Small Nuclear Powerpack

AFAIK, no. You either get a lot of power from controlled nuclear fission or a much smaller amount of power from radioactivity. Nuclear fission plants are expensive due to the complication required for controlling the reaction on the edge of criticality, so it is only cost-effective at a large scale.

Some work has been done developing "kilowatt" nuclear power for space applications where the cost of power generation is not a big factor.

Kilopower - Wikipedia

The real problem as I understand it is the critical mass which is in the order of 25 kg for enriched uranium.

If another isotope could be used it might reduce this.

Somehow I feel that there must be a way to make an alternative power plant that might be used for transportation.

The submarines have overcome this but these are still fairly big units.

Shielding for the radiation could be developed if such a plant can be made.

Hi Johan,

Maybe you're onto something, but when you suggest that "Shielding for the radiation could be developed", my experience with shielding involves dense materials like lead and tungsten - I don't believe that there's anywhere significant to go with density from there, which just leaves you with time and distance to protect the humans in the vicinity. BTW, some of the shielding I've been involved with on small research reactors was well over 1m thick lead.

Cheers

Many concerns especially relevant to smaller nuclear power plants can be addressed with an accelerator driven subcritical reactor.

Neutrons are produced by spalation using either an electron or proton accelerator aimed at a target of high neutron content (bismuth, lead, etc) . The high energy neutrons can be used as is or moderated depending on the fuel.

The reactor can be built and maintained substantially sub critical since the accelerator is producing the neutrons for fission there is no need for a certain number of neutrons to be produced per reaction to maintain power levels.

It's the shielding of the radiation that becomes a problem...safety concerns...

Another problem is that nuclear is good for generating a continuous base load but it is difficult to switch off. (Ask the guys at Chernobyl and Three Mile Island about that problem) It continues to produce power even when your demand goes down so you have to find a way of getting rid of the surplus. Satellites are constructed to match their power generation and their power demand. Mega Watt stations are intended to be used with a grid that can absorb any surpluses and switch off different technologies (wind, hydro, gas fired) when the demand goes down. A 50kW nuclear power pack has no market. It is too small to attach to the grid. You can't put it in a plane or vehicle because when it lands/stops you would have to plug it in and suck the surplus power that is still being generated out into a grid. The infrastructure for that does not exist and would also limit where you could travel to and from because you can't stop anywhere without an installed socket. Don't get into a traffic jam behind a truck with a nuclear engine, it just might burst into flames.

The fission reaction can be switched off rather quickly by what they call a Scram when all the control rods are inserted into the reactor. Yes, the fission reaction is stopped, but there is lots of residual heat and radioactivity to deal with. It doesn't go away just because the reaction stopped.

I remember reading,many years ago, about a nuclear power plant that had the fuel encapsulated in ceramic balls.The construction of the balls kept the fission material at the proper distance,with no danger of overheating or meltdown.The balls could be recycled efficiently

No need for immense quantities of cooling water..I do not know the current status of this technology.

I also recall a scientist or engineer that developed a method of producing electricity from nuclear waste.He surrounded the waste with a coil,and used an oscillator circuit to convert the output to the desired voltage/frequency.

According to the article,the neuron emission of the waste material created a voltage in the coil and the collapsing field when the coils were switched by the oscillator circuit.

I have heard nothing about this in many years.

It would be great if we could use our nuclear waste to produce electricity instead of burying it in a salt mine.

Does anyone else remember seeing these technologies?

Maybe this?

Will Nuclear Plants Put Their Faith in Power Balls? (popularmechanics.com)

It would be great if we could use our nuclear waste to produce electricity

The Gen IV (fast) reactor will do that. It uses the "good" that is left in thermal reactor waste and gets a bunch more electricity from it. It does not use WATER as a coolant, because it doesn't want the moderating effect. Instead, it uses molten sodium, lead, bismuth, salt, etc. These coolants do not moderate the neutron energies and result in a fast spectrum of neutrons that can utilize the thermal reactor waste, thorium, U-238, and many of the highly radioactive components of the waste. All resulting in perhaps 100 times less waste volume and radioactivity.

