January 02, 2016

What If We Get Unlimited Cheap Isotopes of Our Choice Like Plutonium 238 or Cobalt 60?



A guest article by Joseph Friedlander

I recall a Poul Anderson science fiction novel with teleportation being one of its' premises and one of the plot points was the main station was on the Moon because you could teleport millions of tons of radium into existence which might pose a huge danger to life on Earth. (IIRC-- and it has been years since I have seen that book, https://en.wikipedia.org/wiki/The_Enemy_Stars)
TheEnemyStars.jpg

In the scientific speculation that underlies the story, Humanity has reached out to the stars in ships that move at half the speed of light. At that speed the ships will take years, decades, even centuries to reach their destinations. And yet the ships' crews serve month-long tours of duty, teleporting to and from their bases on Earth and other worlds instantaneously through what Anderson calls a mattercaster.  
...if the crew cannot find a roughly asteroid-sized body to provide feedstock for the mattercaster, the Exploration Authority will not be able to teleport enough mercury to the ship to provide enough propellant for Southern Cross to resume her journey to Alpha Crucis.
and perhaps I am not recalling correctly, it would eat raw mass on one end --the feedstock--and the mattercaster would weave it into the desired material-- mercury in the case of ion engine reaction mass but potentially millions of tons of radium in case of an enemy hack (thus dangerous, thus located on the Moon)

Incidentally a note about Poul Anderson's "millions of tons" of radium-- say 2.02 million tons would be 2.02 trillion grams which would be 2.1 trillion curies. If teleported into existence an unfortunate observer might or might not have time to scream at a distance of 100 meters 2000000000000 Ci of Ra-226 at 100 Meters before the 1.036895E+008 rads per hour claimed his life.http://www.radprocalculator.com/Gamma.aspx

At 1000 meters away, the observing wretch would be heir to 4.546089E+004 rads per hour, pretty much a lethal dose a minute.  If he could  parachute jump down a giant borehole and rapidly get out of the way I can see him making it into a radiation ward. Wow.  What an intriguing concept.  I liked the book as it was. but the missing other story about the 2 million tons of radium Soooprise! might have been even better!


for those wanting to play with 'fire'--Rad Pro Calculator

http://www.radprocalculator.com/Conversion.aspx
http://www.radprocalculator.com/Gamma.aspx


OK, maybe Poul Anderson wanted a lunar base and got one for free in the story as a side detail. But a side effect of that story's tech setting that  I only thought of later was (obviously) the availability of essentially unlimited amounts of isotopes. Over the years this has bugged me enough that I am writing this to clear my head of the question.  So the grand speculation of this article is: What if we could get unlimited amounts of isotopes cheaply to power all kinds of atomic 50's  style visions?




1958 Ford Nucleon



https://www.youtube.com/watch?v=3GZgYlMekEU


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

http://www.oddlyhistorical.com/2014/07/21/1958-ford-nucleon-nuclear-powered-car/

 https://en.wikipedia.org/wiki/Ford_Nucleon#/media/File:Ford_Nucleon.jpg

The well capitalized and subsidized design work that produced the 1955 Lincoln Futura https://en.wikipedia.org/wiki/Lincoln_Futura (the 1966 Batmobile  base model   http://www.batmobilehistory.com/1966-batmobile.php) and the 1958 Ford Nucleon-- when Japanese car designers would make pilgrimages to America to learn the height of car design art--

https://www.youtube.com/watch?v=Q9v3lIN9EOY


In this article we discuss what happens if we get unlimited availability cheap isotope power.  Radioactive isotopes which can decay spontaneously-- unlike most reactor designs they theoretically need no active control.  They are used in RTGs-- radioisotope thermoelectric generators.

 From
https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

A pellet of 238PuO2 to be used in an RTG for either the Cassini or Galileo mission. This photo was taken after insulating the pellet under a graphite blanket for several minutes and then removing the blanket. The pellet is glowing red hot because of the heat generated by radioactive decay (primarily α). The initial output is 62 watts.

In that Wikipedia picture above note that the watts/gram of pure 238 is .56 so 62 watts means that little thing has 110.7 grams of plutonium 238 in it.
https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator
https://en.wikipedia.org/wiki/Plutonium-238
https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_Power#SNAP-27

 SNAP-27 RTG deployed by the astronauts of Apollo 14 identical to the one lost in the reentry of Apollo 13

Use of RTGs in space exploration http://fas.org/nuke/space/bennett0706.pdf


As Poul Anderson pointed out, isotope-heat based nuclear power is actually potentially quite dangerous.  Before we discuss the applications of what we would do if we have huge tonnages of cheap hot isotopes on demand we should note the various properties of the isotopes under discussion.

First of all we have to discuss biological safety.  The problem is, many of these isotopes would kill if assimilated in the body. Some can kill at a distance if not sheilded because they emit gamma radiation.  Some like Cesium-137 are both  bone-seekers and gamma emitters.  Traditional nuclear reactors produce large amounts of cesium 137 https://en.wikipedia.org/wiki/Caesium-137 and Strontium 90. https://en.wikipedia.org/wiki/Strontium-90

 These are great heat sources--- each roughly 5% of the waste in ordinary nuclear power plants but boneseeker isotopes and very dangerous indeed if ingested. They end up in the bones and the victim gets hammered by radiation from within far more than if they were not biologically concentrated. A megawatt-year  (fissioning 400 grams of uranium-235),  produces 9 grams of strontium-90 (about 2,000 curies), and 14  grams of cesium-137 (also about 2,000 curies).

Strontium 90 does not emit large amounts of gammas-- therefore much more portable without as heavy shielding. Cesium 137 does https://en.wikipedia.org/wiki/Commonly_used_gamma-emitting_isotopes
and is useful in food sterilization  https://en.wikipedia.org/wiki/Food_irradiation#Dosimetry among other uses.
Nasa sterilizes astronaut food at 44 kilogray (sterilizing frozen meat for NASA astronauts doses of 44 kGy ) which is 44 kilogray = 4400000 rad or about 7000 lethal doses for a man.  
http://www.asknumbers.com/RadiationAbsorbedDoseConversion.aspx

Because of these lower shielding requirements, the ex-USSR made over 1,000 strontium-90 sources to power remote lighthouses, radio relays, and scattered electronic installations that had to cope with cold, darkness and horrific weather that made resupply very expensive.

