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FrostyAcanthocephala t1_j5sm9xt wrote

Reply to comment by Shrike99 in NASA to test nuclear thermal rocket engine for the first time in 50 years | CNN by dem676

Right. Fresh fuel isn't dangerous. /s

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Adeldor t1_j5tjf6q wrote

He's more or less right. In its pure form it's as much dangerous from its heavy metal qualities as it is from radiation, hence the person holding this 90% pure plutonium puck wearing gloves.

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FrostyAcanthocephala t1_j5tkjqp wrote

Yeah, that photo doesn't tell me much about the relative dangers. I get that it's fairly safe in a puck as an alpha emitter, but that's not really the danger we are discussing, is it?

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zypofaeser t1_j5un2ng wrote

Just uranium. Like, what is found naturally all over the place.

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Adeldor t1_j5tm2oh wrote

Referring to the earlier comments, I think it is what we're discussing - the pure "unburned" form being relatively safe.

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Shrike99 t1_j5wqvjj wrote

I mean nuclear fuel is typically comprised of uranium-235 and uranium-238, both of which occur naturally and can be found in low levels within all rock, soil, and water. Soil for example contains about 12 milligrams of uranium per kilogram on average.

A typical space-based fission reactor contains abut 30 kg of uranium. If a rocket blew up halfway through the launch and scattered that perfectly over a radius of say 50km, and it was all absorbed by just the top 1cm of soil, that would amount to an additional 0.3 milligrams of uranium per kilogram of soil.

Of course, if it spread over a smaller area the concentration would be higher, but it would have to be a pretty small area for there to be enough to matter, so it's not likely to be a major hazard in the grand scheme of things.

 

In practice it's more likely that the fuel rods would remain largely or entirely intact and end up at the bottom of the ocean somewhere. The ocean contains approximately 4 billion tonnes of uranium, so even if the fuel rods were gradually eroded, they'd quickly be diluted into irrelevance.

Now, there are some ways that it might be possible for someone to be exposed to a dangerous quantity - for example, say something like a gram of uranium being chipped off and somehow ingested by someone, my point is more that it's not going to be a widespread ecological disaster.

Whereas in the case of a disaster like Chernobyl, there were a lot of nasty isotopes present in the partially spent fuel rods, most notably iodine-131, caesium-134, caesium-137 and strontium-90. These isotopes are tens of millions of times radioactive than uranium-235 or uranium-238, so even the most miniscule quantities are dangerous.

I'd also point out that we already regularly launch other dangerous substances on rockets. Hydrazine for example has comparable toxicity per milligram to uranium, and large satellites are regularly launched with literal tonnes of that onboard.

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