1. J. G. Shah1, A. Ananthanarayanan1, B. K. Pannigrahi2, C. David2,
The Role of Glass Composition in Radiation Damage Behaviour of Borosilicate Glasses: In Pile Radiation and Ion Bombardment Studies
J. G. Shah1, A. Ananthanarayanan1, B. K. Pannigrahi2, C. David2,
N. C. Hyatt3 and R. Smith4
1Process Development Division, Nuclear Recycle Group, Bhabha Atomic Research Centre, Mumbai
2Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakam, India
3Department of Materials Science and Engineering, The University of Sheffiled, Sheffield UK
4Department of Mathematical Sciences, Loughborough University, Leicestershire, UK
*Corresponding author:

2. Outline of Presentation
Back-End of Nuclear Fuel Cycle: Overview of Indian Scenario
Three Stage Nuclear Programme
Present Fuel Cycle
Focus Areas of Waste Management
Three Stage Management of High Level Waste (HLW)
Design of Vitreous Matrices
Radiation damage
Contributors and time scales
Effects: Displacement per decay event
Effect on waste form
Methods of radiation damage
Doping active nuclei in glass
In pile radiation
Ion bombardment
Some examples and discussion of same
Concluding remarks

3. Indian Nuclear programme

4. Three Stage Indian Nuclear Programme
Dr. Homi Jehangir Bhabha

5. Indian Nuclear Fuel Cycle: Present Reprocessing of spent oxide fuel
U (natural)
PHWR
PUREX
UOX fuel
Heavy metal
Mixed Oxide fuel for Prototype Fast Breeder Reactor
Non α waste (L&IL)
α Bearing HLW
Volume Reduction
Near Surface Disposal
Vitrification
Interim Storage
Repository
Reprocessing Facility, Tarapur
Vitrified Waste Storage Facility, Tarapur
Vitrification Facility, Tarapur

6. Waste Management – Focus Areas Nuclear Waste Management
Process Development
Processes & Technologies
Safety
Matrices & Materials
Nuclear Waste Management
Environmental Impact
Sustainability
Remote handling
Disposal & long term
Surveillance
Public Acceptance
Instrumentation
& simulation

7. Management of High Level Waste: 3-Stage Programme
Shielded Transport Cask
Canister Welding
Immobilisation
Interim Storage
HLW
Glass Pouring
Deep Disposal
Air cooled Storage
D in progress
Deep Geological Repository
HLW from Reprocessing

8. Vitreous Matrices - Design Formulation
Waste Loading
Vitrified Product
Additives
Temperature
Waste Loading : Solubility of waste components, Decay heat
Limited Solubility - Mo, Tc, Cr, SO4, Fe, U, Noble metals
Heat Generating - 137Cs, 90Sr, 244Cm
Additives : Leachability, Glass pour temperature
Leachability - SiO2, Na2O, BaO
Pour temperature - Na2O, B2O3, PbO, BaO
Temperature : Volatility, Materials corrosion
Volatility: 137Cs, 106Ru

9. Radiation damage: overview

10. Dose and Atomic Displacement: What does the Damage?
Cumulative α dose will exceed cumulative β + γ dose at 105 y
α decay events produce 3 – 4 orders of magnitude greater cumulative atomic displacements than β decay events

11. Glass Properties: Effects
Structural Changes:
Atoms displaced
Thermal energy deposited into network
Polymerization/De-polymerization (crystallization possible)
Consequences:
Production of occluded gases (He & O2)
Changes in waste form properties
Leach resistance
Hardness
Fracture toughness
Stored energy
Glass transition temperature – Tg
Compaction/ Swelling – Density variation

12. Studying Radiation Damage
Doping with 244Cm/238Pu:
Benefits:
 and recoil damage homogeneous
Limitations:
High sample activity
2 – 3 years for damage accumulation
Irradiation in Reactor:
Benefits:
Fast
 and recoil damage homogeneous
Limitations:
High sample activity
Energy of Li nucleus not same as that of recoiling daughter nucleus & energy of α is 1.47 keV as against 5 MeV
Sample
Ion Beam Bombardment:
Benefits:
Rapid
Sample characterization easy/sample not active
Limitations:
Ion energy 10 times higher than α – energy
Recoil damage and α – damage not homogeneous

