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Fission-Fusion hybrid to destroy Fission-Fusion hybrid to destroy nuclear waste nuclear waste

From a challenge to an From a challenge to an opportunityopportunity

M. Kotschenreuther1, S. Mahajan1,

P. Valanju1, and E. Schneider2

UT-IFS Super-X Divertor

Neutronshield

PoloidalCoils

100 MW CFNS core

1Institute for Fusion Studies,

2Department of Mechanical Engineering

The University of Texas at Austin

PPPL April 30, 2009

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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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Nuclear Energy Resurgence - what could fusion add?Nuclear Energy Resurgence - what could fusion add?

• Simplest would be to provide unlimited, low waste and carbon free energy

– Promise so attractive that its pursuit had and has a mandate in spite of difficulties and enormous times expected to be spent in this quest

• Two major developments in the last decade have redefined the overall relevant scales in the “energy debate”:

– Broader recognition of the specter of anthropogenic global warming, caused by carbon-based fuels, haunting our civilization

– Drastic boosts in energy consumption due to rapidly increasing affluence in sections of developing societies

=> We must produce lot more energy while our conventional sources of energy production (coal, natural gas…) have proved unfriendly to the planet

=> => Nuclear Energy must be an integral component of any desirable carbon-free future energy mix (with renewables - some inherently intermittent)

Can fusion neutrons aid nuclear resurgence?- clean the reactor mess?

Is it time to revive the age-old but hybernating Fission-Fusion Hybrid?

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Generic hybrid (H) and the fission only path (FR)Generic hybrid (H) and the fission only path (FR)

• Discussion limited only to transuranic (TRU) waste -

destruction applications - it is assumed that no alternative

environmentally/ socially sound and affordable “waste

disposal” paths exist

• Hybrid here connotes a fission system (generally an FR)

coupled to a source of external neutrons

• FR , in this context, is a “relatively mature” technology (NAS

studies -1990s)- fusion is a technology in the making- The

fission-fusion hybrid is yet to make its debut

• How does one, then, make a case for H (vis a vis FR?)

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Case for a Hybrid - confronting the shortcomingsCase for a Hybrid - confronting the shortcomings

• A generic hybrid is very expensive– Fusion driver similar to ITER- reduced size implies cost ~1/3 of $12b– Typically FR cost is about $3b=> cost of H is double (or more) of FR– The differentials FR-LWR~$1b, H-LWR~$4-5b ( for the same Power)

• Huge issues of Complexity reliability and availability (Mike)• Higher Risk, Time and Cost for develpoment

– FR can be fielded for waste destruction in ~20 yrs.– Though physics of a generic hybrid may be easier, the technology

difficulties are very similar to that of a fusion reactor• Unique safety issues (sub-critical operation notwithstanding)

emerging from the marriage of two complicated technologies- One with a large magnetic field and the other with a very high power density core with liquid metal coolant.

It will surely take several major ideas and innovations to beat these daunting handicaps

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Figures of MeritFigures of Merit

• The Support ratio S– advanced number of light water reactors (LWR) whose TRU waste

can be destroyed by a single advanced reactor (H or FR)– both of these are more expensive than LWRs

• The Unit cost per advanced reactor C

– necessarily more for H than FR ----- Ch > Cfr

• The reprocessing factor R– measures the amount of reprocessing needed in all steps required to burn

the waste to ~99% of the original

• Complexity, safety, and dependability of the technology

An attractive Hybrid solution must, then, be not too complex, and

– Minmize Ch - Cfr , and Rh

– Maximize Sh/Sfr to such an extent that the waste destruction system based on H is (much) cheaper than the system based on FR

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A Scenario uniquely suited to a Hybrid A Scenario uniquely suited to a Hybrid • Judicious Choice of the fuel cycle (IMF-LWR, H)

– Deep Pre-Burn in LWR getting rid of the bulk of TRU~75%

• Invoke Inert Matrix Fuel=> IMF-LWR phase in the Texas reference case

– The H-phase burning the remaining highly recalcitrant 25% residue• Though smaller in mass, still contains most of the original

radioactivity and long-term biohazard• Cannot be stably and safely destroyed in FR• Unique territory for the hybrid

• New fuel cycle => Sh ~ 16-25 while Sfr ~2-4 => Sh / Sfr ~7-8– Rh/Rfr also substantially decreases– A huge reduction in the number of advanced reactors and the reprocessing

costs make the H system considerably cheaper than the FR system.

