Among a flurry of executive actions, Mr. Trump directed the nation’s nuclear safety regulator to speed up approvals for new reactors.

Trump declared a national energy emergency on day one, responding to the first major U.S. power demand surge in decades.

Shares in companies tied to nuclear power jumped Friday, helped by President Donald Trump’s rollout of four executive orders that aim to provide a boost to the sector, but there were concerns about whether there could be much of a near-term impact.