A nuclear power station in Lancashire has been ordered to improve its safety standards after a steam leak injured three workers.
The three men were injured during a serious incident at Heysham 1 nuclear power station on November 19 last year.
Owners EDF said the power station suffered an industrial incident in the form of a 'steam release', which caused a blast of high-temperature steam to escape.
EDF said the incident was "not nuclear related" and did not pose a threat to the public.
But the incident was immediately referred to the Office for Nuclear Regulation (ONR) and the government watchdog launched an official investigation.
After a three-month long inquiry into the incident, the ONR said it had served EDF Energy with two "improvement notices" relating to safety regulations.
A spokesman for the ONR said: "The Office for Nuclear Regulation has served two improvement notices on EDF Energy following a serious incident at Heysham 1 power station on 19 November 2018.
"The incident occurred when a valve failed on a steam system causing injury to three EDF Energy employees.
"There was no release of radioactive material and the two reactors remained operational following the incident.
"The two notices relate to the Pressure Systems Safety Regulations (2000) and require EDF Energy to improve the instructions provided to staff operating steam systems and to also ensure steam systems are properly maintained."
The watchdog said EDF Energy have until September 16 to comply with the requirements of the two improvement notices.
According to the ONR, the investigation is ongoing and the power plant could be subject to further enforcement action.
The spokesman added: "A formal ONR investigation is ongoing to establish the underlying causes of this incident and consider any further enforcement action in line with ONR’s published policies.
"In light of this ongoing investigation, we are unable to discuss any further details at this time."
Director of Heysham 1 station, Richard Bradfield, said EDF will act on any guidance issued by the ONR to ensure such accidents do not happen again.
He also revealed that the three injured workers are continuing with their recovery.
Mr Bradfield said: “Last November three of our colleagues were injured while de-isolating and re-instating an Auxiliary Steam Line at Heysham 1 power station.
"Thankfully, they are recovering well and EDF Energy continues to provide every assistance to all three and their families.
“We set up our own independent panel of inquiry involving a number of off-site company experts to ensure we fully understand what has happened and make sure we capture all the lessons which we are sharing throughout our organisation to ensure this doesn’t happen again.
“We have been working with the ONR and will act on any advice and guidance that they may give us.”
Heysham 1 was declared fully operational in 1989 after ten years of construction. It is expected to remain in operation until 2024, after which it will likely be decommissioned.
In 2013, a defect was found after a regular inspection in one of its eight pod boilers. The defective pod boiler was disabled and in June 2014 further inspections found a crack in the boiler spine.
The power plant was further investigated in 2015 after Heysham 1 suffered a "significant CO2 leak".
The watchdog concluded that there was no immediate nuclear safety or radiological risk as a result of the event.
But the ONR warned EDF that the incident "could have had serious implications if workers had been in the vicinity, including potential fatalities".