I believe you are referring to the pebble bed reactor. This has a circulating system that brings in and takes out balls in accordance with the demand of power.

This is a system that had been developed in South Africa some while back.

What you want is a nuclear battery....and more probably

..."

Radiovoltaic conversion[edit]

A radiovoltaic (RV) device converts the energy of ionizing radiation directly into electricity using a semiconductor junction, similar to the conversion of photons into electricity in a photovoltaic cell. Depending on the type of radiation targeted, these devices are called alphavoltaic (AV, αV), betavoltaic (BV, βV) and/or gammavoltaic (GV, γV). Betavoltaics have traditionally received the most attention since (low-energy) beta emitters cause the least amount of radiative damage, thus allowing a longer operating life and less shielding. Interest in alphavoltaic and (more recently) gammavoltaic devices is driven by their potential higher efficiency.

Alphavoltaic conversion[edit]

Alphavoltaic devices use a semiconductor junction to produce electrical energy from energetic alpha particles.^[9][10]

Betavoltaic conversion[edit]

Main article: Betavoltaic device

Betavoltaic devices use a semiconductor junction to produce electrical energy from energetic beta particles (electrons). A commonly used source is the hydrogen isotope tritium.

Betavoltaic devices are particularly well-suited to low-power electrical applications where long life of the energy source is needed, such as implantable medical devices or military and space applications.

Gammavoltaic conversion[edit]

Gammavoltaic devices use a semiconductor junction to produce electrical energy from energetic gamma particles (high-energy photons). They have only recently (in the 2010s) been considered.^{[11][12][13] [14]}

A gammavoltaic effect has been reported in perovskite solar cells.^[11] Another patented design involves scattering of the gamma particle until its energy has decreased enough to be absorbed in a conventional photovoltaic cell.^[12] Gammavoltaic designs using diamond and Schottky diodes are also being investigated.^[13][14] "...

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

"Making tritium nuclear battery from tritium keyring lights placed between 2 solar garden cells. The tritium keyrings lights are very expensive about 15$ each and they can run 10+ years. So light from tritium rods is absorbed by solar cells and converted into small amount of current, enough to power a calculator."

Need to improve on this design....

Tritium $3.99 ea...

If you could use the tritium batteries to get rolling and use piezoelectric wafers mounted on metal strips between tread layers on the tires, maybe you could build an electric bicycle that never needed charging....probably not so fast though..of course the number of tires is only limited by $$

..."Applying 80 gram force to its tip at a frequency of 60 Hz produces an open circuit voltage of 15V peak between its two electrical leads. When the leads are connected to a 8 Kohm resistive load, the output to the load is 5.3 Vrms, representing a power output of 3.6 mW."...Aug 25, 2020

https://support.piezo.com/article/113-piezoelectric-basics#:~:text=Applying%2080%20gram%20force%20to,power%20output%20of%203.6%20mW.

https://www.altenergymag.com/article/2017/12/piezoelectric-power-generation-in-automotive-tires/27642/

I remember seeing a high school project that split water into hydrogen and oxygen using iron powder in a clear tube,and exposing it to sunlight.No other power source required.I do not know the efficiency or power potential of this method,but it did work.

Has anyone taken this a step further?

You can use aluminum and sulfuric acid...

...and a small hydrogen engine to complete....

Water and iron is cheaper.

"Candy is dandy,but liquor is quicker."(Old Joke)

--Ogden Nash

Thanks for the reference.I only heard it in a joke about dating,and one man took candy to his girlfriend,and the other took liquor.

Afterwards they talked about their dates.

I am sure there are many other uses of this famous line.

Aluminum and sulfuric acid is much much quicker....so

Touch'e

"...Radioisotope Thermoelectric Generators (RTGs) are used when spacecraft require less than 100 kW. Above that, fission systems are much more cost effective than RTGs...." _ https://world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx

100kW?? I don't think so....most are around a few hundred watts....

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

100kW figure (assuming not a typo at the website) denotes a threshold for cost effectiveness. Yes; at 0.54W/g, 100kW (of thermal power) needs 185kg of Pu238 (with included shielding/packing,conversion to electrical power may exceed 1/4th mass of tonne-class satellite). it seems this figure is not feasible leave alone space applications, for any application due to large quantity of Pu-238 involved.

