Virginia Electric and Power Co. has became the first utility to place a new nuclear unit into commercial operation since the Three Mile Island nuclear accident nearly two years ago.

Vepco announced yesterday that it placed its North Anna 2 nuclear unit into commercial operation Sunday. Vepco said customer rates will decline 4.3 percent as a result of the new plant. A Virginia residential customer's bill for 1,000 kilowatt hours will drop by $2.59 a month, from $60.55 to $57.96, Vepco said.

"I am very proud that Vepco has been able to achieve this significant reduction in energy prices to our customers during a year in which consumer prices generally have continued to rise rapidly," Vepco President William W. Berry said.

Nearly three weeks ago, Vepco announced it was abandoning its North Anna 4 plant and planning to charge its customers $165 million over the next 10 years to cover its losses. North Anna 4 is only 10 percent completed and already cost $215 million. The company maintained, however, that because no further expenditures would be made on that plant, customers would end up saving on their monthly bills.

Berry said rates have declined during the year altogether by 7.2 percent.

During next year Vepco said about 42 percent of electrical energy supplied to its customers will come from its four nuclear units.