Anti-nuclear power campaigners have handed in a petition to Downing Street to "keep Wales nuclear-free".
Campaigners handed in the petition at Downing Street
The petition, signed by several thousand, was taken to London by a delegation including three Welsh MPs - two Liberal Democrats and one Labour.
The petition calls for "safer, cleaner and cheaper technology" than nuclear power to be used in Wales.
Prime Minister Tony Blair has said renewable energy could fill some but not all the UK's energy shortfall.
It is believed Mr Blair favours building new nuclear power stations to meet the country's energy needs.
The petition will be presented by Liberal Democrat MPs Lembit Opik (Montgomeryshire), Jenny Willott (Cardiff Central) and Labour MP Nia Griffith (Llanelli) along with representatives from Welsh environmental groups.
The Trawsfynydd nuclear plant in Gwynedd is being decommissioned
Organisers said the petition, which pledges "strong opposition" to nuclear power in Wales, had been signed by between 4,000 and 5,000.
Ms Griffith said:"We simply do not want to down the route of new nuclear build in Wales.
"It's completely unnecessary. It won't meet the timescale required to buy in other energies more quickly. And the legacy of nuclear waste is horrendous."
The Trawsfynydd nuclear power plant in Gwynedd is being decommissioned, while the Wylfa plant on Anglesey is due to close in 2010 - although local councillors have supported the principle of building a second one on the island.
Ms Willott said Mr Blair should not "simply impose" a new generation of nuclear power stations in Wales.
She added: "Our message to the government is clear: nuclear power is not the answer to Wales' energy needs.
"Nuclear power is hugely expensive, has a terrible environmental legacy, and is a huge security risk.
In November, Mr Blair launched a review of UK energy needs which could pave the way for a new generation of nuclear power stations.
The review is headed by Energy Minister Malcolm Wicks and will report by the middle of next year.