After 10 months, the Atucha II nuclear power plant is back online

When a part got stuck inside, the reactor’s operators fixed it by designing bespoke engineering tools

A bespoke claw tool removing a stuck part from Atucha II. Image: provided

Atucha II is a natural uranium-fueled reactor 100 kilometers from Buenos Aires City. It was the last nuclear power plant built by Siemens before the German company abandoned that sector of their business after the Fukushima tragedy in Japan. Atucha II had been producing energy uninterruptedly since 27 June 2014.

Until it didn’t.

Last October, during a routine inspection, the plant’s early warning system detected an obstruction in one of the fuel channels. After a thorough examination, a team discovered that one of the reactor’s four metal internal supports had fallen inside, together with its bolt. It was 14 meters deep, at the bottom of the reactor. 

These 14-kilogram circular supports are 16 centimeters in diameter. The reactor’s only exit channel is 10 centimeters. Since the part didn’t fit through it, the whole plant had to be turned off and disconnected from Argentina’s power grid. The situation was dire. “We have a lot of contacts with the international nuclear industry,” Jorge Sidelnik, vice president of state-owned company Nucleoeléctrica, which manages Argentina’s three nuclear power plants, told the Herald. “We asked around and there is not a tool to repair these objects at this distance in the world.”

The option Siemens recommended was dismantling the reactor, but it would have cost around US$400 million and taken around three years. So, Atucha’s staff decided to make their own tools to fish the piece out of the reactor. They decided on a technique known as spark eroding, a residue-free cutting technique using rapidly-recurring electrical discharges between two electrodes.

Cutting the part into four smaller pieces would mean they could fish it out through the cooling channel. It didn’t need to be replaced — according to Sidelnik, the supports were basically a design error.

The task, which ended on Monday, cost roughly US$20 million and took almost a year. However, the Atucha II workers relied on their vast experience in handling similar crises.

A blast from the past

Argentina has three nuclear power plants: Embalse in Córdoba province, operational since 1983, and the Atucha Nuclear Complex, which encompasses Atucha and Atucha II, two adjacent nuclear power plants near the town of Lima in Buenos Aires Province. The three of them combined produce 10% of the country’s electrical energy. 

In 1988, fourteen years after its opening, Atucha I suffered a malfunction in the reactor’s fuel channels — steel fragments had fallen inside. Things back then were very different: the team had no access to the inside of the reactor as they did not have a camera that could survive the interior of the reactor, and an energy crisis was taking place — the government scheduled power cuts and forbade nighttime public shows.

“Public opinion started to pressure us, the designing company [Siemens] too because we hadn’t done the renovations they wanted, Uruguayan lawmakers said that everything was going to blow up,” Sidelnik said. “It was the perfect storm.”

After being “depressed” for four days, Sidelnik and his team got down to work and could solve the problem — after assessing the situation, they formed a team that fished out the fragments. They even built a mock-up of the lower area of the tank to train the “fishers,” as he calls them.

Newspaper Página/12’s headline at the time was “lo ataron con alambres,” or “they tied it together with wires,” an Argentine adage meaning that something was repaired haphazardly.

“Journalists can be very cruel,” Sidelnik said. “But you have to remember, it was the two-year anniversary of the Chernobyl disaster.”

Cut to 2022. Sidelnik had “total confidence” in his team. “We repaired Atucha I in worse conditions. Now, we already know the reactor.”

The Atucha complex as seen from the air. Image: provided

Through the intervention of multiple sectors of the company and J1 Pumps (a small local Buenos Aires company) all the tools necessary to perform the procedure were designed in-house — including the cutting tool, cutting base, clamping tool, gripper, a basket to place the part and remove it, and a lighting and vision tool to monitor the maneuver. They also had to design a tool to preventively weld the three other supports so they did not come off.

“Many of the tools we built back in ‘88 were the basis for the development of the tools we have today, which are much more sophisticated,” Sidelnik said. For example, the early warning system that alerted them of last year’s malfunction was created after that incident, and the same mock-up model built back then was used to train the “fishers” served in 2023.

“This goes to show that machines do what they want to do and when they want to do it,” Nucleoeléctrica President José Luis Antúnez told the Herald. “But I always knew we would solve it.”

For Antúnez, having nuclear energy in a country like Argentina is an act of sovereignty.

“We have mastered the technology of the three power plants, one by purchase — the Canadian CANDU technology in Embalse was bought together with the power plant and we can use it as many times as we want within the national territory — and the other power plants fell into our hands by default because Siemens’ nuclear division disappeared and Nucleoeléctrica took over the design authority,” he told the Herald.

“Nuclear energy is also an essential component for the decarbonization of the atmosphere, we do not emit one gram of carbon dioxide.”

The day finally came. On June 22, suction cups were put into the reactor and, with that, the separator was moved and prepared for the cutting. Then, the spark eroding tool was inserted. The cutting took two weeks, and then the gripper took the pieces and placed them in the basket for removal from the reactor.

The next step was welding the remaining separators, to avoid the same thing happening to them.

On August 28, 2023, at 21:00, Atucha II was finally back online.


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