** Shares of nuclear power firms jump premarket after U.S. President Donald Trump issued a flurry of orders intended to boost energy production after his inauguration on Monday

** Chris Wright, Trump's pick to head the U.S. Energy Department, said he would prioritize U.S. oil and gas, and nuclear power production last week

** Wright supports some fossil fuel alternatives such as small nuclear power reactors, which are not yet commercially available

** Vistra rises 5.9%, NuScale Power up 6.3% and Nano Nuclear Energy gains 6.3%

** Constellation Energy up 1.7%, Centrus Energy

up 2.9%

** Wright is currently CEO of oilfield service company Liberty Energy , which is up 3.9%

** He is also a director at Sam Altman-backed nuclear startup Oklo Inc , which is up 6%

** Trump declared a national energy emergency; picks for his cabinet are expected to be confirmed by the U.S. Senate this week

(Reporting by Medha Singh)

((medha.singh@thomsonreuters.com))