot feed for the vitrification plant

In August 2012, accumulation of radioactive material discovered at two locations

on the floor of the annulus separating primary and secondary liners

– Leak volume estimated between 190 to 520 gallons

– Significant portion of liquid evaporated

– 20 to 50 gallons of drying waste

7

DNV GL © 2014

AY-102 construction

8

J.K Engeman et al., “Tank 241-AY-102 Leak Assessment Report,” RPP-ASMT-53793, Rev. 0, Washington River Protection Solutions, 2012.

Secondary liner • height: 39 ft.-8 in. • bottom diameter: 80 ft. • wall thickness: ¼ in. • Width of annular space

between primary and secondary liners: 2½ ft.

Construction • Primary tank • Secondary liner structure • Concrete shell • Refractory insulating pad

DNV GL © 2014

AY-102 leak assessment

Leak assessment team formed

Consensus agreement

– Radioactive waste on annulus floor was result of breach of primary liner

– Probable leak cause

– corrosion at high temperatures in the tank

– containment margins reduced by construction difficulties and trial-and-error-

repairs leaving residual stresses in the bottom of the primary liner

9

DNV GL © 2014

Secondary liner concerns

Current concerns

– Effect of leaked waste on integrity

– Estimated life

Focus of ongoing corrosion studies at DNV GL

– Localized corrosion: pitting, LAI corrosion

– Stress corrosion cracking: susceptibility, crack growth rate

10

DNV GL © 2014

Waste Simulants

Waste simulants used for corrosion and SCC testing of tank steel

Represent environments likely to be present on the floor of the annulus

– Liquid

– Semi-solid

Simulant chemistry developed through

– Analytical information from waste samples

– Thermodynamic modeling (OLI)

– Laboratory trials

11

DNV GL © 2014

Waste simulant chemistry

Start with non-radioactive, in-tank chemistry

Atmospheric CO2 equilibration calculation

Partial drying/evaporation calculation

Select bounding conditions of pH, temperature

12

DNV GL © 2014

AY-102 in-tank waste composition

13

• A.R. Felmy, O. Qafoku, “Drying of Hanford Tank AY-102 Waste Compositions: Thermodynamic Modeling Results,” PNNL-22758, September 2013.

• Initial CO2 equilibration and evaporation calculations using OLI done at PNNL

• Certain solution compositions exhibited precipitation and required further investigation.

DNV GL © 2014

Development of liquid simulant recipes

14

• Derived recipe for partially dried, atmospheric-CO2 equilibrated waste simulant recipe through OLI

• Determined composition of crystalline precipitates by XRD • Made adjustments to obtain precipitate-free, homogeneous

simulants

DNV GL © 2014

Atmospheric CO2 equilibration of 50S:50IL mixture

15

OLI survey calculation • Determine CO2 in aqueous phase that is in equilibrium with 300-ppm CO2 in

vapor phase at 50oC. • Determine pH of the waste composition

DNV GL © 2014

Partial drying of CO2-equilibrated 50S-50IL mixture

16

Source Chemical Amount in

1-L solution

Calcium chloride 0.012 g

Potassium nitrate 266.975 g

Sodium nitrite 225.288 g

Sodium nitrate 264.719 g

Sodium acetate trihydrate 35.449 g

Sodium chloride 8.456 g

Sodium carbonate 43.031 g

Sodium bicarbonate 5.828 g

Sodium chromate(VI) tetrahydrate 2.364 g

Sodium fluoride 2.234 g

Sodium orthophosphate hydroxide

dodecahydrate 2.734 g

Sodium hydrogen orthophosphate

heptahydrate 40.373 g

Sodium metasilicate nonahydrate 0.039 g

Sodium sulfate 1.463 g

Sodium oxalate 0.838 g

Simulant recipe developed through OLI by

CO2-equilibration and drying to 41 mass%

water (41.A)

OLI

calculation

pH @

50oC

Solids @ 50oC g

MSE 10.7

Sodium chromate decahydrate

3.45

Fluorapatite 0.011

Aqueous 10.0

Potassium nitrate 34.47

Sodium fluoride sulfate

0.71

Sodium oxalate 0.03

Fluorapatite 0.011

Important differences observed in OLI predictions using MSE and Aqueous databanks: • pH • Solids

• amount • composition

DNV GL © 2014

Simulant Preparation in the lab

17

Precipitate

Interface

Simulant: 41.A (OLI calculated)

Precipitation @ 50oC

pH MSE

pH Aq

pH meter

Yes 10.7 10.0 9.9

XRD Analysis of Crystalline Components of Precipitate

Component

Natratine NaNO3

Trona Na3H(CO3)2∙2(H2O)

