US developing different versions of lunar nuclear power

SpaceNut · 2020-12-10 21:18:56

US developing new nuclear systems to power space missions, new bases, Energy Chief Says by Staff Writers
Washington DC (Sputnik) Dec 10, 2020

It might look something like this image
ultra-safe-nuclear-technologies-nuclear-thermal-propulsion-usnc-tech-ntp-hg.jpg

The United States is developing different versions of nuclear power to use on lunar and other space bases and for long-range interplanetary manned and unmanned probes, Secretary of Energy Dan Brouillette told the National Space Council.
The Energy Department had created closer ties than ever before with the National Aeronautics and Space Administration (NASA) to empower and speed up its programs, Brouillette said.
"We will continue to develop surface fission power, thermal nuclear propulsion technologies and advanced nuclear fuel production capabilities," Brouillette said on Wednesday.
The department was also "ramping up" Uranium isotope-238 production thus clearing a production bottleneck and making possible "quicker mission tempos" to launch more deep space, interplanetary missions through the Solar System through the 2020s, Brouillette continued.
The Energy Department had also already drawn up a new space strategy for the next ten years to support the space missions of NASA and other government agencies. However, it had not been published yet, Brouillette said.
Earlier this year, the Energy Department put out a request to the private sector to construct nuclear power plants capable of operating beyond the boundaries of our planet.
Source: RIA Novosti

Ya reliablity of source but it sure would be step in the correct direction.

https://www.space.commerce.gov/category … e-council/

tahanson43206 · 2020-12-11 05:56:44

For SpaceNut re Post #1 ... It was surprising (to me at least) to see U-238 given as the isotope whose production would be increased.

I would have expected U-235. U-238 ** can ** be used, but it has to be transmuted to Plutonium first.

If someone with insight into this would be willing to comment, I'd appreciate it.

Here is a document published by the European Union about Uranium. It opens with reassurance that U-238 is NOT radioactive.

https://www.radioactivity.eu.com/site/p … 38_235.htm

The document explains that U-238 can be bombarded to make U-239, which decays to Plutonium 239, which ** is ** radioactive.

(th)

kbd512 · 2020-12-11 12:52:09

tahanson43206,

They're talking about using natural Uranium with U235 concentration, "as it's dug out of the ground". That means they get U238 with U235 mixed in with it, or perhaps with some nominal amount of enrichment from the addition of existing U235 and Pu239 from spent fuel rods or active operating nuclear reactors. Natural Uranium absolutely IS radioactive, specifically because it contains unstable isotopes subject to decay. Whomever printed that was lying or ignorant or perhaps thought the general public is ignorant (in general, they are, but they're also afraid of radiation anyway). That said, the radiation associated with U238 is so low that you'd have to physically ingest the material in order for it to be a problem. However, the same is true of U235 and Pu239. If you're not physically handling the material, then it poses very little risk of radioactive contamination, especially with all the rules and regulations for transporting and storing it. For an engine that's only supposed to be operated in a hard vacuum, for purposes of interplanetary transport, the radiation produced really shouldn't pose an actual problem for the general public.

Edit:

I think they were actually talking about ramping up Production of Pu-238 isotopes for RTGs and heat sources. There never was any kind of U238 production bottleneck. The Pu238 has to be produced through neutron absorption / transmutation inside an operating nuclear reactor. We most definitely were running out of Pu238. We have tons of highly enriched U235 and Pu-239 sitting in storage from decommissioned nuclear warheads and nuclear reactors from the US and Russia. The Russians shipped their Pu-239 pits / cores to the US. They're collecting dust right now, but could be used to power interplanetary transports and provide ground power to facilities on the moon or Mars.

Last edited by kbd512 (2020-12-11 12:57:24)

tahanson43206 · 2020-12-11 13:31:43

For kbd512 re #3

Thanks for taking a look at the announcement. I note that SpaceNut indicated the source might be suspect.

Because of what appears to be a poor write-up, I hope that others in the forum will keep watch for a better report on US plans.

