Nuclear Research Institute Řež plc Ústav jaderného výzkumu Řež a.s. 1 Development of waste...

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Nuclear Research Institute Řež plc

Ústav jaderného výzkumu Řež a.s.

Development of waste matrices for immobilization of problematic waste from Czech nuclear power

plants

RCM on CRP „Behaviour of Cementitious Materials in Multipurpose Packaging for

Transportation, Long Term Storage and Disposal

Bucharest, 24– 28 November 2008

Petr Večerník, Monika Kiselová, Antonín Vokál

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Main objectives of the project

1) Optimalization of cement composition and testing of new matrices for immobilization of ion-exchange resins, sludge and oils from Czech Nuclear Power Plants Dukovany and Temelín

2) Understanding of leaching mechanisms from cement matrices to be able to get data for advanced performance assessment codes and waste acceptance criteria (WAC) derivation

3) Starting activities for research of cementitious materials for Deep Geological Repository

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Main streams of problematic waste in Czech NPPs

Wet Ion-exchangers Sludge (often mixed with

ion-exchange resins) Oils

Solid Waste exceeding limits

for near-surface repositories – stored DGR

Dukovany near surface respository

Planned Deep Geological Repository

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Waste Acceptance Criteria for Dukovany repository

Leaching resistance of waste forms with activity higher than 2 x 107 Bq

4 % after 48 hours (test RAWRA K001b)

Compressive strength Cement – 5 MPa Geopolymer – 10 MPa

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Model waste

Organic spent ion-exchangers simulated by saturation of new ion-exchange resins (Purolite A-400 MB OH and Purolite C-100 H) Ion-exchangers were saturated from 90 % and the ratio of cationic to anionic resins was set to the ratio 2:1.

Samples were doped with Cs-137

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Cemented samples

Cements Portland cement CEM I

52,5 R Portland cement with

slag CEM II/A –S 42,5 R

Additives Plastificators (Addiment

FM 935) Fillers (silica, ash)

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Selected procedure

1) Mixing 5 minutes of water with plastificator

2) Mixing 10 minutes cement with filler

3) 28 days curing before testing

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Cement compositions Commercial cement with slag (CEM II/A-S 42,5 R of Lafarge Company) seems to be the most suitable basic materials both for cementation of spent ion-exchangers and sludge.High amount of silica (> 20 %) and water reducing admixtures (plasticizers) (about 10 %) is needed to achieve required properties, namely to withstand immersion test and to meet compression strength higher then 5 MPa. The total content of water must be less then 30 %

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volume (ml) weight (g)OPC 42.5 --- 640ionexchanger (48,8% dry mass) --- 642silikol P (powdered) --- 128water 106 106plasticizer FM 935 42 51.2

Composition of mixture for experiments

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Samples for experiments

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Qualification tests of cement mixtures

Compression strength

(5 MPa cement, 10 MPa geopolymers)

Leaching characteristics (ANSI/ANS 16.1)

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WAC derivation from PAs

Data obtained from leaching experiments, such as ASNSI/ANS 16.1 are not sufficient for performance assessment purposes and WAC derivation. For advanced transport models following data are needed:

1) Effective diffusion coefficient (De)

2) Sorption coefficients

3) Formation factors

4) Solubility limits

Leaching time

Mixture No. 100

[hours]

D [cm2s-1]

Leaching index

Cumulative leaching [%]

2 2,57E-11 10,59 0,08 7 3,52E-10 9,45 0,50 24 5,22E-10 9,28 1,40 48 6,81E-10 9,17 2,59 72 4,99E-10 9,30 3,73 96 1,70E-10 9,77 4,43 120 1,67E-10 9,78 5,23 456 1,91E-10 9,72 7,73 1128 6,90E-11 10,16 9,83 2160 3,00E-11 10,52 11,55

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Evaluation methods

Batch sorption experiments

Through diffusion experiments

Electromigration experiments

wfse DFfD

Da – Apparent diffusion coefficient

De – Effective diffusion coefficients

- Porosity

d - Dry density

Kd – Distribution coefficient

Ff– Geometric (tortuosity) factor

fs – available porosity factor

dd

ea K

DD

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Sorption of 137Cs on cementKD values

0

10

20

30

40

50

0 10 20 30 40 50 60 70time (days)

KD (

ml/

g)

crushed 1:25 crushed 1:10 powdered 1:25 powdered 1:10 pieces 1:10

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Diffusion experimentsTracers

3H 125I

Through diffusion cell

increasing activity A-A0

0

100

200

300

400

500

0 500 1000 1500 2000 2500time (hours)

Al-

A0 (

cp

s)

Da = 1.2 – 1.6 x 10-11 m2s-1

De = 2.6 – 4.6 x 10-12 m2s-1

DW = 2.4 x 10-9 m2s-1

Experiments with 125I

are still running

3H experiments

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Through

electromigration

method

(TEM)

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w

pfF

p – saturated sample conductivity, w – electrolyte conductivity


dxdU

CCN LHe

Electromigratory flux (N): e– ion mobility, U – potential,

CH – high concentration in reservoir, CL – low concentration in reservoir, Cp concentration in pore water

F – Faraday constant, z – charge number

ee

RTD

z F

wfse DFfD

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Advantages of TEM

-much faster than classical through diffusion method-not limited sample dimensions as in through diffusion

Disadvantages of TEM / be careful of

- possible pH changes due to electrolysis- possible changes of solution composition- possible changes in rock sample

Advantages of TEM

y = 3.277E-08x - 5.148E-06

R2 = 9.709E-01

0.00E+00

1.00E-06

2.00E-06

3.00E-06

4.00E-06

5.00E-06

6.00E-06

7.00E-06

8.00E-06

9.00E-06

1.00E-05

0 100 200 300 400 500

time [min]

Iod

ide

co

nc

en

tra

tio

n [

mo

l/l]

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Preliminary results for cesiumDa from leaching experiment = 3 x 10-14 m2/s

Da from sorption and diffusion

experiments = 1 x 10-14 m2/s (calculated from equation

De from tricium through diffusion experiments = 3.6 x 10-12 m2/s

Kd = 2 x 10-2 m3/kg

= 0.15

= 2700 kg/m3

dd

ea K

DD

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Further plans Finish through diffusion and electromigration experiments to acquire data for modelling and to get deeper understanding of transport of radionuclides in cementitios materialsTo start experiments for developing cementitios materials for use in DGR

low pH low water permeability good gas permeability good mechanical properties

To start ageing and permeability measurements of cementitious materials on special prepared equipment

Nuclear Research Institute Řež plc Ústav jaderného výzkumu Řež a.s. 1 Development of waste...

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