"Our investigation shows the two (rods) are safely stored," Northeast Utilities spokeswoman Deborah Beauchamp told Reuters.

In a statement, Northeast Utilities of Berlin, Conn. concluded the rods are safely stored in one of four locations: radioactive waste disposal facilities in either South Carolina or Washington state, at a General Electric Co. nuclear facility in Pleasanton, Calif., or still in the Millstone Unit 1 spent fuel pool.

The company emphasized the rods would not pose a threat to public health and safety or the environment at any of the four locations.

"Due to radiation levels and other security measures, the fuel (rods) could not have been removed from the spent fuel pool in anything other than a specially designed shipping container," said Frank Rothen, Northeast Utilities' vice president for nuclear services.

"Any removal other than by authorized personnel using a heavily shielded container would have been detected by a variety of means," Rothen added.

In a separate statement, the Nuclear Regulatory Commission (NRC), which oversees the safe operation of the nation's nuclear reactors, said: "The rods would not pose any risk of proliferating nuclear weapons due to their low uranium and plutonium content."

HOW THE RODS WERE LOST

The missing rods are about 1/2 inch in diameter and 158 inches, or about 13 feet long, and are filled with uranium pellets that trigger the atomic reaction that produces heat and powers a reactor's turbines.

When spent fuel is removed from a reactor, it is stored in steel-lined cooling pools.

From 1972 to 1980, Northeast Utilities' records show the rods, which were slightly damaged, were stored in the pool at Millstone's now-shut unit 1.

By September 1980, however, the rods had disappeared from the records, and were no longer where old records said they should have been.

Northeast's Beauchamp said it was possible the pins may have been mistaken for another piece of equipment, cut up and removed from the pool and sent to one of the other three locations.

She said the rods are similar in size and shape to low power range monitors, which are also stored in the spent fuel pool.

"These are the only locations that nuclear material from Millstone was sent to, so it must be safely stored in one of these locations or still in the spent fuel pool," Beauchamp said, noting there were about 167,000 rods and other material in the spent fuel pool.

Northeast Utilities sold the Millstone station to Richmond, Va.-based energy giant Dominion earlier this year and turned over its report on the missing rods to Dominion this week.

Dominion, in turn, forwarded the report to the NRC for further investigation.

The NRC said in its statement it will send a team to Millstone next week for about two weeks to evaluate Northeast Utilities' investigation into the missing rods.

Millstone unit 1 was a 660-megawatt (MW) boiling water reactor that began commercial operation in December 1970. The plant ceased operations in 1995.