If we could just make a near term, reliable, and not too expensive

fusion module powering a safe Hybrid

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A Replaceable (and repairable) Fusion ModuleA Replaceable (and repairable) Fusion Module

• Fusion driver as a replaceable module that fits within a fission blanket, but is not physically connected to it

– Very different form a generic hybrid in which the fission blanket is an integral part of the driver, and is located inside the TF coils

– The fusion module may be replaced (as a unit) at the time of fuel shuffling- both maintenance operations could take 4-6 weeks

– The material constraints become much less stringent- the driver components have to withstand fusion neutrons for ~1-2 years << for generic hybrids, fusion reactors- much shorter testing times.

– Hugely reduced MHD issues since the metal coolant samples only the poloidal field aligned essentially along the coolant flow.

– H Design greatly simplified-Fusion fission systems physically decoupled

• Any reasonable compact high power density fusion source ok.

Portability adds somewhat to the cost

Nevertheless, it is the Deep Pre-burn concept plus the Replaceable fusion module that could turn the Hybrid into a potential winner

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The Fusion DriverThe Fusion Driver

A A CCompact High Power Density ompact High Power Density FFusion usion NNeutron eutron SSourceource

(CFNS)(CFNS)

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What may constitute a reference fusion driver?What may constitute a reference fusion driver?

• Fusion power levels similar to a CTF

– ~100 MW

• Choose an ST for engineering advantages when marrying to

fission

– Coil losses not very important for a hybrid with our fuel cycle

• Other advantages outweigh this

– High power density with low coil mass and low capitol cost

– easy maintenance - a much more important consideration

• Slight neutron shielding on center TF to extend life to ~ 1-2 years

– To make room, aspect ratio A~ 1.8 is on high side for ST

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Core physics operation assumed to be Core physics operation assumed to be conservative at this pointconservative at this point

• Below No-wall limit

– estimates by Jon Menard quoted in Jeff Freidberg’s book:

– use TROYON definition <>N with correction for q*

• H-mode confinement (H ~ 1)

• Te = Ti (no enhancements to reactivity for hotter ions)

• Densities far below Greenwald limit (< 0.3)

• Minimum q above 2 (avoids worst NTMs)

• CD efficiency: I neR/Ph= 0.2 x 1020 (<Te>/10kev) A/Wm2

– Most uncertain core physics parameter?- to be investigated by NSTX

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CFNS gross parametersCFNS gross parameters

R (m) 1.35

A 1.8

3

PCD (MW) 50

ne (m-3) 1.3-2 x 1020

neutron 1.1 MW/m2

ne (m-3) 1.3-2 x 1020

n/nG 0.14-0.3

15-18%

Ip (MA) 10-14

Bcoil 7 T

Bplasma 2.9 T B

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• CFNS can use operating modes and “normalized” performance quality which is

reliably experimentally demonstrated on many present tokamaks

- only because SXD allows high power density without degrading the core

Modest Core Physics DemandsModest Core Physics Demands

DeviceDevice Normalized Normalized confinement Hconfinement H

Gross stability Gross stability NN

Poloidal Poloidal / / minor radiusminor radius

Today’s experiments-Today’s experiments-Routine operationRoutine operation

11 < 3< 3 ~ 0.05-0.1~ 0.05-0.1

Today’s experiments-Today’s experiments-

Advanced operationAdvanced operation< 1.5< 1.5 < 4.5< 4.5 ~ 0.05-0.1~ 0.05-0.1

CFNS/CTFCFNS/CTF 11 2-32-3 ~0.05~0.05ITER- basicITER- basic 11 22 ~0.02~0.02ITER-advancedITER-advanced 1.51.5 < 3.5< 3.5 ~0.03~0.03““Economic” pure Economic” pure fusion reactorfusion reactor

1.2 -1.51.2 -1.5 4-64-6 ~0.02~0.02

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Hybrid closer to Today’s experimental achievements than ITER or a Hybrid closer to Today’s experimental achievements than ITER or a pure fusion reactorpure fusion reactor

Device Outer radius

( R + a )

Fusion Power Q = Fusion power/

Heating power

JET, JT-60U(exist)

4 m 16 MW(achieved)

Close to 1(achieved)

Fusion driver for Hybrid(Transmutation)

2.5 mFits inside

fission blanket

100 MW

(~3000 MW fission)

1-2

ITER(being built)

8 m 400 MW(expected ~ 2020)

10(expected ~ 2020)

Pure fusion reactor

7-10 m 2000-3500 MW 10-30

The Hybrid fusion source has a higher power density compared to current experiments and ITER - need SXD