At times in these polar contexts the waste heat was an asset rather than a liability; (traditional RTG designs are very inefficient, only a few percent of the heat goes into producing electrical power)

Because of the fact that they compose together about 10% of nuclear fission waste from today's uranium power reactors, these two isotopes could form the basis of very widespread nuclear isotopic power units. In an all uranium reactor powered world,  with cheap recycling of wastes (good luck) and the present waste distribution with no enhanced burnup (such as you'd see in thorium molten salt reactors) you could probably use around  15-30 thousand tons of fissionables a year.


see my interview with David Leblanc for more
http://nextbigfuture.com/2010/11/david-leblanc-explains-why-thorium.html
assuming 100% of world energy a little high (lets leave at least some space for hydro, biomass, wind and solar!). But yes, 15,000 GWe would only consume 15,000 tonnes of thorium per year, but you are missing a zero in regards to how much U235, by Robert Hargraves' numbers it is 15,000 tonnes, not 1500. Starting on U235 is not quite as efficient as U233 though so to be conservative I'd probably double that value to 30,000 tonnes.

Given 10% output of these two wastes, you would have about 1500 tons a year each of Sr-90 and Cs-137 to play with-- not unlimited by any means in terms of the number of remote sites that could use essentially free power.

3000 tons of the Sr-90 and Cs-137 would constitute a heat source of .96 watts/gram
and .42 watts/gram respectively so 3000 tons (3 billion grams) would yield around 3 gigawatts and 1.2 gigawatts of portable power respectively.

Yet such dispersion would be dangerous from the point of view of "orphaned sources" https://en.wikipedia.org/wiki/Orphan_source  ie when they are old and lost track of -- they are long lived enough that they just don't vanish but remain, potentially outliving even a quite robust container...an  unspeakable environmental danger in case of releases.

For example a mere 5 kilograms could pollute 88 square kilometers at 57 grams per km2.  You couldn't grow agricultural products for direct sale. Grams per square kilometer don't sound like much but doses of many curies tell you that this is dirty bomb territory.  The table below shows you that 7.2 milligrams of strontium 90 is a curie, so 57000 / 7.2 = 7916 curies per square km.
3000 tons is 3 million kg so we are talking about 3 million kg / 5 kg = 600000 square kilometers polluted  t 7916  curies per square kilometer that is 293 terabequerels) 293 trillion individual decays per second


For comparison, 57 grams fission products (from nuclear weapon FAQ below) causes 30 billion, not million, curies (rapidly decaying) for a brief time-- this is because of the huge mix of very short lived isotopes.
http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html
Radioactive isotopes are usually measured in terms of curies. A curie is the quantity of radioactive material that undergoes 3.7x10^10 decays/sec (equal to 1 g of radium-226). More recently the SI unit bequerel has become common in scientific literature, one bequerel is 1 decay/sec . The fission of 57 grams of material produces 3x10^23 atoms of fission products (two for each atom of fissionable material). One minute after the explosion this mass is undergoing decays at a rate of 10^21 disintegrations/sec (3x10^10 curies). It is estimated that if these products were spread over 1 km^2, then at a height of 1 m above the ground one hour after the explosion the radiation intensity would be 7500 rads/hr.
How much cesium 137 was released in Chernobyl? 2.5 megacuries.


http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/cherno2.html
A retrospective view of the Chernobyl accident of Apr 26, 1986 assesses the total radiation release at about 100 megaCuries or 4 x 10e18 becquerels, including some 2.5 MCi of cesium-137. The cesium is the most serious release in terms of long term consequences. The total release was around 4% of the total accumulated activity of the core and compares to a release of 15 Ci at Three Mile Island. The release was then about 7 million times that at TMI. Anspaugh, et al. suggest that essentially all the noble gases and about half of the volatile elements (iodine-131, cesium-134 and cesium-137) were released . The cesium release from all of the atmospheric weapons tests is estimated to be about 30 MCi. The noble gas releases were estimated by Levi to be 45 MCi of xenon-133 and 5 MCi of krypton-85. 

3000 tons of Cesium 137 of which (table below) 12 milligrams is a curie. 
A billion milligrams in a metric ton so 12 tons of Cesium 137 is a billion curies. 12000 tons would be a trillion curies so 3000 tons would be 250 billion curies or 100,000 Chernobyls. If evenly distributed (it wouldn't be) it could pollute to exclusion zone standards the entire land area of the Earth.

Size of red Chernobyl exclusion zone in the picture below is around 2600 square kilometers or 1000 or so square miles. This is an arbitrary standard but set low for safety.  https://en.wikipedia.org/wiki/Chernobyl_Exclusion_Zone

 Chernobyl Cesium 137 only was 2.5 megacuries so the physical quantity of  Cesium 137 released in Chernobyl was 1/400th of that or about 12000kg/400 or a mere 30 kg of Cesium 137 producing this nasty map. For comparison there are said to be 150 million curies of Cesium 137 in the Indian Point holding pool in the eastern United states.

 40 curies a square km is about 104 curies a square mile. Note that  the exclusion zone here is by no means a death zone.  A point mass of 30 kg of Cesium 137 (the entire Chernobyl release) all 2.5 million curies of it at 100 meters would give you a dose of 54.9 rads an hour. It would kill you to camp out there but walking by quickly once would not be a problem. The real problem would be biological integration and uptake of cesium compounds which would then try to become part of your skeleton and fry you from within.
http://pripyat.com/en/articles/ten-myths-about-chernobyl-disaster.html  Pripyat area site explaining reality on the ground
 Russia applies a normative of Cesium 137 content in milk, which should not exceed 100 Bq per liter. In Norway, they use 370 Bq per 1 kilo for baby food. Therefore, in Russia, milk containing 110 Bq is considered radioactive, while in Norway this level is one third of the allowed concentration.

Fukushima release https://en.wikipedia.org/wiki/Radiation_effects_from_the_Fukushima_Daiichi_nuclear_disaster#Caesium-137
https://fas.org/man/eprint/econcon.pdf  Study showing that the cost of cleaning up fallout to various levels hugely dependent upon cleanup  standards. 

Note that the half life of 30 years or so is very long in terms of cleaning up after an accidental release. And obviously we are talking many tens of thousands of years after plutonium 239 until it decays away in case of a spill.
The shorter half life is far preferable.The ideal would be a single isotope with a half life of about a year. A spill would then self-clean in a single generation or two at most. That is in line with the ability of our civilization to guard disused sites.

An example of a very short lived isotope is Polonium 210. Unfortunately this has a rare precursor, bismuth, and in any case is quite toxic (google polonium assassination) and a volatile form. The power output is amazing, though (see the table) 141 watts a gram!  2 million tons of that mattercasted into existence would make  your day with 282 terawatts of radiant power!  Think it would volatilize?

