Palo Verde Nuclear Generating Station

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Palo Verde Nuclear Generating Station

The Palo Verde Nuclear Generating Station is a nuclear power plant located in Wintersburg, Arizona, about 45 miles (80 km) west of central Phoenix. It is the largest nuclear generation facility in the United States, averaging over 3.3 gigawatts (GW) of electrical power production in 2008 to serve approximately 4 million people. Arizona Public Service (APS) owns 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%).

Located in the Arizona desert, Palo Verde is the only nuclear generating facility in the world that is not situated 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.


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.

According to APS, power generation operations to date at Palo Verde have offset the emission of almost 484 million tonnes of carbon dioxide (the equivalent of taking up to 84 million cars off the road); more than 253,000 tonnes of sulphur dioxide; and 618,000 tonnes of nitrogen oxide. The company noted, "If Palo Verde were to cease operation at the end of the original licence, replacement cost of natural gas generation - the least expensive alternative - would total $36 billion over the 20-year licence renewal period."

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 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. Arthur von Boennighausen was one of the Owner's Representatives for Arizona Public Service.

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 2.6 million cubic feet (74,000 m3) enclosed. The three containment domes over the reactors are made of 4-foot (1.2 m) 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 lines from companies like Southern California Edison and San Diego Gas & Electric send power generated at the plant to Los Angeles and San Diego 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 Phoenix were documented by the former Soviet Union 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. Armed guards, security checkpoints with machines, and bomb sensors are standard at every nuclear power plant in the US.

On 2 November, 2007, a pipe with gun powder residue was found in the bed of a contract worker's pickup truck during normal screening of vehicles. It was then confirmed to contain explosives by local police. APS then initiated a seven hour security lock-down of the plant, allowing no one to enter or exit the plant. The site also declared a Notification of Unusual Event, which is the lowest of four Emergency Plan event classifications.

"Our Security personnel acted cautiously and appropriately, demonstrating that our security process and procedures work as designed," said Randy Edington, APS Executive Vice President and Chief Nuclear Officer. "These actions are clearly in line with our goal of ensuring the health and safety of the public and our employees."

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 it 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 because of the prevailing westerly winds, put the Phoenix-Metro area into jeopardy in the event of a major accident. 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 into 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."

On April 21, 2011, the NRC renewed the operating licenses for Palo Verde's three reactors, extending their service lives from forty to sixty years.

Seismic risk

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Palo Verde was 1 in 26,316, ranking it #18 in the nation according to an NRC study published in August 2010.

Surrounding population

The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of 10 miles (16 km), concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about 50 miles (80 km), concerned primarily with ingestion of food and liquid contaminated by radioactivity.

Disaster Plan

The latest disaster plan is available from Arizona. (June 2008) Mr. Don E. Bogardus, Sr. Director EH&S, Security, of Banner Health, the states largest health care provider, also has comments on the plan.


The 2010 U.S. population within 10 miles (16 km) of Palo Verde was 4,255, an increase of 132.9 percent in a decade, according to an analysis of U.S. Census data for The 2010 U.S. population within 50 miles (80 km) was 1,990,846, an increase of 28.6 percent since 2000. Cities within 50 miles include Phoenix (47 miles to city center).

Building Activity

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