The reactor pioneers visited their overseas contemporaries/competitors often and reading their trip reports offers plenty of interest. At a more general level, one aspect I’ve observed is that if you’re a British physicist visiting U.S. laboratories, your eventual report will imply, if not state, that the British are further advanced. The converse is also true, as I noticed in this 1955 Harwell trip report by one of Walter Zinn’s key lieutenants, Joe Dietrich:
Although the British activity on experimental fast reactor physics is comparable to our own, their theoretical work – or at least their work on reactor calculations – seems to be considerable less advanced. Our lead is primarily due to our extensive use of high-speed automatic digital computers. The experiments in the engineering laboratories are in general of smaller goals than our own engineering experiments. . . . The amount of work going on at Harwell on research reactors is quite impressive. One gets the impression, however, that the Harwell work does not get as close to the engineering and construction of power reactors as does our own work at Argonne.
Dietrich, Joseph R. 1955. Visits to Saclay and Harwell, August 23 and 26, 1955. Folder ‘Reading File, December 8, 1955’, Box 326, Laboratory Director’s Reading File, 1949-1957, RG 326, NARA, Chicago, Illinois.