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

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

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

Disposal trenches 1. Introduction

3. Cement container development Final cement selection

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

Approved cement containers for disposal 1. Introduction

Building of cementitious engineered barrier 1. Introduction

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

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

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

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

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

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

Experimental evidence of cement container degradation 1.Corrosion-6 meter –top container – no corrosion down-cap water ingress 2.Presence of SRB-only top container - 3.Diffusion of chlorides from backfill 4.Micro-organisms on surface-top container 5.Resin expansion –small cracks at container lid Cementitious research at Necsa 1.Fix capping methodology 2.New designed waste container 3.Develop analytical technique for water/ chloride penetration 4.New cement formulation for outside container 5.New grout matrix formulation for waste encapsulation 2. Cement container durability-initial studies Repository closed on 2002 to fix “problems” of resin waste container”

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

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

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

3. Cement container development Preparation of cement cubes Water curing -28 daysTensile and compression

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

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

3. Cement container development Container properties- experimental ParametersTechnical Specs.Construct.KoebergNecsa Comp. Tensile Density W/C Ratio Porosity Sorptivity Min 60 MPa Min 5 MPa Min 2400 kg/cm 3 Less than 0.5 Less than 12 % Less than 1.5 gram/hour 35 MPa 2.5 MPa 2200 kg/cm 3 Less than % 3.0 gram/hour 50 MPa 4.5 MPa 2400 kg/cm 3 Less than % 1.0 gram/hour MPa MPa 2700 kg/cm 3 Less than 0.45 Less than 3 % Less than 1.0 gram/hour Disposal site re-opened in 2007

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?

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

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 0.02mm 2. d = average specimen thickness to the nearest 0.02mm. Ρw = density of water = g/mm 3. Samples Pressure readout Vacuum line Water inlet Water outlet Samples submersed in water Silica gel 4. Grout matrix development Porosity 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. Data points to be used in analysis Saturation 4. Grout matrix development Sorptivity (water penetration) determination of different grout matrixes

The American Nuclear Society leaching test method by American national Standards Institute (ANSI/ANS-16.1) was used. (a n /A o ) 2 V 2 -D =  T [1] (  t) n 2 S 2 -D = effective diffusivity, cm 2 /s -a n = quantity of a nuclide released during leaching interval n -A 0 = 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 = t n - t n-1, duration of the nth leaching interval, s -V = volume of cement sample, cm 3 -S = geometrical surface area of the cement sample, cm 2 To simulate a free flow of leachate, water is changed at every time interval where the measurements are taken. 4. Grout matrix development Leaching determination of different grout matrixes Cs -137 Ag -110m Co-60

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

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

Selection of nine (9) grout matrixes for leaching studies of encapsulated radioactive liquid waste

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

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

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

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; 6. Provisional results of encapsulation of contaminated nano-tubes

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

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)

Thank you