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ORNL Restores US Capability To Produce Plutonium-238 (ornl.gov)
hypnosec writes: Oak Ridge National Laboratory has successfully produced 50 grams of plutonium-238, an isotope that produces heat without a lot of other, problematic radiation. This makes it suitable for use in radioisotope thermoelectric generators, which can power space probes. The new sample effectively revives the U.S.'s end-to-end plutonium-238 production capabilities, which have been dormant for around 30 years since work was stopped at the Savannah River Plant in South Carolina. The ORNL is optimistic this important milestone will pave the way for regular production of the material, ensuring constant supply for NASA's future missions.
Yes, it is radioactive, and yes, it is a very nasty heavy metal... but there are still pacemakers ticking away with this stuff as the "battery" 25+ years later.
I wonder if Pu-238 might have some use in areas where batteries are needed and extremely hard to replace other than space projects. Definitely not for a battery for a smartphone, because we don't want Youtubers like TechRax to get radiation poisoning, but airline flight data recorders come to mind.
All plutonium isotopes are not made equal.
Pu-238 = great source of heat, not a great source of boom.
Pu-239 = great source of boom, not a great source of heat.
Pu-240, Pu-241 = not a great source of boom or heat.
Pu-238 is not used in weapons specifically because it fissions too fast spontaneously. That's why it makes so much heat. And, because of this, your weapon would have a significant portion of it reduced to not-plutonum and neutron poisons by the time you want to use it.
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Pu-238 cannot be made into a bomb. It is not fissile. You may be thinking of another isotope.
a,e,i,o,u and sometimes w and y (at be if of up cwm by)
Ugg... Peltiers are about 10% efficient, meaning you'll need to dump 90% of the heat coming out of the PU-238...
Stupid 4+ minute wait.
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It looks like about 4 kg of plutonium-238 is required for a Mars Rover type mission. (Inferred from wikipedia article)
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The process described starts with a solid Neptunium-237 oxide, mixes it with Aluminum, presses it into pellets, irradiates it, chemically separates the Plutonium-238, and then processes it back into a solid oxide. They don't say where the Neptunium itself comes from, other than mentioning an existing inventory. It can be recovered from spent fuel, using another convoluted process starting with solid oxides.
Creating 237Np would be a far more direct process with a LFTR, where the 2% of the fuel which does not fission mostly finds its way to be this very isotope. (The remainder become short-lived fission products.) Naturally, processing a liquid is easier than going through multiple solid oxide steps, and lends itself to a continuous process capable of producing 238Pu in volume. It would be far more interesting if ORNL were developing the processes for this instead.
A not so minor point which deserves mention: the Pu-239 must be >90% pure for weapons. Reactor grade plutonium from spent fuel is absolutely useless for weapons. The only practical method of creating it is to briefly expose U-238 to a neutron flux, separate the Pu-239 out, and repeat many times, which requires a specialized reactor. Pu-239 can't just be pulled out of spent fuel; the plutonium isotopes are too close in mass to make isotopic separation viable.
Might put an ion out.
Table-ized A.I.
According to Wikipedia, one gram of plutonium-238 generates approximately 0.5 watts of thermal power. Thus, 2420 tonnes of Pu-238 will generate 1.21 GW for decades.
An alkaline AA battery weighs 23 g and can put out just over 1 watt of electrical power without overheating. You would need 27830 tonnes of them to output 1.21 GW for about 2 hours.
A golden hamster weighs 125 grams and apparently generates a maximum of 0.4 watts (according to google). This means you need about 378125 tonnes of hamster to generate 1.21 GW for a few hours.
Thus, PU-238 is clearly the most practical solution of those mentioned.
When Argumentum ad Hominem falls short, try Argumentum ad Matrem
Interesting facts.
PU-238 is hard to make.
AA batteries are easy to make.
Hamsters make themselves.
PU-238 is clearly the least practical solution of those mentioned. :)
Pu-238 = great source of heat, not a great source of boom.
Pu-239 = great source of boom, not a great source of heat.
Pu-240, Pu-241 = not a great source of boom or heat.
It's not just that Pu-238 is hot, it's also that it has really benign decay characteristics. It's an alpha emitter (alpha particles are very easy to block and convert to head without getting X rays) and decays to U-234. That's got a much longer half-life (200,000 years) and is also an alpha emitter, and decays to Thorium 230. That's got a moderate half life (75,000 years) and is amazingly also an alpha emitter. That mostly decays (fairly quickly) to Radium 226 via yet more alpha decay. And so on.
It eventually winds up at Polonium 210 which is the first gamma emitter in the decay chain. It's a rare gamma emitter (1 in 100,000 events), and is going to be rate limited by the half-life of U-234 most strongly, as that's the longest half life in the decay chain.
IOW, a chunk of Pu-238 emits very very few gamma rays, and only a bit of beta particles (beta particles can cause X rays to be emitted). The vast majority of the emissions are easy to block alpha particles. That combined with the high power output makes it ideal for space faring RTG since little heavy shielding is needed.
Also, it can be generated in a way that makes little nearby, unwanted isotopes which makes chemical extraction of the stuff reasonably efficient.
SJW n. One who posts facts.
As the previous commenter notes, Pu-238 is not fissile.
