This is the second half, steps 5 through 9, of the Nuclear Fuel Cycle that I started a couple posts ago where I covered steps 1 through 4 – Uranium Mining, Uranium Milling, Conversion and Enrichment.
Step 5: Fuel Fabrication. Since uranium hexifloride gas (UF6) can’t be used in reactors, it must be converted into uranium oxide (UO2) which is formed into fuel pellets. The fuel pellets are small, cylindrical in shape and about a third of an inch in diameter by half an inch long. The pellets are packed in long metal tubes (fuel rods) which are bundled into fuel assembles which is what is used in the reactor. A typical fuel assembly in a light water reactor contains 264 fuel rods bundled into a 5 to 9 inch square by 12 foot long unit.
There are six uranium fuel fabrication facilities in the U.S: Richland, WA; Wilmington, NC; Erwin, TN; Columbia, SC; and two facilities in Lynchburg, VA.
Step 6: Electricity Generation. The fuel assemblies are loaded into a nuclear reactor and fission is begun. Fission is the U-235 isotope is split, producing heat in a process called a chain reaction. The reactor core is inside a water filled steel pressure vessel. The operating temperature exceeds 320 degrees which forms steam either above the reactor core or in separate vessels which drives the turbine that produces electricity. The fuel lasts for about 3 to 6 years.
Simply put, the atomic reaction makes heat that creates steam that turns the turbine that spins the generator that produces electricity.
There are currently 65 nuclear power plants operating 104 nuclear reactors in the U.S. These plants generate 20% of the country’s electricity.
Step 7: Spent Fuel Storage. Spent fuel assemblies are very hot and radioactive when they are removed from the reactor and must be stored under water in order to cool and shield from radiation. The spent fuel can be removed from the water after several years and is sent to a interim storage facility where it is stored in water pools, or dry storage casks. After about 40 years, the fuel in storage is about one thousand times less radioactive than it was when it was removed from the reactor.
Step 8: Reprocessing. Spent fuel is 96% uranium and 1% plutonium and 3% waste products. The uranium which 1% is U-235, and the plutonium can be reprocessed. The recovered uranium is returned to the conversion plant, converted to UF6 and re-enriched at an enrichment plant. There are no reprocessing facilities operating in the U.S.
Step 9: High Level Waste Disposal. Spent nuclear fuel – high level waste – can be safely disposed of underground in deep stable rock formations. The waste is packed in long lasting containers and buried deep in the stable geological formations which have been determined to have stability for over hundreds of millions of years.
Yucca Mountain in Nevada was determined to be a safe underground disposal facility but the project was abandoned in 2011 for political reasons.
Well, that’s it for a quick summary of the nine steps of the Nuclear Fuel Cycle. I plan on expanding on a few, if not all, of these steps sometime in future posts.
References for this post:
World Nuclear Association – How a nuclear reactor makes electricity
World Nuclear Association – Processing of Used Nuclear Fuel
NRC – Fuel Fabrication
NRC – Reprocessing
Wikipedia – Yucca Mountain Nuclear Waste Repository
IAEA – The Nuclear Fuel Cycle