Generation I reactors were developed in 1950-60s, and none are still operating except in the UK. Generation II refers to the class of commercial reactors built up to the end of the 1990s. They generally had a design life of 30 to 40 years, but many have been extended to 50 to 60 years. Generation III (and III+) are designs incorporating improvements 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.
According to Westinghouse, utilities in Georgia and South Carolina have been waiting for the AP1000 Design Certification so that they can move ahead with construction and operating license (COL) applications. Westinghouse estimates that approximately 35,000 jobs will be positively affected by the construction of just two AP1000 units here in the United States.
The NRC Design Certification is based on findings that the AP1000 design is safe and meets all regulatory requirements. This is the second time that the AP1000 design has gone through the rule-making process to receive Design Certification, the first certification being granted in 2006.
Since 2006, the AP1000 design has been modified to meet additional NRC requirements, including those that require the design to withstand the impact of an aircraft crash on its shield building, a steel reinforced concrete structure approximately 3 feet thick that protects the steel containment vessel, which houses the reactor. Both the shield building and the containment vessel play significant roles in the passive safety systems of the AP1000 design, which are intended to shut down safely with no, or minimal, operator action and no AC power.
The passive safety design was recognized by the NRC as providing added capability that allows the plant to safely cope with a Fukushima-type event, a significant reason why the NRC Near-term Task Force Review of Insights from the Fukushima-Daiichi Accident recommended the granting of Design Certification to the AP1000 design.
The accident at Three Mile Island involved a pressurized water reactor; the Fukushima nuclear energy accident involved boiling water reactors. According to the Nuclear Energy Institute, there are no data indicating that pressurized water reactors are more or less safe than boiling water reactors. They both are licensed by the in NRC and operated to the same levels of regulatory requirements and safety.