Re: [Phys-l] Nuclear Power and the Grid

[Spinozalens@aol.com]

In a message dated 9/10/2011 9:52:24 P.M. Eastern Daylight Time,  
bernardcleyet@redshift.com writes:

On 2011,  Sep 10, , at 13:08, LaMontagne, Bob wrote:

> This may be an  incredibly simple minded question, but when the grid 
collapses, why is it  necessary to scram the reactor. Since the reactor 
generates steam for a  turbine, why can't it be vented out the cooling stack until 
the grid has  stabilized?
> Bob at PC


I thought JD answered this  --  that's what happened in Japan even tho 
they'd SCRAM'd before the  Tsunami arrived.  I assume the turbine steam is in a 
closed system, so it  can't be vented.  If it is, Water must be added 
continuously.    With additional heat exchangers it could instead be condensed.  
Question:  How much water is required to condense 300 degree steam when 
heated by 3,000  MW?
 
)))))))))))))))))))))
 
 
A shutdown 3000 MW  nuclear reactor would produce about 200 MW of heat  
immediately after shutdown primarily due to beta minus decay of fission  
products. Fission produces a lot of  neutron over rich isotopes. That's a  lot of 
heat, more than enough to raise the temperature to the melting point if  the 
heat isn't carried away. After about 10 days or so the decay heat will fall 
 to about 15 MW or so and stay that level for a very long time. The core 
stills  needs to be cooled but the it takes much less of a cooling system.
 
Worst case the same numbers apply to the LFTR. But the difference is  that  
after a shutdown the molten fuel drops into special tanks which are  
designed to passively carry away the decay heat. The fuel is already melted, so  
you have a meltdown and its OK  , that how it works.And you don't need  
diesels or electric power in any form to keep the fuel contained.  You do  need 
electric heaters to get the fuel molten again to restart the reactor after  a 
long period of shutdown.  
 
Bob Zannelli 



bc

p.s. one method of restarting would be to use a  small storage pond and 
turbine.  It could be an existing hydro-E  station.