Re: Nuclear Power: Unsafe, Uneconomical, Unsustainable


"daestrom" <daestrom@xxxxxxxxxxxxxxxxxxxxxxxx> ha scritto nel messaggio
news:45c7ccf7$0$28134$4c368faf@xxxxxxxxxxxxxxxxx
I think that PBMRs may be a promising technology, although I am not
convinced that the safety case has been made unequivocally

The only drawback (or one of the few) I found in this design is that
pebble
beds are "inhertly" once-through from the reprocessing fuel point of
view.
In fact reprocessing TRISO fuel,if is possible,it's maybe very difficult
and
surely very expensive;this will not a big problem in the countries where
don't reprocess (like US),but anyway it looses a great energy potential


But IIRC, the burn-up levels for a pebble before discharged are much
higher
than conventional LWR fuel. If a typical LWR LEU bundle can be exposed up
to about 40 GWD/t, the pebble design is something like +90 GWD/t.

That's right

So how
much bad is being just 'once-through'? And why couldn't they be
reprocessed.

daestrom

I didn't say it's not possible,it's surely very difficult and expensive. At
least for a couple of reasons : the high strength of SiC triso kernel and
the low fuel to graphite ratio in the discharged fuel (a pebble sphere
weights 200 g and contains only 9 grams of LEU and thousand of "micro"
pebble). This paper well summarize the issues of triso fuels reprocessing
https://odin.jrc.nl/htr-tn/HTR-2004/B05.pdf
With current technology,in the better case, about 5 % of untouched particles
remains, inducing a lost of an equivalent quantity of uranium,during the
dissolution by the nitric acid. I can't say if some pyrochemical process can
improve overall numbers
Of course economics depend from the compositions of waste stream,for example
actinides produced per GWy or uranium enrichment at discharge,have you got
any data about this?
I repeat that in short term this is not a huge problem in countries don't
recycle nuclear waste

On the other hand it seems that PBMR is the best reactor (given high
burn-ups achievable) to burn plutonium and actinides exctracted from LWR in
a "once through" way,with no repetitive reprocessing (like for example in
"integral fast reactor" program)
http://www.iaea.org/inis/aws/fnss/fulltext/ictp2005_Gudowski_Trieste-2005_DB
..pdf
http://www.nea.fr/html/pt/docs/iem/jeju02/session6/SessionVI-12.pdf
http://aaa.nevada.edu/pdffiles/nov1104/leon.pdf
http://www3.inspi.ufl.edu/icapp04/program/abstracts/4038.pdf








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