The average age of the 435 nuclear power plants that are currently operating worldwide is 25 years and in Western Europe, 75 percent of the plants are in the last half of their operating life, according to the Institute for Economic Research at the University of Munich.
The Institute states that the age structure differs very much in the various regions of the world. The plants are especially old in the Western industrial states. For example, 90 percent of the 104 nuclear power plants in the US are already more than 20 years old and half have been operational for more than 30 years.

In Western Europe 65 percent of the reactors are between 21 and 30 years old; a additional 20 percent have been operational for more than 30 years. The IEA and the plant operators both estimate the lifespan of the of a plant to be 40 to 50 years. Effectively this means that already 75 percent of the reactors are in the last half of their operating life.
The newest nuclear power plants are found particularly in Eastern Europe, India and East Asia. Those nations also have most of the reactors in the world that are under construction or planned.

Organizations such as the IEA and the IAEO (International Atomic Energy Organization) expect an increasing share of atomic energy in the worldwide energy mix. The IEA, considers nuclear power to be a key element of climate policies. The goal of limiting the warming of the atmosphere to 2° Celsius above pre-industrial temperatures would be jeopardised without nuclear power, the IEA fears.

The IAEO expects that improved international cooperation and progress in nuclear power plant technology will advance the construction of new nuclear reactors so strongly that this will more than compensate for the aging effect.

According to the European Nuclear Society, in September 2009, there were a total of 196 nuclear power plant units with an installed electric net capacity of 169,711 MWe in operation in Europe and 17 units with 14,710 MWe were under construction in six countries.