1 a fission-fusion hybrid for waste transmutation m. kotschenreuther, s. mahajan, p. valanju - inst....

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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

experiments operate reliably (tokamaks & spherical tokamaks)

Conservative Core Physics DemandsConservative Core Physics Demands

DeviceDevice Normalized Normalized confinement Hconfinement H

Gross stability Gross stability NN

power / power / heating powerheating power

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

11 < 3< 3 < 0.1< 0.1

Today’s experiments-Today’s experiments-

Advanced operationAdvanced operation< 1.5< 1.5 < 4.5< 4.5 < 0.2< 0.2

Hybrid CFNS- FNF Hybrid CFNS- FNF 11 2-32-3 0.330.33ITER- basicITER- basic 11 22 22ITER-advancedITER-advanced 1.51.5 < 3.5< 3.5 1-21-2““Economic” pure Economic” pure fusion reactorfusion reactor

1.2 -1.51.2 -1.5 4-64-6 4-104-10

-only because Super-X divertor allows high power density without degrading the core

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• “ITER in vessel components generally utilize materials, coolants and operating

temperatures that do not extrapolate to reactor (or hybrid) conditions”

• A Fusion Nuclear Facility FNF will be needed to demonstrate availability

growth before either a pure fusion reactor or a hybrid

• US and EU teams are developing normal coil FNF designs based on ST and

tokamak

– Normal coils - a much more easily maintainable system- for high duty factor

operation

– Device capitol cost- thick shielding of superconductors makes a device much larger

at modest power levels ~ 100 MW (R = 3 - 4 meter vs 1.4-1.9 meter for normal coils)

• We propose using nearly the same design as the FNF as a driver for the

hybrid- since the same advantages apply

– Coil electricity requirements- much less important with a high fission power boost,

and a high support ratio of hybrids to LWRs (fusion ~ 0.2% of system power)

Fusion development pathFusion development path

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• FNF is the first device in the fusion development path to

have an overall duty factor higher than the low percents

• Present goal of FNF- 30% availability (considered a

challenge even with normal coils!)

• Fission plants have an overall duty factor ~ 90%

• How might an early generation hybrid have a high plant

duty factor?

Duty factor is the key challengeDuty factor is the key challenge

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• Fastest maintenance- replace components as large modules, and service

them off-line

– ARIES-ST- replaced the 4000 ton fusion core (1st wall, blanket & centerpost) as a

single unit

– Culham ST reactor study- replaced 800 ton centerpost

– Entire CFNS weight is ~ 400 tons (drained)

• Could replace CFNS components as a small number of modules or even

as a single unit

Use maintenance advantages of Use maintenance advantages of compact normal coil devices compact normal coil devices

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Replaceable Fusion Module ConceptReplaceable Fusion Module Concept

• Whole CFNS is small enough to fit inside fission blanket

• Fission blanket is separate from fusion driver

B A

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Replaceable Fusion Module ConceptReplaceable Fusion Module Concept

B A

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Replaceable Fusion Module ConceptReplaceable Fusion Module Concept

• Put driver B into fission blanket

• 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)

• Fission blanket is outside TF coils (coolant MHD drastically 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

– Operation below No-wall stability limit

– Operation well below density limit

– Operation with low plasma radiation

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• Rough gross metrics normalized to ITER = 1

Disruption severity- relativeDisruption severity- relative

DeviceDevice CFNSCFNS ITERITER Pure fusion Pure fusion reactorreactor

Heat load - divertor Heat load - divertor

(MJ / m(MJ / m22 wetted area) wetted area) ~1/7~1/7 11 44

Heat load- main chamber Heat load- main chamber (MJ/m(MJ/m22 1st wall area) 1st wall area)

11 11 44

Electromagnetic stresses Electromagnetic stresses (in materials) (in materials)

~1/5~1/5 11 11

- CFNS main extrapolations: steady state and SXD

CFNS gross parametersR (m) 1.35

A 1.8

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PCD (MW) 50

ne (m-3) 1.3-2 x 1020

neutron 1.1 MW/m2

ne (m-3) 1.2-2 x 1020

n/nG 0.14-0.3

15-18%

Ip (MA) 10-14

Bcoil 7 T

Bplasma 2.9 T

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Summary Summary

• UT hybrid scheme- uses plasma confinement schemes with the most

highly developed physics basis - tokamaks and spherical tokamaks

• Super-X divertor allows operation in regimes with conservative physics

and low disruptivity

• Employ the fusion driver as a replaceable module to enable higher

availability with a nearer term stage of fusion technology development

• Fission blankets outside the TF coils enormously decouples the fission

and fusion elements- speeding development and reducing safety issues

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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 for MAST Upgrade

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Plasma Issues Plasma Issues

• Reliable long pulse operation (high availability) with current drive and very low disruptions

– In the coming decade, experiments will address this:

– Tokamak - K-STAR, EAST- long pulse

– Spherical tokamak- NSTX/MAST upgrades

• RF current drive- how to drive a current profile with adequate MHD stability?

