1 technologies for decommissioning of nuclear facilities safe decommissioning of nuclear power...
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Проект BG/04/B/F/PP-166005, Програма “Leonardo da Vinci” 2
CONTENTS
2.1 Dismantling and demolition during the decommissioning period – aims, time schedules, activities
2.2 Dismantling techniques – scope of application 2.3 Reactor dismantling techniques 2.4 Novel (modern) techniques
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2.1 Dismantling and demolition during the decommissioning period
Training goals The trainees must be capable of: - Determine the goals of dismantling and
demolition during the decommissioning. - Enumerate the preparatory activities before
dismantling. - Characterize dismantling performance. - Characterize the post-dismantling activities.
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Dismantling of Nuclear Facilities
Consists in dismounting and removal of all nuclear equipment structures, systems and components during the process of the nuclear facility decommissioning.
(Radioactive Waste Management Glossary, IAEA, Vienna 2003)
The dismantling of a nuclear facility comprises cutting and demolition of the following structures:
reactor vessel. reactor core components. heat screens and other structures contaminated with
radioactive products. tanks and pipelines with surface contamination. protective biological screens.
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Selection of dismantling methods techniques
equipment size, shape and accessibility. radiation hazards to the workers and the general public. workplace conditions. radioactive waste produced. non-radioactive waste produced. necessity of post-dismantling activities performance.
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Selection of dismantling methods and techniques
the types and characteristics of materials, equipment and systems to be dismantled;
the availability of proven equipment; the radiation hazards to the worker and the general
public; the environmental conditions of the workplace; the radioactive waste produced; the non-radioactive waste produced; the requirement for development work.
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Ensuring efficiency and safety of the activities
simplicity of operation, decontamination and maintenance.
control over aerosol radionuclides. control over discharges to the environment. water treatment (in case of underwater techniques). effect of the activities on the adjacent systems. determining the type of waste containers, handling
systems and transportation routes.
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Осигуряване на ефективността и безопасността на дейностите
equipment should be simple to operate, decontaminate and maintain;
effective methods for controlling airborne radionuclides should be implemented;
there should be effective control of discharges to the environment;
when underwater dismantling and cutting is used, provision should be made water processing to ensure good visibility and assist in effluent treatment;
the effect of each task on adjacent systems and structures and on other work in progress should be evaluated;
waste containers, handling systems and routes should be defined before the start of dismantling work.
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Determination of the radiation protection conditions during the activities performance.
Placing of protective floor covering. Installation of ventilation equipment. Installation of electric power supply and the
necessary working environment. Scaffolding mounting. …………………….
Preparatory activities before dismantling
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……………………….. switching off the unnecessary equipment. marking the location of the cuts. mounting of protective covering (“protective tent”)
around highly radioactive equipment. transportation of dismantled equipment. preparation of waste transportation containers. training of the working team.
Preparatory activities before dismantling (continuation)
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Post-dismantling finishing activities
removal of the ventilation system. removal of the feeding lines to the auxiliary working
environment. removal of the scaffolding. moving the equipment and tools. removal of the protective coverings and “tents”. transportation of containers filled with dismantled
materials. cleaning the premises.
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2.2 Dismantling technologies – scope of application
Training goals The trainees must be capable of: Enumerate and describe the various manual and
remote dismantling techniques (mechanical cutting, hydraulic cutting, thermal cutting, explosive cutting, novel techniques, etc.)
Explain the specific requirements to dismantling in zones with increased radioactivity.
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Classification of dismantling techniques
with respect to the physical-chemical principle: - mechanical, hydraulic, thermal,
explosive, novel (modern) technologies. with respect to the medium of process
implementation: - air, underwater. with respect to the application method: - manual, remote.
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Manual dismantling
pipelines. heat exchangers. fittings, pumps. ventilation equipment. steel structures. electrical equipment, cables. heat insulation of pipelines. steel lining of pools.
