A unique heavy water design
On the banks of the Paraná de las Palmas River, about 100 kilometers from Buenos Aires, is the Atucha Nuclear Power Station. Its first reactor, Atucha I, began commercial operation on June 24, 1974, making Argentina the first country in Latin America with a commercial nuclear power facility. The station consists of two reactors, Atucha I and Atucha II, which are both pressurized heavy water reactors (PHWRs) of a German KWU design supplied by Siemens.
This design distinguishes Atucha from the more common CANDU-type PHWRs. Instead of hundreds of individual pressure tubes holding the fuel, the Atucha reactors contain the entire core within a single, large pressure vessel, a feature more typical of pressurized light water reactors (PWRs). This makes the Siemens PHWR a unique configuration. The reactors use heavy water (deuterium oxide, D₂O) as both the neutron moderator and the primary coolant. Heavy water is exceptionally efficient at slowing neutrons without absorbing them, which allows the reactor to sustain a chain reaction using natural or only slightly enriched uranium (0.85% U-235).
Atucha I has a gross electrical output of 362 MWe. Its safety systems have been continually modernized to meet current international standards, and a life extension project is underway to allow it to operate for an additional 24 years.
Expansion and a study in longevity
Construction on a second, more powerful unit, Atucha II, began in July 1981. The project faced significant delays due to funding issues and was suspended in 1994 when it was 81% complete. Work officially resumed in 2006 as part of a national strategic plan to bolster the country's nuclear energy sector. Atucha II finally achieved its first criticality on June 3, 2014, and began commercial operation in May 2016. It is a larger version of the first unit, with a gross electrical output of 745 MWe and a thermal capacity of 2160 MWt.
The long operational history of Atucha I, in particular, provides data for nuclear engineers worldwide. The decades of service have supplied important information on the aging and performance of its large pressure vessel under prolonged neutron irradiation. This data helps researchers model material fatigue and predict the operational lifespans of reactor vessels in other plants.
Like other PHWR designs, the Atucha reactors can be refueled while operating at power. This on-load refueling capability increases the plant's availability and efficiency by avoiding lengthy shutdowns for fuel changes, which are required for light water reactors.