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So, breeders convert more fertile material into fuel than the fuel it consumes, but the reprocessing is expensive. Why is it that the fuel has to be taken out for reprocessing at all? Why can't the newly produced fuel be used directly?

Is it possible to design a reactor where fuel rods only have to be put in and taken out once--where the reactor continuously produces fuel from the fertile material and uses it up, until all the fertile material has been converted and all the fuel used up--and the spent fuel rod would be worthless and can be taken directly to disposal without reprocessing?

Joe0Bloggs wrote:So, breeders convert more fertile material into fuel than the fuel it consumes, but the reprocessing is expensive. Why is it that the fuel has to be taken out for reprocessing at all?

Mainly two reasons. Firstly at the enrichment concentrations allowed for civilian fuel the rods accumulate enough fission fragment waste over time that the breeding ratio falls below 1:1 and technically at that point they are high burn up converters, not breeders. Secondly if you use the fuel systems as currently used they can only maintain their physical integrity for a few years, as the Uranium/Plutonium/Actinides fission the fragments continue to build up. These chemicals are less dense than the heavy metals they derive from and hence require more space for the same weight of material. Once you have reached a certain pressure the fuel rods start to stretch, warp, or even crack open from internal pressure and gaseous or volatile fission fragments then escape into the primary coolant.

Why can't the newly produced fuel be used directly?

Well actually quite a bit of it is used directly, however when the fission fragments accumulate they are like ashes on a fire, they tend to smother out the reaction by absorbing neutrons.

Is it possible to design a reactor where fuel rods only have to be put in and taken out once--where the reactor continuously produces fuel from the fertile material and uses it up, until all the fertile material has been converted and all the fuel used up--and the spent fuel rod would be worthless and can be taken directly to disposal without reprocessing?

The short answer is no, provisionally. Instead of using solid fuel rods you can use molten salt as a fuel carrier and constantly separate out the fission fragments while the reactor keeps running 24/7 except for maintenance periods. A Molton Salt reactor consumes actinide metals and produces heat and fission fragments and is so efficient in its neutron economy it can operate as a breeder with Thorium/Uranium/Plutonium/Actinide in a constantly adjusted balance. If reactivity starts to fall the operators can just add fuel directly to the fuel flow channels bringing the reactivity back up. If you want more details simply google MSBR and MOSEL (Molten Salt Breeder Reactor and Molten Salt Epithermal Reactor).

Is it possible to design a reactor where fuel rods only have to be put in and taken out once--where the reactor continuously produces fuel from the fertile material and uses it up, until all the fertile material has been converted and all the fuel used up--and the spent fuel rod would be worthless and can be taken directly to disposal without reprocessing?

They don't use up all of the potential energy in the fuel, but pebble bed reactors do operate continuously as the pebbles cycle down to the bottom, and are just topped up. They are also modular which should reduce construction costs and interest.
http://en.wikipedia.org/wiki/Pebble_bed_reactor

CANDU reactors do not need to stop for refuelling either.

Any comments on the Canadian Slow Poke Reactor. http://www.cna.ca/curriculum/cna_can_nu ... d=Slowpoke

deMolay wrote:Any comments on the Canadian Slow Poke Reactor. http://www.cna.ca/curriculum/cna_can_nu ... d=Slowpoke

I read up on the Slowpoke 3 design back 15 or 20 years ago and thought it was great, the idea of having district heating without any GHG emissions really appeals to me a lot. Though initially designed to run on highly enriched U-235 (20%) the system could also operate on comparable levels of Np-237 or mixed Plutonium recovered from exposed MOX fuel assemblies that are deemed too poor in quality for use in LWR fuel recycle. Because the neutron spectrum is fast it does not need to be high percentage Pu-239/241, the Pu-238/240/242/243 all act as fuel in the fast spectrum a Slowpoke produces.

Basically research reactor style designs are fast burner reactors, if it is fissionable with fast neutrons these gems can use it for fuel. As designed none of them that I am aware of can be refueled, they are small and compact and when they are used up you haul them to a reprocessing plant and just replace them as a unit.

I just wanted to bump this topic as Climatologist (and peak oil advocate) Dr Barry Brooks of Adelaide University, Australia says that just today's nuclear waste could run the world for 500 years.

In summary, he believes:

* IFR’s eat today’s nuclear waste, and are the only way to economically solve the previous generation’s long lived nuclear waste!
* Instead of old waste being an expensive problem to guard for the next 100 thousand years or so, it becomes a fuel that could run the world for the next 500 years! Just the American waste alone would then be worth $30 trillion dollars!
* Nuclear waste from older reactors has to be stored for 100 thousand years, but after ‘burning’ in an IFR it is reduced to 10% of the mass and then only has to be stored for 300 years because it is so radioactive that it quickly burns itself out.
* 500 years of cheap baseload power is attractive in a world of peak oil, gas, and coal, and who knows what other energy alternatives we may have discovered and developed by then?
* If we started building IFR’s today, by the time we ran out of ‘normal waste’ to reprocess, the first few generations of IFR ’super-hot’ waste would have burnt themselves out and could be decommissioned from high security storage and be safe! That’s the nuclear waste problem solved!
* Even at lower concentrations of ore, the particles are so rich in energy that it becomes economical at some point to extract uranium & thorium even from seawater!

http://bravenewclimate.com/integral-fas ... ear-power/

Concentrated, baseload power as long as we need. As an activist for New Urbanism, I'm also a bit sad that I can see "Better Place" electric cars solving the long-distance drive problem with the 2 minute battery swap. (Filling up at your old fashioned petroleum station takes an average of 7 minutes).

Sha Agassi, the founder of Better Place, gave this presentation at a pivotal Australian conference, and claims he can sell electric km's at a fuel equivalent price of about $0.80 cents a litre. (Which is about 30 or 40 cents cheaper than petrol at the moment in Australia).

http://www.abc.net.au/tv/fora/stories/2 ... 656263.htm

Sure there will be horrible economic consequences for having left peak oil too late to adjust to smoothly, and sure we're probably going to face a Greater Depression as the rationing over the next decades kicks in, but by the time my kids are in their 30's I'm guessing society will be largely petroleum free and running on electricity, and that includes mining, agriculture (with nuclear synthesised fuels or maybe biochar syngas), electric airships (solar PV on the outside and maybe some backup hydrogen fuel on the inside... and yes I know hydrogen costs a lot of energy to make), fast rail, and hopefully... if we have half a brain, lots of New Urbanism.

(See this... my favourite summary of New Urbanism in 3 minutes. I hope Kunstler's seen this!)
http://www.youtube.com/watch?v=VGJt_YXIoJI

but there are problems caused by the fact that the Lead and Lead-Bisimuth alloys are very dense, which can cause erosion of the piping as they are pumped from the core to the heat exchangers and back.

Actually the erosion is related to the fact that lead dissolves iron. The solution to this problem is to induce continuous iron oxide formation on the pipe interior wall.

article link

One of the Soviet sub reactor designs based on lead-bismuth is now being commercialized for small scale applications.

Bellona link for LOLz

Russian press link

A lot of the data that Tanada presented in the early part of this thread was from circa 2006; has there been any significant updates on fuel availability, etc.? What's the industries "take" on Japan's moving reactors off-line and Germany's supposed interest in doing the same? (If it's off-topic I understand.)

thanks