Transmutations of Actinides in Fusion-Fission Hybrids –

a Model Nuclear Synergy ?

Stefan Taczanowski  

Faculty of Energy and FuelsAGH University of Science & Technology

Cracow 30 059, Poland 

e-mail: staczanowski@gmail.com 

AGH USTCracowPoland

FUNFI'2011Varenna 12-15.09.11

Presentation Overview

Problems of Nuclear Energy (fission based)

Conclusions

Results of calculations

Analysis of selected propertiesof Fusion-Fission systems

Problems of Fusion Systems vs.

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Selected Problems of the Fusion Power

1. Energy Balance

Size of the Fusion device

i.e. material inventory capital cost

Energy gain from Fusion: Plasma Q

capital & maint. cost

Tritium inventory

Tritium

2. Material Problems

Radiation Damage

maintenance cost

(DPA, Gas production, Plasma-wall interactions)

capital cost

Material consumption Size of the Fusion device

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Tokamak vs. LWR and Mirror

Sizes

Tokamak(PPCS)

10 m

PWR

Mirror

Tokamak sizeis giant, whereas a Mirror

by size resembles rather an LWR

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But in social perception more important is that Fusion Systems threat with no”atomic bomb” type explosion

Selected Problems of Nuclear Energy(fission based)

One of the most important ones is:

the Nuclear Waste i.e. Spent Nuclear Fuel

In particular its recycling is difficult due to:

1) its increasing Minor Actinides (MAs) component,2) a degradation of Pu

- both with recycling

due to the negative nuclear properties of MAs first of all of Transplutonics

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Selected Data of Actinide Fissions( delayed neutron fraction, number of neutrons per fission, η per absorption)

Nuclide

[%]

(thermal spectr.) η

0.025 eV fast* 232Th 2.4* 2.2* ~0 0.11 233U 0.4 2.5 2.29 2.34 235U

0.7 2.42 2.07 2.08

238U

1.7* 2.6* ~0 0.13 237Np 0.4* 3.0* ~0 0.82 238Pu

0.14* 3.1* ~0 2.06

239Pu

0.26 2.88 2.12 2.63 240Pu

0.30* 3.0* ~0 1.38

241Pu

0.55 2.9 2.17 2.70 242Pu

0.65* 3.0* ~0 1.13

241Am

0.12* 3.4* 0.02 0.56 242mAm

0.18 3.3 2.93 3.22

243Am

0.23* 3.5* ~0 0.68 244Cm

0.13 3.3 ~0 1.34

245Cm

0.16 3.6 3.12 3.33 246Cm 0.24* 3.7* ~0 1.07

*fiss.neutrons spectrum

Low values of ß for transplutonics hinder use of them in significant quantities in critical systems

Do we really need an exactly closed fuel cycle ?

Asking some questions

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Lack of uranium is not a threat in the near future But, to abandon recycling of great quantities of degraded Pu does not seem reasonable.For this purpose 14 MeV neutrons can be useful

Addressed to Fusion

Addressed to Fission

Do we really need a fusion option – with 100% of fusion energy?

MAs recycling might be given up ?

Is not enough: fusion confined to be the driving-source ? (key role!)

The number of neutrons born per src.n. in a source-driven subcritical system

is not n = k/(1-k) [thus k=n/(n+1)] but:

1 1j

j

iis kn and thus the k-source is:

1

s

ss n

nk

Therefore a decrease in the plasma Q(energy gain by fusion) proves easier

achievable

The point is that safety of the system depends onits remoteness from criticality 1 – k, not on 1 - ks

ns > n ks > kfor 14 MeV source

Thus, the additional neutron and energy multiplication is achieved in a safer way

Number of neutrons born from one 14 MeV neutron in successive generations vs. the generation number

2.0

0 20 40 60 80 100

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.2

j

n(j)

actual

k jeff

successive generations

i

j

ik

0

n/(j)

Properties of Fusion-driven Subcritical Systems

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The burden of energy production is shifted from Fusion (plasma)-to-Fission (blanket)

The Plasma Q k trade-offin Fusion-driven Systems

at fixed gross power of system

Qp

k0.0 0.2 0.4 0.6 0.8 1.0

0

10

20

30

At realistic values of k the requirements regarding plasma Qp can be significantly relaxed

(to ~0.2)

Earlier calculations have shown that in Mirror configuration about 5 fissions per source neutron can be achieved

(> 1000 MeV/n) [IAEA TEC DOC-1626 (2009)]

It signifies a reduction of needed energy gain from fusion by

factor of several tens thus, the 14MeV neutron yield

as well as the tritium demand

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Superiority of 14 MeV neutrons over the 0.8 MeV ones, not mentioning 2 main natural nuclides232Th and 238U, is particularly distinct for 241Am, 243Am and for 236U – abundant in the spent fuel.

