British Nuclear Fuels has been told it can build a store for intermediate level nuclear waste at Trawsfynydd in the heart of Snowdonia National Park.
The height of the plant's reactors will be reduced
Following a public inquiry last year the Welsh Assembly Government has given planning permission to a new store and to lowering the height of two reactors on the decommissioned site.
The reactors will be lowered from 55 metres to 35 metres and the store will be used to keep the radioactive waste currently on site.
Opponents of the scheme were concerned that radioactive waste would be stored on the site for up to 100 years, and argued for the whole station to be dismantled.
BNFL says the waste could be on site for anything up to 50 years as the government has not yet decided where the UK repository for waste is to be sited.
The company also says it has no plans to bring waste from other stations to Trawsfynydd, which closed in 1993.
But Deilwen Evans of local anti-nuclear group Cadno was sceptical about the promise that the radioactive waste would not be on site permanently.
"I am disappointed that the assembly government has not put much emphasis on the moving of the waste when a permanent store becomes available.
"They have assumed in the report that it will only be there for 50 years.
"But I think it will be there for ever now. They have granted permission to lowering the reactor buildings.
"After that, they will plant trees around it, nature will take over, the building will be forgotten about and the waste buried there for ever."
Ms Evans was also critical of the timing of the announcement.
"I condemn the assembly for announcing this on the first day of the Eisteddfod.
"It is a report of national and international significance, and people should have more time to go through a report on such an important matter."
But station manager Don Nightingale who will be responsible for taking the work forward, said they have worked closely with the community and Snowdonia National Park for the past eight years.
"The local community made it clear they wanted the visual impact of the site to be reduced by lowering the height of the power station's two former reactor buildings and this is what we can now do," he said.
"The roofs will be curved to be more sympathetic with the surrounding landscape and the walls will be clad in a range of materials including local Ffestiniog slate and special tinted stainless steel panels."
The store will be about 91 metres long and 35 metres wide, and 19 metres high.
The go-ahead comes after a three-week planning inquiry held in Penrhyndeudraeth in November and December 2002.
Work should start in twelve months time and should be complete by 2008.