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Fertile to Fissile conversion

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Roger Barlow

on 31 October 2012

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Transcript of Fertile to Fissile conversion

Thorium: Fertile to Fissile conversion with spallation neutrons
and other investigations Thorium in itself is inert
(not a match, just a stick) Roger Barlow
Huddersfield University
and Cristian Bungau, David Cooke, Bob Cywinski and Jake Smith Using thorium in conventional reactors Possible solutions:
Seed with Pu or U-235. Possible, but problems with proliferation and with MA waste
Run an ADSR for months before getting any power out.
Insert in conventional reactors, a few at a time. Suggestion:
Irradiate thorium fuel rods with spallation neutrons, converting enough Th-232 to U-233 to make it useful in a reactor. Like an ADSR - but separating the A and the R Goal is to irradiate complete reactor-ready fuel rods.
No chemical separation or other processing
The equivalent of a microwaved meal Would it work? Simulation Tools : MCNPX and GEANT4 MCNPX version 5.
Out of the box, with default libraries.
Industry standard.
Slow but sophisticated statistics.
Unable to modify source code. GEANT4
Modern C++ library
Adaptable to general problems
Use Liege cascade model + ABLA evaporation/fission code
Validate against Los Alamos neutron spallation data

Needed to fix bug, and add two new features:
Thermal neutron S correction
ability to change 'target' composition with time, in light of previous collisions. How much U-233 is needed? Take simple model of heterogeneous reactor from Nifenecker

MCNP results easy to obtain. Use both heavy water and ordinary water.

GEANT4 results harder to extract: take neutron spectrum from MCNP

Results consistent (where it matters). Criticality needs ~1.8% U-233 in Th-232 enrichment. Take 2% enrichment as target How many protons will this need? Consider 1 GeV protons.
Above this, spallation neutron production scales
Below this, it falls off rapidly Consider cylindrical fuel rod, 120cm long, 1 cm diameter Predict ~1 conversion per proton (agrees with LANL measurements) Requires ~40 hours in a 5 mA, 1 GeV proton beam
Not encouraging Worlds' s most powerful cyclotron at PSI
0.6 GeV, 2.9 mA
So ~ 2 weeks dedicated beamtime
Unrealistic... Going Large-scale 120 cm long
120 cm diameter GEANT4: 27.4
MCNPX: 28.1
conversions/proton Distribution very broad transversely.
Spike in the centre, but spreads widely.
To capture a large part of it, you need to include a large radius
(cumulative plot on right) Longitudinally, peaks in first 10-20 cm, but long tail.
You probably want to swap ends halfway... ~25 conversions /proton seems large, as spallation target only makes ~20 neutrons at this energy.
~20 neutrons emitted from target. Many more in the internal cascade. Benefit from those.
Implies that the target and the fuel must be the same, not separate, for this to work. More detailed studies Replace solid Thorium by grid of rods
(light water, heavy water, void between)
Surround by lead, iron, beryllium
Swap thorium and thoria
Nothing made much difference.. Have not yet put in cladding. No surprises expected Spectrum of neutrons giving conversions (above) compared to overall spectrum (below) shows small thermal neutron contribution, and useless high energy (2-10 MeV) tail. Scope for moderation? 感谢您的关注! Protactinium and other worries Th-232 forms Pa-233
Hangs around for ~27days with high cross section
Would reduce number of conversions No sign of saturation/nonlinearity: MCNPX Or GEANT4 (100 days) Thoria in fuel rods: a related question As the thorium nuclei in the thoria lattice are replaced by uranium, what happens to the structure? The thermal expansion coefft
(which is small)
hardly changes for 0-1-2% U in Th Study materials properties
of Thoria (Thorium dioxide)
modelling with DL_POLY2 Diffusion coefft small
for U(4+)
Larger for 3+ and 5+ Arrhenius plot
ln D against 1/T Pure Thorium
and 10% U(4+) U(3+) and U(5+) No phase changes
Specific heat independent of temperature
and of uranium concentration Conclusion: replacing Th by U(4+) causes no materials problems. Performed at the ILL reactor Measurements needed for data libraries Need data on heavy fission fragment yields from U-233 fissions. Use LOHENGRIN mass spectrometer with Ge detectors. Isotopes produced in mixture of charge states Preliminary 1 GeV of proton energy gives
25 x 0.2 = 5 GeV of fissile energy
Not obviously impractical Can envisage large-scale dedicated accelerator system in which rods are swapped around. Wait 40 hours for first rod, but thereafter get 1 rod every ~2 hours

Not to be done tomorrow - but maybe part of future thorium scenario
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