Re: Pyrochemical N-waste reprocessing


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Alessio wrote:
Hello.

I'd like to understand what is the actual state of the art of "dry"
nuclear
waste reprocessing
systems like pyroprocessing,expecially those who can deal with oxide
fuel
(for example at Russian RIAR).What are their efficiency in extracting
actinides,for example U or Pu and MA in/out and their typical
decontamination factors? What their typical size/footprint ? What about
their estimated cost?

Cost is cheap, but inertia of aqueous processing plants is big,
considering they're big government projects. Another problem is that
pyroprocessing methods dont do Pu extraction well, and most
reprocessing plants are tied to MOX fuel production.

Can you explain me more deeply the features of a such plant: size,estimated
costs and in particular efficiencies of actinides extraction?In some docs I
read for example that IFR pyroprocessing sistems aren't capable of
extracting curium,is it true?What about RIAR or other oxides pyroprocessing
systems?

What do you mean for "inertia" of aqueous reprocessing?

My own idea is,instead to re-burn them in fast reactors (see integral
fast
reactor program) that are costly to buil and difficult to operate with
multiple recycles (I suppose due to low burn-ups achievable),to burn Pu
and
minor actinides in very high burn-up (e.g. > 700 MWg/kg HM),good
neutron
economy thermal reactors with only one reprocessing (pyroprocessing)
cycle.

Bad idea. Use fluid fuel reactors of some sort, like molten chloride
reactors, to continuously process the fuel for better neutron economy,
as well as better economics over all. Essentially all liquid metal
reactors are economic losers, and IFR itself got way more attention
than it deserved. Good fuel processing process, overhyped uninteresting
reactor.

Don't misinterpret me,I'm a huge fan of molten salt reractor,but they aren't
now in costruction or commercial operation;south africans instead will start
to built pebble beds in the next september.So then,I'm asking myself: "what
can we do with existing infractures - or next to build - to burn nuclear
waste actinides?".Forget for a while fast reactors,breeders,Ads accelerators
and of course molten salt reactors,altough I agree with you they are very
promising

If you read the docs I linked,PBMR could be IMHO (I'm not an nuclear expert)
a good start.Nearly all plutonium fissile is burned,an overall 70/80%
actinides eliminated in only one burn cycle,the rest is pu-242 IIRC or other
actinides of low toxicity and low military interst;the overall radiotoxicity
is not so higher than uranium ore in a few century.Of course it needs a
better fuel tecnology - higher burn-ups - developed in the past only in
small scale (but
it still exists!) and an intelligent loading,but it's not impossible
It could a smarter strategy,politically and economically,instead of fast
breeders/IFR systems, but we need an efficient reprocessing to deal with
oxide fuels

You fuel the liquid chloride reactor with the Pu and other minor
actinides, and you ship all the uranium back to whoever wants it; Maybe
back to the enrichment plant, or direct for use in CANDUs. Fission
products themselves you separate for sale on the market, with a few kg
of garbage per GW year that no one will be able to use. Its a bit of an
improvement, 100tons to 100kg.

You'll have lots of excess neutrons to play with, so you might just
want to wrap thorium around it and breed U233 for sale as a LWR reactor
fuel or to fuel liquid flouride thorium breeders.

I think that pebble bed reactors developed in South Africa or generally
HTGR
based could have these features
http://www.technologyreview.com/read_article.aspx?id=12727&ch=energy
http://web.mit.edu/pebble-bed/Presentation/HTGR.pdf

Huh? PBMR's are interestingly inexpensive, but if you're concerned
about waste processing, they're no good at all. They produce higher
volumes of waste that is more difficult to take apart. Its real waste
advantage is direct disposal to dry storage without a cooldown period.

Pebble beds discharge less fuel than LWR reactors,because they use more
enriched uranium and they are more efficient (from neutron and
thermodinamic
point of view);the difference is only the large mass of activated graphite
as low
level waste (a typical triso sphere contains 10 grams of LEU and weigts 200
grams),not "more waste" as plutonium or actinides per unit of electricity
generated - it doesn't seem me a big issue;of course reprocessing TRISO fuel
is more costly than LWR assemblies.In my vision,at the begining we could
start to burn
LWR fuels in pebble beds/htr reactors at least together with low eneriched
uranium use ,after that HTR could burn burn its "own waste"








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