The US DOE overstates its case, perhapsSee the entry for the Shippingport nuclear reactor for 1957. It was the US's first commercial nuclear reactor; there was already one in the USSR, and Calder Hall 1-3 were in operation in what is now Sellafield, in the UK.
Quote from the article: "The Dusquesne Light Company worked in partnership with the Federal Government to build the world's first large scale commercial nuclear power plant. The reactors were designed by the Westinghouse Electric Corporation in cooperation with the Division of Naval Reactors of the Atomic Energy Commission. By the standards of the day, it seemed to belong to a different era."
Now, each Calder Hall reactor had an output of 50MWe; the Shippingport reactor had an output of 60MWe. That would surely make Calder Hall the largest? And the claims of it belonging to a different era are dubious. The MAGNOX design used in Calder Hall was current until the 60s, and there are 500MWe MAGNOX reactors; the Shippingport design, by comparison, was a one-off naval reactor, intended for a cancelled aircraft carrier. Calder Hall 1 was shut down in 2003; Shippingport's reactor was replaced in the 70s.
Finally, the photograph is linked with the text: "The Federation of American Scientists displays a photograph worth a look, especially by readers who might wonder if this description is too grandiose." Which is fine, except that the site shown also contains Beaver Valley nuclear facility; that's what the giant cooling towers are for. Shippingport is that smallish low building.
Not really sure why they've done this. Certainly Shippingport was an achievement; if nothing else it was the first nuclear power plant the US government was able to convince its private nuclear industry to build. But an amazing best-of-breed revolution it was not.