1 TECHNOLOGIES FOR DECOMMISSIONING OF NUCLEAR FACILITIES SAFE DECOMMISSIONING OF NUCLEAR POWER PLANTS Project BG04/B/F/PP-166005, Leonardo da Vinci Programme

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


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.


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.


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.


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.


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.


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.


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


……………………….. 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)


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.


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.


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.


Manual dismantling

pipelines. heat exchangers. fittings, pumps. ventilation equipment. steel structures. electrical equipment, cables. heat insulation of pipelines. steel lining of pools.


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.


Remotely-controlled dismantling

steam generators. reactor vessel. intra-vessel devices. volume compensator. other components of primary

coolant system.


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.



Mechanical hand cutting tools for small-diameter contaminated pipes.



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


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.


Hydraulic techniques

Cutting by means of water jet with abrasive materials.


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.


Thermal techniques

Flame cutting

Flame Cutting with an External Ignition


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.


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.


Electric-arc plasma cutting technique


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.


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.


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.


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.


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.


Reactor dismantling techniques

Remotely controlled processes mechanical: - mechanical hack-saws, disk cutters. hydraulic: - water jet.


Reactor dismantling techniques

Remotely controlled processes thermal: - thermal spear, contact electrode cutting. - (non) melting electrode electric-arc cutting. - plasma arc or circular saw cutting. - laser cutting. explosive cutting.

Documents

1 TECHNOLOGIES FOR DECOMMISSIONING OF NUCLEAR FACILITIES SAFE DECOMMISSIONING OF NUCLEAR POWER PLANTS Project BG04/B/F/PP-166005, Leonardo da Vinci Programme