So the depleted nuclear fuel cannot be used to heat the reactor, but still has plenty of energy in the form of radiation. Why this radiation cannot be used or eliminated by trapping the neutrons from it and produce heat?
In: Physics
It could! We do something like that with nuclear batteries wich are used in space probes.
The issue is simply cost, for the amount of energy you actually get the effort (and especially cleanup+security features) is just way too large.
The use case is really only things where extremely long energy supply without refuels are essential. The energy per weight is pretty good, but you receive it rather slowly, and the cost per energy is incredibly high.
A single RTG (radioisotope generator) costs about 100-150 million USD, wich outputs up to 2kW for 25-30 years. For comparision, a windpark costing that much would easily output 100,000 kW over the same timeframe
It can be reused
France and Russia often reprocessed fuel for reactors to use it again, or mixes it with glass to help with storage, it just takes a ton of equipment to do that on a large scale and make it cost effective, which is expensive
The US for example banned the reprocessing of nuclear waste in 1977, after the practice was controversial, eventually it landed on the side of banning it instead of recycling the fuel
Or it can be used for RTGs, but there’s not a very big demand for those in comparison
As already mentioned, it is being done in various ways. I think this gives a good overview:
[https://en.wikipedia.org/wiki/Atomic_battery](https://en.wikipedia.org/wiki/Atomic_battery)
Regarding RTGs: Their big advantage over the usual reactors is mobility and size. This however means that you want to use fuel that has a very high energy density. So you can fit it onto a space probe for example.
While decay heat can be significant enough to require cooling pumps for spent fuel pools, it’s not really enough to be cost-effective, as far as building a system that would capture heat and use it to generate power. It’d be a substantial fraction of the cost of a nuclear reactor but only generate a tiny sliver of the same energy. Also, the isotopes that are most radioactive also decay the fastest. So you get quickly diminishing returns from decay heat. Now, there is something called beta-voltaics, which involves taking isotopes that undergo beta decay (beta particles are just high-speed electrons) and putting them in a battery-like device to capture that energy. But it’s important that those devices only contain isotopes that undergo beta decay. Beta particles are super easy to stop. Neutrons and gamma rays, not so much. Since you don’t want your nuclear battery to irradiate you, you can’t just shove spent fuel into these things; you have to melt it down and process it and extract only the stuff that decays by spitting out beta particles. Which, again, is expensive. Also, only a very small amount of that spent fuel is going to consist of beta-decay-only isotopes..
If you are talking about recycling and using spent nuclear fuel, that is already done in other countries, France in particular has a pretty effective program. As for the US, the practice never got a foothold because the US government claimed that further investment into nuclear energy and recycling would not only fuel reactors, but it would accelerate nuclear proliferation as well. This stance was taken during the height of the cold war and its effects in the US and nuclear energy will persists today. As expected, novnuclear materials ever have been recycled from a nuclear power plants spent fuel, and now there’s a substantial cost in doing so. Why? We, ourselves, don’t quite have the technical ability and staff to do so effectively and efficiently, will need alot of help, and don’t have the experienced professionals we’ll need to navigate the effective oversight of local and national governments or the International Atomic Energy Agency,
If I took my entire spent fuel pool, about 6 reactor cores of spent fuel, and build a class 1 pressure vessel with control systems, a small turbine, safety systems, etc, and let’s say I just let the decay heat boil water into steam and run a turbine.
I may get 1-3 MW of electricity depending on how recently we offloaded the last core.
It’s very little energy with a high cost to try and utilize it.
Plus having hot pressurized fuel cladding would also further corrode and degrade it. The fuel cladding isn’t designed or tested for extended pressurized operation for more than about 8 years.
The answer is basically “treaties with the ussr”. We take 1% out of nuclear fuel then throw it away because using it more involves taking it through reactions that can be used to make nuclear bombs and everyone agreed to strict limits for that in civilian power generation. It’s not a technology limitation. We just do power generation wrong to not make weapons grade stuff
So power plants are really expensive to build and have a very finite life. The investors who paid for it want as much money back as possible so they want the power plant running at peak capacity all the time.
Fuel rods have an enrichment of u238 which is the main component that gives heat. As the rods get spent, the enrichment drops and they give off less heat (not quite true but works for simplicity). The fuel rods could be used for a bit longer but it results in the reactor not operating at peak capacity so the investors lose out.
Tldr, we could use the spent rods longer and they’d still work but it wouldn’t be as financially beneficial.
There are schemes to re use the spent fuel rods. One such scheme is to utilise plutonium to make spent rods more “potent” to then be put back into conventional reactors
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