I would think a reactor accident is well possible, also. It doesn´t fit to the statements by the eyewitnesses, but, yes, I regard them as possible, too. G IV happened at Gottow/near Kummerdorf, that is almost 30 miles north east of Berlin. The area is closed for public (it was a military training area). We don´t know much about that disaster, but I think it was both, a succes for Diebner and a disaster. One of Diebners coworker, Willi Henning was probably radiated on that special day (he died at 12th of september 1946 by some kind of radiation). But it was a succes, too. He wrote to Hahn: "unser Reaktor ist gelaufen" ("our reactor did run")and the samples indicate that the accident did happen outside the concrete structure for the reactor. That seems to indicate that the accident happend after all mesurements were taken. (Karlsch found in Moscow a document of Diebner, who was telling Heisenberg that the mesurements of the reactor have been almost completed, just a few mesurements in the outer stage are not that good, the inner stage runs good, see in Karlsch, page 332, document number IV) In a procedure at which the reactor should cool down. (it was unknown in 1945 that the outer stage continues to work after 8 additional hours if not cooled efficiently. The process is called Xenon 135 poisoning).