Some background on this: NASA deep space missions have historically used radioisotope thermal generators powered by the decay of the exotic plutonium isotope Pu-238. This isotope has a good balance of lifetime (87.7 year half life) and specific energy (0.5 watts/gram). It is non-fissile -- no risk of criticality. It also decays solely by alpha emission, so there are no problems with shielding the rest of the systems from e.g. gamma or neutron radiation.
American plutonium 238 was formerly produced using Savannah River Site reactors that primarily produced materials for nuclear weapons. With the retirement of those reactors in 1988, and the American nuclear weapons program going to maintenance mode, NASA lost the side-benefit of Pu-238 production using the weapons infrastructure. Deep space missions requiring RTGs had to subsist off of historical Pu-238 stockpiles and additional material purchased from Russia. But the Russian supply has run out too now -- apparently they aren't producing more of it either.
American plutonium 238 production efforts resumed in 2013:
With NASA now paying the full cost, including fixed startup costs, Pu-238 is extraordinarily expensive:
NASA and DOE have estimated the rebooting will cost between $75 million and $90 million over five years. According to NASA officials, the agency expects to have 1.5 to 2 kilograms produced per year, starting 2018.
The high cost and limited supplies of Pu-238 have spurred the search for alternatives to Pu-238 RTGs. A few years ago I remember reading that the European Space Agency was going to try to design its own RTGs using the less powerful but more abundant americium 241 instead of plutonium 238. But a quick search just now doesn't show any concrete development effort.
This Kilopower reactor is an alternative to RTGs for some mission profiles -- in fact offers more power than RTGs and uses cheaper nuclear materials. (Highly enriched U-235 isn't cheap in an absolute sense, but it's far less expensive than Pu-238. And the security of supply is effectively backstopped by its use in reactors for the US Navy.) It can offer ample power for very deep space missions at a cost significantly less than using years' worth of Pu-238 production.
Improved photovoltaic cells have also enabled missions further from the Sun than they could have supported in 1988. The Juno mission, which entered Jupiter orbit in 2016, relies on PV instead of RTGs. It seems plausible that further evolution will eventually push PV's reach out to Saturn missions. But PV is not currently plausible for missions beyond Jupiter, and it is reliant on slowly-evolving battery technology for surface missions on Mars. Martian missions using PV also face significant problems from cell-obscuring dust. This reactor seems too large to be conveniently integrated in a Martian rover, but enabling non-surface missions to avoid Pu-238 use may mean more can be reserved for future rovers akin to the RTG-powered Curiosity.
The Kilopower reactor presents far lower radiological risks than RTGs in the event of complete disassembly within Earth's environment.
Pu-238 has a specific activity of 634 billion Bq/g, nearly 8 million times that of the Kilopower reactor's U-235 fuel (80 thousand Bq/g). Once the reactor attains criticality, it produces fission products that have even higher specific activity than Pu-238. But the reactor can remain safely inactive until the risky launch phase is over. There is no way to inactivate the decay of Pu-238 for the launch phase.
The risks of RTG launch are handled by using designs with high mechanical/thermal robustness to encapsulate the plutonium ceramic. I think that they were already safe enough. But the Kilopower reactor is inherently low-radiotoxicity before criticality, which makes it safer yet during the launch phase.
To simplify the other more detailed response, It's just Uranium at that point. Even highly enriched Uranium isn't that radioactive by itself, it's once you start operating the reactor that it starts generating highly radioactive waste.
The new fuel rods going into it are totally safe from a radioactivity perspective. Here's a picture of a man holding a fuel rod bundle with nothing more than gloves on. http://nuclearstreet.com/images/img/dw037.jpg
One can't help but notice from his shirt and his hair that the picture was taken in the 1970s. Lots of awful practices still existed then; who's to say this isn't a picture of that?
At all stages the material can be handled with no more protection than gloves. It is roughly as dangerous as handling lead fishing weights until the fuel actually attains criticality.
I don't know why people downvoted this, it's entirely correct. Although I guess the larger concern than the radiation would be the heavy metal poisoning but in any case it's still fine, just treat it like you would any other heavy metal.
The Soviets launched over 30 satellites with nuclear reactors in the past. The US also launched one. Most of them are still in orbit and I only know of one that scattered nuclear waste all over Canada.
Edit: it looks like there was one launch failure that ended in the reactor dropping into the ocean, and one end-of-life failure that also resulted in the reactor dropping into the ocean. However, normal procedure was to decommission them by boosting into a higher orbit, which means debris and radiation from them has been an ongoing problem for other satellites - i.e. radioactive droplets of sodium coolant.
American plutonium 238 was formerly produced using Savannah River Site reactors that primarily produced materials for nuclear weapons. With the retirement of those reactors in 1988, and the American nuclear weapons program going to maintenance mode, NASA lost the side-benefit of Pu-238 production using the weapons infrastructure. Deep space missions requiring RTGs had to subsist off of historical Pu-238 stockpiles and additional material purchased from Russia. But the Russian supply has run out too now -- apparently they aren't producing more of it either.
American plutonium 238 production efforts resumed in 2013:
http://www.spacesafetymagazine.com/aerospace-engineering/nuc...
With NASA now paying the full cost, including fixed startup costs, Pu-238 is extraordinarily expensive:
NASA and DOE have estimated the rebooting will cost between $75 million and $90 million over five years. According to NASA officials, the agency expects to have 1.5 to 2 kilograms produced per year, starting 2018.
The high cost and limited supplies of Pu-238 have spurred the search for alternatives to Pu-238 RTGs. A few years ago I remember reading that the European Space Agency was going to try to design its own RTGs using the less powerful but more abundant americium 241 instead of plutonium 238. But a quick search just now doesn't show any concrete development effort.
This Kilopower reactor is an alternative to RTGs for some mission profiles -- in fact offers more power than RTGs and uses cheaper nuclear materials. (Highly enriched U-235 isn't cheap in an absolute sense, but it's far less expensive than Pu-238. And the security of supply is effectively backstopped by its use in reactors for the US Navy.) It can offer ample power for very deep space missions at a cost significantly less than using years' worth of Pu-238 production.
Improved photovoltaic cells have also enabled missions further from the Sun than they could have supported in 1988. The Juno mission, which entered Jupiter orbit in 2016, relies on PV instead of RTGs. It seems plausible that further evolution will eventually push PV's reach out to Saturn missions. But PV is not currently plausible for missions beyond Jupiter, and it is reliant on slowly-evolving battery technology for surface missions on Mars. Martian missions using PV also face significant problems from cell-obscuring dust. This reactor seems too large to be conveniently integrated in a Martian rover, but enabling non-surface missions to avoid Pu-238 use may mean more can be reserved for future rovers akin to the RTG-powered Curiosity.