Source: United States of America – Federal Government Departments (video statements)
High-temperature gas reactors use helium gas and ceramic materials to stabilize the fission process inside the reactor core.
They run on ceramic-coated fuel particles and are designed to efficiently produce heat (~750° Celsius) for electricity generation or to drive energy-intensive manufacturing processes, such as hydrogen production.
High-temperature gas reactors come in two different core designs — prismatic and pebble bed.
1️⃣ Prismatic Gas Reactors use graphite hexagonal blocks to form the reactor core structure and slow down the neutrons produced by fission to sustain the chain reaction. Each block contains channels for directing helium gas flow and holding stacks of TRISO fuel pellets, known as compacts.
Fission heats the helium that is being circulated through the core to a secondary system that heats water to create steam. The steam then turns an electric generator to produce emissions-free electricity.
The gas then returns to the reactor to be reheated in a closed loop cycle.
2️⃣ Pebble Bed Gas Reactors are essentially big “nuclear gumball machines.” The pebble bed core is filled with TRISO fuel pebbles that are surrounded by graphite reflector blocks. Helium is blown down through the pebble bed to extract the heat into a steam generator that produces electricity.
The reactor is continuously refueled by adding fresh pebbles into the top of the core as older ones are discharged from the bottom. The discharged pebbles are evaluated to determine whether they will be reinserted into the reactor or placed directly into on-site storage.
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