metal decontamination techniques used in decommissioning activities n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Metal Decontamination Techniques used in Decommissioning Activities PowerPoint Presentation
Download Presentation
Metal Decontamination Techniques used in Decommissioning Activities

Loading in 2 Seconds...

play fullscreen
1 / 94

Metal Decontamination Techniques used in Decommissioning Activities - PowerPoint PPT Presentation


  • 485 Views
  • Uploaded on

Metal Decontamination Techniques used in Decommissioning Activities. Mathieu Ponnet SCK•CEN. Summary. Objectives and selection criteria Full System Decontamination Decontamination of components/parts Conclusions One detail example (BR3 case) in each part. Definition.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Metal Decontamination Techniques used in Decommissioning Activities' - rosalba


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
summary
Summary
  • Objectives and selection criteria
  • Full System Decontamination
  • Decontamination of components/parts
  • Conclusions
    • One detail example (BR3 case) in each part
definition
Definition
  • Decontamination is defined as the removal of contamination from surfaces by
    • Washing
    • Heating
    • Chemical or electrochemical action
    • Mechanical action
    • Others (melting…)
3 main reasons
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)
decontamination for decommissioning
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)
slide6

Decontamination before Dismantling

Objectives : Reduction of occupational Exposure

Pool, Tank

Open system

Pipe Line System Decontamination

Closed system

  • Hydro jet Method
  • Blast Method
  • Strippable coating Method
  • Chemical Method
  • Mechanical method
slide7

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
slide8

Decontamination Of Building

Objectives : Reduction of radioactive concrete waste or Release of building

Concrete Surface

Concrete Demolition

  • Mechanical Method
    • Scabbler
    • Shaver
    • Blast Method
  • Explosives
  • Jackhammer
  • Drill &Spalling
selecting a specific decontamination technique
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.
parameters for the selection of a decontamination process
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
some examples about the type of material
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.
slide12

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

slide13

Some examples about decontamination factor required

Primary circuit of BWR and PWR reactors

DF

Soft decontamination process

Outer layer : Fe2O3, Iron rich

1-5 µm

1-5

Intermediate layer (CRUD) :

FeCr2O4, Cr2O3, Chromium rich

2-10 µm

5-50

Thorough decontamination process

5 – 30 µm

Base alloy : Fe, Cr, Ni

50-10,000

Right decontamination technique

slide14

Some examples about the type of components

Pipes, tanks, pools…

  • 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…

Right decontamination technique

slide15

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.
overview of decontamination process for metals
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…
decontamination techniques used in decommissioning activities
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
full system and closed system decontamination
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
chemical process
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

multi step decontamination process
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.
chemical reagent
Chemical reagent

MnO4-

HNO3

HBF4

CrIII to CrVI

Oxidizing agent

for chromium oxide

H2C2O4

oxalates

anionic species

CO2

After destruction

Dissolving agent

Minimize secondary waste

H2O2

Water

Destruction agent

Minimize secondary waste

slide22
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.
full system decontamination of the primary and auxiliary loops in 1991
Full System Decontamination of the primary and auxiliary loops in 1991

CORD®: Chemical Oxidizing-Reducing Decontamination

  • 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
chemistry of the process
Chemistry of the process

Oxidation Step with Permanganic Acid HMnO4 at 0.3 g/l

For the oxidation of the Chromium from Cr3+ to Cr6+

Temperature 100°C

Decontamination step with Oxalic Acid H2C2O4 at 3 g/l

Dissolution 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)

process steps for each cycle
Process steps for each cycle

Ion exchange

Resins

Chemicals in solution

Process Steps

Step nr 1: Oxidation

Injection of permanganic acid

Circulation during several hours

MnO4-

Step nr 2:

Reduction + Decontamination

Injection of oxalic acid - Circulation

Purification on ion exchange

C2O42-

Cr, Fe oxalates

anionic species

Ni2+, Mn2+, Co2+

Fixation on

cationic IEX

Step nr 3: Cleaning

Destruction of organics +

purification on ion exchange

Water, CO2

Cr, Fe oxalates

Fixation on

anionic

IEX

primary loop decontamination factors
Primary loop Decontamination factors

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

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

radiological aspects
Radiological aspects
  • 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

135.3 man*mSv

6.4 man*mSv

16.9 man*mSv

The total dose amounted to only 159 man*mSv

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

main data and results
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
lessons drawn from the operation
Lessons drawn from the operation …
  • 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
guidelines for selecting appropriate fsd
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…)
slide33

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
decontamination of components parts
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.
chemical decontamination
Chemical decontamination
  • 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..
cerium iv process
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.
the medoc process has been selected for its high decontamination efficiency
The MEDOC process has been selected for its high decontamination efficiency

MEDOC process at BR3

Objectives

Clearance of material

br3 industrial plant is characterized by three stages

1

BR3 industrial plant is characterized by three stages

O2

Rinsing

loop

2

Decon.

loop

3

waste

treatment

O3

effluents are partially treated by sck and transported to belgoprocess
Effluents are partially treated by SCK and transported to Belgoprocess

