immobilisation and storage of nuclear waste

Immobilisation and Storage of Nuclear

WasteDr John Roberts

Dalton Nuclear InstituteThe University of Manchester

NI Rough Guide to the Nuclear Industry 2010

Radioactive Waste Generation

• Military programmes

• Hospitals and research laboratories

• Nuclear Energy Industry

• Mining and milling of uranium ores

• reprocessing of fuel discharged from reactors

• decommissioning

Massive Source of Energy

• In an AGR reactor 1 tonne of U is equivalent to 20,000 tonnes of coal

• In a fast reactor - equivalent to 2,000,000 tonnes of coal

•A typical nuclear power station requires 40 tonnes of fuel per year - one lorry load per fortnight

•An equivalent coal power station requires 3,000,000 tonnes per year - two train loads per day

WorldwideNuclear Industry

UK RadwasteSources

UK RadwasteVolumes

Nuclear Fuel Cycle

Return to customersReturn to customersfor final disposalfor final disposal

EnrichmentEnrichment

ConversionConversion

UraniumOre

NaturalNaturalUraniumUranium

All plant requiresAll plant requiresfinal decommissioningfinal decommissioning

RecycleRecycleFuelFuel

(MOX)(MOX)

Electric PowerElectric Power

ReactorReactor

TransportTransport

ReprocessingReprocessing

SpentSpentFuel StorageFuel Storage

WasteWasteManagementManagement

FuelFuelFabricationFabrication

RecycledRecycledUraniumUranium

Nuclear Reactor

• Fuel - Originally uranium metal but now many variations

• typically 75 tonnes for 1000 MWe

• Moderators - carbon, H2O, D2O

• Cladding - contains fuel and prevents release of radioactive fission products

• Coolant - gas or liquid circulated through core of reactor for heat extraction

• Control rods - usually B or Cd with large σc

• Shield - usually steel and concrete used for radiation protection and pressure vessel

Magnox Fuel Assembly

1 fuel rod per assembly, Magnox cladding, U metal fuel

PWR Fuel Assembly

264 fuel rods per assembly, Zircaloy cladding, UO2 fuel

AGR Fuel

Pebble Fuel

Storage of Spent Fuel

•Spent fuel is highly radioactive and very (thermally) hot

• Initially stored in ponds at the reactor site

•Water cools the rods and acts as shielding

•Can also be stored in dry stores with air cooling

Storage Pond

Dungeness storage pond, Kent

Storage Pond

THORP storage pond at Sellafield

Water Shielding

Reprocessing

•Only about 4% of U is burnt up

• 235U content reduced to less than 1%

•Some Pu remains from fission reactions

•Reprocessing separates the U and Pu from waste products by chopping up the fuel rods and dissolving them in acid

•U can re-enriched

•Pu can blended with U to produce MOX fuel

•LLW - Wastes not exceeding 4 GBq/t alpha or 12 GBq/t beta/gammadiscarded equipment, tools, protective clothing

• ILW - Above levels of LLW but not significantly heat generatingstripped/leached remains of cladding or PCM

•HLW - Significantly heat generatingfission products

UK Waste Classification

Challenges of Radioactive Waste

Total Waste Volume 2007

Waste by Activity

Total conditioned waste volumes from each business activity Total volume 1,750,000 m3

57%Commercial

Reprocessing

30%Commercial

Reactors

9%Research &

Development

2%Ministry

of Defence

1%Medical &Industrial

<1%Fuel Fabrication &

Uranium Enrichment

Low Level Waste

LLW Container

LLW Repository near Drigg

Magnox Fuel Assembly

1 fuel rod per assembly, Magnox cladding, U metal fuel

Magnox De-canning

Magnox Swarf

Solid Waste

Transport of Drums

Testing of Drums

Container Testing

• Tests are impact from 25 m and 1000 ˚C

• Bounding hazards encompassed by these two criteria are:

• building collapse• roof collapse• aircraft crash• train crash• explosives / explosive gases• crane failure / aggressive feature• seismic fault

• train fire• flammable gases• explosion• electrical fire• package fire• overheating

Results

Vitrification of HLW

Storage of Canisters

80 year lifetime use of electricity for 1

person generates this much high level

waste

Nuclear Power Generation

Dounreay

Dounreay Shaft

Dounreay Shaft - past

• Excavated in the 1950s during construction of under sea tunnel for the discharge of low level liquid effluent 4.6m diameter, 65m deep

• On completion a concrete plug was used to separate the shaft from the tunnel and it was allowed to fill up with groundwater

• In 1958 the Scottish Office authorised the UKAEA to use the shaft as a disposal facility for radioactive waste

• More than 11,000 disposals took place until 1977

• Environmental legislation has been tightened and the UKAEA are now required to remove all waste from the Shaft

Dounreay Shaft 1984

Borehole Plan

Shaft Platform - Schematic

Shaft Platform - Actual

Shaft - Waste Retrieval• The shaft was isolated in 2008 ahead of programme and

budget

• Waste retrieval can now commence

• Radioactive conditions mean that everything must be done by remote control

• Complications include -

• quantity and diversity of the waste

• working depth

• amount of corrosion after 50 years

• Base of shaft is immersed in 60 m of contaminated water

• In March 2010 it was announced that waste retrieval will be deferred until the completion of the site license competition

Waste Retrieval Plant

What next ??

