Radioactive Waste Processingat the

Savannah River Site

Bill Holtzscheiter

April 2014

Outline

• Background– Overview of the radioactive waste process

• A look at the facilities and materials – Highly Radioactive Sludge– Highly Radioactive Glass

• Key Chemistry– Neutralization Reactions– Oxidation-Reduction Reactions– Combustion Reactions

• Processing Objectives– Maximize Waste Loading into the Glass– Increase Waste Throughput

• Summary

SRS High Level Waste System

Vitrification Process Diagram

Actinides-U, Np, Pu

PRFT

221-S

Pump Tank Used for Transfer

Sludge Receipt

Tank

Glass Mix Tank

Melter Feed Tank

Melter

221-S

SAMPLE ANALYSIS HOLD POINT-GLASS ACCEPTABLE?

Waste Acceptance Items/Activities

SRAT Sample

Analyses

WASTE FORM COMPLIANCE PLAN (WCP) AND WASTE FORM QUALIFICATION REPORTS (WQR)

Tank 40

Radioactive Waste

Aqueous Cs-137 stream

Cesium Tank

Actnide Tank

Glass Sample

Defense Waste Processing Facility

Sludge Processing StepsSteps

- Two to three transfers from Tank 40 (7200 to 8500 gallons)

- Caustic Boiling to concentrate contents

- Addition of U, Pu-238, Np- Cool Down and Sample Analysis- Determine the amount of acid

and the blend of formic and nitric

- Concentration/Reflux (Hg Removal) to 6000 gallons

- Add the mildly acidic Cs stream) - Sample to confirm composition- Transfer ~4500 gallons to SME

for further processing

Transfer Pump

Mercury Sump

Diameter 12’Height 18’Volume 11,000 Gal.

Prime Water Line

Salt Stream

90 % Formic Acid

Air Purge Antifoam Agent

50 WT% Nitric AcidSludge (from LPPP)

Sample Pump

Agitator

Three Foil Blade

4 Paddle Flat Blade

Heating Coils

Cooling Coils

Glass Mixing Steps

Steps

• Add glass former frit• Concentrate mixture (as

necessary)• Concentrate mixture• Cool down SME• Sample SME product• Run final Product Confirmation

Calculations (PCCS Model) for quality control, and MOG calculations

• Transfer ~4500 gallons to MFT for feeding of the melter

Diameter 12’Height 18’Volume 11,000 Gal.

Prime WaterLine

Transfer Pump to MFT

Mercury Sump

Formic Acid for Redox

Canister Decon FritAntifoam Agent

Process Frit

Sample Pump

Agitator

Three Foil Blades

4 Paddle Flat Blades

Heating Coils

Cooling Coils

Slurry from SRAT

Air Purge

Melter Feed Tank

Diameter 12’Height 18’Volume 11,000 Gal.

Prime WaterLine

Transfer Pump to Melter

Mercury Sump

Formic/Nitric Acid

Canister Decon Frit

Sample Pump

Agitator

Three Foil Blades

4 Paddle Flat Blades

Heating Coils

Cooling Coils

Slurry from SME

Air Purge Steps

• Typically no adjustments are made to the Melter Feed Tank qualified feed.

• 4-5 cans poured per batch processed

Melter

Feed Tubes

Off Gas

Thermowell

CCTV

Lid Heaters

Pour Spout

Refractory

Electrodes

-Joule heated melter. Pours by vacuum -Receives Feed from the Melter Feed Tank at ~1.2 gpm-Glass Pool Temperature ranges 1120°C – 1145 ° C-Equipped with 4 bubblers each capable of bubbling Argon at rate of 1.5 scfm-Have recently achieved 225 – 230 lbs/hr. -Nameplate 228 lbs/hr.-Each canister holds ~ 4000 lbs of glass

Picture of Melter Top

Actual Radioactive Glass-Crucible

Radioactive Glass Canisters

Waste Form-Borosilicate Glass

Waste Description

• The radioactive waste contains most of the Periodic Table in one form or another.

• Major components include Fe(OH)3, Al (OH)3, Na(NO3), other metals such as Mg, Mn, Ca, Cs, in various forms. Carbonates, nitrogen oxides, sulfur oxides, and Hg.

• There is a sludge component and a salt/supernate component

• The sludge is fed to the process at a pH~ 12• At about 18 weight percent solids (fairly dilute)

Simulated Radioactive Waste

Same Waste-High Viscosity

Measured Radionuclides

Process Chemistry

• Nitric acid is added to the sludge to neutralize the hydroxide and lower the pH to about 6.

• Formic acid (HCOOH) is added to reduce Hg from either the oxide or nitrate states to metallic Hg

• Once in the metallic state, the vessel is boiled and the Hg is removed by a process called steam stripping. The steam literally carries the Hg to another vessel where it is removed from the process.

Selected Reactions

M++ (OH)2 + HNO3 M++O + NOx + H2OM++CO3 + HNO3 M++(NO3)2 + CO2 + H2O

Neutralization ReactionsM= Mg, Fe, Ca, Al, Mn

Reductions Reactions

Nitrite Destruction Reactions

Reductions Reactions

Problematic Chemistry

• Formic acid also produces hydrogen in the presence of Rh, Pt, and Ru

HCOOH H2 + CO2

2H2 + O2 2H2O

• What kind of reaction is the above reaction?• Why would it be an issue?• Why is hydrogen thought to be important to future

green energy in the US?

Hindenberg

BMW 7 Series Hydrogen Car

Small Scale Process Development

Balance Performed for Each Batch of Feed Processed through DWPF

• Maintain H2 generation below safety limits for SRAT/SME cycles while trying to minimize CO2 and N2O production

• Hg reduction and stripping

• Adjustment of rheological properties that allow a maximum wt.% solids target (viscosity)

• REDOX Balancing (prevent foaming or metal deposition in the melter)

• Balancing carbon and nitrogen sources to ensure Melter Off Gas Flammability is met

• Ensuring waste and glass former blending is correct

• Ensuring waste loading commitment is met (have to allow 3-4 WL points based on equipment and analytical uncertainty)

• Ensuring mass per unit volume moved through the facility meets canister production goals

Summary

• Waste process and how it is different from a manufacturing process

• A very important combustion reaction– Resulted in the explosion for the Hindenberg– Provides the basis for the hydrogen economy– Has to be carefully managed when it appears in any chemical process.

• Reviewed terms that you have had in your chemistry course– Combustion reactions– Viscosity– Radioactivity, curies, types of radiation

• You have had a glimpse of a complex chemical process that helps clean up the highly radioactive waste generated during the production of nuclear weapons materials

Where are the Curies?

37 M gal 426 M C i80 M gal

@ 6.44 M N a92 M gal

@ 5.6 M N a

DW PFVITRIFICATION226 MCi

(53%)

180 MCi(42%)

20 M Ci(5%)

DISSO LVED SALT ~ 50 M gal

SUPERNATE

SLUDGE

SALTCAKE

SALT W ASTEPROCESSING FACILITY

Sr. Actinide Cesium Rem oval Rem oval

SALTSTONE

Sr ACTINIDEREMOVAL

R educedC ans toYucca

M ounta in

STORAGE W ITH SALT DISSOLVEDRADIONUCLIDE

REMOVAL

(95 .31% )

(4 .69% )

R educedVaults

3 M gal(9%)

17.5 M gal(47%)

16.5 M gal(44%)