WSRC-MS-2007-00116s
Overview of Tritium R&D at SRNL
Jeffrey Holder
Manager
Hydrogen Processing Group
June 12, 2007
SRNL and the Savannah River Site (SRS)
 SRNL is the technology development division of
Washington Savannah River Co. at SRS
 The SRS Tritium Facilities extracts tritium from
irradiated targets, recycles tritium from field returns,
and loads tritium containing reservoirs for the DoD
 SRNL directly supports the SRS Tritium Facilities by
conducting R&D to improve the safety, reliability, and
maintainability of the Tritium Process
SRNL Tritium Process Support
 Tritium Exposure Program
– Study the compatibility of tritium exposed materials
– Containment Materials, Metal Hydrides, Polymers
 ADAPT Tritium Processing Project
– Develop technologies to improve the Tritium Process
• Tritium Stripping and Separation Systems
• Hydrogen Isotope Separation Systems
• Tritium Process Modelling
• Online Tritium Process Monitoring
 Permeation Barriers
– Aluminide and Al Alloy coatings
 Metallic Permeator Membranes
– Pd and Pd Alloys vs. Non-Noble Metal Alloys
Tritium Exposure Pgm – Containment Materials
 Stainless steels & weldments
 Exposed at elevated temp &
high tritium pressure
 Measure fracture toughness
& crack growth rate in
various alloys as a function
of T and 3He content (age)
– Ductile to brittle transition
 Investigate the role of
microstructure on tritium
compatibility
Tritium Exposure Pgm – Metal Hydrides
 La-Ni-Al alloy used in tritium
storage beds
 Loaded with tritium and aged
at room temperature
 Desorption isotherms
 Tritium aging effects
–
–
–
–
Lower plateau pressure
Increased plateau slope
Reduced capacity
Tritium trapping
Tritium Exposure Pgm – Polymers
 Seals and valve stem tips
 Tritium exposure at 1 atm &
room temp
– UH-MWPE
– PTFE
– Polyimide
 Dynamic mechanical analysis
 Tritium aging effects
– Color change
– Embrittlement
Tritium Processing Project
 Composed of four (4) thrust areas
–
–
–
–
Tritium Stripping & Separation Systems
Hydrogen Isotope Separation Systems
Tritium Process Modeling
Online Tritium Process Monitoring Systems
Tritium Stripping & Separation Systems
 Tritium Stripping Technology
– Remove impurities from
streams rich in hydrogen
isotopes (Q = H, D, or T)
• e.g., N2, O2, CQ4, NQ3, Q2O
• Prepare stream for
separation via diffuser
train
– Remove tritium from streams
rich in nitrogen and inert gases
• Preparing stream for stack
emission
• Minimize loss of tritium to
environment
Tritium Stripping and Separation
Feed
Composition:
Met-Bell
400° C
Products
Scroll Pumps
Diffuser 1
H + D + T (1 - 90%)
Balance:
N2, Ar, He
< 0.2 % O2
Trace H20, CQ4, CO2
675° C
ST
909®
Met-Bell
< 150 µ
400° C
H2, D2, T2
Diffuser 2
400° C
Turbo
Recirculation
Diffuser 3
(low pressure)
High H2 in N2
< 10- 4 torr
250° C
Ion
Chamber
ST
198®
Stack
Ion
Chamber
N2 (Ar, He)
< 5 ppm T2
< 12.8 µCi/cc
SAES St 909 Getter Beds
 Cracking methanes & waters
– CQ4 is major potential source
term for tritium emissions
– CQ4 is not removed by
diffusers or final getter bed
 Multi-Scale Testing Protocol
– Bench-Scale: 10 pellets (6g)
– Pilot-Scale: 500g bed
– Full-Scale: 5 kg bed
 Cracking efficiency depends
on temperature & process
history
Tritium Separation Systems
 Pd-Ag Diffusers (Permeators)
– Separate Q2 from “inerts”
– Low pressure diffuser
developed for 3rd stage of train
• Inside out flow of Q2
• Turbopumped shell
• P < 10-3 torr
– Determine optimum operating
parameters for new diffusers
Hydrogen Isotope Separation Systems
 Thermal Cycling Absorption Process (TCAP)
– Invented and developed at SRNL in the 1980’s
– Demonstrated H2 – D2 separation at full-scale
– Deployed in the Plant in 1994 for D2 – T2 separation
• Pd/k packing inside helical column
• Hot & cold N2 for thermal swing
– Deployed in the Plant in 2004
for H2 – T2 separation
• Larger diameter column
• Internal foam
• Larger capacity
• < 5 ppm T in H2 raffinate
Compact Thermal Cycling TCAP
Throughput = (feed/cycle) (cycles/time)
= (packing efficiency) (thermal efficiency)
Hot/cold N2
Column
Raffinate
H2+ D2
Heating
Jacket
Water/air
Feed
T2+H2+ D2
Pd/k
Column
with
hot/cold
jacket
Plug
flow
reverser
Compressors
CTC
Column
Product
T2
Heater
Heating
Cooling
tube
Gas N2
Liquid N2
Refrigeration
TCAP Development
Improve heat transfer to reduce cycle time
 Tube-In-Tube TCAP
– Hot & cold liquid inside axial tube for heat transfer
– Straight annular columns of Pd/k connected by U-tubes
– Demonstrated H2 – D2 separation at LANL with SRNL
 Induced Natural Convection TCAP
– LN2 cooling with hot N2 heating in a thermal loop
– Heat engine demonstrated at SRNL
 Compact Thermal Cycling TCAP
–
–
–
–
Latest thermal design and geometry
Electric heating and LN2 cooling
Straight columns of Pd/k connected by U-tubes
Eliminates need for Hot and Cold Nitrogen system
Why Permeation Barrier Coatings
• Materials for Hydrogen Service
•Ferritic Steels and Nickel Based Superalloys Are Strongly Embrittled
•Austenitic Stainless Steel Less Affected
•Aluminum and Copper Alloys Relatively Unaffected
•Permeation of Hydrogen and Hydrogen Isotopes
•Mechanical Property Reductions--UTS, YS, %Elongation, RA
•Hydrogen Assisted Fracture
•Hydrogen Isotope Migration
•Past Experience
•Aluminides, TiC, TiN, TiO2, Cr, Si-doped, BN, H3PO4 glass
•Reductions in Permeations 10-10000X
•Aluminides Most Commercially Prevalent--Thermal Spray, Packed Bed
•Intentional Surface Oxidation--Fe-Oxide, Cr-Oxide, Spinels
Aluminide Coating Characterization
•Mostly uniform coating
•Occasional thin spots
•Three distinct layers
• Outer Al rich “A”
• Intermediate “B”
• Interdiffusion layer “C”
A
B
C
Pt Al Coating Characterization
D
E
F
C
• Used in industry to increase
coherence of Al to steels
• Large areas of low quality
coating
• Occasional thin spots
• Four distinct layers
• Outer Pt rich “D”
• Intermediate beta phase “E”
• Mixed phase “F”
• Interdiffusion layer “C”
Permeation Measurements


