26.11.2008Mirkka Ek

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Cementitious materials in handling of radioactive waste

- Overview of activities in Fortum/Finland

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Contents

• Loviisa NPP and solidification plant• Long-term durability experiments

– Full and half scale experiments– Laboratory experiments– Elution experiments

• Solidification experiments (”finding the recipe”)

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Loviisa Power Plant

• Fortum Power and Heat Ltd.Fortum Generation

•VVER-440• Units started their operation

– Loviisa 1 - 1977– Loviisa 2 - 1980

• Electric power, gross 510 MW(net 488 MW) / unit

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Loviisa NPP

L/ILW waste repositoryOperational since -98 (LLW)

Solidification plantFull operation in 2009

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Solidification plant - Background

• Until now: long-term storage of liquid waste• Fortum has carried out extensive research on liquid waste

cementation processes and long-term testing of waste packages performed since late 1970s

• The solidification plant has been designed to solidify waste generated during at least 50 years of operation from units 1 and 2 of Loviisa NPP

• Construction of the solidification plant was postponed several times due to slow waste accumulation rates

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Background cont.

• wastes to be treated:– spent ion exchange resins – bottom sludges of evaporator concentrate

tanks – waste generated during interim storage of

spent fuel and decommissioning• The process is based on use of normal

cement and blast furnace slag. • The waste package is reinforced concrete

container type licensed for final disposal.• The containers will be disposed off in the

repository at the Loviisa site

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Loviisa NPP - Solidification Plant

Solidification lineView towards lidcasting

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Loviisa NPP - Solidification plant

Front side of the process

”Inactive area”

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Loviisa NPP - Solidification Plant

Cross section• Solidification line

and • dosing of binders

and additives

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LONG-TERM DURABILITY EXPERIMENTS WITH CONCRETE-BASED WASTE PACKAGES IN SIMULATED REPOSITORY CONDITIONS

• Full-scale experiment with solidified (cementized) simulated inactive ion-exchange resins:

– experiment started in 1980– waste packages are immersed in slowly flowing water in the

pond of the Pyhäkoski hydro power plant since 1983• Half-scale experiment with solidified (cementized) radioactive

waste product:– experiment started in 1987 – waste packages are immersed in groundwater taken from the

bedrock of the planned repository site since 1987

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Long term durability: Full-scale experiment (I)

• Container: watertight, superplasticizedready-mixed concrete cast in 1980. • Even-surface moist resin solidified with blast-furnace slag cement (inactive resin: 560 kg/m3)• Storage:

– 1980-1981 warm storage– 1981-1983 sheltered outdoorstorage

– 1983- in slowly flowing water in the pond of the Pyhäkoski HPP

• Visual inspection after 1, 3, 5, 13, 15, and 21 years storage period.• More extensive inspection in 1992 and 2004, including samples.

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Full-scale experiment (II)

• The full-scale container has withstood the storage extremely well based on the visual inspection and testing.

• The only external signs of deterioration:– rusting of the lifting lugs and shackles – out-wearing of the thin film of cement paste on the concrete surface

of the container. • No corrosion was found in the reinforcement steels. • The compressive strengths of the cover and side surface concretes, and

waste product averaged 63.0, 82.0 and 36.0 MPa, • The carbonation depth varied between 1 and 7 mm.

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Full-scale experiment (III)

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Half-scale experiment (I)

• Test started 1987• Spent, bead-form, mixed bed ion exchange resin (even-surface moist resin: 331 – 360 kg/m3)• Total activity: 44 GBq/m3 • Slowly hardening sulphate-resistant blast-furnace cement was

used as a binder in the solidification• The binder in concrete containers

was slowly hardening sulphate-resistant Portland cement.• Storage groundwater (from repository site) was stabilized with

concrete.

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Half-scale experiment (II)

• Follow-up programme: – Visual inspection: good condition – Measuring the dimensions and weight: no changes

– Determining the surface dose rate: decreased due to radioactive decay

– Chemical analysis of the storage water: stable after having reached the equilibrium

– Activity analysis of the storage water: most nuclides below detection limit; Cs slightly above – probably due to contamination at the initial stage and not due to leaching

– 33 visual inspections since the start of the experiment.

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Conclusion, full- and half-scale experiments

• The experiments indicate good durability for the waste containers.

• Over 20 yrs storage.• Follow-up continues in the

future.• Next inspections: 2010 (plan).• New cement and concrete

types => new challenges.

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CONCRETE LONG-TERM DURABILITY UNDER FINAL DISPOSAL CONDITIONS - LABORATORY AND FIELD TESTS

• A joint research programme by Fortum and TVO, launched in 1997.• 9 test concretes:

– S1: SR-cement, S2: Portland-composite cement with 10 % silica, S3: Portland cement with 75 % blast-furnace slag and 5 % silica– W/C: 0.35, 0,425 and 0,50

• Accelerated CO2-conditions, • Bedrock groundwater conditions in Olkiluoto• At the laboratory in nine Cl-, SO4- and Mg-solutions:

– SO4: 20 .. 500 .. 1000 mg/l– NaCl: 50 .. 1000 .. 10000 mg/l– MgCl2: 5 .. 100 .. 300 mg/l

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Research programme

• Basic inspections• Carbonation depth • Penetration of aggressive substances• Analysis of microstructure• Chemical analysis of storage water

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Main intermediate results

• Carbonation depth @ 50 a < Reinforcement depth.

