The High Flux nuclear reactor in Petten in the province of Noord Holland was shut down on Thursday because radioactively contaminated water had leaked into the crawl space of the building, owners Nuclear Research and Consultancy Group NGR said in a statement.

According to broadcaster NOS, the leak started during work on a pipe in the pumping installation of the reactor. The site at Petten is used for the production of medical isotopes which are used by hospitals for the treatment of cancer.

According to the NGR the leak posed no danger to the environment although the groundwater near the reactor will be monitored in the days to come. Extra protective measures for the local population were deemed unnecessary by the Dutch nuclear safety and protection body ANVS.

Workers at the scene were checked and were found not to be affected, the NGR said.

The company has started an investigation into the cause of the leak and the amount of contaminated water that was allowed to escape.