Hence many larger PWRs such as the Rolls-Royce UK SMR have external steam generators. PWR types may have integral steam generators, in which case the reactor pressure vessel needs to be larger, limiting portability from factory to site. Some of the already-operating small reactors mentioned or tabulated below do not fit this definition, but most of those described do fit it. This definition, from the World Nuclear Association, is closely based on those from the IAEA and the US Nuclear Energy Institute. Small modular reactors (SMRs) are defined as nuclear reactors generally 300 MWe equivalent or less, designed with modular technology using module factory fabrication, pursuing economies of series production and short construction times. (In this information page the use of diverse pre-fabricated modules to expedite the construction of a single large reactor is not relevant.) A subcategory of very small reactors – vSMRs – is proposed for units under about 15 MWe, especially for remote communities. However, 'SMR' is used more commonly as an acronym for 'small modular reactor', designed for serial construction and collectively to comprise a large nuclear power plant. Together they have been referred to by the IAEA as small and medium reactors (SMRs). The International Atomic Energy Agency (IAEA) defines 'small' as under 300 MWe, and up to about 700 MWe as 'medium' – including many operational units from the 20th century. At the same time there have been many hundreds of smaller power reactors built for naval use (up to 190 MW thermal) and as neutron sources a, yielding enormous expertise in the engineering of small power units and accumulating over 12,000 reactor years of experience. The technologies involved are numerous and very diverse.Īs nuclear power generation has become established since the 1950s, the size of reactor units has grown from 60 MWe to more than 1600 MWe, with corresponding economies of scale in operation.This interest in small and medium nuclear power reactors is driven both by a desire to reduce the impact of capital costs and to provide power away from large grid systems.There is strong interest in small and simpler units for generating electricity from nuclear power, and for process heat.
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