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Segmentation & Dismantling

Techniques

Ispra, 5-8 July 2011

Techniques

JRC Ispra Summer School

Lecture content

• What is decommissioning

• Why segmenting and dismantling ?

• Dismantling and segmentation overview

• Mechanical segmentation techniques

JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011

• Mechanical segmentation techniques

• Thermal cutting techniques

• Water abrasive cutting

• RPV and internals segmentation: a former ‘challenge’

Nuclear Installations

• Nuclear installation is a facility where radioactive materials are used/generated and,for this reason, control is usually implemented by a Regulatory Authority in order toprotect health and safety of workers/public and environment

• Example of nuclear installations: Nuclear Power Plants (production of electricitythrough the fission reaction), Research Laboratories/Plants (research in the nuclearfield by means of radionuclides), Fuel Cycle Facilities (manufacturing, reprocessing of


field by means of radionuclides), Fuel Cycle Facilities (manufacturing, reprocessing ofnuclear fuel for Nuclear Power Plants)

• At the end of the operating life of the installation, parts of the plant are activated (byneutron flux) and parts are contaminated by radionuclides with short or long half-life

• If no further use of the facility is foreseen, the installation is shut down and, to ensurethe long term protection of the public and the environment, Decontamination andDismantling are implemented

Nuclear Decommissioning

According to the IAEA definition (IAEA Glossary), ‘decommissioning’ consists of:

Administrative and technical actions taken to allow the rem oval of some or all ofthe regulatory controls from a facility

• The use of the term decommissioning implies that no further use of the facility (or part


• The use of the term decommissioning implies that no further use of the facility (or partthereof) for its existing purpose is foreseen

• Decommissioning typically includes decontamination and dismantling of the facility (orpart thereof)

• Decontamination is the complete or partial removal of the radioactive contaminationby means of physical or chemical processes

• Some facilities may be decommissioned without dismantling and the existingstructures subsequently put to another use (after decontamination)

Why segmenting and dismantling?

• Decommissioning is not just taking systems apart following a casual approach !

• Many systems must remain in operations up to the final phase (ventilation, electricsystem, fire prevention, etc.)

• Non essential systems may be dismantled having clear in mind the final destination ofthe dismantled materials

• Clearance levels for releasable materials must be authorized; suitable disposal


• Clearance levels for releasable materials must be authorized; suitable disposalrepositories for waste (temporary and/or final) must be available

• The boundary conditions for dismantling are then raised by:

� Emptying space for more complex removal activities or for reuse (e.g. turbinehalls used as waste management facilities or temporary stores)

� Eliminating high dose components in order to reduce worker exposures

�Meeting the acceptance criteria of the repositories (e.g. some repositories in USaccept large component for direct disposal)

Dismantling & segmentation overview

• The decommissioning of nuclear facilities involves the dismantling and segmentationof metallic components and the cutting and demolition of concrete structures.

• Dismantling leaves the equipment parts intact while segmentation requires cutting apiece of equipment into smaller parts by means of various techniques

• Before dismantling or size reducing a contaminated/activated equipment, suitablemeasures must be taken to reduce worker exposure and spread of contamination


measures must be taken to reduce worker exposure and spread of contamination

• Usual ways for dismantling highly irradiated components are: underwater cutting(taking advantage of the shielding capabilities of water); use of remotely operatedtools; reducing the time of presence in case of manual work

• Dismantling contaminated components requires the use of confined anddepressurized areas under controlled access (both in situ or in a different place bymoving the component), suitable ventilation and filtration systems, fire preventiondevices

Dismantling & segmentation process

• Dismantling process should be chosen based on the following major parameters:

� Radiological conditions of the component to be dismantled

� Dimensions and material of the component to be dismantled

� Minimisation of the dose to workers (ALARA principle)

� Efficiency of the available techniques (e.g. cutting speed)


� Efficiency of the available techniques (e.g. cutting speed)

� Secondary waste production

• The main currently available dismantling/segmenting techniques can be grouped inthree categories:

� Mechanical

� Thermal

� Water jet

Mechanical techniques

• Mechanical techniques use mechanical forces and motion, usually driven electrically,pneumatically or hydraulically, to cut the component.

• Mechanical techniques include:

� Nibblers and shears


� Nibblers and shears

� Circular, band, reciprocating saws

� Wall and floor saws

� Circular cutters

� Diamond wire

� Core/stitch drilling

Nibblers and shears

Nibblers

Description

A nibbler is a punch and die cuttingtool operating at a rapid reciprocationrate of the punch against the die,‘nibbling’ a small amount of sheetmetal with each stroke.

ApplicationsStationary shears


Ideal for sheet metal up to 10 mmthick. Pneumatic nibblers can operateunderwater equipped with an exhaustair line

ShearsDescriptions

A shear is a two blade tool operatinglike a pair of scissors and cuttingwithout developing shapeless materialsor secondary waste

Applications

Both for metal sheet/pipes and concreteespecially if contaminated (nosecondary waste)

Hydraulic shears andconcrete ramsHydraulic portable shears

Stationary shearsNibbler

Saws

Description

Saws use reciprocating (hacksaw)or rotating (circular) blades to cutmetal with various shapes andpipes.

Applications

Light weight and compact size;easy to be mounted, can operate

Portable hacksaw


easy to be mounted, can operatewithout control; reduced dose foroperators Also for stationaryapplications. Easily arranged forunderwater applications. Also forthick components. Slow cuttingspeed. Production of secondarywaste from lubricants.