Tritium is interesting with aheat output of (PS = 0.33 W/g). so 3 kg (28.86 megacuries) is 1 kilowatt. But tritiated water https://en.wikipedia.org/wiki/Tritiated_water is such a health hazard that we don't consider it further here even if we got it for free by mattercaster.

A sample isotope hunt sing the Wise Uranium Project site neutron activation calculator  http://www.wise-uranium.org/rnac.html we can see for example the effects of neutron bombarding various isotopes in this case arsenic 
Neutron flux = 10.00e30  per cm2s
Irradiation = 1 s;  Delay = 0 h 

    Original      Reaction      Activation       Half-
    Nuclide                     & Decay (~>)     Life
                                Products


Arsenic:

          As-75    (n,2n) ->           As-74    (17.76 d)

          As-75    (n,3n) ->           As-73    (80.30 d)

          As-75    (n,p)  ->           Ge-75    (82.78 m)

          As-75    (n,A)  ->           Ga-72    (14.10 h)

It's a complicated subject because each daughter isotope must have a endpoint of decay too. Notice that the Germanium-75 generated above has almost a 7 year half life leading to 210 years for a 30 generation decay time and that is assuming all daughter products of THAT are stable. However, if you could isolate all the arsenic from the Germanium then you might have a shortlived isotope package capable of great power for amonth but you wouldn't have a remote-site power pack that could endure for decades.  You would have to FedEx the units and switch them out quickly.  This briefly touches on the selection of the optimum isotope for the job.
Example of a bad spill requiring 30 generation decay:
Initial exposure: 
1 lethal dose per minute  If you sprint you have a bare chance to live.
10 generations of decay later (10 half lives) 1 lethal dose  in 1000 minutes You could walk by once and probably max your lifetime worker exposure limit.

20 generations of decay later (20 half lives) 1 lethal dose  in 1 million minutes 1.9 yrs so you could enter for a few minutes a week.
30 generations of decay later (30 half lives) 1 lethal dose  in in 1 billion minutes 1900 yrs
so totally safe to live there.
10 x 30 year half life is 300 years, 20 is 600 years, 30 900 years.

But with Cobalt 60 instead of Cesium 137 the half life is a fifth as long, and any traces would vanish five tines faster.
Here is the isotope table:
https://en.wikipedia.org/wiki/Curie
Isotope Half life              Mass of 1 curie               Specific activity (Ci/g)
232Th 1.405×1010 years 9.1 tonnes             1.1×10−7 (110,000 pCi/g, 0.11 µCi/g)
238U 4.471×109 years 2.977 tonnes     3.4×10−7 (340,000 pCi/g, 0.34 µCi/g)
40K 1.25×109 years        140 kg                7.1×10−6 (7,100,000 pCi/g, 7.1 µCi/g)
235U 7.038×108 years 463 kg            2.2×10−6 (2,160,000 pCi/g, 2.2 µCi/g)
129I 15.7×106 years         5.66 kg         0.00018
99Tc 211×103 years          58 g                 0.017
239Pu 24.11×103 years 16 g                      0.063
240Pu 6563 years        4.4 g                      0.23
226Ra 1601 years        1.01 g                  0.99
241Am 432.6 years       0.29 g                  3.43
14C 5730 years                 0.22 g                    4.5
238Pu 88 years                       59 mg          17
137Cs 30.17 years           12 mg         83
90Sr   28.8 years                  7.2 mg       139
241Pu 14 years                 9.4 mg         106
60Co 1925 days          883 μg     1132
210Po 138 days           223 μg       4484
3H       12.32 years          104 μg     9621
131I      8.02 days                 8 μg               125000
123I       13 hours                0.5 μg      2000000
And remember that these with yellow highlighting are boneseeker isotopes. Even in a engineering fantasy article like this I don't see them being used by choice for widespread peaceful uses on Earth.  For powering rovers on Mars, you could totally see them.30 kilograms of Cesium 137 would give off .42 watts a gram, so 12600 watts thermal from that mass. If you could make a supercritical CO2 turbine with the heat you could literally have planet wide range for such a rover (if 25% efficient you could have 3 kilowatts electric or hydraulic to play with-- you'd need plenty of shielding (maybe mounted on a trailer 100 meters ahead of the main unit with a tow cable plus a point shield) on the other hand you could probably have amazing gamma ray spectometry from your free point source.

Basically a UNMANNED martian rover with rad-shielded electronics could use it-- and power for a crane, for a sampling arm-- endless possibilities. 3000 tons would let us build 100,000 such rovers, (probably from a factory on one of the Martian Moons, installing the Earth-exported-good riddance- RTG nuclear material up there) and that is enough so each rover would only have to probe around 1440 of the 144.8 million km² of the martian surface. It is plausible that every obviously interesting target on the entire Martian surface could be probed that way, mining samples taken--we could survey the entire planet.


http://phys.org/news/2011-11-reliable-nuclear-device-power-mars.htmlNASA chose to use a nuclear power source because solar power alternatives did not meet the full range of the mission's requirements. Only the radioisotope  allows full-time communication with the rover during its atmospheric entry, descent and landing regardless of the landing site. And the nuclear powered rover can go farther, travel to more places, last longer, and power and heat a larger and more capable scientific payload compared to the solar power alternative NASA studied.
"You can operate with solar panels on Mars, you just can't operate everywhere," said Johnson. "This gives you an opportunity to go anywhere you want on the planet, not be limited to the areas that have sunlight and not have to put the rover to sleep at night."


Read more at: http://phys.org/news/2011-11-reliable-nuclear-device-power-mars.html#jCp




If we have Martian colonization we could even consider huge and heavy RTG units for manned exploration use.  I can see a hot air dirigible kept aloft at day by the sun (a solar montgolfiere) and by night by RTG waste heat.  The manned cabin could be a kilometer below the lifting bag for natural distance shielding. On Earth, a typical two-burner hot air balloon can be around 36 million BTU an hour or around 10.4 megawatts of power. http://www.skysail.org/faq  That is about 30 tons of Cesium-137 for the Martian balloon if the same power factor applies. http://www.rapidtables.com/convert/power/BTU_to_kW.htm  But strontium-90 would be a better choice because of more power nad lighter shielding.

Remember that the gravity is less (as is the atmospheric pressure) so conditions would be utterly different.  If needing to be sufficiently thin (and it probably will be) it might lift well in the day but lose heat rapidly at night.  We can imagine a multi-layered balloon with 10 layers of gasbags around the main lifting cell to insulate the heat losses. The detailed design of such a balloon with a hot gamma emitter is interesting but beyond the scope of this article. At the very least a well insulated RTG well under a base to provide unstoppable heat and power would be a most welcome asset in the Martian polar night. Better yet would be several in case of a system failure in one.