An SRG might be more efficient to charge batteries in a vehicle....

..."Dynamic generators can provide power at more than four times the conversion efficiency of RTGs.^{[citation needed]} NASA and DOE have been developing a next-generation radioisotope-fueled power source called the Stirling Radioisotope Generator (SRG) that uses free-piston Stirling engines coupled to linear alternators to convert heat to electricity. SRG prototypes demonstrated an average efficiency of 23%. Greater efficiency can be achieved by increasing the temperature ratio between the hot and cold ends of the generator. The use of non-contacting moving parts, non-degrading flexural bearings, and a lubrication-free and hermetically sealed environment have, in test units, demonstrated no appreciable degradation over years of operation. Experimental results demonstrate that an SRG could continue running for decades without maintenance."...

https://www.wikiwand.com/en/Advanced_Stirling_radioisotope_generator

This device could run 24/7 for many years with no maintenance, properly designed, and charge the batteries in an EV, you would never run out of charge....

..."The higher conversion efficiency of the Stirling cycle compared with that of radioisotope thermoelectric generators (RTGs) used in previous missions (Viking, Pioneer, Voyager, Galileo, Ulysses, Cassini, New Horizons, Mars Science Laboratory, and Mars 2020) would have offered an advantage of a fourfold reduction in PuO2 fuel, at half the mass of an RTG. It would have produced 140 watts of electricity using a quarter of the plutonium an RTG or MMRTG needs.[11]

The two finished units had these expected specifications:[12]

• ≥14-year lifetime
• Nominal power: 130 W
• Mass: 32 kg (71 lb)
• System efficiency: ≈ 26%
• Total mass of plutonium-238-dioxide: 1.2 kg (2.6 lb)
• Plutonium housed in two General Purpose Heat Source (“Pu238 Bricks”) modules
• Dimensions: 76 cm × 46 cm × 39 cm (2.5 ft × 1.5 ft × 1.3 ft)

We might increase the efficiency here by using the ASRG as a direct drive mechanism rather than just a charging mechanism, of course it would require a much larger multi-cylinder device...probably only good for arctic exploration though... haha

That would be 50 watts per lb....and requires 1000 lbs maybe for 50kw...454 kilos...

https://www.universetoday.com/106604/nasa-halts-work-on-its-new-nuclear-generator-for-deep-space-exploration/

I would think using an Organic Rankine Cycle (ORC) would increase efficiency considerably...

Aha!

13 MWe....just need to scale this down

http://www.holosgen.com/

For 13MWe it looks quite compact even assuming ISO container of 48' x 9'6" x 8'.

This seems like a good idea using nuclear waste as fuel....

https://news.mit.edu/2020/oklo-nuclear-energy-1113

A small fast reactor using nuclear waste could be scaled to work at the 50kw level...and could be made to last probably 60 years without refueling....an ORC reactor would require just low level heat and regulation might not be necessary...just ventilation...

Yes, it is one of the best 'best out of waste' projects to utilize residual radioactive heat from spent fuel rather than allowing it cool in specially built water ponds for years before packing in steel & concrete for long term storage. Shielding has to be taken care of during extraction for power.

Leaded vinyl sheeting would probably be enough....

https://ultraray.com/shielding-materials-fixtures/?gclid=CjwKCAjw3_KIBhA2EiwAaAAliqL4tuTNRyAtPSO1XI6IETSAjn-sc1cSuNWuBX4DSGSLbFMUGzNNVhoCmhkQAvD_BwE

....or perhaps using high assay low enrichment fuel you produce no long lived transuranic waste...

Space is an infinite heat sink,and near absolute zero.

Couple the cold side to the outside of the craft via heat tubes and there will be a very large temperature differential to maximize efficiency.

"... Space is an infinite heat sink,and near absolute zero..."

.

Yeah, but the volumetric heat capacity as well as the conductivity are so low, utilizing it as a heat sink gets far more tricky as power levels increase.