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The CFNS divertor is implausible without the The CFNS divertor is implausible without the Super-X divertorSuper-X divertor

• From Stangeby: sheath limited if S’ = Q||u /n1.75 L0.75 > 1 x10-27

• Benchmark with SOLPS- define

S = Q||u (Bdiv/Bu) /n1.75 L0.75 / 3 x10-27

If S > 1, reliably sheath limited (typically Te plate > 100 eV)

• This would give:

– Negligible radiation/high heat flux

– Unacceptable erosion sputtering

– Low neutral pressure and very likely unacceptable He exhaust

Operating window becomes substantial only with SXD

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CFNS: conservative designCFNS: conservative design

CD power= 50MW

Pfus =100 MW

• At moderate density, no

wall stable regime

• At very low density:

– too much current =>

– poor MHD stability

• Add core radiation to

make H = 1 and “save”

divertor when possible

• Only SXD has S<1

Parameters vs Plasma Density

0

0.5

1

1.5

2

2.5

3

3.5

4

0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2

Density x 1020

Sheath Parameter Sfor SD

H factor

Sheath Parameter Sfor SXD

/ - No wall crit

/ - No wall crit

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CFNS: more advanced scenariosCFNS: more advanced scenarios

CD power= 50MW

• Only SXD has S<1

• 400 MW fusion at <N> ~ 4.5

• Assume H = 1.3 attainable

– More core radiation to “save” divertor if possible

• Required H is high for 400 MW fusion power

Parameters vs N

0

0.5

1

1.5

2

2.5

3

3.5

4

2 2.5 3 3.5 4 4.5

N

Sheath Parameter S for SD

H factor

Sheath Parameter S for SXD

Fusion Power___________ 100 MW

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SXD-from theory to experimentSXD-from theory to experiment

• Worldwide plans are in motion to test SXD

– MAST upgrade now includes SXD

– NSTX: XD and future SXD?

– DIII-D SXD test experiments, possibly next year

– Long-pulse superconducting tokamak SST in

India designing SXD

• SXD: enables power exhaust into much

lower neutron damage region

– Much of ITER divertor technology be used (H2O

cooled Cu substrate- steady Q < 10MW/m2,

20 MW/m2 transient)

SXD for MAST Upgrade

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CFNS Unknowns - Plasma wall interaction CFNS Unknowns - Plasma wall interaction

• SXD is promising, but needs testing

• Success of SXD still leaves further PMI issues

– Tritium retention

– 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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The challenge of devising an attractive The challenge of devising an attractive

fission-fusion hybrid to transmute wastefission-fusion hybrid to transmute waste

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Generic Nuclear Waste Management SchemesGeneric Nuclear Waste Management Schemes

Hybrid variant: use mostly FR with a few hybrids - Hybrid variant: use mostly FR with a few hybrids - for a minority of problematic TRU (minor actinides)for a minority of problematic TRU (minor actinides)

LWR: Uranium Oxide Fuel

LWR: Uranium Oxide Fuel

UOX Spent

Fuel (SF)Direct DisposalDirect Disposal GeologicalRepositoryGeologicalRepository

TemporaryStorage

ReprocessLWR: Uranium Oxide Fuel

LWR: Uranium Oxide Fuel

ReprocessFast ReactorsFast Reactors(FR)(FR)

Fast ReactorsFast Reactors(FR)(FR)

Spent

Fuel

TRU in

Fertile

Matrix

Spent

Fuel

GeologicalRepositoryGeologicalRepository

Using Fast ReactorsUsing Fast Reactors

Fission productsU, Fission products

Unburned TRU

ReprocessLWR: Uranium

Oxide FuelLWR: Uranium

Oxide FuelReprocessFission-Fusion Fission-Fusion

HybridHybridFission-Fusion Fission-Fusion

HybridHybridSpent

Fuel

TRU in

Fertile

Matrix

Spent

Fuel

GeologicalRepositoryGeologicalRepository

Generic fission-fusion hybrid: same as FRGeneric fission-fusion hybrid: same as FR

Fission productsU, Fission products

Unburned TRU

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• National Academy of Sciences (NAS) investigated both fission only

(critical FR) and external neutron driven (subcritical) schemes in

1990s

– Considered critical fast reactors & accelerator neutron sources-

but not fusion!

