Number of nuclear reactors operable and under construction
There are currently 437 operable civil nuclear power nuclear reactors around the world, with a further 66 under construction. A list of reactors operable, under construction, planned and proposed can be found here World Nuclear Power Reactors and Uranium Requirements, updated monthly.
Details of individual reactors operable and under construction can be found in our Nuclear Reactor Database, which uses information supplied by the International Atomic Energy Agency.
It may be useful to consider the sequence: planning, site works (usually about a year), first concrete for reactor, construction (4-5 years), start-up or criticality, grid connection, commercial operation. WNA and IAEA take first concrete to grid connection as "under construction", though considerable work and expense may precede this.
Why do different sources give slightly different figures?
There can be some variation in the assessment of the operational status of a reactor. For example, the Monju reactor in Japan generated electricity for a short time in 1994 and again in 2010. Some organizations consider that Monju entered full operation and is current in a period of long-term shutdown. Others consider that it is still under construction. Also in Japan, although many reactors were unaffected by the earthquake and tsunami of 3 March 2011 and continued operations all had to eventually shut down for refuelling. However, only two had been allowed to return to service, while others seek permission to restart operations.These reactors are still counted as operable by most sources, although others consider them to be in long-term shutdown.
For reactors under construction there may be differences in interpretation of when construction starts. Considerable construction work is done prior to pouring first nuclear concrete. For example, some considered the Vogtle 3 plant to already be under construction in late 2012, although at that time nuclear concrete had not been poured.
Construction can also stop, temporarily or permanently, on reactors. Whether construction will restart and the plant enter operation can be uncertain. In the US construction on the Watts Bar 2 reactor was stopped in 1988, due to lower than expected demand. Construction restarted in 2007. In Russia construction stopped on the Khmelnitski 3 and 4 reactors in 1990, but is now planned to restart.
Some months after a reactor is connected to the grid, hence operable and operating, it will be handed over to the owners and long-term operators. It is then said to be in commercial operation, and some figures list only those.
Finally, with construction starting on new projects, new reactors beginning operations and older reactors being retired throughout the year figures may vary simply because they are updated more or less frequently than others.
The following guide explains some of the definitions.
What is meant by "operable"
An operable reactor is one that is connected to the electricity grid. In most cases these reactors will be generating and supplying electricity to consumers. However, for short periods reactors don't supply electricity to the grid, for example during a scheduled outage for refuelling or maintenance.
What is meant by "under construction"
WNA uses the convention that a reactor is under construction only once 'nuclear concrete' has been poured. This is concrete of a specific grade or specification that is used in the construction of the nuclear facilities on a reactor site. It would not include planned reactors when site preparations are under way or concrete is being used for ancillary buildings or cooling towers.
What is meant by "civil nuclear power reactors"
Civil nuclear power reactors are those reactors used to generate electricity that is supplied to customers through electricity grids. There are hundreds of other nuclear reactors in operation around the world. These include research reactors used at universities and other research establishments, reactors used to power ships and submarines and reactors used to make medical isotopes.