1

Metal Decontamination Techniques used in Decommissioning Activities

Mathieu Ponnet

SCK•CEN

2

• Objectives and selection criteria

• Full System Decontamination

• Decontamination of components/parts

• Conclusions

�One detail example (BR3 case) in each part

Summary

3

Definition

• Decontamination is defined as the removal of contamination from surfaces by

� Washing

� Heating

� Chemical or electrochemical action

� Mechanical action

� Others (melting…)

4

3 main reasons

• To remove the contamination from components to reduce dose level in the installation (save dose during dismantling)

• To minimize the potential for spreading contamination during decommissioning

• To reduce the contamination of components to such levels that may be

�Disposed of at a lower category

� Recycled or reused in the conventional industry (clearance of material)

5

Decontamination for decommissioning

• In maintenance work, we must avoid any damage to the component for adequate reuse

• In decommissioning, decontamination techniques can be destructive, the main goal being the removal of as much activity as possible (high DF)

6

Decontamination before Dismantling

Objectives : Reduction of occupational Exposure

Pipe Line System Decontamination

Closed systemPool, Tank

Open system

�Chemical Method

�Mechanical method

�Hydro jet Method

�Blast Method

�Strippable coating Method

7

Decontamination after Dismantling

Objectives : Reduction of radioactive waste or recycling

Pipes, Components

Open or closed system

�Chemical Immersion Method

�Electrochemical Method

�Blast Method

�Ultrasonic wave Method

�Gel Method

8

Decontamination Of Building

Objectives : Reduction of radioactive concrete waste or

Release of building

Concrete Surface

�Mechanical Method

�Scabbler

�Shaver

�Blast Method

Concrete

Demolition

�Explosives

�Jackhammer

�Drill &Spalling

9

Selecting a specific decontamination technique

• Need to be considered� Safety: Not increase radiological or classical

hazards� Efficiency: Sufficient DF to reach the

objectives� Cost-effectiveness: should not exceed the

cost for waste treatment and disposal� Waste minimization: should not rise large

quantities of waste resulting in added costs, work power and exposure� Feasibility of industrialization: Should not

be labour intensive, difficult to handle or difficult to automate.

10

Parameters for the selection of a decontamination process

• Type of plant and plant process

• Operating history of the plant

• Type of components: pipe, tank

• Type of material: steel, Zr, concrete

• Type of surface: rough, porous, coated…

• Type of contaminants: oxide, crud, sludge…

• Composition of the contaminant (activation products, actinides… and radionuclide involved)

• Ease of access to areas/plant, internal or external contaminated surface

• Decontamination factor required

• Destination of the components after decontamination

• Time required for application

• Capability of treatment and conditioning of the secondary waste generated

11

Some examples about the type of material

• Stainless steel: Resistant to corrosion, difficult to treat, needs a strong decontamination process to remove several µm

• Carbon steel: Quite porous and low resistance to corrosion, needs a soft process but the contamination depth reaches several thousand µm (more secondary waste)

• Concrete: The contamination will depend of the location and the history of the material, the contamination depth can be few mm to several cm.

12

Some examples about the type of surface

•Porous: Avoid wet techniques which are penetrant.

•Coated: Do we have to remove paint ? (contamination level, determinant for the use of electrochemical techniques)

•Presence of crud: what are the objectives ? (reduce the dose or faciliting the waste evacuation)

Right decontamination technique

13

Some examples about decontamination factor

required

Primary circuit of BWR and PWR reactors

Outer layer : Fe2O

3, Iron rich

Intermediate layer (CRUD) :

FeCr2O

4, Cr

2O

3, Chromium rich

Base alloy : Fe, Cr, Ni

DF

1-5

5-50

50-10,000

Soft decontamination process

Thorough decontamination process

1-5 µm

2-10 µm

5 – 30 µm

Right decontamination technique

14

Pipes, tanks, pools…

Some examples about the type of components

Right decontamination technique

� Decontamination in a closed system? (avoids the spreading of contamination…)

� Decontamination in an open system after dismantling? (secondary waste…)

� Connection to the components, dose rate, the total filling up of the component, auxiliary…

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Some examples about the treatment of secondary waste

�Availability of a facility to treat secondary waste from decontamination (chemical solutions, aerosols, debris, …)

� Final products (packaging, decontaminated effluent,…) have to be conform for final disposal.

