Accelerator Driven Subcritical Reactors

or

How Accelerators can save the planet

Roger BarlowInstitute of Physics Meeting

Imperial CollegeApril 12th 2010

Roger Barlow: ADSRs 1

We have to stop burning fossil fuels

Roger Barlow: ADSRs

1.They cause climate change

2.They are increasingly concentrated in countries with dodgy politics

3.They are going to run out

2

Renewables can’t fill the gap

Roger Barlow: ADSRs

Even major (country-scale) developments will not be enough

Alternatives (windmills,tidal power, solar power, improved insulation, retreat to the middle ages) can’t supply the deficit

Turbine typically delivers 1.5 MW peak

3

Nuclear Power

Fossil fuels will need to be replaced by a basket of alternativesIt is hard (impossible?) to put such a basket together without nuclear power

Big issues (real or in the eyes of the public?) with:•Safety: Chernobyl and 3 Mile Island•Waste disposal. Storage for millenia - NIMBY•Proliferation. Rogue states and terrorist organisations

4Roger Barlow: ADSRs

Safe Subcritical Reactors

Conventional:Run with k=1 exactly

k<1 stopsk>1 explosion

Sub CriticalRun with k<1

Use accelerator to supply extra neutrons

Hence: Accelerator Driven Subcritical Reactor (ADSR)

Each fission absorbs 1 neutron and produces ~2.5

Some neutrons lost, leaving k neutrons to produce k fissions

5Roger Barlow: ADSRs

ADSRs

“Manifestly Safe”Switch off accelerator and reaction stopsEnergy balance is OK: need 5-10% of power to run

accelerator

Accelerator

Spallation Target

Core

6Roger Barlow: ADSRs

OFF

ThoriumWhen do we run out Uranium? In about 100 years, unless we move to a fast breeder system.

Uranium is not the only possibility…

Thorium: Fertile, not fissile 232Th +n 233Th233Pa233U • Abundant. (Like lead) and spread around• Much smaller waste problems (no long-lived minor actinides)• Proliferation resistant

7Roger Barlow: ADSRs

Thorium Reactors

Thorium mixed with U or Pu• MSR (1964)• Winfrith (Dragon)• Fort St Vrain (1976)• Shippingport (1977)• Germany Julich (1967), THTR (1983)• Kurchatov Institute/Thorium Power• India

But Thorium and ADSRs go togetherRoger Barlow: ADSRs 8

Energy Amplifier (Rubbia)

Thorium ADSR fast reactor

Idea has been around for years

Lead/Bismuth Eutectic acts as target and coolant and moderator.

Nobody’s built one yet!

Feeling is that the accelerator is the weak point.

9Roger Barlow: ADSRs

Waste from ADSR

Needs storing – but not foreverMinor Actinides (Np, Cm, Cf) are not produced

10Roger Barlow: ADSRs

Transmutation

• Fast neutron flux can burn actinides produced by conventional reactors. MYRRHA project.

• Also destroy most-problematic fission products (e.g. 99Tc: soluble, T½=211,000 Y) by ‘Adiabatic Resonance Crossing’. Lead moderator to ensure neutrons hit the resonance for absorption

11Roger Barlow: ADSRs

Fuel lifetime

Typical Uranium/Plutonium PWR needs refuelling in months, limited by fission product neutron poisoning

Typical Thorium fuel lasts for years as fission product effects counterbalanced by increasing amounts

of 233U Do we need reprocessing? Yes. Not for recycling

of fuel but because 233U storage is problematic Roger Barlow: ADSRs 12

Proliferation

Thorium fuel system does not produce weapons

• Explains why nuclear power went the U/Pu route back in the 1950’s

• Solves today’s dilemma of states like Iran

Specifically1. There is no equivalent to a 235U

device2. Constructing the equivalent of a

Pu device, using 233U, is made very difficult due to contamination with 232U

13Roger Barlow: ADSRs

Summary so far

ADSRs: Nuclear Power that avoids the real and perceived problems of criticality accidents

Thorium as fuel removes problems of • Long-lived waste• Proliferation

Worth a closer look… Lots to do in understanding The reactor. Thorium cross sectionsThe Target and spallationFuel reprocessingAccelerators

14Roger Barlow: ADSRs

Let's look at this

Accelerator requirements

Proton Energy ~ 1 GeV gives ~20 spallation neutrons per proton.

For 1GW thermal power:• Need 3 1019 fissions/sec (200 MeV/fission)• 6 1017 spallation neutron induced fissions/sec (k=0.98

gives 50 fissions/neutron)• 15 1017 spallation neutrons/sec• 7.5 1016 protons/sec Current ~10 mA. Power ~ 10 MW Compare: PSI cyclotron: 590 MeV, 2mA, 1MWISIS synchrotron: 800 MeV, 0.2mA, 0.1 MW

15Roger Barlow: ADSRs

Accelerators for ADSRs

Cyclotron

Energy too high for classical cyclotron. On the edge for other types

FFAG

Looks like the answer

“Cyclotron currents at Synchrotron energies”

Simplicity = reliability

Linac

Can do the job. But VERY expensive

Synchrotron

Current far too high.

Complicated (ramping magnets)

16Roger Barlow: ADSRs

Reliability: the 3rd Frontier

In the real world:Accelerators often trip for

seconds/hours/days. They are complicated systems operating in real world environments

But there are complex real world pieces of apparatus that trip rarely. Planes, computers, radio sets…

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Target runs hot. If beam stops, target cools & stresses & cracks: Require not more than 3 trips per year (or similar numbers)

Straw man scheme: AESIR

Accelerator Energy System with Inbuilt Reliability

18Roger Barlow - UK ADSR programme

Design and build a Thorium ADSR, hopefully with an nsFFAG providing the accelerator

(Other accelerator solutions are acceptable.)

1 GeV 10 mA protons with high reliability and low losses (don't want contamination problems)

Stage I: LOKI

The Low-key demonstrator35 MeV H- system -or H+ or H

2+

High current. (1 mA? 10 mA?) Commercial source RF Quadrupole Standard LinacStudy reliability and build it in from the start. Looks like the Front End Test Stand?? Copy? Move?

Daresbury is the obvious place to do this as -Space availablePeople availableFriendly RDA Cockcroft, Universities, etc...

19Roger Barlow - UK ADSR programme

Stage 2: FREA

FFAG Research for the Energy Amplifier•Add a 2nd stage ring: boost energy to 390 MeV•Why 390? Pion production. But ~300 would still be interesting•Produces spallation. Not as much as 1 GeV, but enough to be interesting.•Continue to emphasise reliability. Increase current to 10 mA•Use a proton nsFFAG – with a cyclotron as fallback. Or Linac•Gives useful proton machine (c.f. TRIUMF, PSI). 99mTc production?•Links to proton therapy 20Roger Barlow - UK ADSR programme

Stage 3: Thor

Add a second ring to give 1 GeVnsFFAG, with RCS and Linac as backup optionsUse with a real target and nuclear core for productionNeed private funding

21Roger Barlow - UK ADSR programme

Conclusions

Things are movingMore peopleMore ideasPossibility of funding at some levelWay ahead for Daresbury

22Roger Barlow - UK ADSR programme