Back on Earth, however, the dangers of boneseeker isotopes' escape into the human crop raising environment are such that for this article, in place of strontium 90, we consider plutonium 238.  In place of cesium 137 we consider cobalt 60.   Are these harmless? No, and no.


Special health hazards of PU 238 or why you really want a good container for your power isotopes...
https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator
The plutonium-238 used in these RTGs has a half-life of 87.74 years, in contrast to the 24,110 year half-life of plutonium-239 used in nuclear weapons and reactors. A consequence of the shorter half-life is that plutonium-238 is about 275 times more radioactive than plutonium-239 (i.e. 17.3 curies (640 GBq)/g compared to 0.063 curies (2.3 GBq)/g[24]). For instance, 3.6 kg of plutonium-238 undergoes the same number of radioactive decays per second as 1 tonne of plutonium-239. Since the morbidity of the two isotopes in terms of absorbed radioactivity is almost exactly the same,[25] plutonium-238 is around 275 times more toxic by weight than plutonium-239.

 But, Plutonium 238 is an alpha emitter, and easily shielded for lightweight applications. Cobalt-60 a heavy gamma emitter, but if sufficiently cheap might give lots of power for heavy shielding applications like submarines.


A great reference on RTGs, Space and isotopes--NEEP 602 Course Notes (Spring 2000) 

Nuclear Power in Space
G.L. Kulcinski, Instructor 
http://fti.neep.wisc.edu/neep602/SPRING00/lecture5.pdf

ray power

rtg specific activity
curies gram and curies watt
Here is a specific activities listing:
http://www.iem-inc.com/toolspa.html
 listing of specific activities, in units of "curies per gram" for a variety of radionuclides. For this listing the elements are shown alphabetically.  The specific activities are written in scientific notation (i.e., 7.2E1 is equal to 7.2 x 10, or 72).

curies/gram




Not sure about the curium data in the table below---JF
Polonium-210  alpha decay .38 yr half life 141.0 watts/gram
Curium-244     a           .45              120.0 watts/gram
Cerium-144     beta,gamma   .78               26.0 watts/gram
Thorium-228     a           1.90             170.0 watts/gram
Cobalt 60      beta, gamma  5.25             17.4 watts/gram
Curium-242      a           18                2.8 watts/gram
Strontium-90  beta, gamma   28                 .96 watts/gram
Cesium 137     beta, gamma 30                   .42 watts/gram
Plutonium-238     alpha     89                   .56 watts/gram




Pu238 advantages https://en.wikipedia.org/wiki/Plutonium-238
are seen above-- low shielding, reasonable output,   .56 watts/gram-- 88 year long half life.
Current crazy disadvantage-- the cost a quarter  megacurie of Plutonium 238 puts out 8400 watts thermal and alleged market price would be 75 to 150 million dollars. I am guessing this is about 15 kilograms.
*Pu-238 specific activity is 17 kCi/kg; decay produces 560 Wt/kg, estimated “price” of $5-10M/kghttp://www.thoriumenergyalliance.com/downloads/plutonium-238.pdf
250 kCi of Pu-238 8400 watts-thermal $75-150M**
Plutonium-238 has a specific power of 0.56 watts/gm or 560 watts per kilogram,
so in theory all you would need is 470 / 560 = 0.84 kilograms. Alas, the thermoelectric
generator which converts the thermal energy to electric energy has an efficiency of only a
few percent. If the thermoelectric efficiency is 5%, the plutonium RTG has an effective
specific power of 560 x 0.05 = 28 watts per kilogram (0.036 kilogram per watt or 36
kg/kW). This means you will need an entire 17 kilos of plutonium to produce 470 watts.
Currently RTGs have an alpha of about 200 kg/kW (though there is a design on
the drawing board that should get about 100 kg/kW). . So an RTG with the theoretical
maximum output of 1 kilowatt would obviously mass 200 kilograms.
Plutonium-238 needs less than 2.5 mm of shielding, and in many cases no
shielding is needed as the casing itself is adequate.

The thermal power of Pu-238 costs $10,000 a gram ($10 million a kilogram)
0.56 watts/gm  for 88 years at the end of which power has declined to half.
Treat it as .56 watts/gm for 44 years and nothing after
rough figure of  24.64 watt years per gram.
At current USA  home electricity not heat prices (10x AS EXPENSIVE AS THE CHEAPEST HEAT) $1 a watt year is typical
so if it cost $25 a gram you would  be paying a typical fair price for convenient power.
$25000 a kilogram maximum plausible for "normal" commercial uses.
At $10 million a kilogram it is about 400 times too expensive. (As we shall see below, it is easily plausible to reduce that number by at least a factor of 30 even with today's technology)
To be competitive with the cheapest heat (coal) it should be at least 10 times cheaper still.
that is for the entire price of the fuel preloaded and neglecting the time value of money.


In the space RTG pdf page 19 http://fti.neep.wisc.edu/neep602/SPRING00/lecture5.pdf the future cost of Cobalt 60 (presumably given reactor breeding) is given as $280 a gram. (incidentally there Pu 238 should be makable on a mass basis today for around $300 a gram not  $10,000.  Current prices are high because of politically dictated engineering decisions taken years ago)

The Wiki page https://en.wikipedia.org/wiki/Plutonium-238  says Reactor-grade plutonium is not useful for producing Pu-238 for RTGs because difficult isotopic separation would be needed.
Pure plutonium-238 is prepared by neutron irradiation of neptunium-237,[citation needed] one of the minor actinides that can be recovered from spent nuclear fuel during reprocessing, or by the neutron irradiation of americium in a reactor. In both cases, the targets are subjected to a chemical treatment, including dissolution in nitric acid to extract the plutonium-238. A 100 kg sample of light water reactor fuel that has been irradiated for three years contains only about 700 grams of neptunium-237, and the neptunium must be extracted selectively. Significant amounts of pure Pu-238 could also be produced in a thorium fuel cycle.
But there may be ways around each of those limitations, to be explored in this and future articles.

 The thermal power of Cobalt 60 --1130 curies a gram 17.4 watts a gram   https://en.wikipedia.org/wiki/Cobalt-60 costs  $280 a gram ($280,000 a kilogram) by one estimate.
 17.4 watts/gram for 5.24 years at the end of which power has declined to half.
Treat it as 17.4 watts/gram for 2.62 years and nothing after
rough figure of  45.588 watt years per gram. (about twice that of  Pu-238)
At current USA  home electricity not heat prices (10x AS EXPENSIVE AS THE CHEAPEST HEAT) $1 a watt year is typical
so if it cost $45 a gram you would  be paying a typical fair price for convenient power.
$45,000 a kilogram maximum for "normal" commercial uses.
At $280,000 a kilogram it is about 6.2 times too expensive.
To be competitive with the cheapest heat (coal) it should be at least 10 times cheaper still.
that is for the entire price of the fuel preloaded neglecting the time value of money.