� In decontamination processes, the final wastes are concentrated, representing a significant radiation source.

16

Overview of decontamination process for metals

• Chemical process� In closed system (APCE, TURCO, CORD, SODP, EMMA,

LOMI, DFD, Foams or various reagents…)

� In open system on dismantled components (MEDOC, Cerium/nitric acid, CANDEREM, DECOHA, DFDX or various reagents, HNO3, HCl, HF,…)

• Electrochemical process (open or close system)� Phosphoric acid, Nitric acid, Oxalic or citric acid, sulfuric

acid or others process

• Physical process (open system)� Wet or dry abrasives, Ultrasonic cleaning, HPW, CO2 ice

blasting, others…

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Decontamination Techniques Used in Decommissioning Activities

• Objectives and selection criteria

• Full system Decontamination� General consideration

� Chemical reagents

� Spent decontamination solutions

� Guidelines for selecting appropriate FSD

� The case of BR3 (CORD)

• Decontamination of components/parts

• Conclusions

18

Full system and closed system Decontamination

• Objectives� Reduce the dose rate and avoid spreading of

contamination during dismantling

� Typical decontamination factor 5 to 40

• Application� Decontamination of the primary circuit (RPV,PP, SG

and auxiliary circuits) directly after the shutdown of the reactor

� Decontamination of components in a closed loop

• Practical objectives� Remove the crud layer of about 5 to 10 µm inside

the primary circuit

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Chemical process

• Chemical process commonly used� CORD Chemical Oxidizing Reduction

Decontamination based on the used of permanganic acid (AP).

� LOMI Low Oxidation State Metal Ion (AP)

� APCE Process based on the use of permanganate in alkaline solution

� NITROX or CITROX based on the use of nitric or citric acid.

� EPRI DFD (Decontamination For Decommissioning) based on the use of fluoroborique acid.

Siemens

England

Russia

Westinghouse

EPRI

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Multi-step decontamination process

• Oxidation step� Oxidation of the insoluble chromium with

permanganate in alkaline or acidic media, Nitric acid or fluoroboric acid

• Decontamination step� A dissolution step is carried out with oxalic acid

to dissolve the crud layer

� The reduction / dissolution step is enhanced by complexing agent

• Purification step� The excess of oxalic acid is removed using

permanganate or hydrogen peroxide

� The dissolved cations and the activity are removed using Ion Exchange Resins.

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Chemical reagent

MnO4-

HNO3

HBF4

H2C

2O

4

oxalates

anionic species

H2O

2

CrIII to CrVI

CO2⇑

After destruction

Water

Oxidizing agent

for chromium oxide

Dissolving agent

Minimize secondary waste

Destruction agent

Minimize secondary waste

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The Full System Decontamination of the primary system of the BR3-PWR reactor

with the Siemens CORD Process

Objectives

• Reduce the radiation dose rate by a factor of 10

• Remove the surface contamination, the so-called

CRUD to avoid dispersion of contamination during

dismantling of contaminated loops

with a particular attention to:

• Minimize the amount of secondary wastes

• Minimize the radiation exposure of the workers

• Minimize the modifications to be done to the plant

for the decontamination operation.