(th)

SpaceNut · 2020-12-11 18:02:10

The u-238 as kbd512 recognized is used in RTG's which are not a high heat outputing device, while NASA uses Pu-238 or plutonium for the deep space probes which is another isotope. It does also output some electrical energy as well from the RTG. So its not going to power a nuclear thermal engine at a very high rate of speed to make use of what we want from it to be as in a high thrust level.

https://en.wikipedia.org/wiki/Isotopes_of_uranium

Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay product uranium-234 is also found. Other isotopes such as uranium-233 have been produced in breeder reactors.

https://rps.nasa.gov/power-and-thermal- … s/current/

Radioisotope Thermoelectric Generators, or RTGs, provide electrical power for spacecraft by converting the heat generated by the decay of plutonium-238 (Pu-238) fuel into electricity using devices called thermocouples. Since they have no moving parts that can fail or wear out, RTGs have historically been viewed as a highly reliable power option.

https://en.wikipedia.org/wiki/Radioisot … _generator

Radioactive materials contained in RTGs are dangerous and can even be used for malicious purposes. They are barely useful for a genuine nuclear weapon, but still can serve in a "dirty bomb". The Soviet Union constructed many un-crewed lighthouses and navigation beacons powered by RTGs using strontium-90( Sr). They are very reliable and provide a steady source of power.

http://www.qrg.northwestern.edu/project … -safe.html

Thus, NASA engineers strive to make them the safest, most indestructible parts of a spacecraft. RTG's can not explode like a nuclear weapon. Nuclear weapons are made of high-grade uranium and have to be arranged very carefully to go into fission. RTGs, at best, can produce a warm fizzle.

https://mars.nasa.gov/internal_resources/788/

Essentially a nuclear battery, the MMRTG contains a total of 10.6 pounds (4.8 kilograms) of plutonium dioxide fuel that

https://medium.com/starts-with-a-bang/n … 0632c9e61a

A pellet of Plutonium Oxide, which is warm to the touch and glows under its own power. Pu-238 is a unique radioisotope ideally suited for fuel for deep space

https://rps.nasa.gov/missions/7/new-horizons/

The compact, rugged General Purpose Heat Source (GPHS)-RTG aboard New Horizons, developed and provided by the U.S. Department of Energy, carries approximately 11 kilograms (24 pounds) of plutonium dioxide fuel. By the time of the Pluto flyby in July 2015, the GPHS-RTG aboard New Horizons will supply 202 watts of power, down from 240 watts at launch.

https://www.acs.org/content/acs/en/educ … ction.html

The complex included five reactors to produce these radioactive materials and two separations facilities to isolate and purify them. SRS produced the Pu-239 from a combination of uranium-235 (U-235) and U-238 in the reactors. U-235 in this “fuel” released neutrons that struck U-238, converting some of

https://world-nuclear.org/information-l … space.aspx

The high decay heat of Plutonium-238 (0.56 W/g) enables its use as an electricity source in the RTGs of spacecraft, satellites and navigation beacons. Its intense alpha decay process with negligible gamma radiation calls for minimal shielding. Americium-241, with 0.15 W/g, is another source of energy, favored by the European Space Agency, though it has high levels of relatively low-energy gamma radiation

https://www.nasa.gov/sites/default/file … 011618.pdf

Novel integration of available U-235 fuel form, passive sodium heat pipes, and flight-ready Stirling convertors § Would provide about 10x more power than the Multi -Mission Radioisotope Thermoelectric Generator • Impact § Could be scaled up to provide modular option for human exploration missions to the Mars/Lunar surface

kbd512 · 2020-12-12 02:35:07

SpaceNut,

Yes, Pu238 is an Alpha emitter that decays and produces quite a bit of heat, roughly 570W/kg, which is nowhere near as much thermal power as a gigawatt-class nuclear reactor core the size of a couple of 55 gallon drums stacked on top of each other, loaded with 93%+ enriched U235. IIRC, each fuel element in the NERVA rocket program produced 1.2MW of thermal power, for an overall thermal power output of about 1.1GW, so roughly 917 of those ceramic fuel elements that Coors (the ceramics company, not the good times on Friday night company) produced for NASA in the 1960s and early 1970s. Of all the info that NASA could possibly lose track of from that development program, they lost the info about how to fabricate the ceramic U235 fuel elements, so BWXT and other corporations had to "rediscover" how to make high temperature ceramic fuel elements that would crack or shatter when superheated and exposed to hot flowing Hydrogen being pumped through them.

