Interaction of glasses with a GDF environment

1
Interaction of glasses with a GDF environment

• Russell J Hand
• ISL
• University of Sheffield

2
Introduction

• Geological disposal facility
• Co-disposal?
• Glass durability
• General issues
• Durability in highly alkaline conditions
• Conclusions

3
Co-disposal
4

• ILW/LLW
• Cemented wastes
• Following emplacement of the wastes the vaults
  would be backfilled when technically required,
  for example with alkaline grout, specially
  formulated to inhibit dissolution of any
  radionuclides, and then sealed.
• June 2008 White Paper Annex A
• HLW
• Vitrified wastes
• Also SNF
• Swedish KBS3 system
• Lets build a copper deposit!

5
Glass durability

• Extensively studied area
• Especially French SON68 / R7T7 compositions
• UK compositions are related BUT
• Higher Mg content
• Do not contain CaO/ZnO/Al2O3/ZrO2 in base glass

6
Silicate glass dissolution

• Neutral and acidic pH
• Diffusional ion exchange
• High pH
• Congruent dissolution

7
Glasses in cements

• Reinforcement of cement and concrete with glass
  fibres
• The use of Portland cements leads to failure of
  the glass-fibre reinforcement owing to their
  aggressive action on glass fibre.
• Majumdar Ryder Glass Technol. 9 (1968) 78-84

Data for OPC reinforced with Pyrex fibres
8

• Alkali resistant glass compositions have been
  specially develope
• Zirconia rich
• E.g. 71.3 SiO2, 15.8 ZrO2, 0.1 CaO, 0.1 MgO,
  11.5 Na2O, 0.8 Li2O and 1 K2O (wt)
• Work is ongoing to develop coatings to increase
  durability of glass fibres under these conditions
• Also alternative, less alkaline, cements

OPC reinforced with AR fibres Data from Purnell
Beddows Cem. Concr. Comp. 27 (2005) 875-884.
9

• SrO-MgO-ZrO2-SiO2 glasses
• 1 M NaOH 75ºC
• 40wt SiO2 glasses more durable in alkaline
  solutions than ones with higher SiO2 contents
• Weight loss (µg mm2) 59.39 114.3Zr
  0.164Sr 20.4Mg
• i.e. durability improved with Sr lt Mg lt Zr
• Karasu Cable J. Europ. Ceram. Soc. 20 (2000)
  2499-2508

10

• Incorporation of waste glass into cement
  concrete
• Very limited pozzolanic activity (if any)
• BUT expansive alkali-silica reaction (ASR) can be
  significant
• Glass acts as an alkali source

CRT glass as fine aggregate in OPC
11
Conventional durability test results
Interdiffusion
V
I
II
III
IV
Resumption of alteration
r(t) rate drop
rf residual or final rate
B
Hydrolysis
Na
Concentration of leached species
Si
End of alteration or phase precipitation
Possible phase precipitation
Time
Initial rate - 1µm/day at 90ºC
1µm/50 day at 50ºC
Final rate - 1µm/50 yr at 90ºC
1µm/170 yr at 50ºC
12
Affinity approach

• Aqueous durability of glasses often summarised by
• Combine terms into a forward rate term r0 which
  depends on
• Glass composition
• Temperature
• pH

13

• Data from Knauss et al Sci. Basis Nucl. Waste
  Management XIII Proc MRS 176 (1990) 371-381
• 55.73 SiO2
• 8.43 B2O3
• 11.68 Al2O3
• 18.2 Na2O
• 5.97 CaO (wt)
• Controlled pH
• SPFT

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• Fitted results
• 25ºC (alkaline)
• 50ºC (alkaline)
• 70ºC (alkaline)
• McGrail et al. J. Nucl. Mater. 249 (1997) 175-189
• 55.91SiO2 5B2O3 20Na2O 12Al2O3 4CaO 1.46K2O
  0.19P2O5 1.44 others (wt)
• SPFT test
• 20 90ºC
• No change in law with pH

15

• Abraitis et al. Appl. Geochem. 15 (2000)
  1399-1416
• MW glass
• 18 4 ºC

B release
Si release
16

• SON68
• Measured over pH range
• 6 10
• Temperature range
• 25 100C
• Frugier et al. J. Nucl. Mater. 380 (2008) 8-21

17

• Conradt
• Calculation of Ea term using ?Ghydr (composition
  dependent)
• Also included an additional surface absorption
  term

22Na2O 6CaO 72SiO2 (wt) Conradt J Amer Ceram Soc
91 (2008) 728-735
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Protective layer

• Gel layer
• Densification of gel layer has a significant
  effect on alteration kinetics
• Densified layers present more of a diffusion
  barrier
• Very insoluble oxides e.g. ZrO2 hinder this
  reorganisation
• Can lead to faster dissolution rates in the
  longer term
• Cailleteau et al. Nature Mater. (2008)

19

• SON68 glass
• 90C static test
• SA/V 50 cm1
• Protective layer fails at higher pH values
• Precipitation of zeolites
• Gin Mestre J Nucl. Mater. 295 (2001) 83-96
• Ribet Gin J Nucl. Mater. 324 (2004) 152-164

20

• The phenomenology of SON68 glass alteration in
  initially pure water reviewed here is not
  sufficient to establish any particular kinetic
  law. The law must also be applied to a variety of
  glass compositions in a range of chemical
  environments to consolidate its robustness and
  guarantee its predictability
• Frugier et al. J. Nucl. Mater. 380 (2008) 8-21

21
Conclusions

• (Boro)silicate glasses are non-durable under
  highly alkaline conditions
• Congruent dissolution
• Special compositions developed for use in cement
• In closed systems involving water low final rate
  is achieved because pH is limited
• At high imposed pH values final rate may NOT be
  achieved
• Co-disposal exposes vitrified HLW to alkaline
  plume
• Cannot assume that final rate behaviour will be
  observed under these circumstances