A small leak was found Thursday in a pipe that forms part of the cooling system at a reactor at the Biblis nuclear power plant in Hesse that has been shut down for renovations, the environment ministry in the western state said.

The problem was detected during routine checks that are being carried out before the reactor is put back on line, the ministry said in a statement, adding that there was no danger to the staff or the environment.

In the northern state of Schleswig-Holstein, a measuring instrument broke down at the Brokdorf plant on December 13, regional authorities said.

The plants are respectively operated by energy groups RWE and E.ON.

In June, two incidents at nuclear power plants in northern Germany operated jointly by E.ON and Swedish group Vattenfall's German subsidiary led to accusations that they had tried to hide the extent of the problems.

The two affected reactors were disconnected from the power grid and are expected to be put back on line in February.

Vattenfall denied a cover-up, but the scandal prompted the head of its Europe branch to quit, and caused an outcry in Germany, which is deeply divided over whether it should be using nuclear energy at all.

The country has begun a long-term phase-out of its nuclear energy programme and expects to mothball the last of its 17 plants sometime around 2020.