Unit 7 at Heysham 2 power station has been shut down to start its planned £30m maintenance outage.
One thousand extra workers will join the site’s 700-strong team during the 10-week period.
The team will carry out more than 15,000 separate pieces of work – each carefully planned during two years of preparation.
The extensive programme of work will see inspections inside the reactor, as well as the installation of new equipment.
The biggest projects include replacing two large gas circulators which help cool the reactor.
The maintenance periods, known as ‘statutory outages’, take place every three years and are planned in advance with the National Grid to ensure that there is no impact on the national electricity supply.
Heysham 2’s other reactor will continue operating normally throughout the period.
Alan Oulton, station director at Heysham 2, said: “We produced enough low carbon electricity in 2014 to power Greater Manchester. That performance is the result of our focus on safety, the expertise of our people and the investments we make at the station.”
“These planned statutory outages bring significant benefits to the local community creating extra work and proving a boost to local business including engineering workshops, food suppliers, shops, hotels, B&Bs, restaurants and taxi services.”