Pu-238 is a great thermal heating material. A gram of Pu-238 generates about 500 mW of heat through radioactive decay and initial release of alpha particles (plain old helium nuclei). Helium nuclei are large and heavy, and are stopped by even a sheet of paper. The decay chain for Pu-238 is mostly a number of alpha particle releases and a slow and gradual walk toward Pb (lead).
In metallic or solid ceramic form, Pu-238 is safe to handle. You could arguably carry around a chunk of it, but the thermal heat generated is significant and you might get burned. Machining it is straightforward, the dust needs to be controlled.
RTGs have survived that and been retrieved. They also have survived reentry. Though there have been a couple that didn't survive.
https://en.wikipedia.org/wiki/...
There have been several known accidents involving RTG-powered spacecraft:
The first one was a launch failure on 21 April 1964 in which the U.S. Transit-5BN-3 navigation satellite failed to achieve orbit and burned up on re-entry north of Madagascar.[26] The 17,000 Ci (630 TBq) plutonium metal fuel in its SNAP-9a RTG was injected into the atmosphere over the Southern Hemisphere where it burned up, and traces of plutonium-238 were detected in the area a few months later.
The second was the Nimbus B-1 weather satellite whose launch vehicle was deliberately destroyed shortly after launch on 21 May 1968 because of erratic trajectory. Launched from the Vandenberg Air Force Base, its SNAP-19 RTG containing relatively inert plutonium dioxide was recovered intact from the seabed in the Santa Barbara Channel five months later and no environmental contamination was detected.[27]
In 1969 the launch of the first Lunokhod lunar rover mission failed, spreading polonium 210 over a large area of Russia [28]
The failure of the Apollo 13 mission in April 1970 meant that the Lunar Module reentered the atmosphere carrying an RTG and burned up over Fiji. It carried a SNAP-27 RTG containing 44,500 Ci (1,650 TBq) of plutonium dioxide which survived reentry into the Earth's atmosphere intact, as it was designed to do, the trajectory being arranged so that it would plunge into 6–9 kilometers of water in the Tonga trench in the Pacific Ocean. The absence of plutonium-238 contamination in atmospheric and seawater sampling confirmed the assumption that the cask is intact on the seabed. The cask is expected to contain the fuel for at least 10 half-lives (i.e. 870 years). The US Department of Energy has conducted seawater tests and determined that the graphite casing, which was designed to withstand reentry, is stable and no release of plutonium should occur. Subsequent investigations have found no increase in the natural background radiation in the area. The Apollo 13 accident represents an extreme scenario because of the high re-entry velocities of the craft returning from cis-lunar space (the region between Earth's atmosphere and the Moon). This accident has served to validate the design of later-generation RTGs as highly safe.
Mars 96 launched by Russia in 1996, but failed to leave Earth orbit, and re-entered the atmosphere a few hours later. The two RTGs onboard carried in total 200 g of plutonium and are assumed to have survived reentry as they were designed to do. They are thought to now lie somewhere in a northeast-southwest running oval 320 km long by 80 km wide which is centred 32 km east of Iquique, Chile.[29]
APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
Actually Pu238 doesn't fission spontaneously. Fission typically refers to the fragmentation of the nucleus into two roughly equal-sized fragments, which thanks to the lower nucleon mass (=higher binding energy) at lower nucleon counts, multiplied by the large number of nucleons involved, results in considerable mass loss and a correspondingly large energy release.
In contrast Pu238 undergoes alpha decay, where it ejects just four nucleons as an alpha particle (helium 4 nucleus), only very slightly reducing the per-nucleon mass in the original nucleus, and actually considerably increasing the mass of the ejected nucleons. (https://en.wikipedia.org/wiki/File:Binding_energy_curve_-_common_isotopes.svg Binding energy peaks at Fe56 (per-nucleon mass is at a minimum), and any transmutation towards 56 nucleons results in mass loss equivalent to the change in binding energy * number of nucleons. As you can see He4 is actually an anomalous peak all by itself, if it wasn't then alpha emission would shed many times as much energy, and probably be far more uncommon.)
I suspect it's also not used in nuclear weapons or reactors because it's not fissile (it won't fission under slow neutron bombardment). Typically fissile isotopes have an odd number of neutrons, causing them to gain considerably more excess energy (1-2MeV IIRC) when absorbing a neutron due to neutron pairing, which makes the resulting nucleus far less stable and more likely to fission. Without that, causing fission requires hitting the nucleus with a neutron going fast enough to destabilize it through kinetic energy alone.
Finally, I suspect Pu238 is also also not used in weapons or reactors because it doesn't emit neutrons - and without neutron emission there can be no critical mass, no chain reactions, and no shortcuts to fission.
Basically, Pu238 totally sucks as a fission fuel, but makes an awesome candidate for RTGs, as explained by serviscope_minor.
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Actually, less than that - it generates 114W/kg in decay heat, versus ~500W/kg for Pu238
It also has a non-negligible spontaneous fission rate, and emits gamma radiation. Less of an issue in space where everything is being radiation bombarded anyway, but it makes it a generally less attractive RTG fuel.
--- Most topics have many sides worth arguing, allow me to take one opposite you.