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The BR3 primary loop

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Full System Decontamination of the primary and auxiliary loops in 1991

• 3 Decontamination Cycles at 80 to 100 °C in 9 days

• For each cycle : 3 steps� oxidation step with HMnO4

� Reduction step with H2C2O4

� Cleaning step with anionic and cationic IEX resins and removal of excess oxalic acid by oxidation with HMnO4 or with H2O2 on catalysts

CORD®: Chemical Oxidizing-Reducing Decontamination

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Chemistry of the process

Oxidation Step with Permanganic Acid HMnO4 at 0.3 g/lFor the oxidation of the Chromium from Cr3+ to Cr6+

Temperature 100°C

Decontamination step with Oxalic Acid H2C2O4 at 3 g/lDissolution step for the hematite dissolution and the activity dissolution

Temperature 80°C to 100°C

Cleaning step: Destruction of the excess oxalic acid by oxidation

with permanganic acid or with hydrogen peroxide on a catalyst

Combined with fixation of corrosion products on Ion Exchange resins

Temperature: 80 to 60°C (last cycle)

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Process steps for each cycle

Step nr 1: OxidationInjection of permanganic acid

Circulation during several hours

Step nr 2:

Reduction + Decontamination

Injection of oxalic acid - Circulation

Purification on ion exchange

Step nr 3: Cleaning

Destruction of organics +

purification on ion exchange

Process Steps Chemicals in solution Ion exchangeResins

MnO4-

C2O

42-

Cr, Fe oxalates

anionic species

Water, CO2⇑

Ni2+, Mn2+, Co2+

Fixation on

cationic IEX

Cr, Fe oxalatesFixation on

anionic

IEX

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Total activity removed for each cycle

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Primary loop Decontamination factors

ComponentDose rate before

mSv/h

Dose rate after

mSv/hDF

HOT LEG 1.74 0.125 14

COLD LEG 1 1.58 0.16 10

COLD LEG 2 0.74 0.11 7

MAKE UP EJECTOR 4.40 1.50 3

PRIMARY PUMP 1 0.46 0.15 3

PRIMARY PUMP 2 0.49 0.13 4

PRESSURIZER 0.47 0.14 3.5

STEAM GENERATOR 0.905 0.05 16

! In some points, still some hot spots due to redeposition in dead zones

horizontal line of the pressurizer, dead zones in heat exchangers..

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• Phase I : Preparatory phase

� manual closure of the reactor pressure vessel

� maintenance of the components

� modifications to the circuits• Phase II : Decontamination operation

� hot run

� 3 decontamination Cycles• Phase III : Post decontamination operations

� evacuation of the liquid wastes

� evacuation of the solid wastes

The total dose amounted to only 159 man*mSv

The dose saving up to now is over 500 man*mSv

16.9 man*mSv

6.4 man*mSv

135.3 man*mSv

Radiological aspects

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Main data and results

• Contaminated surface treated 1200 m2

• Primary system volume 15 m3

• Corrosion products removed 33 kg

• Mean Crud layer removed 5 µm

• IEX Waste volume produced 1.35 m3

• Final waste volume 8 m3

• Dose rate in primary system 0.08 mSv/h

• Dose rate purification system 0.06 mSv/h

• Mean Decontamination factor ~ 10

• Collective Dose exposure 0.16 man.Sv

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• Expected ...� Smooth process, minor operational problems� Careful and detailed preparation is a must� Requires a reactor in full satisfactory conditions� To be performed shortly after the operation� Man-Sv savings for future dismantling justify the

operation

• Unexpected ...� More ion exchange resins needed and higher liquid waste

volume� Pollution of the reactor pool during reactor opening due to

the presence of insoluble iron oxalate and loose crud: could be easily removed by the plant filtration

� Internals of RPV remarkably clean facilitating inspection and dismantling and allowing to evacuate waste in a lower category LAW vs MAW

Lessons drawn from the operation …

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Guidelines for selecting appropriate FSD

• Objectives in terms of Decontamination Factor

• Type of material: Acidic solution is not appropriate for carbon steel

• Volume of secondary waste: preferred regenerative process (Lomi, DfD, CORD…)

• Composition of secondary waste: avoid organic element like EDTA (Complexing agent)

• Type of oxide layer: Select an oxidizing process for high chromium content in the CRUD

• Capability of treatment and conditioning of the secondary waste generated (Evaporation, IEX, Precipitation, filtration…)