Recommended against transmutation schemes

– they were all too costly (hundreds of billions of dollars) and

– took too long (two centuries to reduce transuranics (TRU) by

~99%)

• 2001-2008: fast reactor transmutation schemes were refined

• Recent congressional testimony (2005-2006) on FR approaches:

same objections as NAS study,

and objections to the proliferation dangers of reprocessing

Recent history of transmutation schemes Recent history of transmutation schemes

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• “Generic” hybrid scheme has no clear advantage over proposed FR

schemes in cost, proliferation or time

• However, a generic hybrid has obvious disadvantages; the fusion

driver adds

– Substantial extra cost

– Major complexity

– Major new technology development

– Increased complexity leads to new failure modes and safety issues

A winning Hybrid strategy must

1. find a “way” that hybrids make possible and advantageous

2. find a way to minimize fusion caused (substantial) disadvantages

Devising a winning hybrid based scheme Devising a winning hybrid based scheme

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• Hybrid is “safer”- the fission blanket operates sub-critically

BUT: FR community claims good passive safety while burning TRU

from LWRs - using advanced geometry, materials

• FR safety (criticality accidents)- not raised as a major issue in the NAS

study or recent congressional testimony

– Major issues with FR approach - COST, reprocessing, time

– Hybrid makes cost worse, slightly improves time

• Safety advantage of hybrid is hard to argue persuasively- whereas

disadvantages are clear-cut

The Hybrid concept must find a decisive advantage

way beyond anything the “generic” concept offers

Usual advantage claimed for a hybrid: safety Usual advantage claimed for a hybrid: safety

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• FR safety is made problematic by particular TRU isotopes which only

fission from very fast neutrons (~ 1 Mev)

• Problematic fuel- low fission cross section at lower energy ~ 100 keV

– Such fuel leads to unacceptable controllability of the chain reaction-

high void reactivity, low Doppler stability, low delayed neutrons, etc.

• A rough measure of fuel quality: fission cross section f at ~ 100 keV

Analysis of TRU from LWR Analysis of TRU from LWR

Quality f(100keV)- barns Isotopes Total % in LWR TRU

High ~ 1 Pu239, Pu241,Pu238 54%

Medium ~ 0.1 Pu240 22%

Low ~ 0.01 Am241,Np237,Pu242,Am243 24%

This mixture of TRU can, indeed, be burnt in an FRBut the cost is too high

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• So we constructed an optimal fuel cycle to exploit hybrid’s advantage

• Minimizes total system cost:

– Burn as much TRU as possible in least expensive reactors - LWRs

• These would entail little extra cost- no new reactors must be

built!

• Use hybrid reactors only for the unburned residual

• This minimizes the number of expensive hybrids

• Only low quality TRU are left- residual cannot be burned in

an FR

• A symbiotic relationship - each reactor type does what it does best

– LWR- burns high & medium quality TRU cheaply and quickly

– Hybrid- burns very problematic material safely, but is only used for

the worst TRU that really need it

FR can’t burn very low quality fuel - only Hybrids canFR can’t burn very low quality fuel - only Hybrids can

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• First step: destroy 75% of TRU in LWRs

– Limited by physics: cross sections of ~ 25% of the isotopes are too small in

an LWR neutron spectrum (close to thermal) for destruction

• Thermal spectrum systems also destroy a much larger percentage of fuel in a

single pass- and virtually all Pu239

– Thermal cross sections of easily fissile isotopes are much larger in thermal

spectrum system

– Destruction of most TRU is rapid, significantly reducing time for destruction

– Easily weaponizable isotopes (Pu239, etc.) quickly eliminated in the first step

• The remaining 25% (think “sludge”) must be “incinerated” in a sub-critical

assembly for safety

– An inexpensive, prolific external neutron source is needed- fusion!

– This system does not have any breeding, so no new TRU waste

(proliferation hazard) is created in this step (unlike FRs)

That is if we have a fusion driver

How Optimal?How Optimal?

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New hybrid fuel cycleNew hybrid fuel cycle

ReprocessLWR: Uranium

Oxide FuelLWR: Uranium

Oxide Fuel

Reprocess

ReprocessLWR: Inert LWR: Inert Matrix Fuel (IMF)Matrix Fuel (IMF)

LWR: Inert LWR: Inert Matrix Fuel (IMF)Matrix Fuel (IMF)

Fission Fusion Fission Fusion HybridsHybrids

Fission Fusion Fission Fusion HybridsHybrids

SpentFuel

Trans

uranics

Unburned TRU

FissionProducts+1% TRU

Hard-to-burn TRU

No

Pu239

Remaining 25%

Cheaper burn ~75%

GeologicalRepositoryGeologicalRepository

50%burn

Fission products

Fission products

UT Proposal: IMF-LWRs & Hybrids SybioticallyUT Proposal: IMF-LWRs & Hybrids Sybiotically

