Part 2 of 2 Parts (Please read Part 1 first)
Most nuclear power reactor designs that use an alternative coolant also use an alternative fuel.
TRISO, or tri-structural isotropic particle fuel, is one of the most popular options for fueling advance reactors. TRISO pellets contain uranium, enclosed in ceramic and carbon-based layers. This keeps the fuel contained. It keeps all the products of fission reactions inside and allows the fuel to resist corrosion and melting. Kairos and X-energy are both planning to use TRISO fuel in their reactors.
Other reactors use HALEU which stands for high-assay low-enriched uranium. Most nuclear fuel used in commercial reactors contains between three percent and five percent uranium-235. HALEU, on the other hand, contains between five percent and twenty percent uranium-235. This allows power reactors to generate more power in a smaller space than conventional reactors.
In addition to changing the specific details of things like fuel and coolant, many companies are working to build reactors of different (mostly smaller) sizes.
Small modular reactors (SMRs) are advertised to be quicker and cheaper to build as well as safer to operate.
Today, most nuclear power reactors being connected to the grid are massive, in the range of 1,000 or more megawatts. This is more than enough electricity to power hundreds of thousands of homes. Constructing those huge nuclear projects takes a long time, and each one requires a bespoke process. SMRs could be easier to build, since the procedure is the same for each one. This would allow them to be manufactured in something resembling a huge assembly line.
NuScale has been one of the leaders in this area. Its advanced reactor design uses commercial fuel and water coolant, but the whole thing is scaled down. Things haven’t been going well for the company in recent months, though. Its first project is pretty much dead in the water. NuScale was going to construct a nuclear power plant in southern Idaho with multiple NuScale SMRs and sell the power to a consortium of Utah utilities. However, they failed to raise the additional funding required to finish the project which was recently canceled. NuScale has just laid off nearly thirty percent of its employees in early January. It has also been accused of misleading investors.
Other companies are still carrying the SMR torch. This includes many that intend to alternative fuels and coolants.
There have been many extravagant claims about SMRs in the global media. They were promised but so far that promise hasn't really materialized. Their lower cost estimates were based on economies of scale but in order to reap that benefit, they have to be produced in large quantities. NuScale’s estimate of the cost of their first nuclear project more than doubled in four years. SMRs are supposed to be safer but some designs call for higher temperatures and pressures. There is, as yet no practical knowledge generated with respect to how these temperatures and structures will affect the materials used in the reactors. There is also concern that quality control may fail and result in a number of reactors being deployed that share the same flaws. It is true that they generate less waste than conventional designs but the waste they do generate is still very radioactive and must be dealt with. SMR are not the panacea that many claim.