Because of the radiation in gammas, a few kilograms would be as radioactive as all the Cesium-137 (30 kg) of Chernobyl. Cobalt-60 is used to sterilize bugs, food and so on and needs a heavy radiation shield.

Plutonium 238 is just an incredibly neat isotope and as long as it remains in its thin shield totally safe  The problems then are accidental release and deliberate release-- and the possible added worry of someone trying to make a nuclear bomb out of it. According to this PDF  http://ocw.mit.edu/courses/nuclear-engineering/22-812j-managing-nuclear-technology-spring-2004/lecture-notes/lec17slides.pdf

 “Virtually any combination of plutonium isotopes -- the different forms of an element having different numbers of neutrons in their nuclei -- can be used to make a nuclear weapon... At the lowest level of sophistication, a potential proliferating state or subnational group using designs and technologies no more sophisticated than those used in first-generation nuclear weapons could build a nuclear weapon from reactor-grade plutonium that would have an assured, reliable yield of one or a few kilotons (and a probable yield significantly higher than that)
Isotope Critical Mass (kg) Half Life (years) Decay Heat (watts/kg) Neutron Generation (neutrons/g-sec)  Pu-238 10                                      88 560 2600 
Pu-239 10                                        24,000  1.9 0.02 
Pu-240 40                                           6,600 6.8 900 
Pu-241 13                                                14 4.2 0.05 
Pu-242 89                                        380,000 0.1 1700 
Sorry about the formatting but it didn't copy cleanly. Note the decay heat problem of trying to build a bomb with 238 (duh) but also the neutron generation rate. https://en.wikipedia.org/wiki/Nuclear_chain_reaction#Predetonation

I would think predetonation would exclude it but the quote above in bold seems to indicate not.  So there may be a proliferation problem with 238 but it is far more detectable than 239.  We will neglect it here but could be a show stopper in real life.


Supposing Pu-238 is usable in terrorist explosions?
Yes-- but.   But--you have got to discreetly  haul a heat source that is very hard to cool with the kind of discreet covering you are counting on to conceal it. Eventually it will advertise itself. The police will come.
If you decide to engineer a bomb-- more complications---- there is a learning curve and handling red-hot isotope is not the most forgiving place to learn your bomb making trade.
If your bomb doesn't go off with more than a fizzle you have a slightly dirty bomb but you have lost lots of material.
If it goes off successfully you have a manhunt after you.

With Cobalt-60 as a widely deployed isotope you lose most of the elegant Plutonium-238 man portable applications because of the huge shielding requirements.

I should mention some of these because they are just so cool.

  • Plutonium teapot for the polar regions. Go hiking with this baby and it keeps you warm. Scoop up snow and it melts it for fresh water, wait a little longer and you can wash your hands at the North Pole with hot water, longer still and you have some hot tea to drink.  At night it keeps your tent warm.  Expensive?  What does it cost to cure frostbite or to tend to the medical conditions of those who lose limbs to mountain and polar cold? 
  • Plutonium diving warmsuits  
you can of course wear one of these on your arctic expedition as well.radioisotope backpack heater capable of furnishing around 300 to 400 thermal watts for maintaining body temperature. In addition to use for underwater swimmers, the unit may be used by downed pilots or suits for land operations in the Arctic and Antarctic.
https://patents.google.com/patent/US3402709A/en?q=plutonium&q=diving
  • Plutonium bedwarmers,anyone?  Sounds like a joke but welcome in the mountains or polar regions.
  • Plutonium hot stove/plate for camping
  • Plutonium water distiller for camping, the deserts or spacecraft (waste recycling) https://patents.google.com/patent/US3558437A/en?q=plutonium&q=atomic+energy+commission&q=238&q=drink
  • You can probably list hundreds of uses in the general spirit of this-- anyplace you want unlimited portable power for a generation or more, ideally in the form of heat, independent from the sun cycle, fuel deliveries and totally man-portable.  
  • A laptop with a battery that doesn't die.
  • And atomic cars in the spirit of the Ford Nucleon above! 

Many comments on Scott Lowther's The Unwanted Blog on this general topic (atomic 50s visions in the alternate world of the movie 2001)

http://up-ship.com/blog/?p=22222


    Side roads on the way from 1968 to 2001: 5a 6 comments

let’s call it 215 kilowatts, same as the Tesla Roadster. If we assume RTG power, like the atomic pen, then the car will have a pretty massive battery pack...Even so, at 0.39 watts per gram this system would require at least 551 kilos (1212 pounds) of plutonium 238. Clearly not feasible.

    Avatar
    Simon666
    • 9 hours ago

    The 215 kW figure you gave is peak power. It is utterly useless to design a nuclear battery for this, as when the car is not using peak power, you would need to dump substantial amount of thermal energy.

    If we assume a car is not driven more than 100 km a day on average (most people drive less) and energy consumption is 15 kWh / 100 km, then you'd only need 15 kWh of electric battery (less than a Nissan Leaf) and 15.000 W * 3600 s / ( 24 h * 3600 s / h ) = 625 W of continuous power.

    At 0.39 watts per gram of Pu 238 and assuming 10% efficient conversion of thermal to electric you'd only need 16 kilogram of Pu 238 for a nuclear electric car and a small organic rankine cycle or something to produce only 650 W(electric) continuously, which need not weigh or even cost much either.

    You could then add some spare electric capacity. At night you could usually dump the excess electrical energy from the battery in the grid or top up the battery in case you've driven a long range.

    It is technically completely feasible (hell, you could even make a nuclear powered Tesla Model S, space enough in the frunk for the nuclear generator) but kilogram quantities of Pu 238 would still not be cheap of course, let alone production capacity in the entire world would be sufficient for a small number of vehicles only.
 

