Probably a stupid car question...

[kandrathe]

On a (slightly) unrelated note, just how dense does the shielding have to be to impart Bremsstrahlung from Nitrogen-16 decay? I mean, just how energetic is that beta particle event?

From Wolfram|Alpha... Nitrogen 16. During its decay back to O16, it gives off 5-7 MeV high energy gamma radiation. From Wiki, "Condensate from the condenser is typically retained for 10 minutes to allow for decay of the 16N. This eliminates the need to shield and restrict access to any of the feed water piping or pumps."

For gamma / neutron radiation, here is source for computing necessary shielding.

I still believe it is possible with better engineering. For example, Toshiba has developed a 10MW compact reactor measuring 20 feet x 6 feet. I like the part where they use U238 as a part of the shielding, but over time it becomes enriched and contributes to the total fuel - an ingenious type of breeder reactor. A little too big, and far more power than is needed for a car sized vehicle (150 Kw). So, not an easy proposition to scale this down to 1/66 the energy output, and size by 1/10, but hardly the stuff of science fiction.