SOFIA, Bulgaria — Bulgaria has started building a radioactive waste repository near the country’s only nuclear power plant on the Danube River.

Bulgarian Energy Minister Temenuzhka Petkova on Tuesday called the project at Kozlodui “extremely important for the development of nuclear energy in Bulgaria.”

The low- and mid-level radioactive waste that will go into the repository comes mainly from the decommissioning of four old nuclear reactors.

Bulgaria shut the four Soviet-era reactors at Kozlodui over safety concerns and as a precondition for joining the European Union in 2007.

The country has two Russian-built reactors remaining at Kozlodui.

The repository is scheduled to start operating in 2021.

A fund administered by the European Bank for Reconstruction and Development is financing the 73 million euro ($88 million) project.