An extra 1,000 people have been taken on at the Cumbrian plant
British Nuclear Fuels (BNFL) has announced the completion of a £36m, three year improvement plan after a critical report from the industry watchdog.
The Nuclear Installations Inspectorate (NII) said it was concerned about the number of safety related incidents in 1999 at the west Cumbrian site.
It issued 28 recommendations, which BNFL says it has now completed.
A report by the NII had found there was an increase in the number of safety related incidents in the first half of 1999, and had expressed concern about falling employment levels at Sellafield.
As a result, an extra 1,000 people have been taken on and management systems have been reorganised to deal with the criticisms made by the NII.
The report was one of three highly critical assessments of the Sellafield site, which came out in the wake of the data falsification scandal for MOX fuel bound for Japan.
However, BNFL now says it has firmly put its house "in order" and has the full confidence of its partners.