Enter the Future - TRISO FUEL
The real innovation Of the HTGR Pebble Bed is its nuclear fuel – The TRISO FUEL Pebbles.
The Pebble Bed HTGR reactor uses tennis ball-sized pebbles (see figure) made of thousands of TRISO micro-fuel particles which consist of fissile U-235 surrounded by pyrolytic graphite, which acts as the moderator - slowing down fast neutrons so they more efficiently split the U-235 nucleus. The graphite is further surrounded by a coated ceramic layer of silicon carbide for strength and containment of the fission products..
In it's complexity, lies it's simplicity and safety!
Thousands of pebbles are amassed to create the reactor core, and are cooled by a gas, such as helium, nitrogen or carbon dioxide, that doesn’t chemically react with the fuel pebbles. As the pebbles become used, they drop out of the bottom of the core, and are replaced from above, such that the reactor does not need to shut down to refuel.
Because the reactor is designed to handle high temperatures like 1,600°C, it can cool by natural circulation and still survive any accident. High temperatures provide higher thermal efficiencies and up to 50% more power per unit of fuel than traditional reactors that don’t get much above 400°C..
It's SAFE!
But what really matters to the public is safety. The small size and large surface area-to-volume ratio of HTGRs, make the plant size very small, and along with our innovative designs, allows natural processes to cool it indefinitely in the case of a complete power blackout, with no humans needed to intervene, no AC or DC power, no pumps, and no additional water for cooling.
Translation – NO MELTDOWNS!
This fuel is also tamper resistant for any misappropriation of the nuclear materials contained within it, and it makes it very undesirable for any other use than what it was designed for.
And that is why we need to move forward fast on these new nuclear reactors.
The TRISO Fuel Cell
The TRISO Fuel Cell has been developed over many decades, and is the force behind the HTGR PB.
Safer Waste Disposal.
TRISO FUEL WASTE DISPOSAL
The design of the of PBMR TRISO fuel makes it easy to store the spent fuel, because the silicon carbide coating on the fuel spheres will keep the radioactive decay particles isolated for approximately a million years, which is longer that the activity even of plutonium.
Because the PBMR fuel can be stored on site for at least 80 years, special casks for transporting the spent fuel and storing it at a remote location such as the nuclear waste disposal site. There is no intention to reprocess the spent fuel as this is more difficult than with Koeberg-type fuel. The PBMR fuel also has a greater "burn-up" which makes it less valuable to recycle. More of the useful uranium present in the fuel is used while in the reactor
The spent coated particle fuel can be disposed of in a deep under-ground repository. (Coated particle fuel will maintain its integrity for up to ~ 1 million years in a repository, ensuring that spent fuel radionuclides are contained for extremely long periods of time. The plutonium will have decayed away completely in 250,000 years)