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Thorium, ADSRs…… and ns-FFAGs Bob Cywinski School of Applied Sciences PowerPoint PPT Presentation

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Thorium, ADSRs…… and ns-FFAGs Bob Cywinski School of Applied Sciences. The Carbon Problem. source: Government Energy Support Unit (confirmed by OECD). Meeting the Energy Challenge (2008). Fission. and breeding. U- Pu. Th -U. Thorium as a fuel. Advantages

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Thorium, ADSRs…… and ns-FFAGs Bob Cywinski School of Applied Sciences

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Thorium, ADSRs……

and ns-FFAGs

Bob Cywinski

School of Applied Sciences

The Carbon Problem


Government Energy Support Unit (confirmed by OECD)

Meeting the Energy Challenge (2008)


and breeding



Thorium as a fuel....


233U has superior fissile properties

Robust fuel and waste form

Generates no Pu and fewer higher actinides

Proliferation resistant







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

22 mins




27 days

Annual energy resources

Thorium equivalent


tonnes of coal


barrels of oil


m3 of natural gas


tonnes of uranium

5x103 tonnes of thorium

After Sorenson

Estimated global Th resources

IAEA, status report May 2005

….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…….


Past experiences

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


“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

An alternative approach:

The Energy Amplifier or Accelerator

Driven Subcritical Reactor Concept

MYRRHA: an ADSR transmutation proposal

350 Mev, 5mA

proton beam

The MYRRHA design proposes a windowless

Pb-Bi target:

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

U-Pu MOX core and blanket

Can an ADSR operate on thorium only?



The Energy Amplifier/ADSR energy balance

electrical energy converter












sub critical reactor

232Th + n →233Th →233Pa (27d)→ 233U

Target size

Proton energy

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

Given that a 1 Gev proton produces 24 neutrons (in lead) this corresponds to a proton current of

Proton beam requirements for EA/ADSR

The (thermal) power output of an ADSR is given by

withN = number of spallation neutrons/sec

Ef = energy released/fission (~200MeV)

ν = meannumber of neutrons released per fission (~2)

keff= criticality factor (<1 for ADSR)

So, for a thermal power of 1550MW we require

keff=0.95, i=33.7mA

keff=0.98, i=13.1mA

keff=0.99, i=6.5mA

Proton beam requirements

To meet a constraint of a 10MW proton accelerator we need keff=0.985


Safety margins

...but why has no ADSR ever been built ?

...because existing accelerators are not sufficiently stable and reliable

ADSR geometry (a) single target


232Th core

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

Multiple beams/targets should also alleviate accelerator stability problems

H.M. Broeders, I. Broeders :

Nuclear Engineering and Design 202 (2000) 209–218

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


The over-all power distribution is satisfactory.

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


The over-all power distribution is satisfactory.

Trefoil of 3 ns-FFAGs

each providing 3.5mA at 1 GeV

Three ns-FFAG drivers should be no more expensive than a singe conventional driver....

Pb-cooled Th/U233 subcritical core with:



Molten lead is both core coolant and spallation target

.....and will provide the required reliability margin

ADSR geometry (b) triple target


232Th core

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

ThorEA – the thorium energy amplifier association

The way forward ?

The AESIR project: (Accelerator Energy System with Inbuilt Reliability)












£50 M


Stage 1: LOKI (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).

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)


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!!

(1941) FERMI’slogbookcontainingthedesign of PILE-1


Professor Roger Barlow (Manchester)

Dr Cristian Bungau (Manchester/Cockcroft)

Dr Adrian Bungau (Huddersfield/Cockcroft)

Dr Bill Nuttall and Geoff Parks (Cambridge)


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