Heysham 1 reactor 1 starts maintenance shutdown
During this shutdown known as an 'outage', engineers will inspect one of the four boiler units attached to the reactor and also undertake routine refuelling.
Last year during a planned maintenance shutdown, routine tests on one of the four boilers on reactor 1 prompted further investigations.
As a result the site took the decision, supported by the Office for Nuclear Regulation, to switch the reactor back on at 75% power with one boiler unit isolated.
Ian Stewart, Heysham 1's station director, said: "This current shutdown will see a specialist team go into the area around the reactor and inspect the boiler.
"Our expert teams have been preparing and planning to carry out this maintenance work for months and during the work, some 430 extra contract partners will join us at the power station."
Heysham 1 power station has been generating enough power for around two million homes since it started operating just over 30 years ago.
Its current scheduled closing date is 2019 however EDF Energy expects to be able to extend its life beyond that.
It has generated over 150 terawatt hours (TWh) of safe electricity since it connected to the grid in 1983. Last year it generated 6.5TWh of low carbon energy, producing enough electricity to supply around two million homes.
The station employs more than 550 permanent staff as well as over 200 contractors to ensure the safe reliable generation of power.
Local businesses are also set to benefit from this shutdown, as those extra contract partners use local hotels, bed and breakfasts and restaurants.