Thorium, ADSRs……
and ns-FFAGs
Bob Cywinski
School of Applied Sciences
CONFORM Open Day , 11 May 2008
The Carbon Problem
Energy source
Grammes of carbon
per KWh of electricity
Nuclear
4
Wind
8
Hydro electric
power
8
Energy crops
17
Geothermal
79
Solar
133
Gas
430
Diesel
772
Oil
828
Coal
955
source:
Government Energy Support Unit (confirmed by OECD)
CONFORM Open Day , 11 May 2008
Meeting the Energy Challenge (2008)
CONFORM Open Day , 11 May 2008
Fission....... and breeding
U-Pu
CONFORM Open Day , 11 May 2008
Th-U
Thorium as a fuel....
Advantages
233U
232Th
has superior fissile
properties
g
Robust fuel and waste form
233Th
n
Generates no Pu and fewer
higher actinides
b
Proliferation resistant
22 mins
233U
27 days
233Pa
b
Disadvantages
Requires introduction of fissile
seed (235U or Pu)
233U
is weapon grade unless
denatured
Parasitic 232U production results
in high gamma activity.
Thorex processing of waste
needs substantial development
CONFORM Open Day , 11 May 2008
Annual energy resources
Thorium equivalent
~5x109
tonnes of coal
27x109
barrels of oil
2.5x1012
m3 of natural gas
65x103
tonnes of uranium
5x103 tonnes of thorium
After Sorenson
CONFORM Open Day , 11 May 2008
Estimated global Th resources
CONFORM Open Day , 11 May 2008
IAEA, status report May 2005
IAEA
….in recent times, the need for
proliferation-resistance, longer
fuel cycles, higher burn up,
improved waste form
characteristics, reduction of
plutonium inventories and in
situ use of bred-in fissile
material has led to renewed
interest in thorium-based fuels
and fuel cycles in several
developed countries…….
CONFORM Open Day , 11 May 2008
Past experiences
CONFORM Open Day , 11 May 2008
Current Power Strategy: India 3-stage closed cycle
500 MW prototype FBR is under construction in Kalpakkam is designed to breed
233U-from
Th
The FBR is expected to be operating in 2011, fuelled with uranium-plutonium oxide It will have a
blanket of thorium and uranium to breed fissile U-233 and plutonium respectively
CONFORM Open Day , 11 May 2008
Spallation
“A high-energy nuclear reaction in which a
target nucleus struck by an incident
particle of energy greater than about 50
MeV ejects numerous lighter particles and
becomes a product nucleus
correspondingly lighter than the original
nucleus. The light ejected particles may
be neutrons, protons, or various
composite particles…”
Encyclopaedia Brittanica
CONFORM Open Day , 11 May 2008
An alternative approach:
The Energy Amplifier or Accelerator
Driven Subcritical Reactor Concept
CONFORM Open Day , 11 May 2008
MYRRHA: an ADSR transmutation proposal
The MYRRHA design
proposes a windowless
Pb-Bi target:
350 Mev, 5mA
proton beam
The target surface results
from the vertical co-axial
confluent Pb-Bi liquid metal
flow
The beam impacts the target
vertically from above
MYRRHA is being designed to
transmute Pu waste
Can an ADSR operate on thorium only?
U-Pu MOX core
and blanket
CONFORM Open Day , 11 May 2008
The Energy Amplifier/ADSR energy balance
output
600MWe
MWe
η~40%
electrical energy
converter
1550MWth
20MWe
MWth
10MW
Energy
gain:
155
η~50%
accelerator
sub critical reactor
232Th
+ n →233Th →233Pa (27d)→
CONFORM Open Day , 11 May 2008
233U
Target size
Proton energy
CONFORM Open Day , 11 May 2008
Neutron energies
The energy spectrum of the
spallation neutrons at
different incident proton
energies.
The target is a lead cylinder
of diameter 20 cm
At 1 Gev, approximately 24
neutrons per proton are
produced
CONFORM Open Day , 11 May 2008
Proton beam requirements for EA/ADSR
The (thermal) power output of an ADSR is given by
Pth 
with
N  E f k eff
.
 1  k eff
N = number of spallation neutrons/sec
Ef = energy released/fission (~200MeV)
ν = mean number of neutrons released per fission (~2)
keff= criticality factor (<1 for ADSR)
So, for a thermal power of 1550MW we require
1  k eff
N  9.6  1019 
neutrons.s1
k eff
Given that a 1 Gev proton produces 24 neutrons (in lead) this corresponds to a
proton current of
9.6  1019
1  k eff
1  k eff
i
 1.6  10 19 
amps  640 
mA
24
k eff
k eff
CONFORM Open Day , 11 May 2008
Proton beam requirements
keff=0.95, i=33.7mA
keff=0.98, i=13.1mA
keff=0.99, i=6.5mA
To meet a
constraint of a
10MW proton
accelerator we
need keff=0.985
CONFORM Open Day , 11 May 2008
Safety margins
k=0.985
CONFORM Open Day , 11 May 2008
...but why has no ADSR ever been built ?
