Segmentation & Dismantling Techniques
JRC Ispra Summer School
Ispra, 5-8 July 2011 Lecture content
• What is decommissioning
• Why segmenting and dismantling ?
• Dismantling and segmentation overview
• Mechanical segmentation techniques
• Thermal cutting techniques
• Water abrasive cutting
• RPV and internals segmentation: a former ‘challenge’
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 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 to protect health and safety of workers/public and environment • Example of nuclear installations: Nuclear Power Plants (production of electricity through the fission reaction), Research Laboratories/Plants (research in the nuclear field by means of radionuclides ), Fuel Cycle Facilities (manufacturing, reprocessing of nuclear fuel for Nuclear Power Plants)
• At the end of the operating life of the installation, parts of the plant are activated (by neutron 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 ensure the long term protection of the public and the environment, Decontamination and Dismantling are implemented
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Nuclear Decommissioning
According to the IAEA definition (IAEA Glossary), ‘decommissioning’ consists of:
Administrative and technical actions taken to allow the removal of some or all of the regulatory controls from a facility
• The use of the term decommissioning implies that no further use of the facility (or part thereof) for its existing purpose is foreseen
• Decommissioning typically includes decontamination and dismantling of the facility (or part thereof)
• Decontamination is the complete or partial removal of the radioactive contamination by means of physical or chemical processes
• Some facilities may be decommissioned without dismantling and the existing structures subsequently put to another use (after decontamination)
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 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, electric system, fire prevention, etc.)
• Non essential systems may be dismantled having clear in mind the final destination of the dismantled materials
• Clearance levels for releasable materials must be authorized ; suitable disposal repositories 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. turbine halls 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 US accept large component for direct disposal)
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Dismantling & segmentation overview
• The decommissioning of nuclear facilities involves the dismantling and segmentation of metallic components and the cutting and demolition of concrete structures. • Dismantling leaves the equipment parts intact while segmentation requires cutting a piece of equipment into smaller parts by means of various techniques • Before dismantling or size reducing a contaminated/activated equipment, suitable 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 operated tools; reducing the time of presence in case of manual work • Dismantling contaminated components requires the use of confined and depressurized areas under controlled access (both in situ or in a different place by moving the component), suitable ventilation and filtration systems, fire prevention devices
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 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) Secondary waste production
• The main currently available dismantling/segmenting techniques can be grouped in three categories: Mechanical Thermal Water jet
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 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 Circular, band, reciprocating saws Wall and floor saws Circular cutters Diamond wire Core/stitch drilling
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Nibblers and shears
Nibblers Description A nibbler is a punch and die cutting tool operating at a rapid reciprocation rate of the punch against the die, ‘nibbling’ a small amount of sheet metal with each stroke. Applications Stationary shears Ideal for sheet metal up to 10 mm Nibbler thick. Pneumatic nibblers can operate underwater equipped with an exhaust Shears air line Descriptions A shear is a two blade tool operating like a pair of scissors and cutting without developing shapeless materials or secondary waste Applications Both for metal sheet/pipes and concrete especially if contaminated (no Hydraulic shears and Hydraulic portable shears secondary waste) concrete rams
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Saws
Description Saws use reciprocating (hacksaw) or rotating (circular) blades to cut metal with various shapes and pipes. Portable hacksaw Applications Light weight and compact size; easy to be mounted, can operate without control; reduced dose for operators Also for stationary applications. Easily arranged for Stationary hacksaw underwater applications. Also for thick components. Slow cutting speed. Production of secondary waste from lubricants.
Cutting a glove box with a circular saw Band saw
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Wall and floor saws
Description A diamond or carbide wheel is used to abrasively cut the concrete even in presence of reinforcing steel rods. The dust produced by the cut is controlled by a water spray which constitutes a secondary waste. Applications For any kind of reinforced Wall saw concrete. Can be used up to 3 ft of thickness.
