Argentina’s nuclear utility Nucleoeléctrica SA (NA-SA) says it expects to begin repairs at the Atucha II NPP in June. In preparation, special tools have been designed and manufactured, and a life-size training facility (mock-up) has been built to train the personnel who will carry out the repairs.
Atucha II has been closed since October when a vibration was detected inside the reactor and caused one of four supports (spacers) to fall to the bottom of the reactor. It is expected to be out of service until at least July or August and probably longer. 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 mechanical arm is being developed to help to remove it. However, the tool needed approval from the Nuclear Regulatory Authority (ARN) and had to undergo tests in a laboratory that replicates the internal characteristics of the affected reactor.
Multiple sectors within NA-SA were involved in designing the necessary tools to carry out the procedure. These 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 the three remaining spacers that did not break off.
To develop the mock-up used for training, container used in the repair of the Atucha I in 1988 was reconditioned. All the internal elements were manufactured on a 1:1 scale and placed inside this container. A hyperbaric chamber was designed to test the welding scheme of the separators. Training tests at the mock-up are now underway. ARN is completing its review and approval of all the designs and manoeuvres proposed by the company to carry out the repair.
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 II site (courtesy of Nucleoelectrica Argentina)
