WASHINGTON—The Commerce Department has opened an investigation into whether uranium imports threaten national security, a move that could lead to tariffs or other protections against foreign producers of the radioactive material that fuels nuclear power plants.

Uranium is used in commercial reactors that power a significant portion of the country’s electrical grid, as well as in nuclear weapons and Navy submarines and aircraft carriers. The government could impose tariffs on foreign producers or quotas that require buyers use a certain amount of domestically produced uranium if the investigation finds that imported uranium makes the U.S. too dependent on foreign countries for an essential material.