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Decontamination Techniques Used in Decommissioning Activities

• Objectives and selection criteria

• Full system decontamination

• Decontamination of components/parts� General considerations

� Chemical decontamination

� Electrochemical decontamination

� Mechanical decontamination

� Decontamination by melting

� Guidelines for selecting appropriate decontamination techniques

� The case of BR3 (ZOE - MEDOC)

• Conclusions

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Decontamination of components/parts

• To reduce the contamination of components to such levels that they may be � Disposed of at a lower category -

decategorization� Recycled or reused in the

conventional industry (clearance of material)

• The decontamination can be applied:� In a closed system on an isolated

component (circuits, steam generator…)� In an open system on dismantling

material in batch treatment.

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• Multi-step processes�Same processes : Lomi, Cord,

Canderem

• Processes in one single step (Hard decontamination process)

�Cerium IV process : SODP, REDOX, MEDOC

�HNO3/HF

�HBF4 : Decoha, DfD..

Chemical decontamination

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Cerium IV process

• The cerium IV process is a one step treatment.

• The cerium is a strong oxidizing agent (Eo = 1.61 V) in mixture with acid (Nitric acid or Sulfuric acid)

• The cerium IV dissolves oxide layer and the base metal.

• Cerium can be regenerated and recycled.

• The neutralization of cerium IV and the treatment of the solution for final conditioning are simple.

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Cerium IV process

T (°C) Acid Regeneration

Origin Appli-cation

Speed

SODP Amb HNO3 O3 Sweden Closed loop

Low

REDOX 60-80°C HNO3 Electro-chemical

Japan Open system

High

MEDOC 80°C H2SO4 O3 Belgium Open and

closed loop

High

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The MEDOC process has been selected for its high decontamination efficiency

Clearance of material

Objectives

MEDOC process at BR3

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MEDOC : Only one steptreatment

Regeneration

of cerium IV

Ce 4+

Ce 3+

Cerium solution

O2

Ozone

gas

Contaminated

Material

Free

release

Decontamination

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BR3 industrial plant is characterized by three stages

O3

O2

waste

treatment

Decon.

loop

Rinsing

loop1

2

3

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Effluents are partially treated by SCK and transported to Belgoprocess

Waste

SCK-CEN Belgoprocess

Ph Neutralization

Precipitation

Filtration

15 kg/m3 total

4 Gbq/m3

Cerium neutralization

Nitric acid

10 T< 5 %

0.3 T

Asphalt

42

Medoc workshop after installation

43

Control room

44

Safety precautions taken in the MEDOC installation

Due to the combined radioactive and chemical hazards� construction materials selected to resist to the aggressive

process

� unreacted ozone thermally destroyed before release

� O3 and H2 detectors with automatic actions on the process

� two independent ventilation systems

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Material after decontamination

46

25 tons of contaminated material have already been treated

� Treatment capacity is 0.5 ton per treatment (20 m2)

� Average corrosion rate 2.5 µm/h

� The treatment time is about 4 to 10 hours

� Very low residual contamination < 0.1 Bq/g

Specific activity of material

after decontamination in

200 Liters drums

0

0,02

0,04

0,06

0,08

0,1

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Steam generator and pressurizer decontamination

in May 2002

� Main goal

� Make the demonstration of large components decontamination using MEDOC

� Reach the clearance contamination level after melting

� Steam generator characteristics (primary loop - SS)� 30 tons of mixed stainless and carbon steel� Number of tubes 1400 in stainless steel� Total length of tubes 15 km � Total surface 620 m2� Volume 2.7 m3

7,9

4 m

48

Handling of the SG before decontamination

The SG has been removed

and placed horizontally

to allow the total filling up

of the primary side

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Main circulation loop between SGand MEDOC plant

T01

ROV 01

ROV 17HV 02

ROV 21

ROV 18

ROV 04

ROV 03

F01

ROV 16

RO

V 2

2

T02

RO

V 0

5

ROV 19

ROV 13

P05P02

MS01

ROV 07

ROV 08

R01

ROV 09

FLT 01

RBS 82

RBS81

PCV 02

RBS 85

RBS 80

RBS83

Treatment gas Medoc

RBS 86 RBS 84

RBS 87

Decontamination step I

MEDOC

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Workload

� 30 decontamination cycles are needed :

� Decontamination (2 hours)

� Regeneration of cerium IV (4 hours)

� After 15 cycles, the SG was rotated for homogenous attack on the primary side.

