President Donald Trump on Friday signed orders meant to accelerate the construction of nuclear power plants, including small, untested designs that offer the promise of rapid deployment but haven’t yet been built in the US.

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

The orders grant the U.S. Energy secretary authority to approve advanced reactor designs and projects, taking authority away from the independent safety agency that has regulated the U.S. nuclear industry for five decades.