1 A fission-fusion hybrid for waste transmutation M. Kotschenreuther, S. Mahajan, P. Valanju - Inst. Fusion Studies E. Schneider Dept. of Nuclear Eng.- UT Rob Reed - Dept Nuclear Eng. UCLA Super-X Divertor Neutron shield Poloidal Coils 100 MW Fusion Washington DC Dec 3, 2009
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1 A fission-fusion hybrid for waste transmutation M. Kotschenreuther, S. Mahajan, P. Valanju - Inst. Fusion Studies E. Schneider Dept. of Nuclear Eng.-
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A fission-fusion hybrid for waste transmutation
M. Kotschenreuther, S. Mahajan,
P. Valanju - Inst. Fusion Studies
E. Schneider Dept. of Nuclear Eng.- UT
Rob Reed - Dept Nuclear Eng. UCLA
Super-X Divertor
Neutronshield
PoloidalCoils
100 MW Fusion Washington DC Dec 3, 2009
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• Provide a solution to main public acceptability issue of nuclear fission
with minimal perturbation of the present nuclear industry
• A hybrid-enabled fuel cycle so that a fleet of ~ 100 LWRs requires
only about 5 hybrids for waste destruction
• A fusion driver that
– Dovetails and reinforces fusion program elements leading to pure fusion
– Minimizes issues of combining fission and fusion (potentially severe)
– Provides a practical application for fusion with much easier physics and
technology requirements
UT concept elementsUT concept elements
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• ~ 100 MW DT tokamak or Spherical Tokamak (ST)
– with conservative core physics (like ITER- H mode confinement, below no-wall limit)
• Main fusion extrapolation- high overall duty factor DT operation (ITER ~
4%)
• Attaining such a high duty factor has many new challenges
– Adequate component lifetimes in the severe fusion environment
– 14 MeV neutron damage
– Plasma facing component erosion from long plasma exposure
– Rapid component replacement in highly radioactive, complex devices
– Large tritium breeding / throughput / handling
– Operation with very long pulses and very low disruption frequency
– More severe divertor challenges- Super-X divertor is a key
Fusion driver for such a hybridFusion driver for such a hybrid
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• Fusion Nuclear Facility (FNF) - formerly called a fusion Component
Test Facility (CTF)
• We call the very similar hybrid driver a Compact Fusion Neutron
Source (CFNS)
• Unlike ITER, a CFNS (or FNF) is not primarily self heated by fusion
reactions- like present experiments it is primarily externally
heated
• Hence, it is not necessary to await results from ITER self-heated
plasmas
• Conservative physics suffices for the CFNS-FNF mission
Hybrid driver is very similar to a Fusion Nuclear FacilityHybrid driver is very similar to a Fusion Nuclear Facility
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• CFNS uses operating modes and dimensionless physics parameters where present
• Use driver B while driver A is being refurbished off-line
B A
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• Hybrid CFNS we propose has much less demanding requirements than FNF
testing for DEMO
– Hybrid Neutron wall fluence ~ 2 MW yr / m2
– Pure fusion DEMO requirement ~ 6 MW yr / m2
• Component damage is ~ 3 times less
– Existing materials probably will suffice at ~2 MW yr / m2
– Less material / design development and iteration needed compared to much more
severe material degradation expected at ~ 6 MW yr/m2
• Testing iterations to develop and prove reliability take ~ 3 times less time each
(almost a decade less)
– Adequate reliability / availability adequate for a hybrid could be demonstrated much
sooner than for a pure fusion DEMO
Technology challenges for such a hybrid much less Technology challenges for such a hybrid much less than for a pure fusion DEMOthan for a pure fusion DEMO
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Replaceable fusion driver
• Driver replaced up to yearly while fission fuel rods reshuffled (reduces development time, neutron damage)
• Damaged driver refurbished in remote maintenance bay (easier maintenance)
• Fission assembly is physically separate from fusion driver (failure interactions minimized)
• Fission assembly is electro-magnetically shielded from plasma transients by TF coils (disruption effects greatly reduced)
Modular concept addresses all these issuesModular concept addresses all these issues
We shall now spell these out
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• The availability of each individual fusion driver is <
50%, while the hybrid availability is much higher
• Allows adequate hybrid availability with
considerable less demanding fusion technology
• Neutron damage is ~ 3 times less than pure fusion
DEMO
CFNS: possible at an earlier level of fusion CFNS: possible at an earlier level of fusion technologytechnology
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• The TF coils act as a “cage” to isolate the fission blanket from events in the fusion system
• The cage is strong: magnetic stresses are about an order of magnitude below the cage strength
• Electro-magntic disruption forces are less about half the static forces
• MCNP calculations fully include the cage geometry-fusion neutron losses are modest (~ 20%)
• Outer TF coil legs (Al) should last significantly longer than inner TF centerpost (Cu)
CFNS: Isolates the fission blanket from off-normal CFNS: Isolates the fission blanket from off-normal fusion events using the TF coils as a strong “cage”fusion events using the TF coils as a strong “cage”
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• Calculations by UT Center for Electromechanics using 3D
