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:
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:
Modules would be ready to install right after a state decides to purchase them.
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.
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?
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.
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!
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.
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.
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!Next Chapter