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Remotely-controlled dismantling
Steps in the remotely controlled operations: handling the equipment or device. visual control of the activities. cutting of material. cleaning. radioactivity monitoring (follow up control) packing of material. thorough radioactivity measurements.
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Remotely-controlled dismantling
steam generators. reactor vessel. intra-vessel devices. volume compensator. other components of primary
coolant system.
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Mechanical techniques
Mechanical hand cutting tools, hack-saws and guillotine shears use:
- widely used, especially for cutting of pipelines.
- high cutting speed. - easier radioactive contamination
control (as compared with the thermal
techniques). - fragmentation of metal pieces and
pipelines with diameter up to 60 cm. - manual, remote. price: - low.
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Mechanical techniques
Mechanical hand cutting tools for small-diameter contaminated pipes.
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Mechanical techniques
use: - cutting as the self-propelled
circular saw moves on the object’s outer surface.
- for cutting pipes with particularly large diameter.
- fragmentation of metal pieces and pipelines with diameter up to 6 m and wall thickness up to 7.5 cm.
- remote. price: - low.
Circular cutting machine
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Abrasive cutting technique
principle: - cutting by means of rotating abrasive disk made
of oxide (Al) or carbide (Si) powder and resin as bonding material and glass fiber as strengthening material.
use: - for cutting pipes with particularly large
diameter. - fragmentation of metal pieces and pipelines
with diameter up to 6 m and wall thickness up to 7.5 cm. - remote. price: - low.
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Hydraulic techniques
Cutting by means of water jet with abrasive materials.
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Thermal techniques
Classification with respect to the heat source - flame cutting. - electric-arc cutting. - electric-arc plasma cutting. - oxygen (heat) spear. - laser cutting. - combined cutting.
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Thermal techniques
Flame cutting
Flame Cutting with an External Ignition
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Electric-arc cutting technique principle: - utilization of the cutting
action of a low-voltage electric arc created between the hack-saw cutting disk (d = 760-1630 mm) and the material.
use: - fragmentation of metal
pieces with thickness up to 90 mm. - remote – in air and under
water. price: - high.
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Electric-arc plasma cutting technique
principle: - utilization of the cutting action of a d.c. electric arc
created in an ionized gas medium (stainless steel - argon) between an electrode and any conducting material (the temperature in the plasma jet is T0 = 10 000 - 27 000 oC).
use: - fragmentation of metal pieces with thickness up to 15 cm. - remote – in air and under water. price: - high.
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Thermal (oxygen) spear
principle: - utilization of the chemical reaction of burning a thermal
mixture (steel, aluminum, magnesium) in oxygen at the spear output. parameters: - T0 = 2 250 - 5 500 oC. - spear size: length from 0.5 to 3 m; diameter 6 - 10 mm. use: - fragmentation of metal pieces without thickness limitation. - manual and remote (limited) – in air and under water. price: - low.
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Explosive techniques
Segmentation of materials by means of explosives (PETN, TNT, dynamite)
principle: - the shock waves and the fragments of the shell
(Pb, Al, Cu) in a directed explosion cause cracks (cuts). use: - fragmentation of metal pieces with complex
geometry and thickness up to 15 cm. price: - high.
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Laser cutting principle: - local heating of the metal above the
melting point by using a laser beam. advantages: - melts practically all materials. - absence of noise and vibrations. - easy operation. use: - fragmentation of metal pieces with
thickness up to 10 mm; suitable for remote dismantling
- in air and under water. price: - high.
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Novel (modern) techniques
Techniques under development yet to find widespread application in projects for decommissioning of nuclear facilities.
liquefied gas cutting. utilization of alloys with “memory effect”. use of microwave equipment.
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2.3 Reactor dismantling techniques
Training goals The trainees must be capable of: - characterize the specific features of the
mechanical, thermal, and hydraulic techniques applied in reactor dismantling.
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Reactor dismantling techniques
Remotely controlled processes mechanical: - mechanical hack-saws, disk cutters. hydraulic: - water jet.