The contract for the plant was agreed in July 2007. Announcement of the project start came roughly twelve months after Westinghouse won a bidding contest over other companies. The contract for the new plant involved The Shaw Group, a minority shareholder in Westinghouse. Westinghouse was controlled by Japanese Toshiba. The Shaw Group did provide engineering, procurement, commissioning, information management and project management services. The first pair of reactors were estimated to cost CNY 32.4 billion yuan, later estimates in 2013 gave figures of CNY 40.1 billion. The final sum was CNY 10 billion yuan higher. Groundbreaking for the first and second units was held February 26, 2008. Excavation for the first unit was completed in September 2008. Quality of the pit was certified, putting the project 67 days ahead of schedule. Construction of Sanmen Unit 1 began on April 19, 2009, as the first 5,200 m³ of concrete were poured for the foundation, in a ceremony attended by State Nuclear Power Technology Corporation chair Wang Binghua and Westinghouse CEO Aris Candris. First concrete for Sanmen 2 was poured on December 15, 2009. In June 2014, China First Heavy Industries completed the first domestically produced AP1000 reactor pressure vessel for the second AP1000 unit. The units were originally projected to begin operation in 2014 and 2015. In April 2015, a start date of 2016 was projected for both. One month later, the start date was put back to 2017. In January 2017China National Nuclear Corporation announced that the final reactor coolant pump had been installed with start of operations still foreseen for 2017., Sanmen 1 had completed pre-fuelling safety checks but was not expected to be connected to the grid until the fall of 2018 at the earliest. Hot testing of Sanmen 1 was completed in June 2017, and fuel loading started on April 25, 2018. It subsequently became the first AP1000 reactor in the world to achieve first criticality at 2:09 AM on June 21, 2018, and was connected to the grid on June 30, 2018. Sanmen Unit 1 entered into commercial operation on September 21, 2018. Sanmen Unit 2 achieved first criticality on August 17, 2018 and was connected to the grid on August 24, 2018. Full-power demonstration testing was completed on November 5, 2018, and the unit is now considered to be in commercial operation. In March 2019 Sanmen Unit 2 shut down because of a reactor coolant pump defect, with the root cause still under investigation. A replacement pump has been shipped from the United States by Curtiss-Wright. There have been previous problems with these pumps with impeller blade quality, which involved the return of three pumps to the U.S. in 2013.
