Argentina’s nuclear utility Nucleoeléctrica SA (NA-SA) says it expects to complete repairs at the Atucha II NPP by the end of July.

Atucha II has been closed since October 2022 when a vibration was detected inside the reactor causing one of four supports (spacers) to fall to the bottom of the reactor. The repairs are estimated to cost $2-4m. NA-SA experts said the damage does not represent a threat to the safety of the plant, but compromises it in terms of electrical and financial generation. The damaged 10cm-long component is in an inaccessible part of the reactor and a special mechanical arm had to be developed to help to remove it.

NA-SA has now completed the cutting and extraction of the detached spacer from a depth of 14 metres inside the reactor. The intervention was carried out by a multidisciplinary team, using engineering tools and procedures designed and manufactured by the company together with local suppliers. NA-SA says the next stage of the repair will focus on the implementation of improvements in the design of the plant to reinforce the fixation of the remaining spacers, before operation resumes.

The special tools designed for the procedure included a cutting tool, cutting base, holding tool, gripper, the design of a basket to hold the component and extract it and the design of a lighting and vision tool to be able to monitor the manoeuvre. It was also necessary to develop a pressure welding tool and a method to preventatively weld and strengthen the three remaining spacers.

In order to practice the cutting and extraction maneuvers and to be able to test the tools and methods developed, a full-scale model (mock-up) of the relevant sector of the reactor in was designed, manufactured and installed. The Nuclear Regulatory Authority ARN reviewed and approval of all the proposed designs and manoeuvres.

Argentina has three pressurised heavy water reactors – Atucha I, Atucha II and Embalse – with a total generating capacity of 1,641 MWe which provide 9% of electricity generation. Atucha I, which began construction in June 1968, was the first NPP in Argentina and Latin America. Currently, it has a gross power of 362 MWe. The reactor uses heavy water as coolant and moderator, and 0.85% slightly enriched uranium as fuel. Construction of Atucha II began in 1981 as a joint venture of CNEA and Siemens-Kraftwerk Union but work was suspended in 1994 with the plant 81% complete. It was restarted in 2006 and was first connected to the grid in 2014 starting commercial operation in 2016.

Image: The Atucha plant site (courtesy of Nucleoelectrica Argentina)