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Several generations of reactors are commonly distinguished.
Generation I reactors were developed in 1950-60s, and outside the UK
none are still running today. Generation II reactors are typified
by the present US and French fleets and most in operation elsewhere.
(3rd generation) advanced reactors have been operating in Japan since
1996. Late 3rd generation designs are now being built.
* a standardised design for each type to expedite licensing, reduce capital cost and reduce construction time,
* a simpler and more rugged design, making them easier to operate and less vulnerable to operational upsets,
* higher availability and longer operating life - typically 60 years,
* further reduced possibility of core melt accidents,*
* resistance to serious damage that would allow radiological release from an aircraft impact,
* higher burn-up to reduce fuel use and the amount of waste,
* burnable absorbers ("poisons") to extend fuel life.
* The US NRC requirement for calculated core damage frequency is
1x10-4, most current US plants have about 5x10-5 and Generation III
plants are about ten times better than this. The IAEA safety target
for future plants is 1x10-5. Calculated large release frequency (for
radioactivity) is generally about ten times less than CDF.
The greatest departure from second-generation designs is that many
incorporate passive or inherent safety features* which require no
active controls or operational intervention to avoid accidents in the
event of malfunction, and may rely on gravity, natural convection or
resistance to high temperatures.
* Traditional reactor safety systems are 'active' in the sense that
they involve electrical or mechanical operation on command. Some
engineered systems operate passively, eg pressure relief valves. They
function without operator control and despite any loss of auxiliary
power. Both require parallel redundant systems. Inherent or full
passive safety depends only on physical phenomena such as convection,
gravity or resistance to high temperatures, not on functioning of
engineered components, but these terms are not properly used to
characterise whole reactors.
The goals of the generation IV initiative cover the areas of sustainability,
econpmic competitiveness, safety and reliability and security against weapons
proliferation.