This could be the case.
But the people working on the atomic bomb were carefully screened. People with the slightest suspected loyalties would never come close to the important stuff. That meant anyone with loyalties to a country other than the US; including our allies.
While this might have been a consideration...I think the FBI and military agencies would have had a good handle on this. It would not have required the imprisonment of run-of-the-mill Japanese men, women, and children.
I understand the reasons why it happened. I am suggesting that the atomic program would have been quite far down on the list beyond the traditional reasons given.
That is why I used the word speculation, because in my reading about FDR and Churchill I have yet to find anxious discussions about the German atomic bomb.
Except for those people that weren't.
A fascinating read about how the great majority of the work building the atomic bomb was done by young women between the ages of 18-30.
They were under the strictest orders to keep their mouths shut or there would be serious, in some cases dire consequences if they did.
None did. They all kept their mouths shut.
Amazing.