Advantages of 14 MeV neutrons

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0.00.10.20.30.40.50.60.70.80.91.0

Th 90232

Pa 91231

U 92232

U 92236

U 92237

U 92238

Np 93237

Pu 94238

Pu 94240

Pu 94242

Am 95241

Am 95243

Cm 96244

Cm 96246

sig f

/(si

g g+

sig f

)

14MeV

0,8 MeV

Properties of Fusion-driven Subcritical Systems

Share of fissioning in absorption cross-section of fissible actinides for 14 MeV and 0.8 MeV neutrons

The assembly after collapse remains subcritical

CollapseX-section: z

keff = 0.95

fission & tritium breeding zones

voidkeff = 0.89

X-section: y Model of its Melt-down

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The great advantage Fusion Reactor improbability of super prompt criticality must not be lost in Fusion-Hybrid

Key Question of Fusion-Hybrid Safety

sum

Distribution of Nuclear Heating

x,

neut

Fusion-Driven Incinerator

Fusion reactor

Both Systems:Pure Fusion

and Fusion-Driven

Incineratorare of the

same power

Nuclear heating in Fusion-driven

System as compared with the one in

Fusion Reactor is much more

uniformsum

x,

neut

70 80 90 100 110 120R [cm]

[MeV g]

0.5-6

1.0-6

1.5-6P

ow

er d

ensi

type

r sou

rce

neut

.

0

FW Refl./shield

Fuelzone

1

Fuelzone

2

Fuelzone

3

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70 80 90 [cm] 100R

Rea

ctio

n R

ates

pe

r s

rc.

neut

.

E-7

E-8

E-9

E-10

E-11

[arb.units]

DPA

HeH

FDIFR

Radiation damage vs. system radius

Neutron induced radiation damage in the FDI as comparedwith the one in FR proves much less intense

Both systems: the Fusion-driven Incinerator

(FDI)and pure Fusion Reactor

(FR)have the same power

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93-Np-237 94-Pu-238 94-Pu-239 94-Pu-240 94-Pu-241 94-Pu-242 95-Am-241 95-Am-242m95-Am-243

Nuclides Inventories [kg]

Production Destruction(net)

565 2.8 115.4 112.6 24.4 190 91.2 33.6 57.6 - 23.5

3185 10.4 766.1 755.7 613.2 1831 152.7 180.9 28.2 79.7 781 101.1 269.1 168.0 202.5 784 44.0 60.2 16.2 24.4

1723 36.8 414.3 377.4 58.2 10 354.9 4.2 350.7** - 3.5

1390 36.3 284.4 248.2 36.3 Total 10460 830.0 2 128.0 1 298.1 1 065.7

Destruction (total)

Destruction (by fission)

5

4.265 4.6 48.4 4.6 5.6

Incin. meantime [yr]

* at the BOC**approximate

Performance of Pu and MA Incineration[kg/yr]*

237Np and 243Am are most converted, to 238Pu and 244Cm respectively

Transmutation can be satisfactory when its product is fissile (eg.242mAm).

Incineration of Pu (no U in the system) and of 241Am is quite satisfactory

The conversion of 237Np "poisons" Pu (nonproliferation)241Am is most converted to 242mAm and 242gAm

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CONCLUSIONSThe proposed fusion-driven transmutation concept provides a

feasible way of radical reduction in necessary plasma Q of the fusion reactor to levels achievable in much smaller systems.

Summarising, the development of Fusion can be significantly facilitated by its alliance with Fission.

It has been demonstrated that also the radiation damage can be radically softened in the Fusion-driven System.

E.g. the DPA and Plasma-Wall can be reduced at least by one order of magnitude whereas the gas production by factor of several tens.

Further optimising studies are needed, thus the research is continued.

Similarly – the tritium questions /breeding, inventory, reprocessing/ can be also effectively relaxed in the above option.

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Thank you for your attention