� 60 hours decontamination and 130 hours of regeneration about 3 weeks with 2 working teams.

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• 10 µm or 42 kg of material were removed on the overall surface.

• 2.06 Gbq of Co60

• The tube bundle was manually rinsed via the primary head with pressurized water.

• Low radiation level in the primary head (few µSv/h) - no free contamination

Reach the clearance contamination level after melting

52

Conclusions on MEDOC

� Contaminated materials are successfully decontaminated using a batchwise technique in MEDOC plant.� Up to now, 80% of treated materials have been cleared

and sold to a scrap dealer (including primary pipes) � Remaining 20% can be cleared after melting (< 1 Bq/g)� The loop treatment of the BR3-SG was also a success � It will easy the post-operation dismantling (HPWJC),� It will avoid the evacuation of huge components in a

waste category.

53

HNO3/HF processes

• The sulfonitric mixture is commonly used for the etching of stainless steel � in batch process

� in pulverization solution

• The liquid penetrates the oxide layer to attack the base metal (thorough decontamination process).

• The oxides come off the surface and stay in the solution.

• The oxides are eliminated by filtration.

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• The efficiency increases with the concentration and the temperature.

• However, it decreases with the increasing of dissolved material.

• This is not a regenerative process, new HF has to be added to the solution and produces more effluents.

HNO3/HF processes

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• Application :� Not very attractive in batch

treatment due to the consumption of reagent

�Good result in pulverisation process at low temperature followed by rinsing with pressurised water jet.

HNO3/HF processes

• Safety� Need of special attention to the

worker safety due to the presence of HF and fluoride.

56

HBF4 processes

• The fluororic acid is able to dissolve both the oxide layer and the base alloy on stainless or carbon steel

• This process is used in batch treatment or in pulverization process

• The fluoroboric acid can be regenerated by electrodeposition of the metal.

Decoha or DfD processes

57

Regeneration of HBF4

Cathode (-) Anode (+)

Ion

Exchange

Membrane

H+

Inlet solution

Outlet solution to filter

Metal Particles

Dissolution reaction (Decontamination)

Fe + 2 HBF4

Fe(BF4)

2+ H

2

Cathodics reactions

Fe(BF4)

2+ 2e- Fe + 2 BF

4 -

Anodic reaction

H2O 2 H+ + 2e- + ½ O

2

Recombination after membrane transfer

2H+ + 2 BF4

- HBF4

2H+ + 2 e-- H2

58

Application

• Compared to the cerium or sulphonitric process, it is

less aggressive (lower rate)

• Due to the formation of hydrogen in the

decontamination and regeneration steps, the process

required special safety attention (monitoring,

ventilation, dilution with air…)

• The 137Cs which is not deposited has to be

eliminated in IEX or by added chemical treatment.

59

Advantages for chemical decontamination

• Chemical decontamination allows the treatment

of complex geometry material (hidden parts,

inside parts of tubes,…)

• With strong mineral acids, DF over 104 can be

reached allowing the clearance of material

• With proper selection of chemicals, almost all

radionuclides may be removed

• Chemical decontamination is a known practice in

many nuclear plants and facilities (experience…)

60

• The main disadvantage is the generation of

secondary liquid waste which requires

appropriate processes for final treatment and

conditioning

• The safety due to the chemical hazard with

high corrosive products (Acid, gas,…) and by-

products (H2, HF, …)