Modular Design
Computer interfaced
– Electronic valves
– Automated data acquisition







Temperature capability to 500oC
1" tubing on 2.12" CF flanges
All metal seals
Scroll pump on gas side
Turbo molecular pump on sample side
Flange mounted sample for flexibility
Dual mode
– Mass spectrometer / leak
– Pressure rise
• Calibrated volumes
Permeation Measurements
Bare and Coated 304L Stainless Steel
Tested at 400C and 400 Torr
1.40E+00
Bare
PtAl
PdAl
Al-2
AlSi
Pressure (Torr)
1.20E+00
1.00E+00
8.00E-01
6.00E-01
4.00E-01
2.00E-01
0.00E+00
0
50000
100000
150000
200000
Time (s)
250000
300000
350000
400000
Why Metallic Permeator Membranes
Why are Metal membranes Commercially Attractive?
• Simple to Operate
• Reliable—No Moving Parts
• High Purity Hydrogen Product– on the order of 99.95%
•Selectivities on the Order of 1000 for H2 Reported
• Small Size
• Flexible Designs
• Cost effective—especially non-noble metal based
How the Metallic Permeator Works
Adsorption &
Dissociation
Recombination
& Desorption
Literature Values for H2 Permeability
Metallic Permeators
Pd/Pd-Alloy Membranes
•Pd and Pd-Alloys possess good solubility and diffusion characteristics
•Permeation through Pd is on the order of 10-8 mol H2/m s Pa1/2
•Embrittlement of Pd limits longevity, Pd-alloys ( Cu, Ag) Reduce Susceptibility to Poisoning and
Embrittlement
•Pd/Pd-Alloys High Cost
Alternatives to Pd/Pd Alloys Membranes
•Pd-Coated Porous Ceramics
•Pin-holes/Holidays Create Short Circuit Pathways
•Investigations of V-Al and V-Ni
•V has high solubility and diffusivity but suffers severely from embrittlement
•Attempts at Alloying V have not made significant decrease in embrittlement susceptibility
•Ni-Ti-Group 5A Alloys
•Ni-Ti alloys have been researched for decades due to their shape memory properties
•Ni-Ti Alloys are susceptible to H2 embrittlement and Do Not Posses High Permeability
•Additions of Group 5A Metals ( Nb, V, and Ta)
•Nb Additions have produced high permeation and good resistance to embrittlement
•V-Ni-Ta Alloys
•Preliminary results show permeability > Pd, no embrittlement, and good toughness
SRNL Hydrogen Isotope Testing Capabilities
EXPERTISE
•Hydrogen Embrittlement of Metals and Alloys
•Mechanical Testing
•Fracture Mechanics Theory and Testing
•Structural Integrity Assessment
•Hydrogen Permeation Testing
•Permeation Barrier Coatings
•Transmission Electron Microscopy of Tritium
Exposed Materials
T2 -EXPOSURE TEST
CHAMBER
C-Shape Fracture Test
Specimen Fabrication
H2/D2 Permeation
Test Rig
Helium Bubbles in
Weld Zone of T2
Exposed SS
CAPABILITIES
•Hydrogen and Tritium Charging Systems
•Mechanical Testing, including Chamber
Allowing Testing of Tritium Exposed Samples
and Slow-Strain-Rate testing
•High Pressure H2 Testing Facility
•Optical and Scanning Electron Microscopy
•Transmission Electron Microscopy
•EDM of Novel Sample Geometries from ServiceExposed Components
•Small Sample Punch Testing
SRNL Tritium R&D Summary
Tritium Exposure Program
 Determine the aging effects of tritium and 3He
– Containment materials, metal hydrides, polymers
Tritium Process Support
 Developing Technologies to Enhance the Tritium Process
 Stripping & Separation
– Generate stackable “inert” gases with tritium content < 5 ppm

Hydrogen Isotope Separation
– Use TCAP to generate stackable protium with tritium content < 5ppm
– Compact Thermal Cycling System to eliminate HCN system
Permeation Barriers

Al-Si alloy shows promise as an effective coating for stainless steels
Permeable Membranes
 Non-Noble metal alloys being developed with resistance to embrittlement