No, they already knew about the dangers of fallout.
"the AEC established Project Plowshare amid growing public and political opposition to nuclear programs. Nuclear tests routinely produced unacceptably high levels of fallout, and the subsequent appearance in drinking water, milk, meat, and produce of strontium-90, cesium-137, and other cancer-causing radioactive elements had generated a movement demanding a worldwide ban on airborne nuclear tests."
But "the AEC believed the region [in Alaska where the harbor would be created with nukes] to be an uninhabited Arctic wasteland."
"Environmental scientists, as well as many Alaskan locals, were not sold. They doubted AEC estimates that a bomb crater harbor would be handling $176 million in annual exports within 25 years. Cape Thompson adjoined large deposits of coal and oil, but it also was iced in nine months out of every 12."
"And the cape was only 30 miles south of Point Hope, an Inuit village whose residents subsisted on the region’s abundant wildlife. Irked by critics, Teller vented to economist George Rogers, "We are not interested in preserving the Eskimo as a hunter. We are interested in giving him the opportunity of becoming a coal miner.""[1]
[1] - https://www.historynet.com/an-explosive-plan-to-use-atoms-fo...