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New Small Fission Reactor For Deep-space Missions Demonstrated
cylonlover writes "Exploring the regions of deep space beyond Mars means sending probes where solar power isn't practical. Since the 1960s, NASA has equipped its Apollo missions and unmanned explorers with Radioisotope Thermal Generators (RTGs). These have worked very well, but they run on plutonium 238, which is currently in short supply. Therefore, the Los Alamos National Laboratory is developing a new small nuclear reactor for spacecraft that uses uranium instead of plutonium to power Stirling engines and generate electricity. At the Nevada National Security Site's Device Assembly Facility near Las Vegas, engineers from Los Alamos, the NASA Glenn Research Center and National Security Technologies LLC conducted a Demonstration Using Flattop Fissions (DUFF) experiment that produced 24 watts of electricity using a pair of free-piston Stirling engines."
It's probably less the number of probes we're sending, and more the general decrease in amount of Plutonium. PU hasn't been manufactured much since the end of the cold war; everybody is busy stepping down their weapon programs instead. Now, some of that former-warhead material is great for RTGs, but the stuff degrades. It has a moderately short half-life (it has to, or it wouldn't be active enough to passively generate the heat needed for an RTG) and a lot of the stuff that was viable for spacecraft 30 years ago is pretty cold now (see the Voyager probes, for example, which are running on extremely low power).
They can't just fix the problem by sending more, either; not only is it in short supply in general, but it's too heavy to send much on a spacecraft. Instead, they send enough to run the mission at full capacity for a few years, scaling back over time. That requires a supply of pretty fresh / pure Plutonium though, and that means making and separating more of it... except doing runs into a serious political problem. We *could* keep using RTGs (although they aren't perfect by any means, they get the job done) if we could convince people to let us manufacture their fuel source...
There's no place I could be, since I've found Serenity...
Only critical if combined. If the rocket breaks apart or the engines explode, the core would fall apart; it lacks the explosives necessary to bring the Uranium to super-criticality. Worst likely case would be that the control rod gets jammed but the housing stays intact, but the cooling system is destroyed, leaving the core at critical and causing a meltdown. The odds of that seem extremely low, though.
It'd be a very nasty "dirty bomb" if it blew up in the atmosphere, but no more than that, and a slug of Plutonium hot enough to run a spacecraft for a few years or even decades is a nasty thing to blow up in the atmosphere too. We've been launching those for decades, though.
There's no place I could be, since I've found Serenity...
It seems like you're confusing Pu-239, which is used in weapons and has a half-life of 24000 years, with Pu-238, which is not used in weapons and has a half-life of around 90 years.