Underwater engineering work starts on Tuesday to remove one of the oldest parts of the Sellafield site.
Divers will cut up the last 320 metres of redundant discharge pipeline at the plant in west Cumbria and take it away in containers on barges.
When British Nuclear Fuels got permission in the late 1980s to replace the sea-line at Sellafield, one of the conditions was that it also had to remove the disused pipe.
BNFL says the risk of radioactivity from the operation is "negligible".
There used to be three pipelines which carried waste away from the plant and out to sea.
The pipes, which were installed in 1949 and were 1680 metres long, have been replaced by new pipes, although it has taken 13 years to get rid of this final section.
There have been negotiations with the Environment Agency and Copeland Council, which has set a deadline of the end of 2003 for work to be completed.
The pipe sections will be taken to Workington docks, and then to Drigg where they will be sealed in thick concrete and buried.
Pressure group Cumbrians Opposed to a Radioactive Environment (Core) is worried about whatever residue there might be in the pipe, which it claims is "not low-level waste".