Wylfa was the last and largest of the UK’s Magnox nuclear power stations – the first type of commercial nuclear power station – and ended operations in 2015, after 44 years of generating electricity.
Calder Hall, the world’s first commercial nuclear power station, also completed its defueling programme earlier this month.
Removal of all the nuclear fuel from a site is one of the main pieces of hazard reduction work and accounts for over 99% of the radioactivity. The NDA said the completion of defueling is a huge stride towards the end of all nuclear fuel reprocessing at Sellafield – scheduled for 2020.
It said 87,890 nuclear fuel elements have been removed from Wylfa’s twin reactors since it ended generation.
Decommissioning at Wylfa now moves into another phase - preparation for what is known as "care and maintenance" will get under way in December, as much of the site is cleared.
Buildings will be demolished and the giant turbine halls once powered by steam heated by the nuclear reactors will be dismantled.
Site director Stuart Law said that would take up to seven years, leaving only the two reactor buildings and the empty dry fuel stores.
Under current plans, those final buildings will be monitored for a century - until about 2126 - when radiation will have decreased to manageable levels.