  •  One of the most interesting uses is for remote power. Nowadays you will often see a solar panel near a remote very low power bit of electronics that previously would demand a battery or diesel generator installation and yearly maintenence visitors.   But what if there were extended periods of darkness, cold, horrible weather (polar regions, Mars, etc)  
  • I recall one story of the CIA subsidizing a mountaineer on his way to the Himalayas to plant an RTG to power some remote observing equipment within monitoring sight-lines of denied territory in Tibet, again from the context 1960s. Here is a slightly alarmist account, yep, 1966.  http://www.counterpunch.org/2008/06/30/making-a-billion-hindus-glow-in-the-dark/
The peak was probably around 1971-73 just as the modern lithium pacemaker was beginning to be deployed.  https://en.wikipedia.org/wiki/Artificial_cardiac_pacemaker  This by definition is almost the most portable you can get.  As I kid I read DC comics about Metallo, the man whose head was kept alive by a robot body with a uranium or kyptonite powered heart.  Naturally I confused a mere nuclear pacemaker with an actual plutonium powered heart. Could you really live forever, if the heart never stopped beating as the comic claimed?  I wondered at age 11.
Answer to younger self:  No. Only one of the causes of death has to get you, if the robot heart keeps beating after that it don't help a whole lot.  And on that morbid note, I should mention that at least a few (battery not RTG) pacemakers were given an inadvertent  endurance test inside a crematorium http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1279940/
What happens if a Pu-238 pacemaker gets cremated http://www.osti.gov/scitech/servlets/purl/4126031/
    However this page https://www.orau.org/ptp/collection/Miscellaneous/pacemaker.htm says that The hard titanium case is designed to withstand any credible event including gunshots and cremation.
  • http://uk.reuters.com/article/health-heart-pacemaker-dc-idUKN1960427320071219  Here is a woman who has been saved 5 operations over 30+ years by using a plutonium rather than battery powered pacemaker.  You can say she could have more modern pacemakers every few years instead but you can imagine civilizational resets as occurred in Russia a generation ago or worse where the people who have an atomic pacemaker go on living and the pacemakers that are not available becaus eof blockade/sanctions/civil unrest don't get installed and the people die.

If we could have a choice of unlimited quantities of Plutonium 238 or Cobalt 60 very few people would choose Cobalt 60 yet the proliferation concern may yet force the choice to Cobalt 60. What would be the consequences?

However much we might miss the man-portable applications,  having an Cobalt-60 air-independent heavy power source underground, underwater in the polar reasons and in space for industrial purposes would be very helpful at a reasonable price.


  • Mining without using up oxygen for heavy mining equipment and fume-immune engines,
  • Deep tunneling and drilling (the famed subterrene of science fiction)
  • Lunar polar ice melting and refining prior to a manned landing to have guaranteed water and return fuel
  • Displacing the 7% or so of petroleum burned by ships (certainly heavy enough to mount the armor)
  • Powering long distance heavy vehicles for engineering and military purposes-- locomotives, tanks, etc with a greatly reduced logistics chain.
  • Powering bases outposts and depots in the arctic, remote locations, etc.
If cobalt-60 were available by the ton and constituted a heat source of 17.4 watts/gram then you could get 10 megawatts plus of heat plus about 5 of electricity out of it for say a couple of years.(It would also per ton constitute a radiation source of 1130 curies a gram or 1.1 gigacuries a ton. Unshielded that gives you 1.012890E+005 rads an hour at 100 meters distance. http://www.radprocalculator.com/Gamma.aspx   Yet with 6 meters of water shielding the dose at 100 meters would be 9.176362E-010 rads an hour. A concrete shielded earth berm would be adequate though for security reasons you probably would want to embed the thing in a hundred tons of concrete with a red radiation trefoil sticking out of it on a pole.

 If it sold for $5 million for that ton It would pay to use it today for many applications 
Could it be made that cheaply?

Imagine a world where we could reliably trigger D-D fusion 

and have no shortage of neutrons available for isotope formation.
Thorium 232 to U 233


\mathrm{n}+{}_{\ 90}^{232}\mathrm{Th}\rightarrow {}_{\ 90}^{233} \mathrm{Th} \xrightarrow{\beta^-} {}_{\ 91}^{233}\mathrm{Pa} \xrightarrow{\beta^-} {}_{\ 92}^{233}\mathrm{U}

U 238 to Plutonium 239

\mathrm {^{238}_{\ 92}U\ +\ _{0}^{1}n\ \longrightarrow \ _{\ 92}^{239}U\ {\xrightarrow[{23.5\ min}]{\beta ^{-}}}\ _{\ 93}^{239}Np\ {\xrightarrow[{2.3565\ d}]{\beta ^{-}}}\ _{\ 94}^{239}Pu}

Cobalt 59 to 60
59Co + n → 60Co

29 kg of deuterium fused would enable production of  about 115 kilos of Co-60 2.4 mt equiv

252 kilos of deuterium fused would enable production of  about 1 ton of Co-60  20.8 mt equiv

Hot an efficient energy bucket to say the least! Treat it as 17.4 watts/gram for 2.62 years and nothing after
rough figure of  45.588 watt years per gram. ( 45.5 mw yrs per ton thay is 398580 mwhrs
https://www.unitjuggler.com/convert-energy-from-MWh-to-kT.html

342.94646271511 kT
Conversion base : 1 MWh = 0.0008604206500956 kT Conversion base : 1 kT = 1162.2222222222 MWh
20.8 mt equiv /0.343= 1.6% efficient
on other hand trading 252 kilos of  deuterium  at $500 a  kg worth $126,000 getting a million plus in power would pay if the processing was say only a couple of hundred thousand dollars more.  Some versions of Project Pacer held promise for that level of costs (one version had the net cost per thermonuclear device be a mere $1000---I hope to write an article about Project Pacer soon with more on this.)


The nuclear weapons FAQ says this on the Mike Device, the only tested D-D bomb:
The total fusion yield was thus 2.4 megatons, which corresponds to the efficient thermonuclear combustion of 29.1 kg of deuterium (172 liters), or the inefficient combustion of 41.6 kg (249 liters). The total fission yield was 7.9 megatons, the fission of 465 kg of uranium.


The central problem is that however easy it gets to generate Cobalt-60 it gets even easier to turn Thorium-232 to U-233 and Uranium-238 to Plutonium-239 (NOT 238 but rather prime nuclear bomb material)
And not just that but four times the yield in terms of kilos--


1kg D can transmute by neutron flux only 4 kg of Co-59 to Co-60

but 16 kg Uranium 238 int  16 kg of Plutonium-239

29 kg of deuterium fused would enable production of  about 115 kilos of Co-60 2.4 megatons equivalent
252 kilos of deuterium fused would enable production of  about 1 ton of Co-60  20.8 megatons equivalent
29 kg of deuterium fused would enable production of  about 465 kilos of Plutonium-239 2.4 megatons equivalent

252 kilos of deuterium fused would enable production of  about 4 tons of Plutonium-239  20.8 megatons equivalent

And not just that but you could get more power out of the Plutonium-239 if completely fissioned, equivalent of around 17.4 kilotons per kg  than  you could get from the Cobalt-60 if completely decayed. which as we saw before was only 0.342 kt per kg. That is 50 times more energy per mass of generated product and about 200 times more energy per neutron of D-D fusion realized.
Convenient Energy Content Approximations
Fission of U-233:  17.8 kt/kg
Fission of U-235:  17.6 kt/kg
Fission of Pu-239: 17.3 kt/kg
Fusion of pure deuterium: 82.2 kt/kg
Fusion of tritium and deuterium (50/50): 80.4 kt/kg
Fusion of lithium-6 deuteride: 64.0 kt/kg
Fusion of lithium-7 deuteride
Total conversion of matter to energy: 21.47 Mt/kg
Fission of 1.11 g U-235: 1 megawatt-day (thermal)
http://nuclearweaponarchive.org/Nwfaq/Nfaq12.html
 So from an efficiency standpoint small plutonium reactors look much better than isotope power. Arthur C. Clarke did not favor this.