Peak power density for NERVA was 5.2GW/m^3 for the entire core volume, so nuclear fission produces an absolutely insane amount of thermal power in a tiny package. A cubic meter of Pu238 (the oxide fuel cell. The lower thermal power density NERVA experiment fuel elements peaked at 3.6kW/cm^3, but could go as high as 8.2kW/cm^3. In contrast, 1 cubic centimeter of oxide-based Pu238 from a NASA RTG is 9.6g (pure Pu238 metal's density is 19.8g/cm^3) produces a whole 5.472W of thermal power output, so only 5.472MW/m^3 (absurdly worse than any kind of usable chemical rocket engine and the heating element alone would weigh 9,600kg to boot). Therefore, nuclear fission in a propulsion application has a power density between 658 and 1,499 times as much power, as compared to the decay heat produced by Pu238. Even run-of-the-mill power plant reactors used here on Earth have volumetric thermal power density measured in tens of megawatts per cubic meter. Put another way, a Japanese auto maker created an 88kg 4-banger that produced well over 400hp and fit inside a suitcase. A 50% efficient thermal engine loaded with 88kg of Pu238, with 100% efficiency for every other component involved in power transfer to produce motive force, could produce a maximum of 33.6hp. That's why any realistic use for a Pu238-based thermal power core would involve charging batteries or super capacitors if the goal is to produce usable motive power. There was a guy named Gary Conley who made model engines produced a 12 pound supercharged V8 engine that produced up to 20hp nitromethane fuel about 10 years ago (only 9.5hp at 10,000rpm when powered by ordinary gasoline), the Conley Stinger 609 V8 (100cc / 6.09 cubic inches). There are now numerous miniature V8 and V12 engines that could fit in your hand that can also produce up to 33hp. All of them are a pain to keep running and are absurdly expensive for the power generated (Conley wanted $7,000 for his Stinger 609), but they do actually work. Pu238 is "only" $2M or so per kg. What can I say? We have lots of disposable income here in America.

Pu238 is produced by bombarding U238 with Deuterium (heavy Hydrogen), producing Neptunium 238, which rapidly beta decays to Pu238 a couple of days later. Pu238 then decays to U234 (Pu238's half life is 87 years or so), then Lead 206 (after a couple hundred thousand years or so. U234 has a half life of some 245,000 years, or something like that, so decay to a stable isotope takes quite some time.

In contrast to the irradiation process used to produce Pu238, the process for enriching Uranium is generally done through comparatively simplistic but energy intensive centrifuging of natural Uranium to separate U235 from U238. There was also a multi-stage gas diffusion process, but these days I'm pretty sure it's all done with centrifuges. Anyway, U238 can also be transmuted through irradiation into fissile Pu239 in a breeder reactor. That's why everyone focused so heavily on Uranium-based fast (fast neutron spectrum) breeder reactors in the early days- we wanted the weapons. Shortly thereafter, our militaries realized that they had no practical use for such weapons, even though they spend enormous sums of money to maintain them, despite the dangers to themselves and everyone, else irrespective of any nuclear war, which everyone knows full well is completely un-winnable for absolutely everyone on the planet. At least the Chinese were smart enough to recognize the futility of that endeavor, so they quit making them shortly after they started. There are other isotopes that can also work, but Pu239 is the best material for that purpose. Similarly, transmuting U233 from Th232 is the absolute best from the perspective of minimizing unwanted long-lived byproducts from fission, but also terrible for making weapons at the same time- perhaps the best reason to base all sincere civil nuclear power programs on Th232 and U233. Either way, it's much easier and cheaper to obtain U233 from Th232 or U235 from natural Uranium or Pu239 from U238, than it is to produce Pu238 from U238. However, all of the fissile isotopes are also completely unusable outside of a nuclear reactor. That's where Pu238 really shines. It's a special isotope that provides a decent half life- not so radioactive that it's unusable, very little gamma if it's pure, and more than enough heat to power a motor vehicle on another planet.

Long story short, if we can make fuels and oxidizers on Mars, then hybrid vehicles are the easiest to maintain. Pu238 clearly provides the most power output over the long term if money is no object. If we used the electromagnetic energy from the Alpha particles thrown off from Pu238, that's about an order of magnitude more energy to tap than its thermal power output from decay, so maybe some bright young person will decide to convert that electromagnetic energy into electricity so we get a much better ROI on the cost of producing that Pu238, or so I hope.

