Atucha II is a nuclear power plant in Argentina, located in Lima, Buenos Aires, on a site next to Atucha I. Its construction started in June 1981 under a contract with Siemens. Like Atucha I, it is a pressurized heavy-water reactor (PHWR), but was planned to have a much higher power (thermal power approx. 2,000 MW, electrical 750 MW). At the time when it was started, it had the largest reactor pressure vessel of any nuclear power plant worldwide. The total cost is now (2006) estimated at US$3.8 billion, or about $5500/kWe, considerably higher than the worldwide mean of about $1500/kWe.
Partly as a response to the energy shortage caused by natural gas crisis of 2004, the issue of Atucha II was taken up by the Argentine government. In 2005 President Néstor Kirchner signed a decree to reactivate the construction and pledged to finish it by 2009. New technicians were hired and a budget of about $120 million was requested for 2006. Eduardo Messi, president of Nucleoeléctrica Argentina S.A. (the firm in charge of the plant), told reporters that 93% of the components were either in storage or already installed.
On 23 August 2006 the government announced the re-activation of the national nuclear programme, and updated its promise to finish Atucha II by 2010, devoting a total of 1,850 million pesos ($596/€466 million). The plant was slated to come online with an installed capacity of about 750 MW (3% of Argentina's total electric installed capacity).
Atucha II was "pre-started" on September 28, 2011 by President Cristina Fernández de Kirchner and it was scheduled to start commercial service by mid-2013.
On June 3, 2014 reached its first criticality, and on June 27, 2014 began to produce energy.
On 19 February 2015, the plant reached 100% power production for the first time, increasing the percentage of nuclear power in argentina's energy mix from 7% to 10%.