LWR: Uranium Oxide Fuel

LWR: Uranium Oxide Fuel

UOX Spent

Fuel (SF)Direct DisposalDirect Disposal GeologicalRepositoryGeologicalRepository

TemporaryStorage

ReprocessLWR: Uranium Oxide Fuel

LWR: Uranium Oxide Fuel

ReprocessFission-fusionFission-fusionHybridsHybrids

Fission-fusionFission-fusionHybridsHybrids

Spent

Fuel

TRU in

Fertile

Matrix

Spent

Fuel

GeologicalRepositoryGeologicalRepository

Generic Hybrid CycleGeneric Hybrid Cycle

Fission productsU, Fission products

Unburned TRU

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• Isotopes which grossly dominate the long lived biohazards of fission waste

are in not destroyed in the first LWR step

– Pu242 half life 4 x 105 years

– Np237 half life 2 x 106 years

• Geologic disposal is difficult precisely because these specific isotopes

remain for such long times

– Example: DOE analysis of Yucca Mountain finds that:

these isotopes lead to surface radiation doses much higher than

allowed by any other man made source 2-4 x 105 years in future

• The fast spectrum incinerator is needed to eliminate these

makes acceptable geological isolation much easier to guarantee at long

times, which is why geological disposal is technically difficult

Why it is important to destroy the remaining 25% residueWhy it is important to destroy the remaining 25% residue

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UT-Hybrid vs Fission-only CycleUT-Hybrid vs Fission-only Cycle

Hybrid Route Fission-only

US Light Water Reactors 100 100

Fast-spectrum waste

destruction reactors4-6 37-56

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

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Reactor Requirements for Waste Reactor Requirements for Waste Transmutation for different schemesTransmutation 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 above all LWRs

(LWR equivalents)

19-28 19 28 15 4-6

FR cost = 1.5 LWR, Hybrid = 2 LWR

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• First hybrid based scheme with this advantage (to our knowledge)

• This advantage is more than enough to overcome the cost

disadvantage of individual hybrid vs an individual FR

The system cost advantage may be enough to overcome the other

disadvantages of the hybrid:

Complexity, stage of development, new failure pathways

• We turn to these drawbacks momentarily

This hybrid based scheme has a major This hybrid based scheme has a major system cost system cost advantageadvantage over an FR based scheme over an FR based scheme

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• Crucial technologies:

Fission:

– IMF fuels

– Commercial scale reprocessing for fast spectrum fuels

Fusion:

– Qualification of structural materials for 14 MeV neutrons

– Advanced divertor technology

– First wall technology with adequate tritium retention, erosion, surface

evolution, etc.

– Very long pulse system reliability (CD, control systems, profile control, etc.)

– Tritium breeding / processing at large through-put

• Each of these is “crucial”- without it, there is no attractive hybrid

– IMF is certainly not the most difficult or expensive technology to develop

The new scheme relies heavily on IMF fuel-The new scheme relies heavily on IMF fuel-but but manymany technologies are crucial technologies are crucial

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The challenge of making a hybrid The challenge of making a hybrid

a nearer - term taska nearer - term task

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• Many say:

– Physics easier, but engineering as bad or worse than pure fusion

– Licensing even harder than pure fission: complexity => new safety issues

Development of generic hybrids sooner than pure fusion unlikely

• Compare generic hybrid to US and EU FR programs

– FRs: expect ~15-20 years development before a commercial prototype FR

– FRs start with 60 years of experience with many FRs

• Fusion technology development is at least several times harder than FR-

It is contended that generic hybrids and pure fusion have similar and long time scales.

Generic Hybrids - Serious issuesGeneric Hybrids - Serious issues

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Fusion driver:• Complexity/availability

– A fission core is a collection of simple identical rods with coolant flowing past- compare that to a tokamak/stellarator

• Internal maintenance, with TF coils and vacuum vessel,– “Like disassembling a ship in a bottle”

• Damage from 14 MeV neutrons is greater than fission neutrons– Helium generation => more material degradation

• No engineering experience long pulse devices with fusion spectrum– Fast Fission spectrum reactors have 60 years of experience in

many devices

Fission blanket is connected to fusion driver:• Mechanically => new failure modes, difficult to certify safety in unlikely

accident scenarios• Magnetically => coolant flow impeded via MHD• Electro-magnetically => plasma disruptions cause mechanical EM

loads

Hybrid: Interacting fusion - fission systems Hybrid: Interacting fusion - fission systems

