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. IntroductionLocation of disposal site

Disposal trenches

1. Introduction

3. Cement container developmentFinal cement selection

Cement composition of approved waste containers

Cement composition corresponds to Type V sulfate-resistant concrete, as established in ASTM C150

1. Introduction

Approved cement containers for disposal

1. Introduction

Building of cementitious engineered barrier1. 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 degradation1. Corrosion-6 meter –top container – no corrosion down-cap water ingress2. Presence of SRB-only top container -3. Diffusion of chlorides from backfill4. Micro-organisms on surface-top container5. Resin expansion –small cracks at container lid

Cementitious research at Necsa1.Fix capping methodology2.New designed waste container 3.Develop analytical technique for water/ chloride penetration4.New cement formulation for outside container5.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 concrete Partially painted porous concrete

Fully painted porous concrete

Analytical tool for water penetration- connection of pore structure

Porosity

0%

5%

10%

15%

20%

0% 5% 10% 15% 20%Gravimetric

NR

AD

Before Radiation : EffectiveporosityAfter 1 Radiation : TotalporosityAfter 2 Radiation : Totalporosity

Conformation of NRAD as technique for measuring porosity

Analytical tool to indicate porosity

3. Cement container developmentPreparation of cement cubes

Water curing -28 days Tensile and compression

Temp. cyclic studiesWater penetration studies with different aggregates by Nrad

Chloride penetration studies with Nrad

3. Cement container development

Initial After 24 hours

in water bath

After 96 hours

In water bath

3. Cement container developmentWater diffusion by NRAD technology

3. Cement container developmentContainer properties- experimental

Parameters Technical Specs. Construct. Koeberg Necsa Comp.TensileDensityW/C RatioPorosity Sorptivity

Min 60 MPaMin 5 MPaMin 2400 kg/cm3

Less than 0.5Less than 12 %Less than 1.5 gram/hour

35 MPa2.5 MPa2200 kg/cm3

Less than 0.4520 %3.0 gram/hour

50 MPa4.5 MPa2400 kg/cm3

Less than 0.453 %1.0 gram/hour

70-80 MPa5.2-5.8 MPa2700 kg/cm3

Less than 0.45Less than 3 %Less than 1.0 gram/hour

Disposal site re-opened in 2007

4. Grout matrix developmentLiterature 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 developmentManufacturing 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 0.01gMs0 = 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.

Samples

Pressure readout

Vacuum line

Water inlet

Water outletSamples submersed in water

Silica gel

w

ssw

Ad

MMn

0

4. Grout matrix developmentPorosity 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 √tt = 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 developmentSorptivity (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.

(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.

4. Grout matrix developmentLeaching 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

4. Grout matrix developmentSelection 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 penetrationPorosity(3d Image locating pore’s and cracks-should computer time be available)

• Thank you