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The Palo Verde Nuclear Generating Station, commonly referred to as Palo Verde Power Plant, is a nuclear power plant located in Wintersburg, Arizonamarker, about 45 miles (80 km) west of central Phoenixmarker, and is currently the largest nuclear generation facility in the United States, averaging over 3.2 gigawatts (GW) of electrical power production in 2003 to serve approximately 4 million people. Arizona Public Service (APS) owns the largest portion (29.1%) of the station and operates the facility. Other owners include Salt River Project (17.5%), El Paso Electric Co. (15.8%), Southern California Edison (15.8%), PNM Resources (10.2%), Southern California Public Power Authority (5.9%), and the Los Angeles Dept. of Water & Power (5.7%).

Palo Verde is the only nuclear generating facility in the world that is not located adjacent to a large body of above-ground water. Instead, it evaporates water from the treated sewage of several nearby municipalities to meet its cooling needs. The water consumed by the Palo Verde Nuclear Generating Station represents about 25% of the annual overdraft of the Arizona Department of Water Resources Phoenix Active Management Area.


The facility is on 4,000 acres (16 km²) of land and consists of three Combustion Engineering pressurized water reactors, each with an original capacity of 1.27 gigawatts electrical, current (2007) maximum capacity of 1.24 gigawatts electrical, and typical operating capacity 70%–95% of this. The plant is a major source of power for Phoenix and Southern California, capable of serving about 4 million people. The plant provides about 35% of the electricity generated in Arizona each year. The plant was fully operational by 1988, taking twelve years to build and costing $5.9 billion, eventually employing 2,386 people. The plant employs 2,055 full-time on-site workers.

It supplies electricity at an operating cost (including fuel and maintenance) of 1.33 U.S. cents per kilowatt-hour. This is cheaper than coal (2.26 cents/kW·h) or natural gas (4.54 cents/kW·h) in the region at the same time (2002), but more expensive than hydro (0.63 cents/kW·h). Assuming a 60-year plant life and 5% long-term cost of capital, the depreciation and capital costs not included in the previous marginal cost for Palo Verde are approximately another 1.4 cents per kilowatt-hour. In 2002, the wholesale value of the electricity produced was 2.5 cents/kW·h. By 2007, the wholesale value of electricity at the Palo Verde hub was 6.33 cents/kW·h.

Due to its location in the Arizona desert, Palo Verde is the only nuclear generating facility in the world that is not located adjacent to a large body of above-ground water. The facility evaporates water from the treated sewage of several nearby municipalities to meet its cooling needs. 20 billion US gallons (76,000,000 m³) of treated water are evaporated each year. This water represents about 25% of the annual overdraft of the Arizona Department of Water Resources Phoenix Active Management Area. At the nuclear plant site, the wastewater is further treated and stored in an 80 acre (324,000 m²) reservoir for use in the plant's cooling towers.

The nuclear steam supply for each unit was designed and supplied by Combustion Engineering, designated the System 80 standard design — a predecessor of the newer standard System 80+ design. Each primary system originally supplied 3.817 GW of thermal power to the secondary (steam) side of each plant. The design is a so-called 2 × 4, with each of four main reactor coolant pumps circulating more than 111,000 gallons per minute of primary-side water through 2 large steam generators.

The main turbine generators were supplied by General Electric and when installed were the largest in the world, capable of generating 1.447 GW of electricity each. They remain the largest out of 60 Hz turbine generators.

Bechtel Power Corporation was the Architect/Engineer/Constructor for the facility initially under the direction of the Arizona Nuclear Power Project (a joint APS/SRP endeavor), later managed exclusively by Arizona Public Service. Edwin E. Van Brunt was the key APS executive in charge of engineering, construction, and early operations of the plant. William E. Bingham was the Bechtel Chief Engineer for the project.

Unlike most multi-unit nuclear power plants, each unit at Palo Verde is an independent power plant, sharing only a few minor systems. The reactor containment buildings are some of the largest in the world at about enclosed. The three containment domes over the reactors are made of thick concrete.

