transmutations of actinides in fusion-fission hybrids – a model nuclear synergy ? stefan...
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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: [email protected]
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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CracowPoland
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