Whether you are new to nuclear energy or a seasoned professional, the industry's alphabet soup of acronyms and technical terms can be daunting. This glossary covers the most important terms you will encounter when following nuclear energy news, policy, and technology developments.

Regulatory and Government Agencies

NRC (Nuclear Regulatory Commission) — The independent U.S. federal agency responsible for licensing and regulating civilian nuclear power plants and other uses of nuclear materials. The NRC reviews reactor designs, issues operating licenses, and conducts inspections to ensure safety compliance.

DOE (Department of Energy) — The U.S. federal department responsible for energy policy, nuclear weapons programs, and funding for advanced nuclear research. The DOE Office of Nuclear Energy oversees programs supporting existing reactors and developing next-generation designs.

IAEA (International Atomic Energy Agency) — The United Nations agency that promotes the peaceful use of nuclear energy and works to prevent its use for military purposes. The IAEA conducts international safeguards inspections and publishes safety standards.

NEI (Nuclear Energy Institute) — The trade association for the U.S. nuclear energy industry. NEI represents nuclear plant operators, suppliers, and technology companies before Congress and federal regulators.

ANS (American Nuclear Society) — A professional organization for nuclear scientists and engineers that publishes technical journals, hosts conferences, and advocates for nuclear science and technology.

Reactor Types and Technology

SMR (Small Modular Reactor) — A nuclear reactor with an electrical output of 300 megawatts or less, designed to be factory-built and transported to a site. SMRs promise lower upfront capital costs and faster construction timelines compared to traditional large reactors. Examples include NuScale's VOYGR design and GE Hitachi's BWRX-300.

LWR (Light Water Reactor) — The most common type of nuclear reactor worldwide, using ordinary (light) water as both coolant and neutron moderator. The two main subtypes are Pressurized Water Reactors (PWRs) and Boiling Water Reactors (BWRs).

MSR (Molten Salt Reactor) — An advanced reactor design that uses liquid salt as fuel, coolant, or both. MSRs can operate at higher temperatures and lower pressures than traditional reactors, potentially improving safety and efficiency. Kairos Power's Hermes reactor is a fluoride salt-cooled design.

HTGR (High-Temperature Gas-Cooled Reactor) — A reactor that uses helium gas as a coolant and graphite as a moderator, operating at very high temperatures. X-energy's Xe-100 is a pebble-bed HTGR design.

SFR (Sodium-Fast Reactor) — A reactor cooled by liquid sodium that uses fast (unmoderated) neutrons. TerraPower's Natrium project is a sodium-fast reactor design.

Gen III+ / Gen IV — Classification systems for reactor designs. Gen III+ refers to evolutionary improvements on current designs (like the AP1000). Gen IV refers to revolutionary next-generation designs being developed for deployment after 2030, including molten salt, gas-cooled, and fast reactors.

Fuel and Materials

HALEU (High-Assay Low-Enriched Uranium) — Uranium enriched to between 5% and 20% U-235, higher than the fuel used in current reactors (typically 3-5%) but below weapons-grade levels (20%+). Many advanced reactor designs require HALEU fuel. The U.S. is actively building domestic HALEU production capacity.

LEU (Low-Enriched Uranium) — Uranium enriched to less than 20% U-235, the standard fuel for commercial nuclear power plants.

MOX (Mixed Oxide Fuel) — Nuclear fuel made from a blend of plutonium and uranium oxides. MOX fuel can recycle plutonium from spent fuel or decommissioned weapons.

SNF (Spent Nuclear Fuel) — Nuclear fuel that has been irradiated in a reactor and is no longer efficient for sustaining a chain reaction. SNF remains radioactive and must be stored safely. The U.S. currently stores spent fuel at reactor sites in pools and dry casks.

Regulatory and Licensing Terms

ADAMS (Agencywide Documents Access and Management System) — The NRC's public document database containing licensing applications, inspection reports, safety analyses, and correspondence.

COL (Combined Operating License) — An NRC license that authorizes both construction and operation of a nuclear power plant. This streamlined process replaced the older two-step construction permit/operating license approach.

Part 50 / Part 52 / Part 53 — Sections of the NRC's regulations (Title 10 of the Code of Federal Regulations). Part 50 covers traditional licensing, Part 52 covers combined licenses, and Part 53 is a new risk-informed framework being developed for advanced reactors.

EIS (Environmental Impact Statement) — A document required under the National Environmental Policy Act (NEPA) that evaluates the environmental effects of a proposed nuclear facility.

Industry and Market Terms

Capacity Factor — The ratio of actual electricity output to maximum possible output over a given period. U.S. nuclear plants consistently achieve capacity factors above 90%, among the highest of any electricity source.

Baseload Power — The minimum amount of electric power delivered or required over a given period at a steady rate. Nuclear plants are ideal baseload generators because they produce power continuously and reliably.

PPA (Power Purchase Agreement) — A contract between an electricity generator and a buyer (often a utility or large corporation). Several tech companies have signed PPAs for nuclear power to meet their clean energy goals.

LCOE (Levelized Cost of Energy) — A measure of the average cost of electricity generation over a plant's lifetime, including construction, fuel, operations, and decommissioning. LCOE allows comparison across different energy sources.

This glossary is maintained by ReactorBrief and updated regularly as new terms enter the nuclear energy conversation. Subscribe to get nuclear industry news delivered three times per week.