C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Mon, 29 Dec 2008 20:15:12 -0300 (CLST)

While reading around about the Iranian enrichment plant at Naratz I
started wondering about the design of the centrifuges.  I had always
assumed that they would have a large radius (like, several meters)
(centrifugal force is proportional to omega^2 * radius, where omega is the
rotational velocity).

In fact it's quite possible to reach the physical limits of the materials
involved at just a few cm (10cm radius in Iran, I think) by using
sufficiently high rotation speeds.  Things are more complicated, because
what is being optimised isn't separation by one "small" rotor, but total
throughput in a cascade.  So it appears that the optimum design is a
vertical rotation axis, with a tall rotor and the physical limit to
rotation speed seems to be related to resonance (in a vertical mode)
rather than simple tensile strength (a centrifuge designed to operate
above the lowest resonant frequency - there are other modes at higher
frequency of course - is called "super-critical").

It's still not clear to me why it's not better to make more, shorter
centrifuges that have higher critical frequencies.  Part of the issue may
be costs associated with bearings and motors (which are per centrifuge and
so get cheaper with length).

Anyway, there's a very details report here -
http://www.pnl.gov/main/publications/external/technical_reports/PNNL-14480.pdf

One thing that surprised me was Argentina's appearance in the lists of
countries developing technologies.  I assume that was linked to the
military regime?  Scary local politics.

Andrew