A generation III nuclear reactor is a development of any of the generation II nuclear reactor designs incorporating evolutionary improvements in design developed during the lifetime of the generation II reactor designs. These include improved fuel technology, superior thermal efficiency, passive safety systems and standardized design for reduced maintenance and capital costs.

Improvements in reactor technology result in a longer operational life (60 years of operation, extendable to 120+ years of operation prior to complete overhaul and reactor pressure vessel replacement) compared with currently used generation II reactors (designed for 40 years of operation, extendable to 80+ years of operation prior to complete overhaul and RPV replacement). Furthermore, core damage frequencies for these reactors are lower than for Generation II reactors — 60 core damage events per 1000 million reactor–year for the EPR; 3 core damage events per 1000 million reactor–year for the ESBWR significantly lower than the 10,000 core damage events per 1000 million reactor–year for BWR/4 generation II reactors.

The first generation III reactors were built in Japan, while several others have been approved for construction in Europe. A Westinghouse AP1000 reactor is scheduled to become operational in Sanmen, China in 2013.

Generation III reactors

• Advanced Boiling Water Reactor (ABWR) — A GE design that first went online in Japan in 1996.
• Advanced Pressurized Water Reactor (APWR) — developed by Mitsubishi Heavy Industries.
• Enhanced CANDU 6 (EC6) — developed by Atomic Energy of Canada Limited.
• VVER-1000/392 (PWR) — in various modifications into AES-91 and AES-92

Designs not adopted

• AP600 — A Westinghouse Electric Company design that received final design approval from the NRC in 1998; the EIA states that "Westinghouse has deemphasized the AP600 in favor of the larger, though potentially even less expensive (on a cost per kilowatt or capacity basis) AP1000 design."
• System 80+ — a Combustion Engineering (now incorporated into Westinghouse) design, which "provides a basis for the APR1400 (Generation III+) design that has been developed in Korea for future deployment and possible export."

Generation III+ reactors

Generation III+ designs offer significant improvements in safety and economics over Generation III advanced reactor designs certified by the NRC in the 1990s.

• Advanced CANDU Reactor (ACR-1000)
• AP1000 — based on the AP600 with increased power output
• European Pressurized Reactor (EPR) — an evolutionary descendant of the Framatome N4 and Siemens Power Generation Division KONVOI reactors.
• Economic Simplified Boiling Water Reactor (ESBWR) — based on the ABWR
• APR-1400 — an advanced PWR design evolved from the U.S. System 80+, which is the basis for the Korean Next Generation Reactor or KNGR
• VVER-1200/392M (PWR) — in design of AES-2006 with mainly passive safety features
• VVER-1200/491 (PWR) — in design of AES-2006 with mainly active safety features, international sold as MIR.1200
• EU-ABWR — based on the ABWR with increased powert output and compliance with EU safety standard.
• Advanced PWR (APWR) — 4th Generation of PWR from Mitsubishi Heavy Industries

Generation III++ reactors

• B&W mPower — an Advanced Light Water Reactor in development by Babcock and Wilcox and Bechtel