Currently, the most common reactors in the U.S. are boiling water reactors (BWR) and pressurized water reactors (PWR), both variants of the light water reactor (LWR). The large majority of operating LWRs are PWRs (64 of the 96 nuclear power reactors operating in the US are PWRs[1]). The combination of pressure and temperature of the coolant is the main difference between BWRs and PWRs. This difference enables various designs between the two types of reactors. These reactors utilize water as both a coolant to control the fission reaction as well as to generate steam to turn turbines, generating electricity. In a BWR, the water evaporates in the same vessel it comes in contact with the nuclear fuel. In a PWR, the superheated water is kept under high pressure until it reaches a secondary chamber, where it then evaporates.

The nuclear industry is similar to the automobile industry in that safety and economic improvements are constantly made, and an LWR can undergo many significant changes in its lifetime such as component change-outs, power uprates, safety system additions and more.[2]


Used nuclear fuel is often reprocessed in order to extract fissile materials for recycling and to reduce the amount of high-level waste. Reprocessing nuclear fuel creates a closed fuel cycle, which in turn reduces the need for uranium mining and enrichment, reduces the volume of waste in geological repositories, mitigates the risk of proliferation by avoiding the production of separated plutonium, and creates a waste byproduct that is less toxic than single-use uranium. According to the World Nuclear Association, “the principal reason for reprocessing used fuel has been to recover unused plutonium, along with less immediately useful unused uranium, in the used fuel elements and thereby close the fuel cycle, gaining some 25% to 30% more energy from the original uranium in the process.”[3] Approximately 100,000 tonnes of used fuel from commercial power reactors has been reprocessed. The annual reprocessing capacity is now about 5,000 tonnes per year from normal oxide fuels (not all of it operational). From 2010 to 2030, about 400,000 tonnes of used fuel is expected to be generated worldwide, with about 60,000 tonnes of used fuel generated in North America.[4]


Used nuclear fuel is a toxic, long-lived byproduct of nuclear power generation – some components of this spent fuel can be radioactive for millions of years. Spent nuclear fuel is expected to accumulate at an average rate of about 2,200 metric tons per year in the U.S. By 2067, the currently operating reactors are expected to have generated about 139,000 metric tons of spent nuclear fuel, most of which is expected to be transferred to dry storage.  Spent nuclear fuel from commercial nuclear power reactors is stored at 75 sites in 33 states, frequently where it was generated. The spent nuclear fuel is stored wet in pools of water or dry in storage systems that typically consist of stainless steel canisters housed in protective casks. Over the past several decades, the inventory of commercial spent nuclear fuel in storage in the U.S. has increased to about 72,000 metric tons.[5]

Two federal agencies—the U.S. Nuclear Regulatory Commission (NRC) and the U.S. Department of Energy (DOE)—are primarily responsible for the regulation and disposal of the nation’s spent nuclear fuel. NRC regulates the construction and operation of commercial nuclear power plants and spent fuel disposal facilities, as well as the storage and transportation of spent fuel. DOE is responsible for developing a disposal facility for the long-term management of used uranium fuel from America’s nuclear power plants.[6] However, the DOE does not have a program for the management of used nuclear fuel from commercial nuclear energy facilities and high-level radioactive waste from the government’s defense and research activities. Thus, nearly all commercial used fuel is stored safely and securely at the reactor sites in steel-lined concrete pools filled with water, or in airtight steel or concrete-and-steel containers (dry cask storage).[7]

Updated November 2020 by Kristen Johnson