Rolls-Royce’s small modular reactors and the UK’s clean energy sector?
Archie Bowers
With the growing climate crisis, the demand for clean, reliable energy has never been higher. Small Modular Reactors (SMR) look to contribute to the UK’s promise of becoming net zero by 2050, and the global efforts to make carbon-zero fuels, such as hydrogen and synthetic kerosene, usable and affordable. But what are SMRs? ‘ A reactor is called “ small ” if its capacity is less than 300 megawatts (MW) ’ 1 and it can be defined as being modular if its parts are able to be manufactured and then constructed together in a factor to then be transported to the desired site, instead of being built on site. The standard large water reactors (LWR) have a capacity of up to 1000 MW in comparison. In terms of the mechanisms that transpire inside the reactor to create electricity, there is little to no difference between an SMR and the larger reactors that are currently standard, except the reaction occurs at a smaller scale inside an SMR. The reactor generates energy by nuclear fission, which is the process of splitting one large atom into two smaller atoms, releasing energy (heat) in the process. A slow-moving neutron is absorbed by an atom of uranium-235, supplied by a fuel rod which is composed of many small pellets of enriched uranium. The atom of uranium-235 becomes unstable, and it decays into two smaller atoms, releasing energy (heat) and more neutrons. These neutrons collide with a moderator, usually made of graphite, and transfer momentum to the moderator, gradually slowing down until they are moving slowly enough to be absorbed by more uranium-235 atoms instead of rebounding off the nuclei. The process repeats, creating a chain reaction and an exponential increase in energy. To control the reaction, there are control rods present in the reaction chamber, which absorb excess neutrons. The energy is then removed from the reaction chamber and used to generate electricity.
There are 3 main designs of fission reactors, all of which use water to generate electricity.
Firstly, there are Pressurized Water Reactors (PWR), and these make up 70% of global reactors. They have 2 water circuits, 1 of which flows through the core of the reactor and cools it, whereas the other is used to create steam which drives the turbine and generates electricity. The primary circuit is pressurized to prevent boiling, and the secondary is kept at a pressure which allows it to boil and vaporize into steam. 2
1 https://acee.princeton.edu/distillates/small-modular-reactors/. 2 https://www.world-nuclear.org/nuclear-essentials/are-there-different-types-of-reactor.aspx.
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