13. Studying Radiation Damage
Doping with 244Cm/238Pu:
Benefits:
 and recoil damage homogeneous
Limitations:
High sample activity
2 – 3 years for damage accumulation
Irradiation in Reactor:
Benefits:
Fast
 and recoil damage homogeneous
Limitations:
High sample activity
Energy of Li nucleus not same as that of recoiling daughter nucleus & energy of α is 1.47 keV as against 5 MeV
Sample
Ion Beam Bombardment:
Benefits:
Rapid
Sample characterization easy/sample not active
Limitations:
Ion energy 10 times higher than α – energy
Recoil damage and α – damage not homogeneous

14. Comparison of α damage Irradiation in reactor He 1.47 Mev B (n,α)LI
Accelerated particle bombardment
He Mev
Vacancies/ion
Range (Long) um
Energy loss (%) Ions Recoils Ions Recoils
Ionizations
Vacancies
Phonons

15. Comparison of recoil damage (Li7 & U238) U 238 (simulation of Np 237)
Irradiation in reactor
Li Kev - B (n,α)LI
Accelerated particle bombardment
U Kev
Vacancies/ion
Range (Long) um (439 A)
Energy loss (%) Ions Recoils Ions Recoils
Ionizations
Vacancies
Phonons

16. In-pile irradiation

17. Details of irradiation
Design Basis for Irradiation (SHARAD & ORIGIN-2 Codes utilized)
Total alpha accumulation for 5000 years (1-3 m Ci of Am 241) ~ 5x 1018 alphas/gm
Available neutron flux x 1013 n/cm2/sec
Thermal Calculations
(Reactor safety requirement at 20 MW reactor power)
Heating rate in the sample < 50 watts
Maximum temperature of the sample < 70o C
( Rise in temperature was not observed in any sample capsules during irradiation)
Sample mass is limited to < 10 gm / vial
Total irradiation time ~70 days
Total irradiation MWD
Activation calculations
The expected contact dose rate due to activation of
Fe59, Ba13, Cr51, Ce141
(60 days irradiation and 60 days cooling) calculated ~ 2.27 R / hr Each capsule
Actual observed contact dose
(60 days irradiation , 60 days cooling) ~ 2.5 R / hr / Each capsule
Lead shielding during transport of the sample for analysis ~ 75 mm

18. Neutron Flux Profile in Cylindrical Sample (Borosilicate Glass)
Non uniform damage to the matrix.
Property measurement to be carried out at
uniform flux. (Average flux = 34.4%)
Variation of α damage could be evaluated with
varying flux across the sample.
Powdered sample predominately meant for
evaluating chemical durability
Uniform flux damage to the powdered sample
ensured by surrounding the coarse sample
grains with fine glass powder.
Schematic of Sample Assembly
Cylindrical glass Glass Pellet Glass grains

19. Post Irradiation Characterization
Density Variation
Density increases 1 – 3 %
Chemical Durability Unchanged
Summary of Results of In-Pile Irradiation
Microhardness:  ~ 20%
Tg:  ~ 1 – 3% (Thermal relaxation/annealing effect?)
Stored Energy: LTRS base: 93 J/g; R7T7 base: 44 J/g

20. Bubbling/Occluded GasesHe
H2O O2
Typical Mass spectrum of gas released at 873 K
Observations and Inferences
No oxygen release at lower temperature (573K)
Total He : ~2 x 1019 atoms (20% of expected value)
Total O2 : ~4 x 1020 atoms
Occluded He and O2 in irradiated glass indicates breaking of oxide bonds, due to He and recoil damage

21. Post Irradiation characterization
Evolution of silicate polymerization
Raman spectroscopy
AVS glass
Increasing boroxyl rings
Hints at phase separation under irradiation
Tetrahedral BO4 converted into trigonal BO3
Possible reduction in microhardness by plastic flow
Recorded under Indo-French CEA Project

22. Post Irradiation Characterization _ continued.
Raman spectroscopy
Increase in Q3 and Q4 structural units implies the network polymerization.
Small peak around 1550 cm-1 after irradiation of R7T7 may be the presence of oxygen at the surface.