• HLW and ILW can be successfully immobilised in either cement, glass or bespoke ceramics

• Where should the waste be moved to for storage (retrievable) or disposal (non-retrievable) ?

Possible Options

• Disposal in Space

• Disposal in Ice Sheets

• Disposal in Subduction Zones

• Direct Injection

• Disposal at Sea

• Sub-seabed Disposal

• Dilute and Disperse

Probable Options

• Indefinite Storage

• Near Surface Disposal

• (Phased) Deep Disposal

• Very-deep Borehole Disposal

Underground Storage

•USA have (de)selected Yucca Mountain

•South Korea have selected Gyeongju

•Finland have selected Olkiluoto

•Sweden has selected Forsmark

•France, Belgium and Switzerland all have experimental sites

What is the UK doing ?

• Set up a committee - CoRWM

• Committee for Radioactive Waste Management

• Presented recommendations to government in July 2006

• Government accepted all the recommendations in November 2006

CoRWM Summary

• Geological disposal is the best form of long-term management

• Coupled with safe and secure interim storage

• Development of volunteerism/partnership approach to secure facility siting

• Government’s response

• Accepted CoRWM’s proposal on geological disposal

• Accepted need for safe and secure interim storage

• Supportive of exploring the concept of volunteerism/partnership arrangements (recognising that geological/scientific requirements must be met)

Nuclear Decommissioning Authority

• Established April 1st 2005

• All civil nuclear liabilities

• Two aims

• reduce the predicted cost of nuclear clean-up

• maintain the required skillsbase

• £70 billion budget

NDA Sites

Hunterston A

Hunterston A

• Located near West Kilbride, 2 units 160 MWe each, first grid connection 1964, shutdown 1990

• Area of 15 hectares

• Current site end state plans are removal of all waste and buildings to be cleared with the site delicensed, landscaped and available for alternate use

• Key dates

• 2006 - Construction of ILW store complete

• 2014 - All operational ILW retrieval/processing complete

• 2017 - Entry into care and maintenance stage

• 2090 - Final site clearance and closure

Hunterston ILW Store

Sellafield

Sellafield

• Located on the West Cumbrian coast, supported the nuclear power programme since the 1940s. Operations include processing of fuels removed from nuclear power stations, mixed oxide (MOX) fuel fabrication and storage of nuclear materials and radioactive wastes

• Area of 262 hectares

• Site end state will be decommissioned to passively safe state with plutonium and uranium stored on site

Äspö Hard Rock Laboratory

Multibarrier Concept

Spent Fuel Canister

Phased Disposal Concept

Underground Access

Vault Concept

Very-Deep Borehole Disposal

Drill the first stage of the boreholeInsert the casing.

Pour in the cement basement.

Drill the next stage of the borehole.

Insert the casing.

Pour in the cement basement

Drill the next stage of the borehole

Constructing the Borehole

And so on, down to > 4 kms

0.6 - 0.8 m diameter

Constructing the Borehole

Drill the first stage of the borehole

Insert the casing



Insert the casing



And so on, down to > 4 km

Placement of Canisters

Insert the casing

Insert the canisters

Pour in the grout and allow it to

set

Placement of Canisters

Insert the casing

Insert the canisters

Pour in the grout and allow it to set

Separation of Canisters

Insert Bentonite clay

Insert another stack of canisters

Repeat until the bottom km of the borehole is filled

4 kms

Separation of Canisters

Insert Bentonite clay

Insert another stack of canisters

Repeat until the bottom km of the borehole is filled

Sealing the Borehole

Pour in some backfill (crushed granite)

Insert heater and seal the borehole

Pour in more backfill and seal the borehole again

3 km deep (topmost canister)

Fill the rest of the borehole with backfill

Sealing the Borehole

3 km deep (topmost canister)

Pour in some backfill (crushed granite)

Insert heater and seal the borehole

Pour in more backfill and seal the borehole again

Fill the rest of the borehole with backfill

Natural Analogues I

• Isolating Clay

• 50 ancient tree stumps found preserved in Dunarobba, Italy

• Trees had grown 1.5 million years ago

• They had not yet begun to rot

• Clay isolated them from oxygen and water

Natural Analogues II

• Canadian deposit/repository

• Cigar Lake uranium deposit lies430m below ground

• Thickness 1- 20 mWidth 50 -100 mLength 2 km

• Surrounded by clay there is there no radiological trace at the surface

Natural Analogues III

• Fossil Reactors

• Most famous is in Oklo, Gabon

• A layer of uranium ore issandwiched between sandstone and granite.

• Water trickling through moderated the neutrons allowing fission of the uranium

• A chain reaction occurred until the water was boiled away

• Reactor worked on and off for more than a million years

• HLW created held in place by the rocks, Pu had only travelled 3m in almost two billion years

Useful Websites

• http://www.nltv.co.uk

• http://www.nuclearliaison.com

• http://www.rwin.org.uk

• http://www.corwm.org.uk

• http://www.nda.gov.uk

• http://www.sellafield.com

• http://www.nuclearinst-ygn.com

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