"At the risk of making myself appear a reactionary old fogey, I do not believe that uranium and plutonium fuelled devices should be allowed off  the ground" 
https://books.google.co.il/books?id=ch19NjEERFMC&pg=PT39&lpg=PT39&dq=clarke+reactionary+old+fogy&source=bl&ots=zG-yaXjFt4&sig=RbldCdYYqBr390nI6fPX_9IQUH0&hl=en&sa=X&ved=0ahUKEwii0Y788YvKAhWLWBQKHVxCBzsQ6AEIGjAA#v=onepage&q=clarke%20reactionary%20old%20fogy&f=false


A sufficiently small reactor could be super-hardened (less than 1 meter in size) to be crashproof up to a couple hundred meters a second. Yes there are design tricks that can enable survival at greater speeds yet but part of me is thinking that subsonic light planes would be one thing but faster or bigger might be a very bad idea.
On the other hand this gives light planes global range.(In about 40 hours of flight time)  So proliferators suddenly have a global strike force. (assuming they can get through air defense)  https://en.wikipedia.org/wiki/Swarming_(military)

 Hm. I am trying to keep this a civilian article and I keep running into military risks. Oh, well.

The source isotope for the plutonium-239 would be common natural or depleted uranium, ideally the depleted stuff.

https://en.wikipedia.org/wiki/Depleted_uranium#Safety_and_environmental_issues
About 95% of the depleted uranium produced until now is stored as uranium hexafluoride, (D)UF6, in steel cylinders in open air yards close to enrichment plants. Each cylinder contains up to 12.7 tonnes (or 14 US tons) of UF6. In the U.S. alone, 560,000 tonnes of depleted UF6 had accumulated by 1993. In 2005, 686,500 tonnes in 57,122 storage cylinders were located near Portsmouth, Ohio, Oak Ridge, Tennessee, and Paducah, Kentucky.[154][155] The long-term storage of DUF6presents environmental, health, and safety risks because of its chemical instability. When UF6 is exposed to moist air, it reacts with the water in the air and produces UO2F2 (uranyl fluoride) and HF (hydrogen fluoride), both of which are highly soluble and toxic. Storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated lifetime of the steel cylinders is measured in decades.[156]
There have been several accidents involving uranium hexafluoride in the United States.[157] The vulnerability of DUF6storage cylinders to terrorist attack is apparently not the subject of public reports. However, the U.S. government has been converting DUF6 to solid uranium oxides for disposal.[158] Disposing of the whole DUF6 inventory could cost anywhere from 15 to 450 million dollars.[159]


Over a million tons of DU in the world could supply enough plutonium for 40 million 25kg class plutonium micro reactor  fuel loadings. (See below)

Assuming easy and quick extraction and processing, we can, since we are looking at compact power,  compare a burner reactor (not a breeder, the fusion breeds the Plutonium-239 for free, our job is just to burn the 239 as compactly and cheaply as  possible),. We base our model on the  MITEE (MInature ReacTor EnginE) reactor http://www.lpi.usra.edu/meetings/outerplanets2001/pdf/4084.pdf 
the baseline MITEE engine achieves a specific impulse of ~1000 seconds, a thrust of 28,000 newtons, and a total mass of only 140 kilograms, including reactor, controls, and turbo-pump. Using higher performance nuclear fuels like U-233, engine mass can be reduced to as little as 80 kilograms. 
which theoretically could use around 25-50 kg of near bomb grade material as competition for unlimited Pu-238 isotope power.

Supposing we could obtain unlimited cheap isotopes  for micro reactors like this (140 kg or less for the nuclear core, possibly in the low ton range for a supercritical CO2 nuclear gas turbine) which use highly enriched fissionables are definite candidates to power anything a Cobalt-60 shielded system could, with finer power control--- but, alas, also having cesium-137 and strontium 90 produced internally as it fissions away.


http://connection.ebscohost.com/c/articles/8944977/mitee-b-compact-ultra-lightweight-bi-modal-nuclear-propulsion-engine-robotic-planetary-science-missions
MITEE-B (MInature ReacTor EnginE - Bi-Modal) can deliver 1000s of kilograms of propulsive thrust when it operates in the NTP mode, and many kilowatts of continuous electric power when it operates in the electric generation mode.
. The high propulsive thrust NTP mode enables spacecraft to land and takeoff from the surface of a planet or moon, to hop to multiple widely separated sites on the surface, and virtually unlimited flight in planetary atmospheres. 
The continuous electric generation mode enables a spacecraft to replenish its propellant by processing in-situ resources, provide power for controls, instruments, and communications while in space and on the surface, and operate electric propulsion units. 
ix examples of unique and important missions enabled by the MITEE-B engine are described, including: (1) Pluto lander and sample return; (2) Europa lander and ocean explorer; (3) Mars Hopper; (4) Jupiter atmospheric flyer; (5) SunBurn hypervelocity spacecraft; and (6) He3 mining from Uranus. 

https://www.researchgate.net/publication/234998002_MITEE_A_new_nuclear_engine_concept_for_ultra_fast_lightweight_solar_system_exploration_missions
Representative design parameters for the baseline MITEE reactor are: 75MW(th) power level, 1000 second Isp, 100 kilogram mass, 10 MW/Liter fuel element power density, 39 cm core diameter/height. Total engine mass, including turbo pump assembly, nozzles, controls, and contingency, is estimated...
MITEE: A new nuclear engine concept for ultra fast, lightweight solar system exploration missionshttps://www.researchgate.net/publication/234998002_MITEE_A_new_nuclear_engine_concept_for_ultra_fast_lightweight_solar_system_exploration_missions [accessed Dec 31, 2015].


