What directives were issued to U.S. nuclear power plants by the NRC, to be implemented by December 2016?
A. All nuclear reactors must be built on the coast, where there is a plentiful supply of cooling water.
B. All nuclear reactors must be built underground.
C. Venting systems for boiling water reactors must be improved.
D. All reactors must be supported by sufficient portable safety equipment to be used in the event of a power shut-down.