Ispra Summer School

Operational Decommissioning Experience in the UK

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R HallardHallard Associates Ltd

July 2011

Objectives

• Overview of UK decommissioning

• Radiation protection issues

• Dismantling and Demolition

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• Dismantling and Demolition

• Waste Management

Overview of UK Decommissioning

• 15 Magnox or Prototype Pu Fast Reactors on 13 separate sites being decommissioned.

• Three Fuel Cycle Sites with major decommissioning projects

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projects

�Sellafield�Springfields�Capenhurst

• Two more reactors will shut down in 2 years.

Sellafield

• Started operations in late 1940’s.

• Three generations of plant for both magnox and

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magnox and oxide. Oldest are now being decommissioned.

• Scale of the task is huge.

Radiation Protection Issues

• Decommissioning Challenges

• Risk reduction and control measures during dismantling

• Dose Management

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• Dose Management

Decommissioning Challenges – Beta / Gamma Facilities

• Identifying the sourcescan be difficult and involve high dose uptake

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dose uptake

Plutonium Facilities - 1

• Internal hazard needs containment, ventilation and PPE.

• Hazards include

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• Hazards include wounds, glove or PPE failure.

Plutonium Facilities - 2

• External radiation. Old Pu241 decays to Am241 (14 yr H/L).

• Levels can be surprisingly high – up

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to 10’s mSv/hr.

• 60keV Ŵ - lead loaded aprons and gloves are effective

Risk reduction and control measures duringdismantling

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Radiation protection principles

• Source elimination / reduction• Engineering controls, external sources

� Robotics & remote working� Shielding

• Engineering controls, Internal sources� Containment

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� Containment� Ventilation

• Operational controls (Systems of Work)• Personal Protective Equipment

Source Elimination / Reduction

• Limited options for eliminating source in decommissioning work

• Main option is

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• Main option is decontamination / removal of the source term.

Risk reduction – External Sources

• Source term up to 10’s or 100’s mSv/hr gamma

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Fully remote operations

• Operator controlling dismantling robot from Control

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from Control Room

Robotics

• Can be used to dismantle very hazardous facilities.

• Effective, but expensive and slow.

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expensive and slow.

• Impractical for fine work.

Typical ROV

• Zero dose, but slow and can be expensive

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Manipulators• Good solution, but expensive

and not always practical.

• Complex - designed to be able to perform wide variety of tasks. Also need to be powerful and robust.

• Complexity and sophistication can make them unreliable.

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can make them unreliable. Repair difficult and leads to radiation dose.

• Alternative is specifically designed tool for one job only. Much simpler and cheaper. If it fails or doesn’t do job, make another.

Radiation shielding

• You can shield the operator as well as the source.

• Used lead shielded capsule lowered into the access port

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into the access port to allow manual repair.

Risk reduction - Internal sources

• Containment

• Ventilation

• Personal Protective Equipment

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New / replacement ventilation system

• Needs to be considered early in project planning.

• Existing system will be old and may be unsuitable for decommissioning &

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decommissioning & modern standards.

• May need better ventilation off gas treatment for decommissioning than operation!

Modular Containment System

• Tunnel area and buffer zone free of loose contamination

• Atmosphere in work area passed through 2

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area passed through 2 or 3 layers of HEPA filters & discharged into lab atmosphere

Tenting operations• Essential tool for

containing activity during any intervention, especially decommissioning work.

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work.

• Multi chamber to allow good segregation and undressing.

Glovebox decommissioning

• Removal of complete glovebox in a container for treatment off line

• size reduction in

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• size reduction in situ for removal in drums

• Wounds or major failure of PPE are the main hazard

Plasma Arc

• Plasma arc – very efficient and quick.

• High velocity gas plasma at up to 25,000o C

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25,000o C

• Surprisingly low risk to operator

• Can cut through several cm of metal.

Operational Dose Management

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Identify the source(s) - Gamma Camera

• Gamma camera

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• Gamma camera can show the main radiation sources

Dose Management - 1

• In high radiation work, often better to authorise a few people to a high dose to complete a job more efficiently, than require lots of people to work to low doses.

Phase of Work Dose uptake

Entry & handover, 15 min, Bgd radiation 100 µSv/hr ɣ

25 µSv ɣ

15 min working time.Bgd radiation 200 µSv/hr ɣ

50 µSv ɣ

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• In this example, workers authorised to 100 µSv ɣ. Half of the individual dose taken up by entry, exit and handovers. Not ALARA

Exit & handover, 15 min, Bgd radiation 100 µSv/hr ɣ

25 µSv ɣ

Individual Dose control level.

100 µSv ɣ

Dose Management - 2

• In this example, workers authorised to 500 µSv ɣ.

• Much longer working time, 2 ¼ hours. Much more work done, so more efficient.

Phase of Work Dose uptake

Entry & handover, 15 min, Bgd radiation 100 µSv/hr ɣ

25 µSv ɣ

2 ¼ hours working time.Bgd radiation 200 µSv/hr ɣ

450 µSv ɣ

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more efficient.

• Collective dose also much lower.

• Much better use of the dose. 90% of dose doing work, which is ALARA.

Exit & handover, 15 min, Bgd radiation 100 µSv/hr ɣ

25 µSv ɣ

Individual Dose control level.

100 µSv ɣ

Waste management

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Issues

• Minimisation of active waste

� Decontamination

� Segregation into lowest waste route

• Monitoring and Clearance

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• Monitoring and Clearance

• Disposal

Minimisation – Reactor Pond decontamination

• Surface of pond decontaminated with very high pressure water.

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Disposal

• VLLW disposal in a LLW Disposal Site is expensive and very inefficient – space is limited and needs to be kept for active waste.

• UK has introduced disposal of VLLW and controlled burial of LLW in Landfill

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burial of LLW in Landfill Sites. Two sites have been authorised so far.

• VLLW = 4MBq/te total acty.

• One of the sites, Lillyhall near Sellafield, has been authorised for disposal of about 600,000m3 of VLLW.

• Established in 1959• The site has received about

1M m3 LLW, and currently receives 30,000 m3 per year

� Low Level Waste makes up more than 90% of the UK's radioactive waste legacy by volume but

UK LLW Disposal Site near Drigg, Cumbria

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legacy by volume but contains less than 0.1% of the total radioactivity

� 70% is from Sellafield� 30% is from nuclear

operators, hospitals, research facilities, MoD

Minimisation - Windscale pile chimney

• Chimney was build as part of an early (military) air cooled reactor. Twin of the reactor which caught fire in 1957.

• All waste was monitored

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• All waste was monitored using a conveyor monitor. Most was demonstrated to be clean and disposed of as inactive waste.

Crushing and monitoring of the concrete• The primary control is

likely to be the history of the waste

• The originator needs to know the unbroken

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know the unbroken history to be certain there is no radioactivity.

• Monitoring is to confirmthere is no activity.

Pile chimney dismantled

• Chimney dismantled and waste disposed of as inactive

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Waste monitoring

• Efficient and accurate Monitoring is essential.

• Used for segregations if

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segregations if history is less clear or for reassurance.

Steelwork decontamination: Wheelabrator

• Redundant metal items fed into Wheelabrator

• Aggressive surface cleaning using grit blasting

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using grit blasting

Wheelabrator output

• Surface finish reduced to bare metal.

• Waste needs to be labelled for

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be labelled for sentencing and control purposes

End of Presentation

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Thank you for your attention