The waste is not the issueRussell J Hand

Immobilisation Science LaboratoryDepartment of Engineering Materials

University of Sheffield

Nuclear power

• Utilises the binding energy of the nucleus– Not chemical energy

• 1 t natural U produces ~ 44 GWh(e) = 158 TJ(e)

• 1 t coal (Drax) produces ~ 2.6 MWh(e) = 9.4 GJ(e)

• ~ 17000 times difference!

Waste• All human activities produce

waste– E.g. Burning fossil fuels produces

CO2 as a waste– Nuclear reactors produce

radioactive waste

• What we do with the waste depends on the level and type of hazard posed– Biological– Chemical– Physical – Radiological

• Radioactive wastes are a hazard BUT we have technologies for dealing with them

Waste category

Toxic LLW ILW HLW

Ann

ual U

K a

risi

ngs

/m3

100

101

102

103

104

105

106

107

UK radioactive wastes• Very low level waste (VLLW)

– < 400 kBq / 0.1m3 β and γ– Not considered as radioactive waste

and may be treated as conventional waste

• Low level waste (LLW)– < 4 MBq kg1 α, < 12 MBq kg1 β– Largest volumes – Smallest hazard– Cemented

• Intermediate level waste (ILW)– Greater activity levels than LLW

but not significantly heat generating– Cemented

• High level waste (HLW)– Wastes in which are self-heating

due to radioactive decay– Smallest volumes – greatest hazard– Vitrified Percentage contribution to volume

0 20 40 60 80

Per

cent

age

cont

ribu

tion

to

tota

l rad

ioac

tivi

ty

0

10

20

30

40

50

60

2007 data

Nuclear waste category

LLW ILW HLW

Tot

al U

K w

aste

vol

ume

/m3

101

102

103

104

105

106

107

Origin of wastes• Contaminated materials• Nuclear fuel

– During fission in a nuclear reactor a wide range of (often radioactive) fission products are generated

• Some fission products are particularly efficient at capturing neutrons

• Other fission products may change the structure of/pressurise the fuel

• Eventually fuel removed from the reactor and is placed in cooling ponds

• Currently in the UK spent nuclear fuel is re-processed to recover re-usable U and Pu– Re-processing leads to high level liquid waste

• However re-processing is not an essential element of nuclear power programmes– The spent nuclear fuel (SNF) can simply be stored and

eventually placed in a repository

– This is the approach currently used in e.g. the US and Sweden

• Activity of SNF relative to U ore (SKB)

0.1 1 10 102 103 104 105 106

Time /years

106

105

104

103

102

10

1 0.1

TotalFission & activation products

Actinides and daughters

Radioactivity of mined uranium ore

Cement encapsulation in UK

• Used for LLW and ILW• Can incorporate a number

of different species– Alkaline environment

immobilises many species

High level waste• Heat generating wastes• Contains both short- and long-

lived radionucleides– e.g. 137Cs – half-life 30.07 years –

heat generating • Smallest volumes – greatest

hazard• Vitrification is used to

immobilise high level liquid waste

• Waste is chemically bonded into the glass matrix

Each canister is 42 cm in diameter and 1.3 m high and holds ~400 kg glass

Spent nuclear fuel• Initial above ground storage

• For disposal SNF would be emplaced in canisters– Swedish/Finnish model is for external copper

canisters with internal cast iron linings

Current wastes versus future wastes

• Current waste arisings are not representative of future waste arisings

• Even reactors of the same nominal type involved changes in design– Particularly an issue with

Magnox reactors

• Magnox reactors used fuel less efficiently than current designs

Reactor type

Mag

nox

AG

R

PWR

(cu

rren

t)

PWR

(fu

ture

)

Fue

l dis

char

ged

(t/G

W(e

)y)

0

100

200

300

400

Packaged SNF/HLW/ILW

Existing wastes (CoRWM baseline)10 AP1000s for 60 years

Packaged LLW

Final disposal

• Deep repositories– Typically designed to

be ~0.5 km beneath the surface of the earth

– These involve multiple barriers to prevent he radionuclides reaching the biosphere again

• Deep borehole disposal– Burial at 4-5 km depth

Multiple engineered barriers

• Wasteform – Cement, glass, SNF

• Canister– Stainless steel, cast iron

surrounded by copper

• Backfill– Bentonite

• Engineered repository walls• Rock

FEBEX experiment – Grimsel URL

• In general under static conditions where saturation is possible we get

I II III IV

Con

cent

rati

on o

f le

ache

d sp

ecie

s

Time

VInterdiffusion

rf:: residual or final rater(t): rate drop

Hyd

roly

sis

Resumption of alteration

End of alteration or phase precipitation

Possible phase precipitation

Si

BNa

Initial rate - ~1μm/day at 90ºC ~1μm/50 day at 50ºC

Final rate - ~1μm/50 yr at 90ºC ~1μm/170 yr at 50ºC

Natural analogues

• Oklo natural reactors, Gabon– U deposits found with

unusually low levels of 235U

– ~1.7 billion years ago 16 reactors operated

• Probably operated intermittently for ~ 1 million years

• At least 10 tonnes U reacted

• Pu formed in reactor zones has moved ~ 3 m from where it was formed in 1.7 billion years

http://www.ocrwm.doe.gov/factsheets/images/0010_gabongeology.gif

• Basaltic glasses– Last in the environment for millions of

years– Surface palagonisation

• Maqarin, Jordan– Hyperalkaline conditions

• Analogue of a cementitious repository

Summary• Nuclear power provides low carbon baseload

electricity generation• We have technologies and solutions for the safe

handling and ultimate disposal of nuclear waste– Vitrification – HLW

– Cementation – ILW

– Canisters for spent nuclear fuel

• Final disposition of the waste– Other countries are developing repositories

– The issues here are not technical they are political