D&D Technologies

• Technologies are classified broadly as:– Decontamination– Equipment removal and size reduction– Demolition

Decontamination

• Used to reduce occupational exposure• Reduce potential for release of

material• Reduce potential for uptake of

material• Permit the reuse of selected

components

Decontamination

• Facilitate management of the waste generated

• Decision to decontaminate must be weighed against the total dose and the cost

• Always preceded by a careful radiological survey of the facility

Decontamination Techniques

• Selection criteria– Cost– Surface layer thickness to be removed– Final end state of material surface– Decontamination aim– Allowed dose to decontamination personnel– Amount of secondary waste generated and

treatment required

Decontamination Techniques

• Techniques are primarily characterized as:- chemical - mechanical

Decontamination

• Chemical - Uses concentrated or dilute solvents in contact with the contaminated surface

• Mechanical – physical techniques that generally clean the surface and/or remove the surface

• May be used together or separately depending on the situation

Chemical Decontamination

• Water or steam Strong mineral acids

• Acid salts Weak acids• Alkaline salts Complexing agents• Oxidizing agents Reducing agents• Detergents Surfactants• Organic solvents

Chemical Decontamination-Advantages

• Can be used for inaccessible surfaces• Generally requires fewer work hours• Can decontaminate equipment in place• Often can be performed remotely• Produces few airborne hazards• Uses chemicals that are readily available• Wastes produced can be handled remotely• Allows recycling of wash liquors (after

processing)

Chemical Decontamination-Disadvantages

• Not usually effective on porous surfaces• Can produce large volumes of waste• May generate mixed wastes• Can result in corrosion and safety

problems when misapplied

Chemical Decontamination-Disadvantages• Requires different reagents for different

surfaces• Requires drainage control• May require construction of chemical

storage and collection systems for large jobs

• May require addressing criticality concerns

Mechanical Decontamination

• CO2 blasting Wet ice blasting

• Hydroblasting Shot blasting• Grinding Scarifiers• Drill and spall Plasma torch• Paving breaker Chipping hammer• Scabbling

Mechanical Decontamination - Advantages

• Physical technique involving removal of surface

• Usually very fast• High decontamination factors• Effective for large areas

Mechanical Decontamination - Disadvantages

• Work piece must be accessible• Crevices and corners are hard to

decontaminate• Creates airborne dusts• May require construction of

enclosures to control area

Acceptable Surface Contamination Levels - USNRC

• U-nat, U-235, U-238 and associated decay productsAverage* – 5,000 dpm/100 cm2

Maximum* – 15,000 dpm/100 cm2

Removable – 1,000 dpm/100 cm2

* Dose rate from beta and gamma-emitters should not exceed 0.2 mrad/h at 1 cm and 1.0 mrad/h at 1 cm, respectively.

Acceptable Surface Contamination Levels - USNRC

• Transuranics, Ra-226, Ra-228, Th-230, Th-228, Pa-231, Ac-227, I-125, I-129Average* – 100 dpm/100 cm2

Maximum* – 300 dpm/100 cm2

Removable – 20 dpm/100 cm2

* Dose rate from beta and gamma-emitters should not exceed 0.2 mrad/h at 1 cm and 1.0 mrad/h at 1 cm, respectively.

Acceptable Surface Contamination Levels - USNRC

• Th-nat, Th-232, Sr-90, Ra-223, Ra-224, U-232, I-126, I-131, I-133Average* – 1,000 dpm/100 cm2

Maximum* – 3,000 dpm/100 cm2

Removable – 200 dpm/100 cm2

* Dose rate from beta and gamma-emitters should not exceed 0.2 mrad/h at 1 cm and 1.0 mrad/h at 1 cm, respectively.

Acceptable Surface Contamination Levels - USNRC

• Beta-gamma emitters (nuclides with decay modes other than alpha emission and spontaneous fission) except Sr-90 and others noted previouslyAverage* – 5,000 dpm /100 cm2

Maximum* – 15,000 dpm /100 cm2

Removable – 1,000 dpm /100 cm2

* Dose rate from beta and gamma-emitters should not exceed 0.2 mrad/h at 1 cm and 1.0 mrad/h at 1 cm, respectively.

Equipment Removal and Size Reduction

• Physical dismantling and segmenting of equipment such as piping, pumps, tanks, hot cells, laboratories, etc.

• Technique classes– Mechanical– Thermal– Other

Equipment Removal and Size Reduction

• Removal method must consider:– Radiological criteria– Availability or adaptability of suitable

equipment– Knowledge of problems to be tackled– Time available to complete tasks– Cost-effectiveness of method

Equipment Removal and Size Reduction

• Equipment chosen should be:– Easy to use– Familiar to the workforce– Reliable– Well constructed – Proven technology– Adaptable to remote use

Examples

• Power nibblers and shears• Conventional mechanical saws• Circular cutters• Abrasive cutters• Plasma arc cutting• Oxygen cutting• Flame cutting

Demolition

• Controlled blasting• Wrecking ball or slab• Backhoe-mounted rams• Rock splitter• Bristar demolition compound• Paving breakers • Chipping hammers

Protective Clothing

• Appropriate for radiation exposure– Leaded gloves– Leaded aprons– Protective eyewear– Other devices

• Anti-contamination clothing– May be effective for certain radiations

Internal Radiation Exposure Control

• Internal radiation dose control• Contamination control program• Internal radiation dosimetry• Monitoring and surveillance programs• Protective equipment and devices• Records

Contamination Control Program

• Use of exposure time• Engineering controls• Access control and alarm systems• Radiation safety procedures• Radiation work permits (RWP)• Work and exposure planning• Dose reduction activities (ALARA)

Control of Low-level Radioactive Waste

• Minimizing the production of waste• Decontamination and reuse of tools and

equipment• Collecting, sorting, and classifying waste• Radioactive waste volume reduction• Storage, disposal and recycling of waste• Records

Contamination Control

• Dry method –wipe off• Tape press- physically remove • Wash with water/ soap• Sweat it out- wear glove sweating action will

work contamination out• More aggressive actions

Questions?