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we have a plutonium problem this is Dragonfly NASA's flying rover designed to explore Titan the icy moon of Saturn 1.5 billion km away from Earth and it will do it while being powered by the final few kg of a nuclear fuel currently left in the United States stockpile tucked inside this drone nestled between thermouples there is a small 4.8 kg chunk of a man-made isotope plutonium 238 and the United States is running out of this vital material and the shortage has already affected NASA missions like the Europa Clipper mission to Jupiter's
moon where it will need to get by with the power provided to it with its solar panels which will receive extremely low intensity light in the distant reaches of our solar system many at JPL believed Europa Clipper should have been powered by plutonium 238 but with the material in short supply it was saved for missions like Dragonfly this isn't good it's quite bad actually we really need more plutonium 38 to do cool science stuff so what are we going to do about it this hasn't always been a problem some positive things did come out of the world's relentless
race to expand nuclear weapon arsenals during the Cold War like this and this and even this deep within secretive processing facilities around the world in the 1950s scientists began producing fisol plutonium 239 in vast quantities the United States Russia United Kingdom France China and Israel all developed nuclear weapons during this time and in the process of refining and extracting weaponsgrade plutonium other isotopes emerged useless for warheads and discarded as waste or so it seemed nasa saw something different what the military
considered a byproduct they saw as an opportunity among the leftovers were the ingredients to make plutonium 238 an isotope unlike its bomb-making counterpart it doesn't sustain a chain reaction but instead it emits a steady reliable heat this isotope could be harnessed as a safe lifeline for spacecraft venturing into the darkest coldest corners of the solar system the only way to create this element is to bombard other elements with neutrons in a nuclear reactor this isotope is differentiated from the one that leveled Nagasaki by just a single neutron this
single neutron difference changes plutonium from one of the most tightly controlled substances in the world to this wonderful material glows redot for hours not for days not for weeks or months or years but decades a slow consistent radiation of heat that halves every 88 years and this heat can be used to generate electricity but more on that later since its discovery as a power source plutonium 238 has been vital to NASA's missions first used in the Apollo lunar surface experiments it later powered the Voyager probes which are still transmitting from
interstellar space cassini explored Saturn with its help the Curiosity and Perseverance rovers roamed Mars with its heat and now Dragonfly will rely on it to explore Saturn's moon Titan keeping its instruments running in the extreme cold and providing the energy needed for powered flight on another planet's moon so why are we running out of this wonderful material in 1988 with aging reactors and a nuclear weapon stockpile so large they could end the world instantly the United States halted its production of weaponsgrade plutonium i think we can all agree this was
a good thing but this decision has hindered deep space exploration with the shutting down of the K reactor in the Savannah River site the US lost its ability to produce plutonium 238 forcing NASA to ration a dwindling supply of the valuable material this problem became even worse when in 2010 the US stopped importing the isotope from Russia so a decade ago NASA and the Department of Energy restarted its complex production but with current production at just 550 g per year supply is not keeping pace with demand so what is NASA doing to address this problem there are some alternatives
if plutonium refining does not increase to meet demand the first thermal generator tested by NASA in 1959 used palonium 210 as its nuclear source a single gram of pelonium 210 generates 140 watts of power however its short half-life means its power output halves in just 138 days the fastest ever journey to Mars took about the same time during that time the spacecraft would have to radiate that heat generated by the fuel to space losing half your power before you've even arrived isn't ideal ruling it out of most space missions the unique demands of space exploration gave rise
to three primary engineering requirements for a nuclear fuel suitable for spacecraft the first requirement is that the fuel must last long enough to power a mission without sacrificing energy density this means the isotope's half-life should be between 15 and 100 years out of nearly 2,900 radioisotopes this criterion reduces the options to just 22 next the fuel must only emit radiation that is easy to shield ensuring the protection of both the spacecraft's sensitive instruments and any personnel handling it during preparation this means of alpha beta and gamma particles we
