Nuclear Disasters

US nuclear site's collapsed tunnel may have gone unnoticed

The large sinkhole that caved in a tunnel filled with radioactive waste at a sprawling Washington state nuclear waste repository may have gone unnoticed for days before its discovery because workers do not patrol tunnel sites daily, a spokesman for the U.S. Department of Energy said Thursday.

The sinkhole was found Tuesday, prompting an emergency at the Hanford Nuclear Reservation with evacuations of some workers and orders for others to stay inside buildings scattered across the 500 square-mile (1,300 square-kilometer) safekeeping location for radioactive waste dating from World War II.

Authorities plan to investigate why and when the roof of the tunnel suffered a partial...