German nuclear power station officials have admitted losing the keys to top security areas within their own plant.
The Philippsburg nuclear plant in Germany is now under investigation after owners reported that they have been searching for the keys to vital areas around the reactors since March 10.
The plant is run by German company EnBW, which reportedly took an entire week to inform the authorities about the loss of the keys.
Prosecutors have opened an investigation "against unknown perpetrators" for theft.
The company has announced that the locks are being changed, but German Environment Ministry spokesperson Karl Franz criticised the delay in reporting the case.
He said: "We received no explanation as to why it took so long to report the occurrence."