Nuclear power plants are typically designed to operate for 30 to 40 years. Between 2010 and 2020 a large number of nuclear power plants in the world and in OECD member countries, in particular, will reach their 30th or 40th anniversary. 1 As of June 2011, out of 440 nuclear power plants operating in the world, approximately 81% had been in operation for more than 20 years and about 35% for more than 30 years.2 In OECD member countries there are at present 339 nuclear reactors in operation, of which 135 reactors (39.8% of the total number) are over 30 years old and 15 reactors (4.4% of the total number) are over 40 years old. All nuclear reactors in Finland have reached their 30th anniversary while in the United States 56% of all reactors are beyond 30. In the United Kingdom and Germany about 42% of nuclear reactors are older than 30 years while in Canada, France and Japan, the respective percentages in this age bracket amount to 22%, 34% and 30%.