Niter KNO3

Natrophosphate Na7F(PO4)2∙19(H2O)

Partially dried, CO2-equilibrated 50S-50IL mixture

DNV GL © 2014

Preparation of homogeneous simulant

18

Simulant: 41.B (41.A minus oxalate, phosphate, fluoride)

Precipitation @ 50oC

pH MSE

pH Aq pH

meter

No 10.7 10.1 10.2

Simulant: 41.C (41.A minus 40 g/L KNO3)

Precipitation @ 50oC

pH MSE

pH Aq

pH meter

No 10.6 10.0 9.7

Simulant: 41.D (41.A minus oxalate, phosphate, fluoride and 40 g/L

KNO3)

Precipitation @ 50oC

pH MSE

pH Aq

pH meter

No 10.5 10.1 10.0

Simulant of partially dried,

CO2-equilibrated 50S-50IL mixture

ADJUSTMENTS

Simulant 41.B preferred for corrosion testing as it did not involve reduction of nitrate content

DNV GL © 2014

Modeling of semi-solid waste simulants

Simulant of partially dried, semi-solid

waste observed on annulus floor

termed as “poultice”

Formulation developed from

analytical information on annulus

waste sample

Carbonate/Bicarbonate ratio adjusted

at constant TIC (total inorganic

carbon) through OLI calculation to

achieve target pH of 11

19

Source Chemical mol

Water 10.172

Potassium nitrate 0.997

Sodium chromate(VI) tetrahydrate 0.006

Sodium aluminate 0.349

Sodium carbonate 2.888

Sodium nitrite 1.276

Sodium nitrate 1.922

Sodium fluoride 0.045

Sodium hydrogen orthophosphate heptahydrate 0.022

Sodium metasilicate nonahydrate 0.047

Sodium oxalate 0.034

Sodium formate 0.068

Sodium chloride 0.040

Sodium sulfate 0.011

Sodium bicarbonate 0.704

pH-OLI (20oC) 11.5

pH-meter 1:1 mixture by weight with DI water (~25oC) 10.82

pH-meter 1:1puddle by weight with Equilibrium Liquid (~29oC) 10.51

pH-OLI (50oC) 11.0

Composition of poultice simulant

Appearance of

poultice simulant

DNV GL © 2014

Puddle

Various degrees of wetness of

semi-solid waste simulated by

adding “equilibrium liquid” to

poultice

Equilibrium liquid composition

determined through OLI

calculation

Mixture of poultice and equilibrium

liquid termed as “puddle”

20

Mix poultice and equilibrium

liquid recipes. Check pH and

composition of puddles

Original poultice recipe

calculated from

analytical information

in RPP-RPT-54071

Adjust CO3/HCO3

until poultice pH

equal to 11

pH-11 poultice

recipe

pH-11 equilibrium

liquid recipe

Extract aqueous

stream

DNV GL © 2014

Mixer calculation for puddle formulation

Equilibrium liquid pH-11 poultice

21

DNV GL © 2014

Corrosion testing with waste simulants

Corrosion and SCC testing of AAR TC128 steel

Localized corrosion studies

– Pitting

– Cyclic potentiodynamic polarization

– ASTM G192 (Tsujikawa-Hisamatsu Electrochemical) test

– Long-term coupon immersion

– LAI corrosion

– Multi-electrode array

– Partial coupon immersion

SCC studies

– Slow strain rate tests

– Crack growth rate studies

22

DNV GL © 2014

Summary

Leakage of radioactive waste from primary liner of tank AY-102 has raised

concerns about integrity of secondary liner

Corrosion and SCC studies ongoing on liner steel using waste simulants

Formulation of waste simulants developed using OLI modeling, analytical

information, and laboratory trials

Important differences observed in predictions using MSE and Aqueous databanks

23

DNV GL © 2014

Future work

At present, OLI corrosion predictions do not match experimental observations for:

– Polarization curves

– OCP

– Repassivation potential

Further work is needed here as OLI could be used in future risk assessments

24

DNV GL © 2014

Acknowledgments

The work is being performed under sub-contract No. 53247 with Washington

River Protection Solutions, LLC in support of the U.S. Department of Energy.

The discussions with Kayle Boomer, Ted Venetz, Donald Camaioni, Leon Stock,

Bruce Wiersma, Russ Jones, and Scott Lillard in formulating the test plans and

simulant chemistries are gratefully acknowledged.

25

DNV GL © 2014

SAFER, SMARTER, GREENER

www.dnvgl.com

26