...because existing accelerators are not sufficiently stable and reliable
CONFORM Open Day , 11 May 2008
ADSR geometry (a) single target
232Th
GEANT4
core
CONFORM Open Day , 11 May 2008
Flux distribution in ADSR core
Power density distribution improves
with keff but remains non-optimal
Solution is generally to increase
fissile enrichment in several core
zones (eg see step at zone boundary
on left)
A better solution might be to use
several proton beams and spallation
targets
H.M. Broeders, I. Broeders :
Nuclear Engineering and Design 202 (2000) 209–218
Multiple beams/targets should also
alleviate accelerator stability
problems
CONFORM Open Day , 11 May 2008
Triple target ADSR
Power density distribution
(W:cm3) in a lead-cooled
ADSR with Th:U233 fuel.
The three beams with buffer
zones are described by seven
lead-filled fuel element
positions.
The over-all power distribution
is satisfactory.
CONFORM Open Day , 11 May 2008
Triple target ADSR
Power density distribution
(W:cm3) in a lead-cooled
ADSR with Th:U233 fuel.
The three beams with buffer
zones are described by seven
lead-filled fuel element
positions.
Trefoil of 3 nsFFAGs
each providing
3.5mA at 1 GeV
The over-all power distribution
is satisfactory.
Three ns-FFAG drivers should
be no more expensive than a
singe conventional driver....
Molten lead is both core
coolant and spallation
target
Pb-cooled Th/U233
subcritical core with:
keff=0.985
Pth=1550MWth
.....and will provide the required
reliability margin
CONFORM Open Day , 11 May 2008
ADSR geometry (b) triple target
232Th
GEANT4
core
CONFORM Open Day , 11 May 2008
Can thorium fuel be used in conventional reactors?
Miniature spallation target in central
bore of fuel element assembly
High power (MW)
proton beam
Spallation charging of Th fuel rods
232Th
to 233U conversion can be better optimised, with
mitigation against detrimental neutron absorption by
233Th and 233Pa
Modifications to existing reactors are not necessary
Wider global exploitation of nuclear technology is possible
Fuel preparation and burn cycles are decoupled
CONFORM Open Day , 11 May 2008
ThorEA – the thorium energy amplifier association
CONFORM Open Day , 11 May 2008
The way forward ?
The AESIR project: (Accelerator Energy System with Inbuilt Reliability)
Stage 1: LOKI
Cost
Time
£17M
2-3
years
(The Low-key demonstrator)
35 MeV H- system ; High current. (10 mA?)
Commercial source, standard Linac
Stage 2: FREA (FFAG Research for the Energy Amplifier)
2nd stage ns-FFAG ring to boost energy to 390 MeV
emphasis on reliability
Gives useful proton machine (c.f. TRIUMF, PSI).
£50 M
+
4-5
years
£1-2B
+
7-8
years
Stage 3: THOR
Add a second ns-FFAG ring to give 1 GeV
Use with a real target and nuclear core for
First operational ADSR system
“.. dream the unthinkable because we desperately need new ideas”
Carlo Rubbia (ThorEA meeting, Huddersfield, April 2009)
CONFORM Open Day , 11 May 2008
Summary
Thorium is an underexploited fuel resource that could meet all our
power generation requirements for many centuries
Thorium fuel is proliferation resistant and produces relatively low level
radiotoxic waste
Although thorium is fertile, not fissile, it may be possible to construct
safe and reliable EA/ADSR power systems, using spallation neutrons
to drive the transmutation/fission process
Similar processes could provide thorium fuel elements for conventional
power reactors
The key to both technologies is the development of compact, cheap
and reliable accelerators: We believe ns-FFAGs may fit the bill
Thorium might just save the planet!!
CONFORM Open Day , 11 May 2008
(1941) FERMI’s logbook containing the design of PILE-1
CONFORM Open Day , 11 May 2008
Acknowledgements
Professor Roger Barlow (Manchester)
Dr Cristian Bungau (Manchester/Cockcroft)
Dr Adrian Bungau (Huddersfield/Cockcroft)
Dr Bill Nuttall and Geoff Parks (Cambridge)
RCUK, EPSRC, STFC
CONFORM Open Day , 11 May 2008