Transcript TITLE

Metal Decontamination Techniques used
in Decommissioning Activities
Mathieu Ponnet
SCK•CEN
1
Summary
•
•
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•
Objectives and selection criteria
Full System Decontamination
Decontamination of components/parts
Conclusions
 One detail example (BR3 case) in
each part
2
Definition
• Decontamination is defined as the removal
of contamination from surfaces by
 Washing
 Heating
 Chemical or electrochemical action
 Mechanical action
 Others (melting…)
3
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)
4
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)
5
Decontamination before
Dismantling
Objectives : Reduction of occupational Exposure
Pipe Line System Decontamination
Pool, Tank
Closed system
Open system
Chemical Method
Hydro jet Method
Mechanical method
Blast Method
Strippable coating Method
6
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
7
Decontamination Of
Building
Objectives : Reduction of radioactive concrete waste or
Release of building
Concrete Surface
Concrete
Demolition
Mechanical Method
Scabbler
Explosives
Shaver
Jackhammer
Blast Method
Drill &Spalling
8
Selecting a specific
decontamination technique
• Need to be considered
 Safety: Not increase radiological or classical
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


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.
9
Parameters for the selection of
a decontamination process
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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
10
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.
11
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
12
Some examples about
decontamination factor
required
Primary circuit of BWR and PWR reactors
Soft decontamination process
1-5 µm
2-10 µm
DF
Outer layer : Fe2O3, Iron rich
Intermediate layer (CRUD) :
FeCr2O4, Cr2O3, Chromium rich
1-5
5-50
Thorough decontamination process
5 – 30 µm
Base alloy : Fe, Cr, Ni
50-10,000
Right decontamination technique
13
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
14
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.
15
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
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General consideration
Chemical reagents
Spent decontamination solutions
Guidelines for selecting appropriate FSD
The case of BR3 (CORD)
• Decontamination of components/parts
• Conclusions
17
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
Siemens
England
Russia
Westinghouse
EPRI
 CORD Chemical Oxidizing Reduction
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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.
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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
MnO4HNO3
HBF4
H2C2O4
oxalates
anionic species
H2 O 2
Oxidizing agent
for chromium oxide
Dissolving agent
Minimize secondary waste
Destruction agent
Minimize secondary waste
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CrIII to CrVI
CO2
After destruction
Water
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
CORD®: Chemical Oxidizing-Reducing Decontamination
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•
3 Decontamination Cycles at 80 to
100 °C in 9 days
For each cycle : 3 steps
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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
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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)
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Process steps for each cycle
Process Steps
Chemicals in solution
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
C2O42Cr, Fe oxalates
anionic species
Step nr 3: Cleaning
Destruction of organics +
purification on ion exchange
Ion exchange
Resins
Ni2+, Mn2+, Co2+
Fixation on
cationic IEX
Cr, Fe oxalates
Water, CO2
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Fixation on
anionic
IEX
Total activity removed for each cycle
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Primary loop Decontamination
factors
Component
Dose rate before
mSv/h
Dose rate after
mSv/h
DF
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
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horizontal line of the pressurizer, dead zones in heat exchangers..
Radiological aspects
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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
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
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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
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Mean Decontamination factor
~ 10
•
Collective Dose exposure
0.16
30
man.Sv
Lessons drawn from the operation …
•
Expected ...
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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 ...
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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
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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)
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• 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.
34
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..
35
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
Regene
ration
Origin
Application
Speed
SODP
Amb
HNO3
O3
Sweden
Closed
loop
Low
REDOX
60-80°C
HNO3
Electrochemical
Japan
Open
system
High
MEDOC
80°C
H2SO4
O3
Belgium
Open
and
closed
loop
High
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MEDOC process at BR3
The MEDOC process has been selected for
its high decontamination efficiency
Objectives
Clearance of material
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MEDOC : Only one step
treatment
O2
Cerium solution
Ce 4+
Ozone
gas
Free
release
Ce 3+
Regeneration
of cerium IV
Contaminated
Material
Decontamination
39
BR3 industrial plant is
characterized by three stages
O2
2
Rinsing
loop
1