23. ION bombardment

24. Characterization Techniques: What are we looking at
Characterization Techniques: What are we looking at? – Matching damage and characterization volume
Characterization Volume = Damage Volume
Only radiation damage effects can be observed
Minimal substrate effects
Bulk
Damaged Layer
Characterization Volume >> Damage volume
Very difficult to isolate damage effects
Bulk effects dominate
Interface region: Mysterious
How does the bulk region affect the radiation damaged layer?
Does the bulk region act as a “heat sink” to absorb deposited energy?
Does Bulk helps in annihilation the damage events
So, how do we choose the bombardment energy?

25. Choose the smallest energy that creates a reasonable damage volume
SRIM Simulations
Au implantations into NBS ( ) glass. Sn/Se ratio as a function of implantation energy and distance into surface
Choose the smallest energy that creates a reasonable damage volume

26. DPA calculations
Dpa profile as a function of fluence (ions cm-2) in NBS ( ) glass 2 MeV Au ions
2 Mev

27. Comparison of recoil damage U 238 (simulation of Np 237) and Pb 207
Pb 207– Kev
U Kev
Vacancies/ion
Rang (Loneg) um (431 A) (439 A)
Energy loss (%) Ions Recoils Ions Recoils
Ionizations
Vacancies
Phonons

28. Comparison of α damage Irradiation in reactor He 1.47 Mev B (n,α)LI
Accelerated particle bombardment
He Mev
Pb 207– Kev
Vacancies/ion
Range (Long) um
Energy loss (%) Ions Recoils Ions Recoils
Ionizations
Vacancies
Phonons

29. Composition Range of Boro-Silicate Glass
Composition and structural parameters of NBS glasses
Component
NBS-1 (Mole %)
NBS-2 (Mole %)
NBS-3 (Mole %)
SiO2
55.00
60.00
53.40
B2O3
20.00
26.66
Na2O
25.00
Na2O/B2O3 (R)
1.25
1.00
0.75
SiO2/B2O3 (K)
2.75
3.00
2.00
Rmax
0.67
0.69
0.63
Rd1
1.19
Rd2
3.56 -
f(SiNBO)
0.40
0.20
0.12 f1
(BO3/2 with 0 NBO)
0.32
0.31
0.37
f2 (BO4 with 0 NBO)
0.66
f3 (BO3 with 1 NBO and 2 BO)
0.053
f4 (BO3 with 2NBO and 1 BO)
0.014
Glass Transition Temperature (Tg)
518oC
537oC
479oC
Calculations using Dell, Yuan and Bray model of Borosilicate glass
Rmax = K/16
Rd1 = K/4
Rd2 = K/4
Planar BO3 converted into BO4
No NBO on Si tetrahedra
Further formation of Si NBOs and breakup of reedmergnertite units
Conversion of planar diborate into pyroborate by formation of NBO on BO3 planar rings
Additional Na forms NBO on silicate reedmergnerite* groups
High depolymerization of all structural units
Glass stability low
* 0.5(Na2O.B2O3.8SiO2)
NBS-1
NBS-2
NBS-3 R

30. 11B MAS-NMR All the samples have very similar BO3/BO4 ratios
Composition variation causes changes almost exclusively to the silicate network
Spectra of NBS-3 glasses exhibit a small shift in the BO4 position to more negative chemical shifts
The quadrupolar broadened BO3 resonance is centred around 10 ppm for BO3 and near 0 ppm for BO4 units. It is evident that all the samples have very similar BO3/BO4 ratios. This indicates that the composition variation causes changes almost exclusively to the silicate network.
The spectra of NBS-3 glasses exhibit a small shift in the BO4 position to more negative chemical shifts. This could be linked to the changing relative speciation of danburite and reedmergnerite units in the glass, however, comprehensive assignment will require high resolution NMR

31. Effect of Radiation Bombardment: FTIR
Harder glass shows crystallization under 2MeV Bi irradiation (left)
Softer glass shows crystallization behaviour under 2 MeV He (right)!!
Softer glass gets re-amorphized under high doses (1015 ions/cm2)

