AW: [ RadSafe ] [RadSafe]Mission to Mars---Fission Propulsion

[Jerry Lahti]

While the 1960s Nerva design had some crew compartment shielding, the main 
neutron shielding was provided by the liquid hydrogen propellant between the 
reactor and the crew compartment. The reactor operating time (and time to 
empty the hdrogen tank was about 30 minutes.  With that short of a run time, 
the buildup of fission products was small compared to an operating commercial 
power reactor.

This was indeed an interesting shielding analysis.

--
Jerry Lahti
Naperville IL


---------- Original Message -----------
From: "Bernard L. Cohen" <blc+ at pitt.edu>
To: Rainer.Facius at dlr.de
Cc: radsafe at radlab.nl
Sent: Wed, 01 Oct 2008 10:25:43 -0400
Subject: Re: AW: [ RadSafe ] [RadSafe]Mission to Mars---Fission Propulsion

> Rainer.Facius at dlr.de wrote:
> > Considering a mass shielding between the reactor and the astronaut 
compartment thick enough to shield sufficiently against neutrons and gammas 
emitted by the fuel, my guess was that only a very minor fraction of 
the 'soft' Bremsstrahlung photons from beta decays of the fission products 
would reach the skin. 
> >   
> One point missing from this extensive discussion is that the reactor 
> could be placed a large distance away from the people-- maybe even a 
> mile or more away (?) -- with a rigid rod connecting them. This 
> would greatly reduce radiation exposures and shielding requirements.
> 
> -- 
> Bernard L. Cohen
> Physics Dept., University of Pittsburgh
> Pittsburgh, PA 15260
> Tel: (412)624-9245  Fax: (412)624-9163
> e-mail: blc at pitt.edu  web site: http://www.phyast.pitt.edu/~blc
> 
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------- End of Original Message -------