Decon.
loop
3
waste
treatment
O3
40
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
41
Medoc workshop after installation
42
Control room
43
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
44
Material after decontamination
45
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
0,1
0,08
Specific activity of material
after decontamination in
200 Liters drums
0,06
0,04
0,02
0
46
Steam generator and
pressurizer decontamination
in May 2002
7,94 m
 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
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Number of tubes 1400 in stainless steel
Total length of tubes 15 km
Total surface 620 m2
Volume 2.7 m3
47
Handling of the SG before
decontamination
The SG has been removed
and placed horizontally
to allow the total filling up
of the primary side
48
Main circulation loop between SG
and MEDOC plant
RBS 87
RBS 86
RBS 84
RBS 82
PCV 02
RBS 85
RBS81
Decontamination step I
Treatment gas Medoc
ROV 07
R01
ROV 13
RBS83
MEDOC
T01
ROV 04
ROV 08
ROV 05
ROV 22
ROV 01
T02
ROV 09
MS01
ROV 03
RBS 80
ROV 21
HV 02 FLT 01
ROV 17
ROV 18
49
P02
ROV 16
F01
ROV 19
P05
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.
50
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
51
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.
52
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.
53
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.
54
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.
55
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.
56
Regeneration of HBF4
Inlet solution
Dissolution reaction (Decontamination)
Cathode (-)
Anode (+)
Fe + 2 HBF4
Ion
Fe(BF4)2 + H2
Cathodics reactions
Exchange
Fe(BF4)2 + 2e2H+ + 2 e--
Membrane
H+
Anodic reaction
H2O
Metal Particles
Outlet solution to filter
Fe + 2 BF4 H2
2 H+ + 2e- + ½ O2
Recombination after membrane transfer
2H+ + 2 BF4 57
HBF4
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.
58
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…)
59
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 byproducts (H2, HF, …)
• Chemical decontamination is mostly not
effective on porous surfaces
60
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
61
Electrochemical
decontamination
+
bath with acid or
salt
High current
density at low
voltage
-
Electrolyte
chemical or
electrochemical
•
•
•
•
Phosphoric acid
Nitric acid
Sulfuric acid
Sodium sulfate
62
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, …)
63
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
64
Principle of electropolishing
+
bath with
phosphoric acid
-
6000 A
at low voltage
before
after
Oxide skin
H2PO4
chemical or
electrochemical
Base material
65
Stainless Steel in Acid Bath
66
Stainless Steel after
Electropolishing
67
Regeneration of Phosphoric
Acid
• Recycling of Phosphoric acid
by - adding oxalic acid
- precipitate the dissolved iron as
- iron oxalate
• Reuse acid for
decontamination
- extracting the iron oxalate
- vaporization
• Thermolysis of iron oxalat
- heating the iron oxalate
- transformation into iron oxide for final storage
68
Schematic principle of
Regeneration
Dilute acid to concentrated
69
Thermolysis plant for iron
oxalate
190°C
70
Example „Secondary Steam
Generator“
Vessels of three Steam Generators
decontaminated from 20,000 Bq/cm²
to free release
producing only 1,5% radioactive waste
71
Electropolishing processes
Electrolyte
Conc
Current
density
A/m2
20-30
Electrode
Time
AEA/
Harwell
HNO3
M
1
CEA/
UDIN
HNO3
2
100-300
Basket
Ti
1-3
16 – 20
Toshiba
H2SO4
0.5
3000 –
10000
60°C
NC
<1
60-240
Eldecon
ABB/
Sweden
Na2SO4
0.5
10006000
NC
<1
60
72
Ti
Hours
2
Corrosion
rate
µm/h
NC
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.
73
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
74
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.
75
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
76
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,…)
77
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)
78
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)
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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.
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Abrasives in wet environment
at BR3
Roof opening for large pieces
Operator at work
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Abrasives in dry environment
• Working in enclosed area
• Decontamination (Metal,
plastics, concrete…)
• Decoating
• Cleaning
• Degreasing
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Abrasives in dry environment
at Belgoprocess
• Automatic process in
batch treatment
Declogging filter (ventilation)
Load of material
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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…)
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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.
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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
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Melting of metals
• The melting of metal can be considered as
a decontamination technique
are eliminated in fumes and dust
 Heavy elements coming from oxide are
eliminated in slag (radioactive waste)

137Cs
• The melting technique is used for
 The recycling of material in nuclear field
(container,..)
 The clearance of ingots after melting
(measurement of activity easier …)
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Melting of metals
Country
Capacity
Material
Product
Carla
Germany
3t
CS, SS,
Al, Cu
Ingot, shield
blocks,
containers
Studsvik
Sweden
3t
CS, SS,
Al
Ingot
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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)
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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
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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
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