Hybrid fusion fission reactor prospects

[ensabah6]

since fusion is not commericially feasible, does hybrid fusion fission reactor change that?

http://www.nature.com/nphys/journal/v5/n6/full/nphys1288.html

With the increasingly urgent need to find solutions to the impending energy crisis, there is growing interest within the fusion community in revisiting the concept of the fusion–fission hybrid reactor. But how soon could such reactors be realized, and could they meet the challenges of the coming century?

http://www.newscientist.com/article/mg20527505.900-hybrid-fusion-the-third-nuclear-option.html

Hybrid fusion: the third nuclear option

 

[Astronuc]

It would depend on how much energy is generated (more importantly recovered) from the fusion process. If the majority of thermal energy originates from fission, there is not much point adding a fusion process to the system. Fusion would only add to the complexity and capital cost.

We can already build fast or thermal breeders for utilizing fissile/fertile resources, which themselves are finite.

 

[HotCells]

In 2006 we published an article on this topic in the Lect. Notes. Phys. 694 (Springer, Berlin Heidelberg 2006). The book is entitled: Lasers and Nuclei: Applications of Ultrahigh Intensity Lasers in Nuclear Science. The full contents of this book are online at...
http://www.springerlink.com/content/v31121251rh7/

The title of the article is "Potential Role of Lasers for Sustainable Fission Energy Production and Transmutation of Nuclear Waste" http://www.springerlink.com/content/9803n15542276654/fulltext.pdf.

The basic idea here was to use very high power lasers (which are currently being developed in Europe and the US) to produce large numbers of neutrons through laser induced fusion of D-T. The neutrons could then be pumped into a nuclear reactor to produce power or transmute nuclear waste. The big advantage of the approach is that long before "engineering breakeven" can be obtained in fusion reactors, one will have "scientific breakeven". This scientific breakeven is enough to generate large neutron fluxes which can then be used in fission reactors. More information can be found at http://www.nucleonica.net.

 

[mheslep]

In 2006 we published an article on this topic in the Lect. Notes. Phys. 694 (Springer, Berlin Heidelberg 2006). The book is entitled: Lasers and Nuclei: Applications of Ultrahigh Intensity Lasers in Nuclear Science. The full contents of this book are online at...
http://www.springerlink.com/content/v31121251rh7/

The title of the article is "Potential Role of Lasers for Sustainable Fission Energy Production and Transmutation of Nuclear Waste" http://www.springerlink.com/content/9803n15542276654/fulltext.pdf.

The basic idea here was to use very high power lasers (which are currently being developed in Europe and the US) to produce large numbers of neutrons through laser induced fusion of D-T. The neutrons could then be pumped into a nuclear reactor to produce power or transmute nuclear waste. The big advantage of the approach is that long before "engineering breakeven" can be obtained in fusion reactors, one will have "scientific breakeven". This scientific breakeven is enough to generate large neutron fluxes which can then be used in fission reactors. More information can be found at http://www.nucleonica.net.

I don't see the point of a hybrid that expects little or no energy from the fusion side. Why are fission reactors in need of an external/additional neutron flux? If the fuel is fissionable, sufficient neutrons are produced via fission. If the fuel is merely fertile (e.g. U238), then breeders answer.

 

[HotCells]

I don't see the point of a hybrid that expects little or no energy from the fusion side. Why are fission reactors in need of an external/additional neutron flux? If the fuel is fissionable, sufficient neutrons are produced via fission. If the fuel is merely fertile (e.g. U238), then breeders answer.

It's a question of timing. Maybe in the long-term we will have pure fusion systems working.

...but pure fusion is still some way off. Before a fusion reactor becomes available (at engineering breakeven) powerful neutron sources will become available based on the inertial laser fusion systems with D-T fuel.

A major problem with fission reactors is the so-called neutron economy. There are just not enough neutrons available due to neutron poisoning by fission products. This is why the fuel must be periodically removed from the reactor and be replaced by fresh fuel or reprocessed to remove fission products.

The basic idea of the hybrid system proposed is to take the best properties of each system and combine them. Thus inertial fusion systems are good at producing neutrons - and fission reactors have already been built and are in use.

hope this helps.

 

[mheslep]

A major problem with fission reactors is the so-called neutron economy. There are just not enough neutrons available due to neutron poisoning by fission products. This is why the fuel must be periodically removed from the reactor and be replaced by fresh fuel or reprocessed to remove fission products.

Well there are several reasons why fuel must be removed periodically. Given these reasons, you contend that an additional neutron source could extend the life of existing fuel rods and burnup percentage?

 

[HotCells]

Well there are several reasons why fuel must be removed periodically. Given these reasons, you contend that an additional neutron source could extend the life of existing fuel rods and burnup percentage?

Yes. Fission reactors need to be critical. As soon as they go sub-critical, the reactor will switch off. Before this happens, new fuel must be intoduced into the system. Alternatively, one could use an external source of neutrons. Then one has a has a neutron driven sub-critical system. This is the basic idea behind accelerator driven systems (ADS). The so-called k_eff (neutron multipication factor) of the system (which should be 1 for a critical system) can be significantly less than 1. In accelerator driven system, the extra neutrons come from spallation using high energy protons. In the laser driven system (used in the fusion-fission hybrid proposal mentioned earlier), the neutrons come from laser dirven fusion of D-T. In such an LDS, values of the k_eff of 0.7 and lower are conceivable.

 

[mheslep]

Yes. Fission reactors need to be critical. As soon as they go sub-critical, the reactor will switch off. Before this happens, new fuel must be intoduced into the system. Alternatively, one could use an external source of neutrons. Then one has a has a neutron driven sub-critical system. This is the basic idea behind accelerator driven systems (ADS). The so-called k_eff (neutron multipication factor) of the system (which should be 1 for a critical system) can be significantly less than 1. In accelerator driven system, the extra neutrons come from spallation using high energy protons. In the laser driven system (used in the fusion-fission hybrid proposal mentioned earlier), the neutrons come from laser dirven fusion of D-T. In such an LDS, values of the k_eff of 0.7 and lower are conceivable.

Yes it is clear how in isolation from other issues external neutrons can burn fuel what otherwise be a sub-critical system. It is not clear to me that there is an advantage to external neutrons in an actual light water reactor, as advantage depends on what limits the burn. Does fission product poisoning dominate the neutron absorbing control rods? Do other concerns drive the fuel rod replacement time, such as material fatigue and accumulation of fission product-volume?

Edit: To further illustrate, see this high burnup cladding research at Argonne, making the point that cladding material limits fuel rod life in these designs, not burnup.
http://www.ne.anl.gov/capabilities/ip/highlights/light_water_reactor.html