Reports out of Germany suggest that the city of Aachen plans to sue the Tihange nuclear power plant over what it claims is the plant’s failure to adequately address safety issues at the facility.

Aachen—a city with roughly 250,000 people—is located about 71 km (44 miles) west of Cologne on Germany’s border with Belgium and the Netherlands. The nuclear plant is located about the same distance southwest of Aachen in Belgium.

The Tihange site has three pressurized water reactor units. The 962-MW Unit 1 was commissioned in 1975 and is owned equally by Electrabel and Electricité de France. The 1,008-MW Unit 2 and the 1,046-MW Unit 3 were commissioned in 1983 and 1985 respectively, and are owned jointly by Electrabel (89.9%) and SPE (10.2%).

A Questionable Reactor Vessel

The city is alarmed by reports that Tihange Unit 2’s reactor vessel has thousands of flaw indications in its steel walls. The flaws were first discovered in August 2012 when the reactor vessel, made by Rotterdam Dry Dock Co., was subjected to a rigorous ultrasonic inspection. The testing was conducted because earlier that year flaws had been found in Electrabel’s Doel Unit 3 reactor vessel, which was manufactured by the same company and had a similar casting and forging history.

After further investigation, the indications were determined to be hydrogen flakes.

During the production of steel, small bubbles can form as the material cools down and hardens in the presence of too much hydrogen. In this particular instance, the bubbles formed in the steel rings that were later used to construct the reactor vessel. It was calculated that the hydrogen flakes would have an average length of 12 mm to 16 mm, if pressed flat, and would be the thickness of a cigarette paper. It was determined that these hair-like laminar lines ran parallel to the curvature of Unit 2’s reactor vessel wall.

Restart Allowed

In May 2013, after months of testing and evaluation, Electrabel supplied sufficient evidence to satisfy the Federal Agency for Nuclear Control (FANC)—the Belgian agency responsible for oversight of the country’s nuclear industry—that Tihange Unit 2 was safe to operate. Although Unit 2 restarted on June 7, 2013, metallurgical testing continued using a French steam generator that had been built for a nuclear plant but had not been used (it had been rejected due to the presence of hydrogen flakes).

A sample from the steam generator was irradiated in a research reactor to simulate the cumulative radiation exposure of 40 years of operation. Mechanical properties of the material were subsequently tested. The results were unexpected; the sample became embrittled much faster than had been theorized. On March 25, 2014, Unit 2 was shut down again as a safety precaution.

More Material Testing Needed

Further testing and analysis was conducted through November 2015. Electrabel submitted a safety case report to the FANC, which was assessed by various teams of national and international experts. In the end, the FANC said that the company was able to demonstrate that the unexpected test results of March 2014 were probably due to specific material properties of the sample. Tests on another material specimen with hydrogen flakes and on material from the reactor vessel itself showed that prolonged irradiation has no abnormal effect on the mechanical properties of the Tihange Unit 2 reactor vessel. On November 17, 2015, the FANC authorized the restart of Tihange Unit 2.

But the FANC’s pronouncement that the reactor vessel is safe has done little to reassure the city of Aachen. In what was reported to have been a unanimous decision by government officials, the city’s authorities agreed to bring a lawsuit to the Belgian administrative court, suing for breach of European law over the operation of a faulty reactor.

The goal of the suit is to get Unit 2 decommissioned. If unsuccessful with this step, a second claim could be filed at the European Union–level in Brussels.

Aaron Larson, associate editor (@AaronL_Power, @POWERmagazine)