The Shaw Group Inc. has signed a new three-year contract with Arizona Public Service Co. to provide maintenance, modifications, construction and radiological protection services to the Palo Verde Nuclear Generating Station in Arizona, a news release says.

Palo Verde is 55 miles west of Phoenix and is the largest nuclear power plant in the United States with three reactors capable of producing more than 4,000 megawatts of electricity.

Shaw did not disclose the value of the contract but will include it in the company’s Plan Services segment backlog of unfilled orders in the first quarter of fiscal 2012.

Arizona Public Service is the state’s largest and oldest electric utility, serving more than 1.1 million customers.