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Replaceable Fusion Driver ConceptReplaceable Fusion Driver Concept

• Due to SXD, the whole CFNS is small enough to fit inside fission blanket

• CFNS driver to last about 1-2 full power years

• It can be replaced by another CFNS driver and refurbished away from hybrid

• CFNS driver itself is small fraction of cost, so a spare is affordable

B A

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Replaceable Fusion Driver ConceptReplaceable Fusion Driver Concept

• Pull CFNS driver A out to service bay once every 1-2 years or so - at

the same time when fission blanket maintenance is usually done

• Refurbish driver A in service bay - much easier than in-situ repairs

B A

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Replaceable Fusion Driver ConceptReplaceable Fusion Driver Concept

• Put driver B into fission blanket

• This can coincide with fission blanket maintenance

• Use driver B while driver A is being repaired

B A

40

Replaceable fusion driver

• Driver replaced roughly yearly while fuel rods

reshuffled (neutron damage, availability)

• Damaged driver refurbished in remote

maintenance bay (maintenance, availability)

• Fission blanket is outside TF coils (coolant

MHD drastically reduced)

• Fission blanket is electro-magnetically

shielded from plasma transients by TF coils

(disruption effects greatly enhanced)

• Fission blanket is physically separate from

fusion driver (complexity, development time,

safety)

A new design concept: addresses all these issues in one strokeA new design concept: addresses all these issues in one stroke

We shall now spell out each one

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• Driver is only exposed to about one year of damage• In traditional hybrids/fusion reactors, components must be exposed for

about 3-4 years because the replacement time is so long• Fusion driver walls would be exposed to ~ 1 Mwyr/m2 (~ 30 dpa/300

appm He)- about what present fusion materials are expected to be able to handle

• This is much less than the ~ 6 MWyr/m2 requirement for a CTF to test pure fusion DEMO components

• With expected CTF availability of ~ 0.3, testing cycle times are– 3 years for hybrid CFNS– 20 years for DEMO

• Many testing cycles are possible for CFNS in 10-20 years, leading to much higher availability growth than the one cycle possible for CTF leading to DEMO

The availability/ neutron damage issues are tremendously ameliorated

Issue: Neutron Damage and Availability Issue: Neutron Damage and Availability

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• Driver is removed as a unit relatively quickly

• Refurbishment of a “spent” driver is done relatively slowly in a remote

maintenance bay

• Rapid inspection/replacement of components of the “ship in a bottle”

method- which we don’t know how to do- is avoided

Credible inspection/maintenance improves the credibility of high

availability

Issue: Maintenance of highly radioactive driverIssue: Maintenance of highly radioactive driver

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• Fission blanket power density is ~ 1 1/2 orders of

magnitude higher than pure fusion- MHD drag on coolant

could be a show-stopper 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 orders of magnitude from

standard hybrid configuration

MHD coolant effectsMHD coolant effects

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• The L/R time of the fairly thick, highly conducting TF is ~ 1

second (even with substantial holes to let neutrons

through)

– Disruptions as fast as ~ 1 ms

• TF slows down EM transients in the fission blanket which

arise in the plasma by orders of magnitude

Eddy currents and forces are reduced orders of

magnitude

Electromagnetic disruption effects on blanketElectromagnetic disruption effects on blanket

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• Failures that arise inside the complex fusion driver do not directly

affect the fission blanket

• The fission blanket can consist of conventional fuel rods

– Much of fission FR technology can be used by hybrid- speeding

development

• Licensing safety analysis is tremendously simplified

• The fusion driver has no fission products/TRU in it

• It can be designed/developed/tested/qualified into a reliable unit

without having fission hazards which would tremendously slow

development

Physical separation of Driver and fission blanketPhysical separation of Driver and fission blanket

46

• The new hybrid is technologically much more credible

Together with the advantages of the IMF-hybrid fuel

cycle,

the new hybrid emerges as a potentially

attractive and credible endeavor

New Hybrid versus Generic Hybrid New Hybrid versus Generic Hybrid

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• Development of a hybrid would tremendously advance

fusion technology - hybrid-fusion are symbiotic

The performance/cost of a hybrid improve as the

physics and technology improves towards the

requirements of pure fusion

The requirements for initial operation of this hybrid are

low enough that a substantially quicker application

of fusion may become credible

Hybrid in the context of fusion reasearch - Hybrid in the context of fusion reasearch - an intermediate milestone an intermediate milestone