Two reactors drive two turbine generators and then three electric motors that power the propellers, producing a propulsive power of 60 MW. The replenishment cycle is quoted at 6-7 years, or with a capacity factor of 65%, replenishment is every 7-10 years, the review at 20 years, for a lifespan of 60 years. In the United States Navy, refueling and reconditioning (ROH) refers to a lengthy reconditioning process or procedure performed on nuclear-powered naval vessels, involving the replacement of spent nuclear fuel with new fuel and general maintenance repair, refurbishment, and often modernization of the entire ship. In theory, such a process could simply involve just refueling or just a review, but in practice, nuclear refueling is always combined with a review.
An ROH usually takes one to two years for submarines and up to almost three years for an aircraft carrier, made in a naval shipyard. Time periods between RoHS on a ship have historically varied from approximately 5 to 20 years (for submarines) to 25 years (for Nimitz class aircraft carriers). For modern submarines and aircraft carriers, RoHs are generally carried out about half their useful life. There are also shorter maintenance arrangements called availability for ships periodically in the shipyards.
A particularly lengthy refueling, maintenance and modernization process for a nuclear aircraft carrier can last up to almost three years and is known as a refueling complex (RCOH) overhaul. Once fuel assemblies are manufactured, trucks transport them to reactor sites. Fuel assemblies are stored on-site in new fuel storage tanks until needed by reactor operators. At this stage, uranium is only slightly radioactive, and essentially all of the radiation is contained within the metal tubes.
Typically, reactor operators change approximately one-third of the reactor core (40 to 90 fuel assemblies) every 12 to 24 months. The enriched UF6 is sealed in containers and allowed to cool and solidify before being transported to a nuclear reactor fuel assembly plant by train, truck, or barge. In a nuclear fuel manufacturing facility, UF6, in solid form, is heated to gaseous form, and then UF6 gas is chemically processed to form powdered uranium dioxide (UO). These two reactors, according to The Encyclopedia of Ships, drive four propellers that produce a maximum speed of 30 knots.
The nuclear fuel cycle consists of initial steps that prepare uranium for use in nuclear reactors and subsequent steps to safely manage, prepare and dispose of spent, used or spent, but still highly radioactive, nuclear fuel. The nuclear reactors that power some aircraft carriers typically consume their nuclear fuel at about half of their desired 50-year lifespan. Nuclear reactor designs require higher concentration (enrichment) of the isotope U-235 to operate efficiently. As the ship is ready, towards the end of the ROH, the power plant heats up or restarts to the desired operating temperature and pressure so that it can start up when it is ready.
Because it is so radioactive, removing a nucleus with spent nuclear fuel from a reactor requires elaborate radiological handling precautions. Once a reactor core has become critical, meaning that it has been used during the operation of a reactor, highly radioactive nuclear fission products have formed in the core, and the core has become highly radioactive. The reactors aboard the George Washington contain enough nuclear fuel to fully power the ship and all its needs on board for approximately 20 years. The final step in the nuclear fuel cycle is the collection of spent fuel assemblies from temporary storage sites for final disposal in a permanent underground reservoir.
Refueling involves taking the spent core out of the reactor and putting in a new core with new nuclear fuel. The next step in the nuclear fuel cycle is to convert yellow cake to uranium hexafluoride (UF) gas in a converter facility. .