I have heard this story before about the German scientists and the 2 Japanese science officers on U-234 carrying a nuclear bomb. In fact I think I read it in one of Clive Cusslers fiction books. From reading Heisenbergs War, the Germans were far from making the atom bomb. The allies managed to bomb Germany's heavy water plant in Norway.
From what I read was that the Germans abandoned the research and the development of the nuclear bomb. Hitler though that a nuclear bomb would be too destructive and that no one would ever dare to use for one in a war, so it was no use for Germany to continue devolping a bomb. Hitler wanted them to continue the research for a nuclear power plant instead. We all know that we here in the United States had the "balls" to drop a bomb on the Japanese, something Hitler regarded as unthinkable. After the fact the Germans were shocked.