EM codes
• Disruptions: as fast as ~ 1 ms
• The thick conducting cage slows the disruption speed
in the fission blanket to ~ 100 ms
• Electromagnetic forces in the fission blanket reduced by an
order of magnitude
Electromagnetic disruption effects on blanketElectromagnetic disruption effects on blanket
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• Fission blanket power density is much higher than
pure fusion- MHD coolant problems could be very severe
for a hybrid
• Magnetic field outside the TF coils is only from PF, and is
almost exactly vertical- aligns almost perfectly with the
coolant flow direction
MHD drag effects reduced by ~ 2 orders of magnitude
MHD coolant effectsMHD coolant effects
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A CFNS/CTF has high plasma power density - A CFNS/CTF has high plasma power density - exhausting the plasma power harmlessly is crucialexhausting the plasma power harmlessly is crucial
• Power is exhausted as hot plasma and
follows magnetic field lines to a divertor
• The plasma that hits the divertor cannot
be at too high a temperature- or else:
– It quickly erodes through the divertor
– It sputters atoms off the wall into the plasma
– Very low helium ash exhaust ultimately
choking off the fusion reaction
• A Standard Divertor (SD) - too hot
• Super-X Divertor (SXD)- allows exhaust to
expand and cool
Standard Divertor
Super-X Divertor
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Super-X Divertor (SXD) provides the desired Super-X Divertor (SXD) provides the desired operation - unlike the standard divertoroperation - unlike the standard divertor
• SXD -Magnetic geometry is
changed so exhausted hot plasma
expands and cools
• Analysis using best available
simulation (SOLPS - as for ITER)
• Standard divertor - exhausted high
power plasma is unacceptable
– “sheath limited”- very hot and
damaging
• SXD- exhausted plasma is
desirable
– “partially detached”- what ITER
design aims for
– T < 10- 20 eV
Calculations by John Canik ORNL
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The CFNS core plasma can operate conservatively- The CFNS core plasma can operate conservatively- minimizing chances of disruptionsminimizing chances of disruptions
• Low plasma density allows strong plasma current to be driven
controllably (ECCD, EBW, NB, HHFW)- with many benefits:
• Strong current enables low disruptivity
– H- mode confinement suffices, avoiding need for ITB with tricky control
– Effect of loss of wall conditioning on plasma performance?
– Will material surfaces evolve acceptably at long times (e.g., will
erosion / re-deposition lead to wall flaking & plasma disruptions?)
– Will surfaces survive a rare disruption without unacceptable
damage?
• Liquid metal on porous substrate looks like a promising
potential solution to all of these
– NSTX might be able to test it sometime in the future?
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Scientist and Businessman - A rare meeting of mindsScientist and Businessman - A rare meeting of minds
Jim Hansen - Tell Obama the Truth-The Whole Truth:• However, the greatest threat to the planet may be the potential gap between that
presumption (100% “soft”energy) and reality, with the gap filled by continued use of coal-fired power. Therefore it is important to undertake urgent focused R&D programs in both next generation nuclear power and ---
• However, it would be exceedingly dangerous to make the presumption today that we will soon have all-renewable electric power. Also it would be inappropriate to impose a similar presumption on China and India.
Exelon CEO John Rowe Interview - Bulletin of American Scientists:• We cannot imagine the US dealing with the climate issue, let alone the climate
and international security issues without a substantial increment to the nation’s nuclear fleet
• I think you have to have some federal solution to the waste problem ---- If it (the Federal Government) ultimately cannot, I do not see this technology fulfilling a major role
Renaissance of Fission Energy is emerging as a global imperative - everyone
is talking!
A believable technical solution to the nuclear waste problem- a scientific imperative
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UT-Hybrid vs Fission-only CycleUT-Hybrid vs Fission-only Cycle
Hybrid Route Fission-only (AFCI)
US Light Water Reactors 100 100
Fast-spectrum waste
destruction reactors4-6 30-40
Required Reactor fleets for zero net transuranic nuclear waste
production from the current ~100 US utility reactors
Under our proposal
4-6 new utility-scale hybrid reactors would suffice
Waste reprocessing for fast-spectrum reactors will also be
reduced by roughly an order of magnitude
Reactor Requirements for Waste Transmutation for different schemes
Reactors needed to destroy waste from 100 LWRs
Fast Reactors BR= 0.5
Fast Reactors BR= 0.25
Hybrids burning all TRU
Hybrids burning only
Np & Am
IMF pre-burn followed by hybrids
Number of FRs 39-56 37 0 20 0
Number of Hybrids 28 5 4-6
Total # of Fast systems
39-56 37 28 25 4-6
“Excess”
Cost
(LWR equivalents)
19-28 19 28 15 4-6
FR cost = 1.5 LWR, Hybrid = 2 LWR
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• The ST has somewhat greater extrapolation than a conventional tokamak
• But, we believe the main extrapolation risk from today to a hybrid driver is in neutron damage and
high duty factor- not physics
• Furthermore, we believe the ST has advantages in coupling to a fission blanket and in maintenance
• Hence, we have opted for the ST initially to ameliorate the technology risks through easier
maintenance
Size and B field ExtrapolationsSize and B field Extrapolations