• Chemical decontamination is mostly not

effective on porous surfaces

Disadvantages for chemical decontamination

61

Electrochemical decontamination

• Electrolytic polishing is an anodic

dissolution technique

• Material to be decontaminated is the

anode, the cathode being an

electrode or the tank itself

• Objectives :

� removed hot spot

� lowered dose rate

� decategorisation of material

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+

-

chemical or

electrochemical

bath with acid or

salt

Electrochemical decontamination

• Phosphoric acid• Nitric acid• Sulfuric acid• Sodium sulfate

Electrolyte

High current

density at low

voltage

63

Application

• Electropolishing can be used for the treatment of Carbon steel, Stainless steel, Aluminum

• Electropolishing requires conducting surfaces (the paint must be removed)

• Not really adapted for small or complex geometry material with hidden parts (current density inside pipes, …)

64

Special technique at KRB A plant in Gundremmingen

Decontamination of

stainless steel parts with

phosphoric acid

• quick processing time• reliability• less secondary waste• maximal recycling

effect

Electropolishing

65

Principle of electropolishing

Oxide skin

Base material

before after

+

-

H2PO

4

6000 A

at low voltage

chemical or

electrochemical

bath with

phosphoric acid

66

Stainless Steel in Acid Bath

67

Stainless Steel after Electropolishing

68

Regeneration of Phosphoric Acid

• Recycling of Phosphoric acid by

• Reuse acid for decontamination

• Thermolysis of iron oxalat

- adding oxalic acid

- precipitate the dissolved iron as

- iron oxalate

- extracting the iron oxalate

- vaporization

- heating the iron oxalate

- transformation into iron oxide for final storage

69

Schematic principle of Regeneration

Dilute acid to concentrated

70

Thermolysis plant for iron oxalate

190°C

71

Example „Secondary Steam Generator“

Vessels of three Steam Generators

decontaminated from 20,000 Bq/cm²

to free release

producing only 1,5% radioactive waste

72

Electropolishing processes

Electro-lyte

Conc

M

Current density

A/m2

Elec-trode

Time

Hours

Corro-sion rate

µm/h

AEA/ Harwell

HNO3 1 20-30 Ti 2 NC

CEA/UDIN

HNO3 2 100-300 BasketTi

1-3 16 – 20

Toshiba H2SO4 0.5 3000 –1000060°C

NC <1 60-240

EldeconABB/

Sweden

Na2SO4 0.5 1000-6000

NC <1 60

73

Advantages of Electropolishing

• Commercially available and relatively inexpensive

• Large panel of material and geometry (water box of SG, tanks, large pieces,…) can be treated with this technique

• High corrosion rate and quick treatment

• Low volume of secondary waste.

74

• Electropolishing does not remove fuels, sludge or any insulating material

• Inside parts of tubes or hidden parts are treated poorly

• Like chemical processes, secondary liquid waste are generated. This method is less applicable for industrial decontamination of complex geometries:� limited by the size of the batch in immersion

process

� The access to contaminated parts and free space are required when an electrode (pad) is used

• Handling of components may lead to additional exposure to workers

Disadvantages of Electropolishing

75

Mechanical decontamination

• Mechanical decontaminations are often less aggressive than the chemical ones but they are a bit simpler to use.

• Mechanical and chemical techniques are complementary to achieve good results

• The two basic disadvantages� The contaminated surface needs to be accessible

� Many methods produce air bone dust.