want the material to only emit alpha particles which generate more heat and are easily blocked the alpha particles emitted by plutonium 238 are essentially helium nuclei traveling at 15% the speed of light and carrying 5 mega electron volts of energy as they collide with electrons and nuclei within the fuel they release their energy as heat but if emitted near the pellet's edge the alpha particles are easily stopped by light materials but it's not the only alpha emitter take curium 244 its half-life of 18 years is a little short but still within the acceptable range
curium 244 was initially considered as a potential substitute due to its high power density which is five times greater than that of plutonium 238 and it has a stable high temperature oxide fuel form but its higher gamma and neutron emissions resulting from its higher rate of spontaneous fision significantly increases the need for heavy shielding to protect both handlers and spacecraft equipment plus producing curium 244 is far more difficult the best way to create it is for plutonium 239 to capture successive neutrons and for it to decay into curium
this is expensive and impractical so there is currently no infrastructure to produce it in the large quantities needed for space missions stability under extreme conditions is equally critical the fuel has to withstand launch accidents and atmospheric re-entry we don't use completely pure plutonium 238 in spacecraft instead they rely on plutonium oxide pellets which are encased in aridium shells to contain the material safely iridium was chosen because of its high temperature material properties being strong and ductile even at 1,00° C allowing it to
safely deform and contain the radioactive pellets in the event of an accident in 1967 a plutonium generator was recovered from the Pacific Ocean after a failed launch of a weather satellite its plutonium 238 was reprocessed and successfully used in another mission similarly during the Apollo 13 mission the lunar modules generator sank intact to the ocean floor where it remains safely contained keeping some local fish warm finally the fuel must be cost-effective and producible in sufficient quantities using existing infrastructure like nuclear reactors galdinium 148
is another great option with a long half-life of 75 years with only alpha decay mechanisms but the only way to produce it is to bombard targets with very high energy protons requiring very expensive particle accelerators so to produce it in enough quantities a much larger investment is needed so in short plutonium 238 is just a miracle material that is perfect for space exploration nasa has two options to tackle this supply and demand imbalance either increase production or figure out a way to use current supplies more effectively the current method of extracting electricity relies on the
CBEC effect the CBEC effect essentially allows us to generate an electric current through a heat differential as charge carriers both electrons and electron holes will move from hot to cold so if we have two semiconductors one with charge carriers in the form of electrons and one with charge carriers in the form of holes a potential difference between the two semiconductors will form when a heat gradient is applied this potential difference causes a current to flow in the external circuit these two semiconductors need to be both thermally insulating to ensure
this heat gradient is maximized but also electrically conductive to maximize the current these two material properties are typically linked copper is both a great electric and heat conductor while iron is a poor electric and heat conductor having a single material that is a great electric conductor and a poor heat conductor is extremely rare for this reason two unique materials are used for the P and N type semiconductors lead teluride for the N type and an alloy commonly called tags for the PT type which is formed from telurium silver germanmanium and antimony nasa has explored
more efficient ways to generate electricity with the heat plutonium 238 provides including the use of the sterling cycle this cycle operates by alternating compressing and expanding a gas in a sealed system allowing heat to be converted into a mechanical energy which then drives a generator to produce electricity nasa focused its efforts on developing an advanced sterling engine a highly efficient system designed to work in the vacuum of space and be able to survive the harsh vibrational forces of the launch traditional radioisotope thermmoelect electric generators only convert
heat to electricity at an efficiency of only 6 to 7% sterling engines can achieve efficiencies of up to 30% this would more than quarter the quantity of plutonium needed for these space missions unfortunately in 2013 after a decade of development NASA canled the advanced sterling radioisotope generator project due to technical issues with the piston underestimated costs and schedules and budget constraints so increasing production is the only option left production restarted in 2015 and while initial production was just 50 g per year to date their
production level is 550 g with plans to raise that to 1.5 kg per year the current production entails three different facilities in three different states during the Cold War the Savannah River site separated and produced 400 kg of neptunium its long halflife means it's still usable as a target even to this day all of the plutonium in the future lunar landers and the dragonfly mission will be made from neptunium made decades ago stored in a site in Indiana the neptunium as a solution gets transferred to the Oakidge National Laboratory there they distill the solution and
