[ RadSafe ] Graphite SWAG Answer - Helium on tubine?

[Jaro]

Dear Julian,

The PBMR will use fuel with an enrichment of 8% U-235 -- well below the 20%
limit for low-enriched uranium.
It is about double that of PWR fuel however, so the buildup of denaturant
Pu-238 will be correspondingly higher.
Also, reprocessing pebble fuel is waaaaay more challenging than reprocessing
the metal fuel of dedicated weapons-Pu production reactors. Even though the
fuel uranium oxide - hence theoretically manageable with the same chemical
process (PUREX) as ordinary powerplant fuel - the tiny particles are coated
with multiple layers of containment barriers, which are reportedly VERY
difficult to breach (by crushing, for example).

 Jaro
^^^^^^^^^^^^^^^^^^^^^



-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl]On Behalf
Of JGinniver at aol.com
Sent: Saturday, November 12, 2005 2:23 PM
To: hflong at pacbell.net
Cc: radsafe at radlab.nl
Subject: Re: [ RadSafe ] Graphite SWAG Answer - Helium on tubine?

In a message dated 12/11/2005 18:34:08 GMT Standard Time,
hflong at pacbell.net
writes:

Penner  said he expects metallurgy to enable direct turbine rotation by
superheated  helium
in a few years.


Howard,
the following link
_http://web.mit.edu/pebble-bed/papers1_files/PBReactors.pdf_
(http://web.mit.edu/pebble-bed/papers1_files/PBReactors.pdf)  is  to a
paper produced by MIT that describes the current state of development of
the
Pebble Bed reactor around the world.  It states that ESKOM  in  South Africa
is
currently developing a direct cycle gas turbine which will use  the helium
gas
circulating through the core to generate electricity without any
intermediate
heat transfer steps. You might also want to check out the IAEA  KNowledge
base
on HTGR technology at _http://www.iaea.org/inis/aws/htgr/index.html_
(http://www.iaea.org/inis/aws/htgr/index.html)

It may also be worth remembering that the core still uses slightly enriched
uranium, and that this can still be reprocessed to extract plutonium.  As
far
as I know the best hope for a fuel cycle that can't be used to produce
nuclear weapons is the Thorium to Uranium-233 fuel cycle.  I believe that
it was
only India that has worked on this option in recent years.

Regards,
    Julian

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