The facility's design incorporates many features to enhance safety by addressing issues identified earlier in the operation of commercial nuclear reactors. The design is also one of the most spacious internally, providing exceptional room for the conduct of operations and maintenance by the operating staff.

The Palo Verde 500 kV switchyard is a key point in the western states power grid, and is used as a reference point in the pricing of electricity across the southwest United States. Many 500 kV power line from companies like Southern California Edison and San Diego Gas & Electric send power generated at the plant to Los Angelesmarker and San Diegomarker via Path 46, respectively. In addition, due to both the strategic interconnections of the substation and the large size of the generating station, the Western Electricity Coordinating Council considers a simultaneous loss of 2 of the 3 units the worst case contingency for system stability.

The site was granted a construction permit for two additional units in the late 1970s, however these units were canceled in the mid-1980s for economical risk reasons. Contrary to popular belief, the two additional units would not have been on the same arc as the three existing units — they would have been arranged south of Unit 3 on a north-south axis. As originally conceived they would have used dry cooling towers rather than the forced-draft wet cooling towers used in the existing design.


Palo Verde was of such strategic importance, due to a variety of its features, that it and Phoenixmarker were documented by the former Soviet Unionmarker as target locations in the event of nuclear conflict during the Cold War. In March 2003, National Guard troops were dispatched to protect the site during the launch of the Iraq war amidst fears of a terrorist attack.

The site team and nearby town of Wintersburg remain a key focus of work in regard to homeland security, ranking in importance along with Arizona's major cities, military bases, ports of entry, and tourist sites.

Security guards working for the utility are armed with semi-automatic weapons. They check identification and search vehicles entering the plant. Other security measures protect the reactors, including X-ray machines, explosive "sniffers", and heavy guarded turnstiles that require special identification to open. It should be noted that many armed guards, thorough security checkpoints and machines, and bomb sensors are standard at every nuclear power plant in the US.

Safety concerns

In an Arizona Republic article dated February 22, 2007, it was announced that the Nuclear Regulatory Commission had decided to place Palo Verde into Category 4, making it one of the most closely monitored nuclear power plants in the United States. The decision was made after the NRC discovered that electrical relays in a diesel generator did not function during tests in July and September 2006.

The finding came as the "final straw" for the NRC, after Palo Verde had several citations over safety concerns and violations over the preceding years, starting with the finding of a 'dry pipe' in the plant's emergency core-cooling system in 2004.

During a March 24, 2009 public meeting, the NRC announced that is cleared the Confirmatory Action Letter (CAL) and has returned Palo Verde to Column 1 on the NRC Action Matrix. The commission's letter stated that "The U.S. Nuclear Regulatory Commission has determined that the Palo Verde Nuclear Generating Station has made sufficient performance improvement that it can reduce its level of inspection oversight." “Performance at Palo Verde has improved substantially and we are adjusting our oversight accordingly,” said Elmo E. Collins, NRC’s Region IV Administrator. “But we will closely monitor the plant. We are reducing our oversight, but not our vigilance.”


The selection of the present site for Palo Verde was controversial. Critics claim that the site was not the first choice because it was in the middle of nowhere, had no water supply, and put the Phoenix-Metro area into jeopardy in the event of a major accident, because of the prevailing westerly winds, would endanger the capital. Critics claimed that that site was selected over alternatives because it was owned by a relative of Keith Turley, who received almost $2 million for the land. Keith Turley was the president of APS, and a member of the Phoenix 40. Units 1 and 2 went commercial operation in 1986 and Unit 3 in 1988.

On November 18, 2005, the U.S. Nuclear Regulatory Commission announced approval of uprates at two of Palo Verde's reactors. According to the NRC press release, "The power uprates at each unit, located near Phoenix, Arizona, increases the net generating capacity of the reactors from 1,270 to 1,313 and 1,317 megawatts electric, respectively, for Units 1 and 3. The licensee intends to implement the uprate by the end of December for Unit 1, and by the end of 2007 for Unit 3."


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