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Nuclear power plant in Calvert County, Maryland, US

The Calvert Cliffs Nuclear Power Plant (CCNPP) is a nuclear power plant located on the western shore of the Chesapeake Bay near Lusby, Calvert County, Maryland in the Mid Atlantic United States. It is the only nuclear power plant in the state of Maryland.

The plant is owned and operated by Constellation Energy and has two 2737 megawatt thermal (MWth) Combustion Engineering Generation II two loop pressurized water reactors. Each generating plant (CCNPP 1&2) produces approximately 850 megawatt electrical (MWe) net or 900 MWe gross. Each plant's electrical load consumes approximately 50 MWe. These are saturated steam plants (non superheated) and are approximately 33% efficient (ratio of 900 MWe gross/2700 MWth core). Only the exhaust of the single high pressure main turbine is slightly superheated by a two stage reheater before delivering the superheated steam in parallel to the three low pressure turbines. Unit 1 uses a General Electric–designed main turbine and generator, while Unit 2 uses a Westinghouse–designed main turbine and generator. The heat produced by the reactor is returned to the bay, which operates as a cooling heat sink for the plant. Unit 1 went into commercial service in 1975 and Unit 2 in 1977. Unit 1 had its two steam generators replaced in 2002 and its reactor vessel closure head replaced in 2006, while unit 2 had its two steam generators replaced in 2003, and its vessel closure head replaced in 2007. The water around the plant (see lower right center of photograph) is a very popular place for anglers. Unit 1 & 2 each takes in bay water (from the fenced in area) to cool its steam driven turbine condensers plus other bay water–cooled primary and secondary system heat exchangers. The bay water is pumped out at a nominal flow rate of 1.2 million gallons per minute (75,000 L/s) per unit (Unit 1 and 2) for each steam turbine condenser. The water is returned to the bay no more than 12 °F (6.7 °C) warmer than the bay water. Unlike many other nuclear power plants, Calvert Cliffs did not have to utilize water cooling towers to return the hot water to its original temperature. As the water comes out very quickly and creates a sort of artificial rip current, it can be a dangerous place to fish. CCNPP 3 will only need about 10% of the bay cooling water volume needed for Unit 1 and 2 combined. The increase in fish and shellfish impingement and entrainment will be less than 3.5% over Unit 1 and 2 existing conditions. In February 2009, Calvert Cliffs set a world record for pressurized water reactors (PWRs) by operating 692 days non stop. In addition, Unit 2's capacity factor in 2008 was a world record high of 101.37 percent.

The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of 10 mile (16 km), concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about 50 mile (80 km), concerned primarily with ingestion of food and liquid contaminated by radioactivity. The 2010 US population within 10 mile (16 km) of Calvert Cliffs was 48,798, an increase of 86.4 percent in a decade, according to an analysis of U. S. Census data for msnbc. com. The 2010 U. S. population within 50 mile (80 km) was 2,890,702, a decrease of 2.0 percent since 2000. Cities within 50 miles include Washington, D. C., (45 miles to city center).

In 2001, when the Dominion Cove Point LNG plant was scheduled to reopen, many local residents were concerned about the proximity to this nuclear power plant (3 miles). Residents thought that the FERC did not consider the risks could be caused by an attack or an explosion before opening the plant.

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Calvert Cliffs was 1 in 100,000 for Reactor 1 and 1 in 83,333 for Reactor 2, according to an NRC study published in August 2010.

Scientists at Johns Hopkins University became concerned that the discharge of heated cooling water from the plant would be detrimental to a crucial element of the Chesapeake Bay ecosystem, the bay's famed blue crabs. In the late 1960s, litigation borne of Congress's National Environmental Policy Act eventually spawned one of the most celebrated environmental cases in American history, Calvert Cliffs' Coordinating Committee, Inc. v. Atomic Energy Commission, forcing the Atomic Energy Commission (now the Nuclear Regulatory Commission) to consider the environmental impact of building and maintaining such an atomic energy plant.