Well, that was pretty rambling and disorganized. That's probably enough for this post.

tahanson43206 · 2020-12-12 09:23:21

For kbd512 re Post #6

SearchTerm:Pu238 http://newmars.com/forums/viewtopic.php … 78#p174778

Pros and cons of various isotopes of Uranium
Discussion of production methods
Relative costs
Call for harvesting alpha particles

Actually kbd512 ... harvesting alpha particles rings a bell .... Recently, while trying to find the current status of fusion research, I ran across an article about a company founded by a couple 80+ year old physicists to try to make fusion using Boron 11 and Hydrogen nucleii ... the output of the reaction is a set of three alpha particles, and a scenario for collecting power from the equipment was a method of harvesting those alpha particles.

I didn't read too far into the discussion, because the main point of the article was that the heating requirements for plasma able to fuse these two components was so much greater than other candidate fusion components.

Never-the-less, I did note that some thought had been invested in the harvesting problem, and perhaps something from that work could be adapted to the Pu238 opportunity you've pointed out.

***
For SpaceNut ... this is an opportunity for you to go back to Post #5 to correct the reference to Uranium 238 ....

Someone may come along in future to read this topic, so correcting that post would help to reduce confusion.

(th)

GW Johnson · 2020-12-12 11:52:43

I'm no expert, but to the best of my knowledge, uranium isotope U-238 is definitely not fissionable at all, and by itself is hardly radioactive, because the stuff is stable over gigayears of geologic time. The fissionable isotopes of uranium are U-235 and U-233. Both are quite radioactive.

U-235 is radioactive and so exists in nature in very small quantities, only about 0.3% of natural uranium, the other 99.7% being nonfissionable U-238. U-233 is bred from thorium Th-232 in a breeder reactor, and does not exist in nature at all.

The "low-enriched uranium" (LEU) is at or under about 10% U-235 in U-238, as I understand it. The "highly-enriched uranium" (HEU) is at or above 50% U-235 in U-238. "Depleted uranium" is the leftover from the enrichment process. It still has very tiny amounts of the radioactive U-235 in it, so depleted uranium actually is slightly radioactive, just barely enough to worry about. However, it is at least as dangerous to humans as a heavy metal poison, as it is a radioactive hazard.

Super-highly radioactive plutonium also does not exist in nature. It has to be created by being bred from a source material in a breeder reactor. The most fissionable isotope is Pu-239, which is bred from U-238. It is both a severe radioactive hazard to humans, and a severe heavy metal poison.

If exposed, it is a race to see which kills you first: the radiation or the heavy metal effects. But kill you it does, and within minutes to an hour or so.

There is an almost not-fissionable but very radioactive isotope of plutonium Pu-238, which can be used in a radioisotope generator of electricity. It generates heat by radioactive decay, not really fission. You can make electricity out of that heat, if you are clever and you have the supporting technology. I think it is done by thermionic conversion.

The "238" in "Pu-238" versus "U-238" is the source of a lot of confusion about these things, what they are, and what they can do. Those two are NOT the same material. Not at all.

GW

kbd512 · 2020-12-12 16:23:23

GW,

U238 is fertile but not fissile material. Nuclear reactors can and do convert U238 into various fissile isotopes, primarily Pu239. However, natural Uranium contains a small quantity of U235 mixed in with U238. There are reactors, such as the Canadian CANDU design, that uses natural Uranium as fuel. Using natural Uranium does set a minimum size for the reactor and reflector- CANDU used heavy water as a neutron moderator to assist with maintaining the chain reaction, but it does work. Enrichment produces more volumetric power output, at the expense of the extra cost associated with the enrichment process and unused U238.

I think the "super high radioactivity" of Plutonium that you're referring to is actually from the Pu240 isotope, which emits gamma and neutrons from spontaneous fissioning of Pu239. Pu240 can induce spontaneous fission of Pu239 and both products are mixed together. Pure Pu239 is an Alpha emitter while it decays into U235, so relatively benign compared to Pu240, which is present in nearly all Plutonium produced, and in quantities significant enough to be a serious health hazard from radioactivity. The US Navy spent quite a bit of money on procuring "super grade" Pu239 (<3% Pu240) for that reason- sailors are in close proximity to any nuclear weapons carried at all times. If all of the Pu240 was removed, which is nearly impossible for any reasonable cost, then Pu239 would still be a radiation hazard and carcinogen if it was ingested, but safe to handle with a pair of rubber gloves since your skin stops Alpha particles. That said, Pu240 is highly radioactive and present in very significant quantities in nearly all grades of Plutonium, so Plutonium, generally being a mixture of Pu239 with significant quantities of Pu240, is not something to trifle with.