Stationary hacksaw

Cutting a glove box with a circular saw

Band saw

Wall and floor saws

Description

A diamond or carbide wheelis used to abrasively cut theconcrete even in presence ofreinforcing steel rods.

The dust produced by the cutis controlled by a water spraywhich constitutes a


which constitutes asecondary waste.

Applications

For any kind of reinforcedconcrete. Can be used up to3 ft of thickness.

Floor saw

Wall saw

Circular cutters

Description

A circular cutter is a self-propelled unit that cuts as it


propelled unit that cuts as itmoves around thecircumference of a pipe heldto a structure which is sizedto fit the outside diameter ofthe pipe.

Applications

Suitable for pipes up to 42’’and 6’’ thick

Rotary pipe cutter

Diamond wire

Description

Diamond wire cutting uses a series of pulleyswhich draw a continuous loop of multistrand wireequipped with a series of diamond beads. Thewire is wrapped around the object to be cut andcontact tension is applied on the wire by thepulleys. The spinning wire cuts a path through theconcrete or even metal.


concrete or even metal.

Applications

Almost any thickness can be cut with thistechnique. Ideal for cutting unusual configurationsin radioactive environment (e.g. biological shields)

Suitable measures must be taken to reduce thepossible spread of contamination due to swarfwhich can be carried from the cutting area by thewire. Secondary waste in case of water cooling

Diamond wire saw

Diamond wire

Core/stitch drilling

Description

The stitch drilling process is anextension of the simple core drillingtechnique. It requires drilling a seriesof close pitched holes with theircenterline located along the desiredbreaking plane in the concrete.

When a line of holes has been drilled


When a line of holes has been drilledalong the breaking plane, bars areinserted in the holes and a force isapplied to break the remainingconcrete and complete the removal ofthe slab.

Applications

Ideal for non reinforced concrete andlow accessibility applications

Thermal cutting techniques

• Thermal cutting techniques use heat to increase the temperature of theworkpiece beyond melting point. The melted metal is then blown away bya gas flow.

• Thermal cutting techniques include:


� Oxyacetylene cutting

� Plasma cutting

� Laser cutting

Oxyacetylene cutting

Description

Oxyacetylene cutting uses a mixture of fuel gas(usually acetylene or propane) and oxygen, ignited atthe orifice of a torch.

When the metal reaches appr.ly 800°C the oxygen jetis turned on and the heated metal undergoes a rapidexothermal oxidation reaction and is blown away asslag.


slag.

Generation of fumes and aerosol as secondary waste.

Applications

Technique suitable for ferrous materials (ad hocfeatures of the flame must be adopted in case ofaluminum or alloy metals cutting, in order to overcomeproblems related to the formation of refractory oxides).

Suitable for thick component (up to 60’’ in air). Cuttingthickness is reduced in underwater applications due toheat loss.

Plasma cutting

Description

The technique uses a current arc betweenan electrode and the workpiece(conducting metal). The arc is establishedin a gas mixture flowing through the torch.The plasma formed in the gas reaches avery high temperature (≈25.000°C) and


very high temperature (≈25.000°C) andspeed which blow the metal slag away.Waste produced: metal parts, moltenpieces; secondary waste production(debris, aerosol) must be controlled withtight filtering (HEPA) systems .

Applications

The torch, which operates both in air andunderwater, can be manually driven ormounted on a robotic arm.Suitable for all metals even of highthickness (up to 8-9’’)

Laser cutting

Description

Use of focused high power laser beam to heat themetal past its melting point, thereby cutting it.No reaction forces; low production of fumes andaerosol. Easily adaptable to remote operations androbotics.

Applications


Applications

Cut of metal components and pipes even withcomplex configurations with thickness up to 1’’(even 6’’ with more than one passage).Development in course for underwater applications.Waste produced: metal parts; secondary waste(small amount of debris and aerosol)

Water-abrasive jet cutting

DescriptionThe technique involves the use of a highpressure water jet (up to 6.000 bar) mixedwith abrasive (quartz sand, silica carbide,etc.) and forced through a wear resistantnozzle where it acquires a very highvelocity producing erosion of the


velocity producing erosion of theworkpiece. Always mounted on a remotecontrolled arm.Secondary waste production:contaminated abrasive frit to be recoveredby filtration of water. Better use in confinedenvironmentApplicationAlmost all materials can be cut with such atechnique. Thickness up to 8’’ (30-40%less underwater).

RPV and internals segmentation: a former challenge

• Reactor Pressure Vessel and internals are the most radioactive components in aNPP after the removal of fuel elements

• Activation by severe neutron flux can lead to 1011 – 1014 Bq/g of specific activity inthe component metals, hence leading to dose fields of up to several Sv/h

• Final disposal repositories in Western Europe do not accept such components fordirect disposal. Hence segmentation is necessary

• The mentioned doses are not compatible with manual dismantling or segmentation• Remote operated equipment has to be used together with shielding (e.g.

underwater segmentation)


underwater segmentation)• The number of cuts has to be optimized with reference to parameters like length of

the operations, internal dimensions of the containers (hence their number),shielding capabilities of the containers, radiological characteristics of the parts

Segmentation plan for the Wurgassen RPV

A really tough job !! But it can be done, and…

Segmentation and dismantling of RPV internals

…it’s been actually done !


Excerpt from a E.On. video posted on Youtube relevant to the RPV internals dismantling of NPP Stade

segmentation & dismantling techniques2011.radioactivewastemanagement.org/download/04 -...

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