Demolition work which will change the Sizewell A nuclear power station skyline is part of a programme of tasks costing between £3million and £4million due to start next month.

Although the huge reactor building will remain, the administration and engineering blocks and a large crane on the south side of the redundant power plant are be dismantled and materials either recycled on the nuclear site or taken away by lorry.

Parts of the two offshore rigs, once used as cooling water input and output, are also to be removed to reduce danger.

The rigs have been in a deteriorating condition for years.

Repair of cladding on the reactor building will continue and parts of the site perimeter fence, now 60 years old, are to be replaced.

Magnox, which manages the A station on behalf of the Nuclear Decommissioning Authority (NDA), expects the latest phase of work to be completed by the end of March next year.

Sizewell A began generating electricity in 1966 and shutdown in 2006, after 40 years of electricity generation – producing 110 TWh of power, enough to boil more than one trillion kettles.

Defuelling began in 2007 and the removal of the 52,000 fuel elements took eight years to complete. This was done ahead of schedule and Magnox said it had removed 99% of the radiological hazard.

The site has has been undergoing the initial stages of decommissioning.

The power station is due to be put in a “care and maintenance” phase by 2027 and will not be due for major demolition and clearance for up to 80 years – unless NDA policy changes.

Allen Neiling, Magnox closure director, told the latest meeting of the Sizewell Stakeholder Group (SSG), that after 2027 the power station doors would be welded shut and the site would remain fenced, locked and monitored.

Detailed plans about security had yet to be approved.

The Office for Nuclear Regulation (ONR) would carry out regular inspections to ensure the plant remained in a safe condition while radiation levels reduced.

Rowland Cook, ONR site inspector, said the most radioactive part of the power station to remain would be the graphite reactor cores. No decision had yet been made about when they would be removed.