More MITEE links

https://www.google.com/search?q=mitee+reactorreactor
http://www.freerepublic.com/focus/news/673317/posts

As illustrated in Sidebar 2, the MITEE nuclear engine consists of a close-packed assembly (typically 37) beryllium pressure tubes. Each pressure tube contains an outer annular cylinder of 7LiH moderator, and an inner annular rod of perforated tungsten 235UO2 metal matrix composite fuel sheets. Cold hydrogen propellant flows downwards at ~100 K along the outer surface of the 7LiH moderator, then radially inwards through the moderator and the tungsten - UO2 fuel sheets. The hydrogen propellant emerges from the final fuel sheet at 3000 K, and then flows longitudinally down through a central hot gas channel to the exit nozzle at the end of the pressure tube. The MITEE engine is similar to the Particle Bed Reactor (PBR) engine which underwent development for defense applications (see Nuclear Thermal Propulsion), except that it is smaller and lighter, uses multiple pressure tube construction instead of a single pressure vessel, and tungsten -UO2 metal matrix fuel sheets instead of a packed bed of small HTGR type fuel particles. The main features of MITEE are summarized in Sidebar 3. 

http://www.physics.ohio-state.edu/~kagan/phy596/Articles/IonPropulsion/CompactNuclearRockets.pdf

With engine diagram

Another design family-- Adams atomic engines design philosophy http://www.atomicengines.com/engines.html

One can imagine variants of small designs that meet entire families of design needs-- some optimized for long life operation, some capable of reprocessing their own fuel in molten salt form over years, some optimized for exotic conditions.

In reality the first MITEE engine might cost a billion dollars, sourced in single digits they might cost a few hundred million dollars, but in sufficient production (high hundreds of thousands and up)  there is no engineering reason it would not be available for a million dollars or so plus fuel loading. Since the big assumption of this article is near-free isotopes we can pick out of the air these assumptions:
Power output of MITEE-- say 2 mw thermal, 500 kw electric.
cost of heat energy-- $4 million for 2 years, (4 megawatt years) $1 a watt year, stops cold

A megawatt year of electricity would be at 10 cents a kilowatt hour, $100 an hour or  $3504000. The three megawatt years of waste heat would be a bonus.
Rate = 1.24gm/day The unit of (thermal) megawatt-days per metric tonne of fuel,

Such a reactor could probably produce several megawatt years of power and at say $30000 a kilo of consumed uranium a reactor of that kind, designed by Powell and Maise, https://www.google.com/search?q=mitee+reactorreactor  would be an amazing commercial power source. Its; very compactness is both its' strength and weakness-- it is portable within a delivery truck--good--the associated danger of 25 kg or so of bomb material seizable in one go--not so good-- remember the blue plutonium isotopes table above?  D-D Fusion generated plutonium 239 would be ideal bomb material-- supergrade material--and if we are designing the unit to be under a ton, it is by definition field portable.   Perhaps the answer is to security in transit plus require embedding it in concrete so it can't be moved inconspicuously when installed (but that of course kills mobile applications). Another answer is to require full time guards with offsite live monitoring but the problem with that is it only flags a determined attempt but does not stop it. The real problem is that we need a civilized world to deploy this marvelous technology in but that is a more speculative future than anything else in this article.

By contrast the advantage then of pure isotope power is that it is a known quantity with one half life in case of a release, not an ever changing mixture (the uncharitable say witches brew) of fission products. (with many resulting complications needing management in regular fission reactors, such as detailed here. https://en.wikipedia.org/wiki/Neutron_poison  and here http://www.templar.co.uk/downloads/0203_Pouret_Nuttall.pdf ) By contrast, pure isotope power has been called an atomic battery  in its; RTG form as an analogy to hint at its' simplicity of operation.

https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_Power#SNAP-27
 Now if we had the Poul Anderson mattercast rock to isotope technology in real life we would have not merely free isotopes but a transporter and replicator and that is more than I want to focus on in a single article. but in real life if you want a minor rather than a major physics miracle the one you would wish for would be a pathway that could turn Uranium 238 under neutron bombardment not into Plutonium 239 but Plutonium 238,  That would be an utter game changer.

 As it is now pure 238 comes from pure neptunium 237, itself quite rare. Reactor grade Pu-238 exists but is entangled with Pu-239 and other isotopes. Easy isotope separation would be a different but welcome physics miracle that would cause a whole different article but that would also enable Uranium 235 so--proliferation again. Sigh.

https://en.wikipedia.org/wiki/Plutonium-238 
Pu-238 makes up only one or two percent, but it may be responsible for much of the short-term decay heat because of its short half-life relative to other plutonium isotopes. Reactor-grade plutonium is not useful for producing Pu-238 for RTGs because difficult isotopic separation would be needed.
Pure plutonium-238 is prepared by neutron irradiation of neptunium-237,one of the minor actinides that can be recovered from spent nuclear fuel during reprocessing, or by the neutron irradiation of americium in a reactor.[1] In both cases, the targets are subjected to a chemical treatment, including dissolution in nitric acid to extract the plutonium-238. A 100 kg sample of light water reactor fuel that has been irradiated for three years contains only about 700 grams of neptunium-237, and the neptunium must be extracted selectively. Significant amounts of pure Pu-238 could also be produced in a thorium fuel cycle.[2]

At 560 watts a kg, a ton would be 560 kilowatts, a respectable power. That would be 59 milligrams a curie so 59 tons for a gigacurie so 1 ton would be 16.94 megacuries  A megaton of 238 would therefore be 17 teracuries and for a generation give  560 gigawatts of portable power. (560 million kilowatts== enough by the above estimate to make 560 million portable car generators  to top up your electric car and then your house when that was done.).  Every generation or so we would need to process a few million tons of U238 (which we do for reactors anyway) and if this tech miracle existed we could have everything be either Pu-238 powered if portable or 235 powered in once through reactors. This might last for a thousand years or so but at some point we would hit limits. Alas, I know of no way to easily convert U-238 to Pu-238. Poul Anderson style mattercasting to turn common rock into isotopes of choice  is an entrancing vision but as far as we know is just a vision. (If you think about it that kind of conversion ability would be tantamount to the ability to turn any matter to energy and back again in which case-- why not just use the energy of ordinary matter  once it is destroyed and skip the wasted motion of turning it into isotopes!?)

In any case, fission is sufficiently dirty that it is a stage soon best passed by. We have enough fissionables on this planet (which is actually richer than many extraterrestrial bodies in fissionable deposits) to last for about 60,000 years in an all nuclear world at American rates of energy consumption.  But to do that will require mastering D-D fusion to produce Uranium 233 and Plutonium 239.  The most likely method to do that would be a variant of Project Pacer, to be covered in a future article.





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