– Consider same technologies as ITER- ECCD, FW, NBI

– ECCD: most desirable- 2nd or 3rd harmonic is accessible-also EBW?

– Ion Cyclotron- High Harmonic Fast Wave

– Neutral beam- very undesirable for hybrid- avoid large penetrations of fission blanket

• Selenoid free start-up

– ~50 MW of EC should make this possible

• Plasma facing components for ~ 1 year exposure

– Lithium in porous substrate- promising possibility- NSTX?

• Density control for ST operation at low Greenwald

– Lithium pumping in NSTX and cryo-pumping in MAST

• Super-X Divertor Testing- MAST, NSTX, DIII-D, SST- others?

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• Properties and reliability of components damaged by 14 MeV neutrons

– High He generation

– Walls, magnets, RF antenna/wave guides, etc.

• Tritium retention/diffusion in CFNS components

• Maintenance:

– Can all coolant/power lines be from above/below for easy CFNS removal?

– How low can the CFNS replacement time be?

• Development of high current power supplies/bus for the magnet

• Magnet design window for neutron damaged Cu and Al

• Plasma disruption forces on CFNS and fission blanket

• PFC and fusion component cooling

Fusion Technology IssuesFusion Technology Issues

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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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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

DeviceDevice size extrapolation size extrapolation (factor x) (factor x)

B extrapolation B extrapolation (factor x) (factor x)

From NSTX-U and From NSTX-U and MAST-U to CFNS/CTFMAST-U to CFNS/CTF

1.61.6 2.52.5

From JET/JT-60U to A = From JET/JT-60U to A = 2.5 CFNS2.5 CFNS

0.60.6 1.51.5

From JET/JT-60U to From JET/JT-60U to ITERITER

22 22

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Time ScalesTime Scales

• US Plan for the development of fusion energy- CTF operating in 2023

• UK- ST-CTF operating in 2026

• Three independent groups working on CTFs world wide, to deliver ~ 1 MW/m2 in the

time frame above:

– ORNL- Spherical tokamak (ST)

– General Atomic- advanced tokamak

– Culham- Sherical tokamak (ST)

• Since the CTF is nearly identical to the CFNS, we presume a CFNS can be built ~

2025

• Based on schedule for CTF, and the easier materials requirements of CFNS,

estimate ~ 5-10 years operation to attain acceptable availability

• Then, fission blanket could be added ~ 2030-2035 for the hybrid DEMO

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SXD-allows lowish plasma density SXD-allows lowish plasma density so there are several current drive optionsso there are several current drive options

• Current drive efficiency appears adequate from a number of drivers

– ECCD or EBW - highly desirable - no access from side needed, antennas are

protected (Current drive efficiency estimated by A. Ram, B. Harvey)

– HHFW - no access from side, well developed CW sources- but large antennas

(Current drive adequate from literature calculations for STs)

– Beams- least desirable- side access needed through fission region

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• Rates per full power year

Neutron damage ratesNeutron damage rates

Dpa He appm

First Wall (steel) 17 121

Vacuum Vessel 9 23

Fission blanket wall 9 7

Divertor Plate 2 16

Al TF front face 42 18

Al TF back face 17 20

Cu center TF 6 18

Tritium breeding ratio = 1.3

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• Monte Carlo neutron

codes (MCNP) used to

calculate nuclear

performance

• Assistance from nuclear

engineers on fission (UT)

and fusion (UCLA)

• Destroy waste from 100

LWRs using only 4-7

hybrids

– and using same LWRs

– Several times less fast

spectrum reactors than

fission-only methods

Use neutron codes to calculate transmutation potentialUse neutron codes to calculate transmutation potential

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SXD allows desirable physics SXD allows desirable physics and engineering for CFNSand engineering for CFNS

• With SXD:

– low input power, low

radiation, H-mode

confinement, low heat

flux

• Without SXD, to

“save” the divertor

– high density, high

input power, high

radiation (~ 90%),

unacceptable wall

heat flux