[ RadSafe ] Chinese fast reactor starts supplying electricity

[Brennan, Mike (DOH)]

I am not a liquid metal reactor guy: I am a light water reactor guy (in
fact, I am a pressurized water reactor guy, as I consider boiling water
reactors to be anathema).  As I understand it, the reason for using
liquid metals is the high Z atoms reflect high energy neutrons without
absorbing as much energy as something with low Z, such as hydrogen.
There are applications where high energy neutrons work better than
thermal neutrons, such as breading fissile material in U238 or Th232.
There are also applications that allow for much higher power densities,
which is why they have been looked at for shipboard use, despite their
obvious drawbacks.  I believe sodium is used because of its melting
point is at a useful temperature and it has an acceptably low fast
neutron absorption cross-section, and because it isn't very dense (the
other molten metal coolant I've heard of is lead-bismuth, which has to
be difficult to work with just because of the weight).  

I understand that when you have a really neat idea, such as breeding
more fuel than you use, it is tempting to focus on that, and downplay
the challenges.  But tons of molten sodium, flowing through pipes, being
moved by pumps, and passing though a heat exchanger, perhaps with WATER
on the other side of the tubes.  Dang.       

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Peter Miller
Sent: Wednesday, July 27, 2011 4:34 PM
To: radsafe at health.phys.iit.edu
Subject: Re: [ RadSafe ] Chinese fast reactor starts supplying
electricity


> I can take rad in stride, but tons of molten sodium, surrounded by
> water, would make me nervous.  

Why was liquid sodium selected as the coolant ?

It was a sodium leak that caused the shutdown of Japan's Monju
fast-breeder 
reactor in 1995. Plant operators tried to cover up the accident, which
didn't 
help their credibility, but did ensure continued shutdown. The spent
fuel rods 
that were supposed to be re-processed at Monju remained at Fukushima,
making 
that accident worse than it would have otherwise been. 

As for the Chinese fast-breeder reactor, one hopes they will do better
than 
they've done with high-speed trains. 

-- Peter Miller
   Kamakura, Japan

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