Much like the impurities in natural Methane that we discussed in the micro capsules topic, you never get a perfectly isotopically pure product with most radioactive materials, which is why so many of them are more dangerous to handle than they otherwise would be, if they were pure or nearly pure. Any gamma emitter or material that spontaneously fissions, which produces neutrons and radioactive daughter products, is going to be difficult to adequately shield against.

GW Johnson · 2020-12-12 16:31:22

Like I said, I'm no expert. I had not heard of Pu-240. But what you say about it explains a lot of the plutonium radiation hazard that I did know about. Remember, in my time, there were still diesel submarines.

GW

SpaceNut · 2020-12-21 19:41:54

The Nuclear Energy That Will Send Us to the Moon and Mars

BB1c6WcJ.img?h=400&w=799&m=6&q=60&o=f&l=f

https://www.nasa.gov/press-release/nasa … propulsion

BB1c6PAa.img?h=300&w=482&m=6&q=60&o=f&l=f

"Space Policy Directive-6" is all about space nuclear power and propulsion (SNPP), an umbrella category that includes providing electrical and heat energy for planned installations on the moon as well as the propulsion system that will likely, eventually carry NASA to Mars. The White House explains on its fact sheet:

It might be nice to have but is not needed to make the moon...

Further down the road, NASA’s interests include experimental nuclear reactors that are popular for Earth research, too, like fusion or molten salt. It doesn’t necessarily make sense to wait until fusion is mature before you start to examine how fusion might work on the surfaces of other planets or as the propulsion system for an intergalactic spacecraft.

Mars_B4_Moon · 2022-05-19 13:28:10

DIU selects nuclear-powered spacecraft designs for 2027 demonstrations

https://spacenews.com/diu-selects-nucle … strations/

Mars_B4_Moon · 2023-08-14 08:36:30

An Improved Radioisotope Thermoelectric Generator Could Dramatically Reduce The Weight Of Interplanetary Missions
https://www.universetoday.com/162772/an … -missions/
Radioisotope thermoelectric generators (RTGs) are the power plants of the interplanetary spacecraft. Or at least they have been for going on 50 years now. But they have significant drawbacks, the primary one being that they’re heavy. Even modern-day RTG designs run into the hundreds of kilograms, making them useful for large-scale missions like Perseverance but prohibitively large for any small-scale mission that wants to get to the outer planets. Solar sails aren’t much better, with a combined solar sail and battery system, like the one on Juno, coming in at more than twice the weight of a similarly powered RTG. To solve this problem, a group of engineers from the Aerospace Corporation and the US Department of Energy’s Oak Ridge National Lab came up with a way to take the underlying idea of an RTG and shrink it dramatically to the point where it could not potentially be used for much smaller missions.

Calliban · 2023-08-14 09:24:40

A bigger problem for RTGs is the scarcity of 238Pu. This is produced by neutron capture in neptunium-237 and subsequent beta decay. It is rare and expensive.

One potential alternative is Strontium-90, which is a more common fission product. The problem here is that the beta particles emitted by Sr-90 decay generate x-rays if they approach a heavy nucleus, including strontium itself. That makes strontium-90 RTGs difficult to handle. One solution might be to dissolve the strontium into a low-Z material. Lithium-strontium alloy is a possibility.

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#1 2020-12-10 21:18:56

US developing different versions of lunar nuclear power

#2 2020-12-11 05:56:44

Re: US developing different versions of lunar nuclear power

#3 2020-12-11 12:52:09

Re: US developing different versions of lunar nuclear power

#4 2020-12-11 13:31:43

Re: US developing different versions of lunar nuclear power

#5 2020-12-11 18:02:10

Re: US developing different versions of lunar nuclear power

#6 2020-12-12 02:35:07

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#7 2020-12-12 09:23:21

Re: US developing different versions of lunar nuclear power

#8 2020-12-12 11:52:43

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#9 2020-12-12 16:23:23

Re: US developing different versions of lunar nuclear power

#10 2020-12-12 16:31:22

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#11 2020-12-21 19:41:54

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#12 2022-05-19 13:28:10

Re: US developing different versions of lunar nuclear power

#13 2023-08-14 08:36:30

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#14 2023-08-14 09:24:40

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