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