Radioisotope thermoelectric generator and health risks

[mrmcp1]

I am just interested in whether Radioisotope thermoelectric generator's are safe to humans and the environment. In KSP I usually just put a few RTG's on the side of my rover to power it and was wondering if to humans it would be safe for them to be in close proximity to an RTG.

I have no idea if I have put this under the correct prefix.

Thanks

[xenomorph555]

Pu-238 releases alpha radiation if I am correct and is therefore mostly safe. Most of the probes using it are going to places no-one is ever going to so it's fine.

[SargeRho]

They have very little shielding requirements, as they only emit alpha radiation assuming it's a Plutonium-238 powered one. The space suit of an astronaut and the hull of a ship is more than adequate to shield against that. The Apollo missions were at least partially powered by RTGs.

[mrmcp1]

Thanks, i thought that they were safeish, do you think the casing of the RTG would be thick enough to absorb the alpha particles?

[SargeRho]

Yes, the case will probably absorb most of the alpha particles, at least it can be built to do so. But I'm not an engineer. Nibb can probably answer that one better.

[SuperFastJellyfish]

Thanks, i thought that they were safeish, do you think the casing of the RTG would be thick enough to absorb the alpha particles?

IIRC, alpha radiation can be absorbed by a sheet of paper or a tee shirt so I would say yes.

[Creature]

It's a huge particle (a helium nucleus) and can only travel a few centimeters in air. On skin it's mostly absorbed by the outer (dead) layer of the skin so it's very safe in that regard. The only problem is if you're exposed to an alpha active substance so that it gets inside your body, the high energy in the particles will cause massive damage to your DNA. This is usually the real danger when working with any radioactive substances.

So to answer your question, it's safe as long as it's kept inside the casing. On a planetary scale a single RTG isn't an environmental hazard but the plutonium inside is a terrible poison if it gets into contact with anything living.

[mrmcp1]

Thanks for the reply's its a good point that they can be very dangerous if it gets into the body.

[PakledHostage]

An interesting side note is that NASA policy required MSL "Curiosity" to be launched in daylight because it carried RTGs. Ref: Mars Science Laboratory Mission Design Overview. They were also restricted from using a launch trajectory that overflew major population centres in Africa. If I remember correctly, they were even required to have contingency plans in place to retrieve the RTGs within a fixed period of time should they come down on land after a failed launch.

[lajoswinkler]

RTGs, even if they're powered by Pu-238 (which is not a strong penetrative-ionizing source, it spits out mostly helium nuclei), are not safe for humans, regarding the rays only.

For a 100 watt unit, it goes as high as 27 milisieverts per hour in the immediate proximity. That's 27,000 microsieverts per hour. There are environments on Earth's surface where radioactivity doses are almost 100 microsieverts per hour, but this is more than 100,000 times higher than average background radiation.

It's safe to say it would be a bad idea to live in the same room where the unshielded source is. Short manipulation, like putting the unit inside a rover would not pose a problem, but prolonged exposure is a no no.

If the source was Cs-137 or Sr-90, the danger would be immense because they irradiate with a lot more gamma and beta rays.

Radiologically speaking, all of them are completely fine unless the casing is not opened. If you open the case and there's plutonium dioxide pellet inside, you're pretty much ok because that's a ceramic material. Caesium would come as a chloride, which is soluble in water and hygroscopic, thus the potential for dispersal is enormous.

Edited July 2, 2014 by lajoswinkler