Transmutations of Actinides in Fusion-Fission Hybrids – a Model Nuclear Synergy ? Stefan Taczanowski Faculty of Energy and Fuels AGH University of Science & Technology Cracow , Poland AGH UST Cracow Poland FUNFI'2011 Varenna

Presentation Overview Problems of Nuclear Energy (fission based) Conclusions Results of calculations Analysis of selected properties of Fusion-Fission systems Problems of Fusion Systems vs. AGH UST Cracow Poland

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 AGH UST Cracow Poland

Tokamak vs. LWR and Mirror Sizes Tokamak (PPCS) 10 m PWR Mirror Tokamak size is giant, whereas a Mirror by size resembles rather an LWR AGH UST Cracow Poland 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 AGH UST Cracow Poland

Selected Data of Actinide Fissions (  delayed neutron fraction, number of neutrons per fission, η per absorption) 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 AGH UST Cracow Poland 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: and thus the k-source is: Therefore a decrease in the plasma Q (energy gain by fusion) proves easier achievable The point is that safety of the system depends on its remoteness from criticality 1 – k, not on 1 - k s ns > nns > n ks > kks > k for 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 successive generations n/(j) Properties of Fusion-driven Subcritical Systems AGH UST Cracow Poland

The burden of energy production is shifted from Fusion (plasma)-to-Fission (blanket) The Plasma Q  k trade-off in Fusion-driven Systems at fixed gross power of system QpQp k At realistic values of k the requirements regarding plasma Q p 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 AGH UST Cracow Poland

Superiority of 14 MeV neutrons over the 0.8 MeV ones, not mentioning 2 main natural nuclides 232 Th and 238 U, is particularly distinct for 241 Am, 243 Am and for 236 U – abundant in the spent fuel. Advantages of 14 MeV neutrons AGH UST Cracow Poland 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 Collapse  X-section:  k eff = 0.95 fission & tritium breeding zones void k eff = 0.89 X-section:  Model of its Melt-down AGH UST Cracow Poland 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 Incinerator are of the same power Nuclear heating in Fusion-driven System as compared with the one in Fusion Reactor is much more uniform sum   x,   neut R [cm] [MeV g] Power density per source neut. 0 FW Refl. / shield Fuel zone 1 Fuel zone 2 Fuel zone 3 AGH UST Cracow Poland

708090[cm] 100 R Reaction Rates per src. neut. E-7 E-8 E-9 E-10 E-11 [arb. units] DPA He H FDIFR Radiation damage vs. system radius Neutron induced radiation damage in the FDI as compared with the one in FR proves much less intense Both systems: the Fusion-driven Incinerator (FDI) and pure Fusion Reactor (FR) have the same power AGH UST Cracow Poland

* at the BOC **approximate Performance of Pu and MA Incineration [kg/yr]* 237 Np and 243 Am are most converted, to 238 Pu and 244 Cm respectively Transmutation can be satisfactory when its product is fissile (eg. 242m Am). Incineration of Pu (no U in the system) and of 241 Am is quite satisfactory The conversion of 237 Np "poisons" Pu (nonproliferation) 241 Am is most converted to 242m Am and 242g Am AGH UST Cracow Poland

CONCLUSIONS The 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. AGH UST Cracow Poland

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