Houston — The 728-MW Pilgrim Nuclear Power Station commenced early retirement Friday after 47 years online because lower power prices have made operating the unit uneconomical.

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The plant is among eight US nuclear power units with combined capacity of 6,306 MW that have been shut since September 2009, according to data S&P Global Platts provided.

Now 10 units with combined capacity of 10,585 MW have specific closure announcement dates, including Exelon's Three Mile Island Unit 1, Entergy's Indian Point Units 2 and 3, and Pacific Gas and Electric's Diablo Canyon Units 1 and 2.

Pilgrim, located in Plymouth, Massachusetts, was built by Bechtel for Boston Edison at a price reported at the time of $231 million. It was commissioned in December 1972.

The facility was bought in 1999 by Entergy Nuclear Generation. Pilgrim's original operating license expired in 2006, but Entergy sought an extension that was good until 2032.

But by 2013, Entergy became concerned with how the high operating and maintenance costs of small, single-unit facilities such as Pilgrim and the 635-MW Vermont Yankee facility matched up against facilities that used low-price natural gas.

Saying it expected power prices to remain low in the Northeast market, Entergy began seeking regulatory approvals to sell its subsidiaries that owned nuclear units.

Vermont Yankee was permanently shut December 29, 2014. Pilgrim, which went into service just one day after Vermont Yankee and had the same make and model reactor--the GE Mark I--was finally shut Friday night.

10 NUCLEAR UNITS TO RECEIVE ZECS

According to the US Nuclear Regulatory Commission, there are currently 98 commercial nuclear power reactors generating electricity.

As part of a move to keep nuclear facilities operating, three states -- Illinois, New York and most recently New Jersey -- have seen zero-emission credit programs established that are designed to compensate nuclear facility generation and keep them operating.

According to the data, 10 nuclear units with combined capacity of 10,270 MW are, or will soon, be compensated with ZEC payments.

Exelon owns a majority stake in seven of those units, which have combined capacity of 6,534 MW.

The New Jersey Board of Public Utilities decided April 18 to award ZECs to PSEG Power's Hope Creek facility and to Salem Units 1 and 2, which PSEG owns with minority stake holder Exelon. The three facilities have combined capacity of 3,736 MW.

NJBPU president Joseph Fiordaliso said at the time of the announcement that the board had voted 4-1 in favor of granting the ZECs. "We have a moral obligation to our fellow citizens to do everything we can to decrease carbon emissions," he said in the release.

Both PSEG and Exelon said they would have closed the facilities if the state legislature had not approved the ZEC program.

US nuclear unit closures and closure announcements Unit name Operator State MW Date shut Announced closure Crystal River-3 Duke Florida 912 Sep-2009* San Onofre-2 Southern California Edison California 1,127 Jan-2012* San Onofre-3 Southern California Edison California 1,127 Jan-2012* Kewaunee Dominion Wisconsin 581 May-7-13 Vermont Yankee Entergy Vermont 635 Dec-29-2014 Fort Calhoun Omaha Public Power Nebraska 526 Oct-24-2016 Oyster Creek Exelon New Jersey 670 Sep-15-2018 Pilgrim Entergy Massachusetts 728 May-31-2019 Three Mile Island-1 Exelon Pennsylvania 890 Sep-30-2019 Indian Point-2 Entergy New York 1,067 Apr-30-2020** Indian Point-3 Entergy New York 1,080 Apr-30-2021** Davis-Besse FirstEnergy Solutions Ohio 971 2020 Perry FirstEnergy Solutions Ohio 1,319 2021 Beaver Valley-1 FirstEnergy Solutions Pennsylvania 1,011 2021 Beaver Valley-2 FirstEnergy Solutions Pennsylvania 1,008 2021 Palisades Entergy Michigan 845 May-31-2022 Diablo Canyon-1 PG&E California 1,197 2024* 2024 Diablo Canyon-2 PG&E California 1,197 2025* 2025 Total 16,891 * Date units shut for technical reasons, retirement announced in 2013 ** Planned closure listed, but could be extended 3-4 years in requested by grid operator Source: Operator announcements

Nuclear units set to get state-level ZEC payments Clinton Exelon Illinois 1,098 Quad Cities-1 Exelon Illinois 994 Quad Cities-2 Exelon Illinois 994 Hope Creek PSEG New Jersey 1,250 Salem-1 PSEG New Jersey 1,254 Salem-2 PSEG New Jersey 1,232 FitzPatrick Exelon New York 849 Ginna Exelon New York 597 Nine Mile Point-1 Exelon New York 640 Nine Mile Point-2 Exelon New York 1,362 Total 10,270

-- Jeffrey Ryser, jeffrey.ryser@spglobal.com

-- Edited by Valarie Jackson, newsdesk@spglobal.com