Cracks have been found in bricks that make up the graphite core of one of the two reactors, at EDF Energy's Hunterston B nuclear power plant in North Ayrshire, the UK.
The plant operator EDF Energy said that two cracked bricks were discovered following a maintenance inspection of 6,000 bricks.
EDF clarified that the cracks were expected and did not pose any safety issues.
Hunterston B station director Colin Weir said: "Every time we take the reactor out of service for planned maintenance we inspect the graphite core, which is made up of around 6,000 bricks.
"During the current Hunterston outage we found two bricks with a new crack which is what we predicted during Hunterston B's lifetime as a result of extensive research and modelling. It will not affect the operation of this reactor and we also expect that a few additional cracks will occur during the next period of operation.
"The small number of cracked bricks found during routine inspection is in line with our expectations, the findings have no safety implications and are well within any limits for safe operation agreed with our regulator."
The nuclear plant commenced operations in 1976 and was initially slated to be closed in 2011. However, its life was extended to 2016.
Following a technical and economic evaluation of the plant, EDF said that the facility could operate until 2023.
BBC quoted the EDF spokeswoman as saying that turbine balancing process was currently being undertaken and the rector would commence supply of power 'some time soon'.
Image: EDF Energy-built Hunterston B reactors. Photo: © EDF Energy 2014.