Like many similar plants, it was constructed by Bechtel, and was powered by a General Electric BWR 3 boiling water reactor inside of a Mark 1 pressure suppression type containment and generator.

[3] On October 13, 2015, the plant's owners announced that it would close by June 1, 2019, citing "market conditions and increased costs," which would have included tens of millions of dollars of necessary safety upgrades.

[4] Built at a cost of $231 million in 1972 by Boston Edison, the plant was sold in 1999 to the Louisiana-based Entergy Corporation, part of a complex deal that was the result of deregulation of the electrical utility industry.

[5] Pilgrim kept its spent nuclear fuel in an on-site storage pool, waiting for federal direction on the correct disposal process.

The state attorney general also raised questions about, among other issues, the dangers posed by the onsite storage of spent nuclear fuel.

[9] In July 2013, the plant had to reduce output during a heat wave despite very high electricity demand, because the temperature of water drawn from Cape Cod Bay exceeded 75 °F, the limit set by the NRC.

It was the first time in the station's history that reactor water level reached a low-low condition and activated emergency core cooling systems.

The resulting shadow effect killed plant and animal life around reactor discharge systems by curtailing the light and oxygen they need to survive;[19][better source needed] however, the intake and discharge canals remained a popular and lucrative local recreational fishing spot for local residents.

[20] The NRC's estimate of the yearly risk of an earthquake strong enough to cause core damage to the Pilgrim reactor was 1 in 14,493, according to their study published in August 2010, making it the second-most-at-risk plant when it was still operating.