Do Nervs pollute the atmosphere?

[KerikBalm]

On 12/25/2015 at 8:50 AM, MarvinKitFox said:

At full operating thrust, the engine emits a fast neutron flux of about 2 * 10^14 neutrons per square cm per second, at a distance of 3 meters outside the unshielded motor casing.

Even ignoring the gamma flux, this is a 100% lethal dose of neutrons in 1/8600 of a second!!!!!!!!!

Or a lethal dose in ONE SECOND at a range of 300m

I wonder what the radiation intensity would be at the end of a burn after the reactor has been shut down. It will surely be much lower, but after repeated use (as in refueling a tug), the reactor itself will be quite radioactive even when not operating... how much shielding/distance is needed then?

[MarvinKitFox]

19 hours ago, KerikBalm said:

I wonder what the radiation intensity would be at the end of a burn after the reactor has been shut down. It will surely be much lower, but after repeated use (as in refueling a tug), the reactor itself will be quite radioactive even when not operating... how much shielding/distance is needed then?

Once a reactor is shut down, the problem is greatly simplified.

A shutdown, intact reactor is only really dangerous as a gamma source. And that gamma flux is 10^6 or more weaker than the operating levels.

Remember that, as a rough rule of thumb, each 1mm of lead shielding will halve the gamma passing through it. (varies by gamma energy, of course)

 

A ship could park a few tens of meters away, and its normal shielding against space radiation will keep it safe.

The nuclear rocket itself will almost ignore the residual radiation, as it already has shielding to handle millions of times that output.

 

Maintenance becomes problematical, of course. The reactor core and casing will become so radioactive as to quite preclude on-site work by human or electronic-operated tools. You would need to use long, mechanical devises, etc... Better design it to never need maintenance.

 

In most cases, reactor radioactivity is only a problem when there is a possibility of some actual material passing from it to the environment.

The nuclear thermal reactor is almost the exception to this rule, as under operation it output ludicrous amounts of radiation, *and* one simply cannot afford to encase the core in a thousandth of the shielding you would normally want to, due to mass/weight restrictions.