Nuclear's supporters want world leaders in Paris to commit to 1000 gigawatts of nuclear generation out to 2050.

While an increase in the global reactor fleet would be great news for Australia's uranium hopefuls and others across North America, Africa and in Europe, the potential downside involved in nuclear power generation are substantial.

World Nuclear Association's director general Agneta Rising said to implement the goals of an ambitious COP 21 agreement governments "need" to develop policies that encourage investment in low carbon generation, especially nuclear energy.

"We need 1000GWe of new nuclear capacity by 2050 to combat climate change. This will require effective regulation and markets that value low carbon emissions and reliable supplies," she said.

The Inter-Governmental Panel on Climate Change says that emissions from the electricity generation sector should fall by 80% by 2050 to prevent a greater than 2C rise in average global temperatures.

She said countries such as Switzerland, Brazil, Sweden and France have all achieved low carbon electricity supplies through combinations of generation from nuclear energy and renewables.

"Nuclear energy is a proven provider of affordable, reliable low carbon electricity. Over the last fifty years nuclear generation has been estimated to have avoided the emission of more than 60 billion tonnes of carbon dioxide," Rising said.

That's more than 10 times the annual carbon dioxide emissions from the world's road transport fleet.

"France has shown that with nuclear energy an affordable low carbon generation mix is achievable. COP 21 must deliver an agreement that helps us achieve a low carbon emissions world," she said.

Her words echoed a call from lobby group Nuclear for Climate, a global initiative supported by more than 140 regional and national nuclear associations and technical societies.

The group says that nuclear should be left on the table as a viable option, and that the choice should not be prejudiced against by the new United Nations Framework Convention on Climate Change protocols, specifically with regards to access to climate funding mechanisms such as green climate funds.

The IPCC identified three types of carbon-free electricity: renewables, nuclear energy and fossil fuels with carbon capture and storage.

The group is concerned that nuclear will be left out in the cold, with all the cash being focused on clean, renewable, more distributed options.

"We strongly believe the world must use all available low-carbon energy sources, including nuclear energy, if it is to mitigate the effects of climate change and reduce greenhouse gas emissions while meeting development goals and not impeding on economic growth," French Nuclear Energy Society director-general Valerie Faudon said.

European Nuclear Society secretary general Jean-Pol Poncelet said all possible solutions have to be carefully considered and all ideologically or doctrinally driven decisions avoided.

"States should recognise nuclear energy as a greenhouse gas-reducing technology necessary for us to achieve the sustainability we want," he said.

India is one country looking to a large expansion in nuclear power to supply a quarter of the country's electricity, while not adding to the risk of catastrophic climate change.

Globally, 438 reactors generate around 11% of the world's electricity, with almost no greenhouse gas emissions.

In the European Union, nuclear energy accounts for more than half of all low-carbon electricity, although that number is falling as Germany moves away from nuclear in the wake of the Fukishima disaster.

In the United States, it accounts for 63% of all low-carbon electricity.

China is expected to account for one-third of the world's installed nuclear energy capacity by 2050 to meet its energy and climate change goals.

However, none of the groups addressed the massive government subsidies needed to make nuclear generation commercially viable, or the considerable cost and time over-runs that commonly affect nuclear construction.

In September French state-controlled utility EDF announced that the Areva-designed 1650 megawatt European pressurised reactor it is building in Normandy is again running behind schedule and over budget.

The Flamanville reactor had been scheduled to start in 2012 and was scheduled to cost $4.4 billion. It will now start in 2018 and cost 15.5 billion.

It is supposed to be the first of a new series of safer next-generation reactors to replace France's ageing fleet of 58 nuclear reactors.

A similar EPR reactor built by Areva in Finland, on which construction started in 2005 and was scheduled to start up in 2009, has suffered even longer delays.

Olkiluoto 3 will now not start before 2018.

Two more EPRs are under construction in China and EDF plans to build two in Hinkley Point, Britain at an eye-watering $50 billion, of which an estimated $35 billion are in subsidies.

The build will take a decade. Hinkley Point could begin generating in 2026 and provide enough power to meet 7% of UK electricity demand.

In the US the Vogtle and VC Summer facilities in the US are three years behind schedule in construction and each is expected come in billions of dollars over their original budgets, and are acting to discourage further US investment in nuclear power in the near term, with existing, older generation reactors being extended well beyond their lifespans.

Fitch Ratings says the US Energy Information Administration's forecasts of nuclear generation falling by 10,800MW through 2020 could be understated due to political pressure and higher-than-expected operations and maintenance costs which are accelerating plant retirements.

At the same time, the US is reporting that for the first quarter of 2015 84% of new electricity generation capacity was from renewables, primarily solar and wind facilities.

Utility-scale solar power now accounts for 1% of total US electricity generation capacity with small-scale solar an estimated 0.7%, and wind accounting for 5.6%.