76

�Cleaning with ultrasons

�Projection of CO2 ice or water ice

�Pressurized water jet

�Decontamination with abrasives in wet or dry environment

�Mechanical action by grinding, polishing, brushing

Typical Mechanical decontamination

77

Cleaning with ultrasons

• The cleaning in ultrasonic batch is only applicable for slightly fixed contamination

• Does not allow to remove the fixed contamination

• This technique is used in combination with detergent (Decon 90, …)

• However, it is mainly used to enhance the corrosion effect in chemical decontamination processes (Medoc,…)

78

Projection of CO2 ice or water ice

• CO2 ice pellets are projected at high speed against the surface

• The CO2 pellets evaporate and remove the contamination

• The operator works in ventilated suit inside a ventilated room to remove CO2 and contamination

• Needs some decontamination tests before selecting the process (not efficient for deep contamination)

79

Pressurized water jet

• Low pressure water Jet : 50 – 150 bar� Pre-decontamination technique

� Removal of sludge or deposited oxide

� Decontamination of tools

• Medium pressure water Jet : 150 – 700 bar� Usually used for the decontamination of equipments or

large surfaces (pool walls,…)

� Large water consumption (60 – 6000 L/h) and contaminated aerosols

� Requires a suitable ventilation system and a recirculation loop with filtration (recycling of water)

80

Decontamination with abrasives

• Uses the power of abrasives projected at high

speed against the surface

�Wet environment: fluid transporter is water

�Dry environment: fluid transporter is air

• Imperative to ensure the recycling of the

abrasive to reduce the secondary waste

production

• Needs a suitable ventilated system to remove

contamination and aerosols.

81

Abrasives in wet environment at BR3

Roof opening for large pieces

Operator at work

82

Abrasives in dry environment

• Decontamination (Metal, plastics, concrete…)

• Decoating• Cleaning• Degreasing

• Working in enclosed area

83

Abrasives in dry environment at Belgoprocess

• Automatic process in batch treatment

Declogging filter (ventilation)

Load of material

84

Comparison of the wet and dry sandblasting

• Choose an abrasive with a long lifetime (recycling)� Minerals (magnetite, sand,…)� Steel pellets, aluminum oxide� Ceramic, glass beads� Plastic pellets� Natural products

• Wet and dry techniques allow to recycle the abrasive by separation� Filtration or decantation in wet sandblasting� On declogging filter (ventilation) in dry

sandblasting

• The air contamination in dry sandblasting is much more important (cross contamination…)

85

Advantages/Disadvantages abrasive-blasting

• Advantages� Effective and commercially available

� Removes tightly adherent material (paint, oxide layer…)

• Disadvantages� Produces a large amount of secondary

waste (abrasive and dust…)

� Care to introduce the contamination deeper in porous material.

86

Mechanical action by grinding, polishing, brushing

• Large range of abrasive belts or rollers available on the market

• Ideal to remove small contaminated surface

• Due to the production of dust, used in a ventilated enclosure, the operator wears protection clothes

87

Melting of metals

• The melting of metal can be considered as a decontamination technique

� 137Cs are eliminated in fumes and dust

� Heavy elements coming from oxide are eliminated in slag (radioactive waste)

• The melting technique is used for

� The recycling of material in nuclear field (container,..)

� The clearance of ingots after melting (measurement of activity easier …)

88

Melting of metals

Country Capacity Material Product

Carla Germany 3 t CS, SS, Al, Cu

Ingot, shield blocks,

containers

Studsvik Sweden 3 t CS, SS, Al

Ingot

89

Advantages of melting

• Advantages of redistributing of

radionuclides in ingots/slag and

dust: decontamination effect

• Essential step when releasing

components with complex

geometries (allows the

measurement after melting)

90

Conclusions

• Selection criteria of decontamination techniques for metals� The geometry and size of pieces

� The objectives of the decontamination (dose rate or waste management…)

� The nature and the level of contamination

� The state of the surface and the type of material

� The availability of the process

91

Needs for decommissioning

• For decommissioning we need several complementary techniques� To reduce the dose rate before dismantling

♣ FSD� To treat materials with complex geometries

♣ Chemical decontamination� To treat materials with simple geometries

♣ Sand blasting or electrochemical decontamination� To decontaminate tools or slightly contaminated

pieces♣ High pressure jet♣ Manuel cleaning♣ Other mechanical techniques

� To remove residual ‘hot spot’ after decontamination♣ Mechanical techniques : grinding, brushing

� To help in the evacuation route of materials♣ Melting of metals