Sizewell B nuclear power station was one of the sites named in the reports
The government has denied that a list of sites for new nuclear power stations has already been drawn up.
The Department for Business said the process was ongoing and reports to the contrary were "nonsense".
Its comments follow reports that ministers have already selected sites alongside existing reactors such as Sizewell, Dungeness and Hartlepool.
The prime minister has called for "a renaissance of nuclear power" as an alternative to fossil fuels.
Reports suggest ministers have already identified sites alongside a number of existing reactors - Heysham, Hinkley Point and Bradwell are among the others mentioned - as the most suitable places for the new nuclear stations.
But the Department for Business issued a statement saying: "This is nonsense. There is no pre-determined list of sites for building new nuclear power stations.
'Expensive and dirty'
"We are currently undertaking a strategic siting assessment process which will identify the criteria to assess the suitability of sites and will also identify a list of sites nominated which meet those criteria.
"The government has set out a clear vision for nuclear new build. Energy companies have been invited to bring forward proposals for new nuclear power stations as part of the solution to the UK's future low carbon energy needs."
Mr Brown has previously called for the UK to increase its nuclear power capacity as an alternative to burning fossil fuels, which many experts believe to be a cause of climate change.
In January ministers announced that they backed new plants and published a review of possible sites where there have been nuclear power plants before.
However opponents of the plans say new reactors will be expensive, dirty and dangerous.
Campaign group Greenpeace argues that research suggests that even 10 new reactors would cut the UK's carbon emissions by only about 4% some time after 2025.