In 2000, the Nuclear Regulatory Commission extended the license of the plant for 20 additional years, making Calvert Cliffs the first nuclear plant in the United States to receive such an extension. President George W. Bush visited the plant in June 2005, the first time a president had visited a nuclear power plant in nearly two decades.

UniStar Nuclear Energy announced plans to build a unit of the Evolutionary Power Reactor (US EPR variant) at Calvert Cliffs. UniStar Nuclear Energy, a Delaware limited liability company, was jointly owned by Constellation Energy (CEG) and Électricité de France (EDF), the French builder and supplier of nuclear power plants. The proposed unit was to produce approximately twice the energy of each individual existing unit. On July 13, 2007, UniStar Nuclear Energy filed a partial application to the Nuclear Regulatory Commission to review its plans to build a new nuclear power plant, Calvert Cliffs Nuclear Power Plant 3 (CCNPP 3) based on the AREVA US Evolutionary Power Reactor (US EPR), Generation III+, four loop pressurized water reactor. The third reactor was intended to address a need for more baseload power generation in the Mid Atlantic region. The unit proposed to be located south of the existing units 1 and 2, set back from the shoreline. Although only a single unit, its power plant footprint was almost twice the size of the existing units together. It was to have a closed loop cooling system using a single hybrid mechanical draft cooling tower, incorporating plume abatement for no visible water vapor plume from the tower. Units 1 and 2 use an open cycle heat dissipation system without cooling towers. The cooling tower of the Unit 3 reactor was to release two thirds of its waste heat to the atmosphere. The proposed EPR design was a saturated steam plant with one high pressure turbine in tandem with three low pressure turbines and a main generator design similar to Unit 1 and 2. Alstom was to supply the main steam turbine and main generator. On November 13, 2007, UniStar Nuclear Energy filed an application for a certificate of public convenience and necessity with the Maryland Public Service Commission for authority to construct CCNPP 3. This application is being considered in Case Number 9127. Opponents and supporters of the proposed third reactor at Calvert Cliffs were involved in a series of public hearings before officials of the US Nuclear Regulatory Commission. In March 2009, Bill Peil of southern Calvert County asked the Nuclear Regulatory Commission to deny an emissions permit for the reactor due to health and safety concerns he asserted that the plant posed to the community. UniStar Nuclear Energy President and CEO George Vanderheyden urged the NRC to approve the air permit application. In October 2010, Constellation Energy said that it had reached an impasse in negotiations for a federal loan guarantee to build the proposed third reactor. The government sought a fee of $880 million on a guarantee of about $7.6 billion, to compensate taxpayers for the risk of default. Constellation Energy replied that such a fee would doom the project, “or the economics of any nuclear project, for that matter”. In November 2010 a deal to transfer Constellation Energy Group's stake in a nuclear development company to its French partner, EDF Group, closed, according to the SEC. A month prior, Constellation agreed to sell its 50 percent stake in UniStar Nuclear Energy to EDF for US$140 million, giving EDF sole ownership of the joint venture and its plans to develop a third unit at Calvert Cliffs in Southern Maryland. The deal called for EDF to transfer 3.5 million shares it owns, valued around US$110 million, to Constellation and give up its seat on the Constellation board. EDF designee Samuel Minzberg resigned. In April 2011 the Nuclear Regulatory Commission (NRC) stated that UniStar is not eligible to build a third reactor, as it is not a US owned company since Constellation pulled out of the partnership in 2010. The NRC would continue to process the application, but a license would not be issued until the ownership requirements were met. The reactor was estimated to cost $9.6 billion. Constellation Energy merged into Exelon in 2012. In 2015 Areva, struggling with internal restructuring of its corporation, withdrew from the certification process for the US EPR reactor design, effectively putting on hold plans for the deployment of a European reactor in the US.

Unit 2 at the Calvert Cliffs nuclear power plant was shut down on September 5, 2013, after a malfunction during testing. It was re opened September 10, 2013, after the required maintenance was performed.