Generation IV Nuclear: Can We Solve the Remaining Issues Nuclear Faces?

13 minute read

Updated on Wed Mar 03 2021

In the last chapter we learned that there are four fundamental problems with Nuclear Energy:

  • Nuclear waste
  • Nuclear explosions
  • High cost
  • Long construction time

We’ll assess various ideas using this scheme:

The easy one: building Small Modular Reactors

Instead of building a big reactor on-site, what if we mass-produce smaller components in a factory and ship them to where they need to be? They could be ready to install very quickly after a state decides to purchase them. These reactors are called Small Modular Reactors (SMR). They are ‘modular’ because multiple small reactors (called ‘modules’) can be combined at the site to provide the same power as a conventional big reactor:

Small Modular Reactors

Modules would be ready to install right after a state decides to purchase them.

SMRs use Uranium and water like conventional reactors. However, many SMR designs are capable of passive cooling, meaning that a power outage does not cause a nuclear meltdown and explosion.

How do you think this could improve nuclear energy?

The first SMRs are being put into operation and more are under development and in the licensing process. Full commercialisation is expected around 2030.

Unfortunately, SMRs still have an issue with nuclear waste because they use regular nuclear fuel.

More efficient - Molten Salt Reactors (MSR)

The reactors we discussed in the last chapter use water as a coolant (to get the energy out) and as a moderator. Molten Salt Reactors (MSR) instead use molten salt as a coolant. Molten salt is really what it sounds like - liquid salt.

Molten Salt Reactor
Molten Salt Reactor

Why molten salt?

  • High temperature: Regular water-based reactors only produce temperatures of up to 300°C. MSRs could reach up to 850°C. This improves thermodynamic efficiency and thus the fuel usage, and would allow MSRs to supply heat for high-temperature industrial processes that are today fulfilled by fossil fuels.
  • High efficiency: MSRs have 30% higher fuel efficiency than water-based reactors, meaning a little less waste for the same power.
  • No explosions: Like all modern (even today’s) reactors, MSRs shut down when they overheat, meaning they wouldn’t explode.

Sadly, the nuclear waste issue still persists. Moreover, there are currently no affordable materials that can contain molten salt at temperatures as high as 850°C for a long time. This means more basic research and innovation is needed to make MSRs a reality.

Can we recycle nuclear waste to use as fuel?

Can we recycle nuclear waste?

Remember from the last chapter that nuclear waste largely comes in two forms:

  • Depleted Uranium-238: Natural Uranium is 99.3% U-238 and 0.7% U-235, but needs to be 4-5% U-235 for reactors. When creating this enriched fuel, we leave a large amount of U-238 behind.
  • Spent fuel: When a reactor has used the enriched fuel for a while, it is replaced with new fuel. What remains is called spent fuel.

Do you remember which one is still super dangerous?

Traveling Wave Reactors (TWR) are designed to use depleted Uranium-238 as fuel. TWRs produce 80% less radioactive waste (by mass) than conventional reactors.

Even more excitingly, TWRs could in principle recycle spent nuclear fuel, but significant research advances are needed for that.

The key idea behind these reactors is that they make their own fuel. This can look as follows:

Fuel Breeding

Here, we start off with U-238, which on its own can’t power normal nuclear reactors. Then, by adding a neutron, we turn it into U-239. U-239 quickly decays and becomes Plutonium-239, another radioactive material. This is what then powers the nuclear fission reactions and creates the heat that ultimately becomes the energy we get out of the reactor. All of this happens within the reactor!

Like all other modern reactors, TWRs would shut down if there was a power outage, meaning they wouldn’t explode.

Work on TWRs has been going on for decades - unsuccessfully. But after years of computer models and re-thinking designs, a company called Terrapower (funded mostly by Bill Gates) now thinks they can achieve stable long-term operation.

Their prototype was supposed to be ready for use in 2022, but political tensions between the US and China meant that building stopped in 2018. We will see where we go from here.

So, what should we do?

Small Modular Reactors (SMRs) and conventional reactors are available now. They could replace coal for baseload electricity generation with near-zero CO₂ emissions. As outlined in the last chapter, modern nuclear reactors are extremely safe and don't cause explosions. While nuclear waste is bad, we have to compare this to the dangerous CO₂ emissions and other pollution produced by burning fossil fuels.

Simultaneously, governments should allow companies to test advanced nuclear reactors at a much faster pace.

We need more research

If you want to learn more about Advanced Nuclear, check out some of the concepts that we haven’t discussed in this chapter:

  • Using Thorium: Instead of Uranium-235, using an element called Thorium as fuel.
  • Other coolants: Instead of water or molten salt, we can use gas or liquid metals.
  • Reactors without moderators: Fast Reactors can work directly with fast neutrons (today’s designs have to use a moderator to slow neutrons down, as discussed in the last chapter). Conventional reactors need to slow neutrons to allow them to split U-235.

Now, on to renewable energy!

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