precipitate the neptunium to create a metallic powder this material is then carefully pressed into pellets and then encapsulated in aluminium to prepare it for a radiation the encapsulation ensures the neptunium remains contained during its transformation in the reactor maintaining safety and preventing contamination next the encapsulated neptunium is placed inside a nuclear reactor where it under goes irradiation inside the reactor the neptunium 237 nuclei absorbs neutrons to form neptunium 238 this isotope is highly unstable and quickly decays into plutonium 238 through beta
decay the reactor's neutron flux and duration of radiation are carefully controlled to optimize the conversion rate and ensure the production of highquality plutonium 238 after a radiation the targets containing plutonium 238 are removed from the reactor and processed to extract the newly formed plutonium this involves dissolving the irradiated material in acid and using chemical techniques to separate plutonium 238 from any residual neptunium 237 and other byproducts the extracted plutonium 238 is then purified further to meet the rigorous standards required for use
in space missions finally it's converted into a ceramic oxide form which is stable and suitable for use in radioisotope power systems and sent to the Los Alamos lab in New Mexico to be formed into the final pellets and placed inside the thermal generator in 2011 when the Department of Energy started up the process none of these facilities were ready for large-scale operation they needed $90 million for modifications to existing facilities all of this is simple in theory and the overall process has been known since the Cold War so why has it been so hard to build up the
stockpile engineers and researchers are fighting a losing battle against unstable elements that are impossible to see it's easy to write the diagram where Neptunium simply turns into the right kind of plutonium by absorbing a neutron but in reality this is a statistical process in the hot messy and energetic environment of the target anything can happen neptunium might absorb one neutron and then split ideally it absorbs a neutron and becomes neptunium 238 but once formed this neptunium is also exposed to the same neutron bombardment this is actually the main way Neptunium 238 decays 85%
of the neptunium 238 that is created is destroyed by neutron triggered vision then in the off chance that everything goes well and the plutonium 238 starts to build up in the target it is still being irdiated too creating even more undesired isotopes we need 85% pure plutonium 238 and trying to separate two isotopes that differ in mass by one or two neutrons is almost impossible these interactions are incredibly difficult to control during one cycle 1 gram of neptunium would yield just 0.5 gram of plutonium to maximize the likelihood of plutonium 238 forming we want to
expose the target to a stream of very concentrated neutrons for a short time in cycles in between the cycles the target is allowed to cool while unwanted byproducts decay further there are very few facilities capable of doing this just two the high flux isotope reactor at the Oakidge National Laboratory and the advanced test reactor at the Idaho National Laboratory and there is huge demand for these reactors nuclear physicists depend on these slots being available to study different isotopes so the lack of places to irdiate the targets in addition to the low yield means the
number game is not in our favor to build up the stockpile so where do we go from here the production process is slow and complex the Oakidge National Laboratory is on track to produce 1.5 kg of plutonium 238 per year the Dragonfly mission alone will need around 4.8 kg taking 3 years to produce so we desperately need to increase supply because there are many more exciting missions that could use this incredible material if it was available the success of the restart of US plutonium production has sparked interest in other space organizations the ESA is well positioned to
create their own manufacturing plant france having a large nuclear power base already has a full facility meant to extract plutonium and uranium from spent nuclear fuels in Leh looking to the near future the possibility of using plutonium 238 for lunar missions is gaining attention while the moon offers better conditions for solar power compared to deep space certain lunar regions such as permanently shadowed craters at the poles require alternate power sources these regions are of high scientific interest as they may contain water ice and other valuable resources
a steady plutonium 238 supply could enable extended exploration of these areas powering landers rovers and even infrastructure like communication relays or habitat systems during the long lunar nights ultimately there is only one answer to this problem scaling up plutonium 238 production to support both lunar and deep space missions is going to require a lot of money and do you know what else requires a lot of money these videos this is the very first video I ever made it was basically free to make i taught myself how to animate over the course of a long weekend
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