32. Raman: Post Irradiation (NBS-3)
Increase in boroxol ring species: Strengthening of shoulder between 600 cm-1 and 800 cm-1 particularly in case of sample irradiated with 2MeV He
Narrowing of Si – O – Si bond angle under Bi irradiation: 492 cm-1 band upshifted under Bi irradiation
Depolymerization of silicate network: Qn peak shows larger contribution at lower wavenumbers in Bi irradiated samples
Bi irradiated samples crystallized and then reamorphized? Low Tg of NBS-3 could play a role?
Raman band at 492 cm-1 in the parent glass and the He irradiated sample is shifted to 506 cm-1 in both the Bi (750 keV and 2 MeV) irradiated samples
The shift in this band to higher wavenumbers is an indication of a narrowing of the Si – O – Si bond angle in the glasses
The Raman band at 630 cm-1 is more strongly expressed in the Bi irradiated samples
The signal region corresponding to the boroxol rings and B – O- vibrations is most defined in case of the He irradiated sample, which agrees with its more ordered nature, observed in FTIR
There is also a change in the shape of the region of the Raman spectrum between 900 cm-1 and 1300 cm-1 in case of the Bi irradiated samples
Bi irradiated samples show a shift in this peak toward lower wavenumbers indicative of a lower overall polymerization of the glass network
Also indicate reorganization of the network under Bi irradiation?

33. Possible Mechanisms
Radiation damage driven by change in role of Na+ from charge compensation for BO4 to network modifying
NBS-1 has high Na2O fraction: Silicate network already modified; largest NBO fraction implying change in role of Na+ more demanding
NBS-2 has lower Na2O fraction: Role change for Na+ possible in case of large energy deposition such as Bi where energy is deposited over a smaller volume
Re-amorphization unlikely in NBS-2 due to high Tg
NBS-3 low silica network modification and low Tg: Na+ change from charge compensating to silicate network modifying easy; rapid crystallization under 2 MeV He irradiation
High energy deposited in small volume by Bi ions: Remelting and quenching of crystallized region.

34. Scanning white light interference microscopy
Irradiation with 2 Mev Au+
ions
Half sample masked with Si
wafer during irradiation
~ 50 nm downward step
observed shows compaction
Increase in density ~ 4 % as
that observed in in-pile
radiation experiment.

35. Further Evidence from SEM (NBS-3)
NBS-3 unirradiated side
NBS-3 2 MeV He irradiated side
Crystallization evident in SEM on irradiated side
No such tracks visible on the masked side

36. Looking More Closely (NBS-3)
Crystallized region in the sample
Large scale crystallization evident in NBS-3 on the He irradiated side
The tracks seem consistent with the “scanning raster” used for He bombardment
Further studies underway to definitely identify the crystalline regions

37. Comparing NBS-1, 2 and 3 NBS-1 NBS-2 NBS-2 Hi-mag NBS-3
No Crystallization post irradiation
NBS-2
NBS-2
Hi-mag
Crystallization covers full surface
Caused by spherical cascade region localized just below the surface
Gas bubbling also evident
NBS-3
He ions penetrate ~10μm into the sample
Most of the crystallization too far into the sample to observe near the end of the ion track
Small amount of crystallization at ion impact site, causing raster like feature

38. Variable Dose Experiments
Original peak barycentre: Higher polymerization
Peak shift: Lower polymerization
Change in network polymerization evident at 1013 and 1014 ion/cm2
Possible network re-amorphization in 1015 ions/cm2 sample
High doses can lead to reamorphization (but higher fictive temperature structure: still looking into this)

39. Other Results in Brief
Glasses with high Na2O content but low B2O3 and high Tg are resistant to radiation damage
Chemical durability concerns addressed by Al2O3/ZnO addition in NBS-1
No major changes in glass structure, or radiation damage behaviour
Chemical durability boosted significantly

40. Future Perspectives
Perform NMR measurements on pre and post irradiated samples (thin bulk and also film)
Evaluate the effect of other additives such as RO
Compare crystallization behaviour of glass samples pre and post irradiation

41. Questions/Suggestions
Questions/Suggestions? Thanks to: ICTP 2016 Organizers Indo-UK research Team EPSCRC
Thank You all