By Susanna Twidale

LONDON, Sept 7 (Reuters) - TerraPower, the U.S. nuclear developer backed by Bill Gates, expects its Natrium reactors to begin generating electricity in Britain by 2034, its CEO told Reuters, making the UK its first market outside the United States.

Britain has backed the development of small modular reactors (SMRs) to help to increase energy security and meet climate targets, launching an Advanced Nuclear Framework this year to support privately funded projects.

Chris Levesque, TerraPower's president and CEO, said progress on the company's first Natrium reactor, due to be completed in 2031, showed that "2034 nuclear electricity in the UK from Natrium is very possible". 

The technology has cleared regulatory requirements in the United States, where the first plant is being constructed in Wyoming and is currently being assessed under Britain's Generic Design Assessment (GDA) process. 

Each sodium-cooled Natrium reactor generates 345 megawatts of baseload power and includes storage capable of boosting output to 500 MW for more than five hours. The reactors run on high-assay, low-enriched uranium (HALEU).

Britain and the U.S. are both building plants to produce the fuel, which was previously only commercially available from Russia.

Levesque said electricity generated by Natrium plants would be competitive with other low-carbon technologies, including combined solar-and-battery projects, at less than £100 ($135.32) per megawatt hour.

TerraPower has yet to choose a site for its first UK project, but said its British subsidiary is likely to be based in Liverpool, northwest England, close to the country's nuclear regulator.

In the U.S., the company has an agreement with tech giant Meta to develop up to eight reactors. Levesque said TerraPower could seek similar partnerships in Britain.  

($1 = 0.7390 pounds)

(Reporting by Susanna Twidale. Editing by Mark Potter)

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