1. Metal Decontamination Techniques used in Decommissioning Activities
Mathieu Ponnet
SCK•CEN

2. Summary Objectives and selection criteria Full System Decontamination
Decontamination of components/parts
Conclusions
One detail example (BR3 case) in each part

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 system
Pool, Tank
Open system
Hydro jet Method
Blast Method
Strippable coating Method
Chemical Method
Mechanical 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
Concrete Demolition
Mechanical Method
Scabbler
Shaver
Blast Method
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. Right decontamination technique
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. Soft decontamination process Thorough decontamination process
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

14. Pipes, tanks, pools… Right decontamination technique
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

15. 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…

17. 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

19. Chemical process Chemical process commonly used Siemens England Russia
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

20. 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.

21. Chemical reagent MnO4- HNO3 CrIII to CrVI HBF4 Oxidizing agent
for chromium oxide
H2C2O4
oxalates
anionic species
CO2
After destruction
Dissolving agent
Minimize secondary waste
H2O2
Water
Destruction agent
Minimize secondary waste

22. 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.

23. The BR3 primary loop

24. 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

25. 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)

26. 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

27. Total activity removed for each cycle

28. 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..

29. Radiological aspects The total dose amounted to only 159 man*mSv
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
man*mSv
man*mSv
The total dose amounted to only 159 man*mSv
The dose saving up to now is over 500 man*mSv

30. 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 m3
Final waste volume 8 m3
Dose rate in primary system mSv/h
Dose rate purification system mSv/h
Mean Decontamination factor ~ 10
Collective Dose exposure man.Sv

31. 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

32. 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…)

33. 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

34. 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.

35. 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..

36. 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.

37. Cerium IV process T (°C) Acid Regeneration Origin Appli- cation Speed
SODP
Amb
HNO3 O3
Sweden
Closed loop
Low
REDOX
60-80°C
Electro-
chemical
Japan
Open system
High
MEDOC
80°C
H2SO4
Belgium
Open and closed loop

38. MEDOC process at BR3
The MEDOC process has been selected for its high decontamination efficiency
Objectives
Clearance of material

39. MEDOC : Only one step treatment

40. BR3 industrial plant is characterized by three stagesO2
Rinsing
loop 2 1
Decon.
loop 3
waste
treatment O3

41. Effluents are partially treated by SCK and transported to Belgoprocess
< 5 %
Asphalt
Waste
15 kg/m3 total
4 Gbq/m3
Ph Neutralization
Precipitation
Filtration
Cerium neutralization
Nitric acid
SCK-CEN
Belgoprocess

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

45. Material after decontamination

46. 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

47. Steam generator and pressurizer decontamination in 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

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

49. 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 01
ROV 13
RBS83
MEDOC
ROV 22
ROV 05
T01
ROV 04
ROV 08
T02
MS01
ROV 09
RBS 80
ROV 03
ROV 21
HV 02
FLT 01
ROV 17
ROV 18
ROV 16
P02
ROV 19
F01
P05

50. 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.

51. 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

52. … and the pressurizer VENTILATION Water H2 Air Detector
ROV 01
ROV 17
HV 02
ROV 21
P01
MS01
ROV 07
ROV 08
FLT 01
RBS 80
RBS83
Gaz treatment unit
RBS 82
RBS 81
RBS 87
Water
Air
RBS 88
RBS 89
VENTILATION
T01
R01 H2
Detector

53. Removal of 30 µm on the surface
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

54. Decontamination factor higher than 5,000.
Before decontamination
more than 350,000 Bq/dm2
After decontamination
less than 100 Bq/dm2

55. 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.

56. 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.

57. The efficiency increases with the concentration and the temperature.
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.

58. Application : Safety HNO3/HF processes
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.

59. Decoha or DfD processes
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.

60. Regeneration of HBF4 Dissolution reaction (Decontamination)
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 e-- H2
Anodic reaction H+
H2O
2 H+ + 2e- + ½ O2
Metal Particles
Recombination after membrane transfer
2H BF4 -
HBF4
Outlet solution to filter

61. 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.

62. 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…)

63. 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

64. 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

65. Electrochemical decontamination+
High current density at low voltage
bath with acid or salt -
Electrolyte
Phosphoric acid
Nitric acid
Sulfuric acid
Sodium sulfate
chemical or
electrochemical

66. 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, …)

67. 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

68. Principle of electropolishing+
6000 A
at low voltage
bath with phosphoric acid -
before
after
H2PO4
Oxide skin
chemical or
electrochemical
Base material

69. Stainless Steel in Acid Bath

70. Stainless Steel after Electropolishing

71. 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

72. Schematic principle of Regeneration
Dilute acid to concentrated

73. Thermolysis plant for iron oxalate
190°C

74. Example „Secondary Steam Generator“
Vessels of three Steam Generators
decontaminated from 20,000 Bq/cm²
to free release
producing only 1,5% radioactive waste

75. 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
Basket
1-3
16 – 20
Toshiba
H2SO4
0.5
3000 – 10000
60°C
<1
60-240
Eldecon
ABB/
Sweden
Na2SO4 60

76. 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.

77. 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

78. 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.

79. 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

80. 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,…)

81. 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)

82. 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)

83. 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.

84. Abrasives in wet environment at BR3
Roof opening for large pieces
Operator at work

85. Abrasives in dry environment
Working in enclosed area
Decontamination (Metal, plastics, concrete…)
Decoating
Cleaning
Degreasing

86. Abrasives in dry environment at Belgoprocess
Automatic process in batch treatment
Declogging filter (ventilation)
Load of material

87. 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…)

88. Advantages/Disadvantages abrasive-blasting
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.

89. 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

90. 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 …)

91. Ingot, shield blocks, containers
Melting of metals
Country
Capacity
Material
Product
Carla
Germany
3 t
CS, SS, Al, Cu
Ingot, shield blocks, containers
Studsvik
Sweden
CS, SS, Al
Ingot

92. 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)

93. 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

94. 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