A generator fire at the Ringhals 3 nuclear plant in Germany in August is believed to have been caused after a spanner and a pen were left inside the newly installed machine.

Around 10 days after being operations the generator short-circuited with the resulting smoke setting off fire alarms and prompting the reactor to shut down.

Supplier Alstom is understood to have conceded that the spanner most likely ended up in the generator during manufacture. The damaged generator will be replaced in mid-October.