Floor saw
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Circular cutters
Description A circular cutter is a self- propelled unit that cuts as it moves around the circumference of a pipe held to a structure which is sized to fit the outside diameter of the pipe. Applications Suitable for pipes up to 42’’ and 6’’ thick
Rotary pipe cutter
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Diamond wire
Description Diamond wire cutting uses a series of pulleys which draw a continuous loop of multistrand wire equipped with a series of diamond beads. The wire is wrapped around the object to be cut and contact tension is applied on the wire by the pulleys. The spinning wire cuts a path through the concrete or even metal . Applications Almost any thickness can be cut with this Diamond wire saw technique. Ideal for cutting unusual configurations in radioactive environment (e.g. biological shields) Suitable measures must be taken to reduce the possible spread of contamination due to swarf which can be carried from the cutting area by the wire. Secondary waste in case of water cooling
Diamond wire
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Core/stitch drilling
Description The stitch drilling process is an extension of the simple core drilling technique. It requires drilling a series of close pitched holes with their centerline located along the desired breaking plane in the concrete. When a line of holes has been drilled along the breaking plane, bars are inserted in the holes and a force is applied to break the remaining concrete and complete the removal of the slab. Applications Ideal for non reinforced concrete and low accessibility applications
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Thermal cutting techniques
• Thermal cutting techniques use heat to increase the temperature of the workpiece beyond melting point. The melted metal is then blown away by a gas flow. • Thermal cutting techniques include: Oxyacetylene cutting Plasma cutting Laser cutting
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Oxyacetylene cutting
Description Oxyacetylene cutting uses a mixture of fuel gas (usually acetylene or propane) and oxygen, ignited at the orifice of a torch. When the metal reaches appr.ly 800 °C the oxygen jet is turned on and the heated metal undergoes a rapid exothermal oxidation reaction and is blown away as slag . Generation of fumes and aerosol as secondary waste. Applications Technique suitable for ferrous materials (ad hoc features of the flame must be adopted in case of aluminum or alloy metals cutting, in order to overcome problems related to the formation of refractory oxides). Suitable for thick component (up to 60’’ in air). Cutting thickness is reduced in underwater applications due to heat loss.
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Plasma cutting
Description The technique uses a current arc between an electrode and the workpiece (conducting metal). The arc is established in a gas mixture flowing through the torch. The plasma formed in the gas reaches a very high temperature (≈25 .000 °C) and speed which blow the metal slag away. Waste produced: metal parts, molten pieces; secondary waste production (debris, aerosol) must be controlled with tight filtering (HEPA) systems . Applications The torch, which operates both in air and underwater, can be manually driven or mounted on a robotic arm. Suitable for all metals even of high thickness (up to 8-9’’)
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Laser cutting
Description Use of focused high power laser beam to heat the metal past its melting point, thereby cutting it. No reaction forces; low production of fumes and aerosol. Easily adaptable to remote operations and robotics. Applications Cut of metal components and pipes even with complex 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)
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 Water-abrasive jet cutting
Description The technique involves the use of a high pressure water jet (up to 6.000 bar) mixed with abrasive (quartz sand, silica carbide, etc.) and forced through a wear resistant nozzle where it acquires a very high velocity producing erosion of the workpiece. Always mounted on a remote controlled arm. Secondary waste production: contaminated abrasive frit to be recovered by filtration of water. Better use in confined environment Application Almost all materials can be cut with such a technique. Thickness up to 8’’ (30-40% less underwater).
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 RPV and internals segmentation: a former challenge
• Reactor Pressure Vessel and internals are the most radioactive components in a NPP after the removal of fuel elements • Activation by severe neutron flux can lead to 10 11 – 10 14 Bq/g of specific activity in the component metals, hence leading to dose fields of up to several Sv/h • Final disposal repositories in Western Europe do not accept such components for direct 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) • 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
A really tough job !! But it can be done, and…
Segmentation plan for the Wurgassen RPV
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011 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
JRC Ispra Summer School Angelo Paratore Ispra, 5 July 2011