10 T

0.3 T

< 5 %

Asphalt

Waste

15 kg/m3 total

4 Gbq/m3

Ph Neutralization

Precipitation

Filtration

Cerium neutralization

Nitric acid

SCK-CEN

Belgoprocess

slide44

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
35 tons of contaminated material have already been treated
35 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

steam generator and pressurizer decontamination in may 2002
Steam generator and pressurizer decontaminationin May 2002
  • Main goal
    • To demonstrate the decontamination 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

7,94 m

slide48

Handling of the SG before decontamination

The SG has been removed

and placed horizontally

to allow the total filling up

of the primary side

slide49

Main circulation loop between SG and MEDOC plant

RBS 87

RBS 86

RBS 84

RBS 82

PCV 02

RBS 85

Decontamination step I

RBS81

Treatment gas Medoc

ROV 07

R01

ROV 13

ROV 01

ROV 05

RBS83

ROV 22

MEDOC

T01

ROV 04

T02

ROV 08

MS01

ROV 09

ROV 03

RBS 80

ROV 21

ROV 17

ROV 18

ROV 16

ROV 19

FLT 01

HV 02

P02

P05

F01

slide50

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.
slide51

Reach the clearance contamination level after melting

  • 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
and the pressurizer

VENTILATION

RBS 88

RBS 81

Water

H2

Detector

RBS 87

Air

RBS 89

Gaz treatment unit

R01

RBS 82

ROV 07

ROV 01

RBS83

ROV 08

MS01

T01

ROV 21

RBS 80

P01

HV 02

ROV 17

FLT 01

… and the pressurizer
slide53

Workload

  • 3 decontamination cycles are needed :
    • Decontamination (10 hours)
    • Regeneration of cerium IV (4 hours)
  • 30 hours decontamination and 12 hours of regeneration about 1 or 2 weeks with 1 working team.

Removal of 30 µm on the surface

decontamination factor higher than 5 000
Decontamination factor higher than 5,000.

Before decontamination

more than 350,000 Bq/dm2

After decontamination

less than 100 Bq/dm2

conclusions on medoc
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.
hno 3 hf processes
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.
hno 3 hf processes1
HNO3/HF processes
  • 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.
hno 3 hf processes2
HNO3/HF processes
  • 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.
  • Safety
    • Need of special attention to the worker safety due to the presence of HF and fluoride.
slide59

HBF4 processes

Decoha or DfD 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.
regeneration of hbf 4
Regeneration of HBF4

Inlet solution

Dissolution reaction (Decontamination)

Cathode (-)

Anode (+)

Fe + 2 HBF4

Fe(BF4)2 + H2

Ion

Exchange

Membrane

Cathodics reactions

Fe(BF4)2 + 2e-

Fe + 2 BF4 -

2H+ + 2 e--

H2

Anodic reaction

H+

H2O

2 H+ + 2e- + ½ O2

Metal Particles

Recombination after membrane transfer

2H+ + 2 BF4 -

HBF4

Outlet solution to filter

application
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.
advantages for chemical decontamination
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…)
disadvantages for chemical decontamination
Disadvantages for chemical decontamination
  • 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
electrochemical decontamination
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
electrochemical decontamination1
Electrochemical decontamination

+

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

High current density at low voltage

bath with acid or salt

-

Electrolyte

chemical or

electrochemical

application1
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, …)
special technique at krb a plant in gundremmingen
Special technique at KRB A plant in Gundremmingen

Decontamination of

stainless steel parts with

phosphoric acid

Electropolishing

  • quick processing time
  • reliability
  • less secondary waste
  • maximal recycling effect
principle of electropolishing
Principle of electropolishing

+

6000 A

at low voltage

bath with phosphoric acid

-

before

after

Oxide skin

H2PO4

chemical or

electrochemical

Base material

regeneration of phosphoric acid
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

schematic principle of regeneration
Schematic principle of Regeneration

Dilute acid to concentrated

example secondary steam generator
Example „Secondary Steam Generator“

Vessels of three Steam Generators

decontaminated from 20,000 Bq/cm²

to free release

producing only 1,5% radioactive waste

advantages of electropolishing
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.
disadvantages of electropolishing
Disadvantages of Electropolishing
  • 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
mechanical decontamination
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.
typical mechanical decontamination
Typical Mechanical decontamination
  • 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
cleaning with ultrasons
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,…)
projection of co 2 ice or water ice
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)
pressurized water jet
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)
decontamination with abrasives
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.
abrasives in wet environment at br3
Abrasives in wet environment at BR3

Roof opening for large pieces

Operator at work

abrasives in dry environment
Abrasives in dry environment
  • Working in enclosed area
  • Decontamination (Metal, plastics, concrete…)
  • Decoating
  • Cleaning
  • Degreasing
abrasives in dry environment at belgoprocess
Abrasives in dry environment at Belgoprocess
  • Automatic process in batch treatment

Declogging filter (ventilation)

Load of material

comparison of the wet and dry sandblasting
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…)
advantages disadvantages abrasive blasting
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.
mechanical action by grinding polishing brushing
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
melting of metals
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 …)
advantages of melting
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)
conclusions
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
needs for decommissioning
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