Finland’s nuclear safety authority said Thursday that radiation levels had risen following an incident at the Olkiluoto 2 nuclear unit in western Finland but there was no radioactivity leakage outside the plant and that the situation was under control.

“There are no indications of a fuel leak from the incident and there are no longer any exceptional radiation levels inside the plant,” the authority, STUK, said in a statement.

It said it had been informed of elevated radiation levels at the reactor at around 1 p.m. local time.

“This is a significant and an exceptional incident and we consider it important to spread correct information about it,” Finland’s minister of social affairs and health Aino-Kaisa Pekonen told reporters.

The elevated readings stemmed from a room regularly showing higher values during normal operations, and no power company employees at the reactor, located 220 kilometers from Helsinki, had been exposed to radiation or were injured, it added.

Jarmo Tanhua, CEO of the nuclear power plant operator TVO, said the incident was an unparalleled event in the facility’s history, Al Jazeera reported. TVO is a consortium of power and industrial companies. Tanhua added that: “There is no danger to people or the environment.”

The International Atomic Energy Agency said STUK had informed it of the incident and that it would provide public information as it became available.

Oskar Njaa, Bellona’s general manager for international affairs, said the age of the Olkiluoto 2 unit could be cause for concern. The reactor, which went into service in 1982, received a lifetime extension from Finnish regulators two years ago, pushing its eventual decommissioning back to 2028.

“We may see more such incidents with an increasingly ageing reactor fleet in Europe,” he said.

Bellona has previously warned that numerous reactors operating in and around Europe are getting older and operating longer than they were designed for. In March, the group published a report showing that 90 of these reactors will reach their intended retirement age within the next decade.

Olkiluoto 2, which has a capacity of 890 megawatts, shut down and would remain offline until Saturday, according to information posted by TVO via power exchange Nord Pool.

Automatic systems detected raised levels of radioactivity in the steam pipes of the reactor’s cooling system, although the cause of the spike was not yet known and investigations are ongoing, Tomi Routamo, deputy director at nuclear safety authority STUK, told Reuters.

Although radiation levels around the plant are normal and there was no external leak, STUK described the incident in a tweet as “serious” and said readiness protocols had been launched in conjunction with the plant’s operator, TVO.

“If there is a fault with the first cooling circuit for the reactor water, it may be a question of a discharge inside the reactor hall itself ­– which has then been isolated to that area,” said Njaa. “Now they have to go in and make further measurements to get more details.”

Njaa urged Finnish officials to conduct a thorough investigation into the incident.

A host of European countries, including Finland, Belgium, France, the Netherlands, Spain, Sweden, Switzerland, the Czech Republic, Hungary, Ukraine and the United Kingdom are currently considering lifetime extensions for many of their reactors. The designed service life for these reactors varies from 25 to 40 years.