Contribution of WCMH MEYER

1. Behaviour of Cementitious Materials in Long Term Storage and Disposal of Radioactive Waste in Necsa (South Africa) Contribution of WCMH MEYER

2. Contents • Introduction • Cement container durability-initial studies • Cement container development • Grout matrix development • Results from encapsulated waste in selected matrixes • Current cementitious research • References

3. 1. Introduction Location of disposal site Vaalputs is the national, near surface, radioactive waste repository for low and intermediate level short lived, radioactive waste

4. 1. Introduction Disposal trenches

5. 3. Cement container development Final cement selection

6. 1. Introduction Cement composition of approved waste containers Cement composition corresponds to Type V sulfate-resistant concrete, as established in ASTM C150

7. 1. Introduction Approved cement containers for disposal

8. 1. Introduction Building of cementitious engineered barrier

9. 1. Introduction Disposal of intermediate level short lived, radioactive waste After 20 years ?

10. 2. Cement container durability-initial studies Opening of experimental trench after 20 years

11. 2. Cement container durability-initial studies Steel ring corrosion SRB

12. 2. Cement container durability-initial studies SRB Microorganisms on cement

13. 2. Cement container durability-initial studies Microorganisms observed on cement surface

14. 2. Cement container durability-initial studies Chloride and sulphate diffusion into cement

15. 2. Cement container durability-initial studies Experimental evidence of cement container degradation • Corrosion-6 meter –top container – no corrosion down-cap water ingress • Presence of SRB-only top container - • Diffusion of chlorides from backfill • Micro-organisms on surface-top container • Resin expansion –small cracks at container lid Repository closed on 2002 to fix “problems” of resin waste container” • Cementitious research at Necsa • Fix capping methodology • New designed waste container • Develop analytical technique for water/ chloride penetration • New cement formulation for outside container • New grout matrix formulation for waste encapsulation

16. Developing of NRAD facility at Necsa-initial experiments Initial setup very crude

17. Conformation of NRAD as measuring technique Porous concrete Partially painted porous concrete Analytical tool for water penetration- connection of pore structure Fully painted porous concrete

18. Conformation of NRAD as technique for measuring porosity Analytical tool to indicate porosity

19. 3. Cement container development Preparation of cement cubes Water curing -28 days Tensile and compression

20. 3. Cement container development Temp. cyclic studies Water penetration studies with different aggregates by Nrad Chloride penetration studies with Nrad

21. 3. Cement container development Water diffusion by NRAD technology Initial After 24 hours in water bath After 96 hours In water bath

22. 3. Cement container development Container properties- experimental Disposal site re-opened in 2007

23. 4. Grout matrix development Literature requirements International specification/guidence for waste encapsulation ? IAEA-Malcolm Grey –no specs must study publications to create data base Could CRP help?

24. 4. Grout matrix development Manufacturing of grout matrixes -Initial manufacturing of different matrixes containing different admixtures: 350 different mixtures -Pre-selection of matrixes -Matrixes manufactured with pre-selected mixtures containing radioactive waste Concentrating on porosity, water penetration and leaching not on compression or tensile due to container design

25. 4. Grout matrix development Porosity determination of different grout matrixes Total porosity is given by: …………………[2] Msw = the vacuum saturated mass of the specimen to the nearest 0.01g Ms0 = mass of the specimen at t = 0 to the nearest 0.01g. A = cross-sectional of the specimen to the nearest 0.02mm2. d = average specimen thickness to the nearest 0.02mm. Ρw = density of water = 10-3g/mm3. Pressure readout Silica gel Vacuum line Samples Water inlet Samples submersed in water Water outlet

26. 4. Grout matrix development Sorptivity (water penetration) determination of different grout matrixes The rate of water movement is given by: Mwt = F x √t ………………..[1] Where: F = slope of the best fit line obtained by plotting Mwt against √t t = time in hours after specimen is first exposed to water on its lower face. Saturation Data points to be used in analysis

27. 4. Grout matrix development Leaching determination of different grout matrixes Cs -137 Ag -110m Co-60 • The American Nuclear Society leaching test method by American national Standards Institute (ANSI/ANS-16.1) was used. (an /Ao)2 V2 -D =  ----- -- T ...........................[1] (t)n2 S2 -D = effective diffusivity, cm2/s -an = quantity of a nuclide released during leaching interval n -A0 = total quantity of a nuclide in the cement sample at the start of the first leaching interval (i.e. after the samples were rinsed for 30 seconds) -(t)n = tn - tn-1, duration of the nth leaching interval, s -V = volume of cement sample, cm3 -S = geometrical surface area of the cement sample, cm2 • To simulate a free flow of leachate, water is changed at every time interval where the measurements are taken.

28. 4. Grout matrix development Selection of cement/grout matrix with CEM 5 cement

29. 4. Grout matrix development Selection of grout matrix with CEM 1 cement

30. 4. Grout matrix development Selection of nine (9) grout matrixes for leaching studies of encapsulated radioactive liquid waste

31. Encapsulation of different PBMR waste stream using one grout type 5. Results from encapsulated waste in selected matrixes

32. Encapsulation of “contaminated” irradiated graphite waste 5. Results from encapsulated waste in selected matrixes Table 1: Initial results of graphite encapsulation into different grout matrixes

33. 6. Current cementitious research Test cementitious systems for the immobilization of Iodine, Tc, HTO , and 14-C (cont.) Use of nanotechnology to reduce radionuclide leaching properties of matrixes and increase physical properties Encapsulation of organic waste embedded in Noctar into cement matrixes Encapsulation of oil embedded in Noctar into cement matrixes Developing “cold ceramic-cement” matrixes for the immobilization of Iodine, Tc, HTO and 14-C

34. 6. Provisional results of encapsulation of contaminated nano-tubes 14 C part of carbon nano tube structure ? Surface modification ensured a 99.9 % removal of 131 I from waste streams Immobilization of nano-tubes into grout-huge advantageous as fixed contamination could decrease leaching of radionuclides from waste matrix;

35. Alternative matrix (cold ceramics) development for I,Tc and 14-C encapsulation 6. Provisional results of encapsulation of contaminated “cold-ceramics” Magnesium potassium phosphate (MKP) ceramics. MgO + KH2PO4 + 5H2O = MgKPO4.6H2O “ Calcium phosphate ceramic . 3Ca3(PO4)2 + CaCl2 → 2Ca5(PO4)3Cl Ca5(PO4)3Cl + CaCl2 → 3Ca2(PO4)Cl

36. Invitation to CRP members Send samples to me and will do Nrad Analysis on samples regarding: Water penetration Porosity (3d Image locating pore’s and cracks-should computer time be available)

37. Thank you