• Only chloride penetration is clearly observed.

• The results indicate a need for enhanced modelling to better comprehend the phenomenology

• The experiment will continue with longer measurement intervals

B4/L6 - Kloridipitoisuus

0,0000,2000,4000,6000,8001,0001,200

0 4 8 12 16 20 24 28 32 36 40Tunkeutumasyvyys (mm)

Pitois

uus (

%)

L6-11kkL6-22kkL6-46kkL7-70kk

B4/L3 - Rikki

0,00

0,50

1,00

1,50

2,00

2,50

0 4 8 12 16 20 24 28 32 36 40Tunkeutumasyvyys (mm)

Pitois

uus (

%)

L3-11kkL3-22kkL3-46kkL3-70kkLähtötaso +0,25% yks.Lähtötaso -0,25% yks.

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Elution experiments (I)

• Started simultaneously with the wastemanagement design in the1980s.

• Latest experiments during the construction of the solidification plant

– real ion-exchange resin– real groundwater taken from the

L/ILW repository, 90 d– ion-exchanged water, 5 d– composition of samples based on

the solidifcation experiments– Cs-134, Cs-137, Co-60

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Elution experiments (II)

Cs-134:n eluoitumisnopeus [Bq/cm2·d]

1,00E-02

1,00E-01

1,00E+00

1,00E+01

1,00E+02

1,00E+03

1,00E+04

29.7.05 5.8.05 12.8.05 19.8.05 26.8.05 2.9.05 9.9.05 16.9.05 23.9.05 30.9.05 7.10.05 14.10.05 21.10.05

C1C2C3C4C5C6D1D2D3D4D5D6

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Preliminary tests for solidification plant – ”Finding the recipe”

Requirements set for succesful solidification• Solidification should finish in 24 hours• Compressive strength after 7 d should be higher than 1MPa

(final criteria 5 MPa after 28 days)• Class A or B after 7-14 days water exposure

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Preliminary tests for solidification plant cont.

Original recipe developed in 1990's:

• 1 portion of ion exchance resin/evaporate• 0.08 NaOH (50%)• 0.5 original hardening Portland cement• 1.5 blast furnace slag→ In 1990’s perfect results for both resins/ evaporateBUT in 2004 resins did not solidify!!

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Solidification tests - "Panic" test matrix

Contentcation / anion 1:1 1 1 1 1 1 1 1 1 1 1Portland cement 0,500 0,500 0,500 0,500 0,500 0,500 0,500 0,500 0,500 0,500slag 1,500 1,500 1,500 1,500 1,500 1,500 1,500 1,500 1,500 1,500 NaOH-solution (50%) - 0,08 - - - - - - - -NaCl-solution (10%) - - - - - - - - - 0,10Na2CO3-powder - - 0,10 - - - - - - -Ca(OH)2-powder - - - 0,18 - - - - - -NaNO3-powder - - - - - - - 0,10 - -KNO3-powder - - - - - - - - 0,10 -Fly ash - - - - - - 0,10 - - -Si-powder - - - - - 0,10 - - - -Water 0,32 0,28 0,35 0,62 0,32 0,40 0,39 0,22 0,20 0,20

Solidification* Start min > 5640 < 5640 1560 - > 5580 > 5580 > 4200 > 4200 < 4230 > 4140* End min - - < 5640 < 5670 - - - - - - < 1440 min (24 h)

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Results of further testing (solidification tests):

• 0.08 parts (50%) NaOH had to be replaced by 0.15 parts Na2CO3 -> solidification ok

• Age and quality of the blast furnace slag greatly impact the process

• Hydration level (age) of Na2CO3 impacts the process

• Anion resins difficult (boron)• Suspect also: More efficient resins in 2004 - more boron?

Anion resin without Na2CO3 – compressive strength 0

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Why did Na2CO3 work and NaOH not? (solidif. tests)

NaOH Na2CO3Na2CO3 vs NaOH?Does NaOH degrade the resin more and thus release more boron to water?

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Role of boron and Na (solidification tests)

Resin simulant was handled with boric acid and treatedwith NaOH or Na2CO3

→Not a significant difference in released boron

BUT: Na content from Na2CO3 is 3x higher (26g/9g)

11

50 %NaOH

10

60 gNa2CO3

73H3BO3 fromresin (g)

30 %NaOH

10 % NaOH

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Effect of boron solution on used recipe (solidif. tests)

Normal recipe: 1 water, 0.50 cement, 1.50 blastfurnace slag, 0.15 Na2CO3

1314161521Compressivestrength (30 d)

<2280<2040<2900<1030< 940Solidificationtime

40g/kg H3BO3, pH 9,540g/kg H3BO3

36g/kg H3BO3

15g/kg H3BO3

UHPwater

< 1440 min

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Current status (solidification tests)

• New recipe works for both types of wastes.• Mechanisms are not fully understood• Repeatibility of small scale tests not high enough (small samples, inhomogeneous composition of slag, cement or used resins).→ End of the solidification is not a good criteria to estimate the functionality of recipe.

• Small specimens behave differently than plant scalewaste packages (less Na2CO3 is needed for solidification,higher temperatures up to 70oC, release of ammonia,etc,).

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Future challenges

• Reliable, continuous solidification• Casting the spaces between waste packages in the final repository with concrete (very large area, small holes, remote operation, no vibration possible)

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Thank you!