エンリコ・フェルミ炉の燃料溶融事故と修復の概要

Abstract

On October 5, 1966, during a slow increase in power, the Enrico Fermi Reactor was shut down in an orderly manner after it was obseryed that the control rods were withdrawn further than normal for 31MWt, that several subassemblies had abnormally high outlet temperatures, and that a small amount of F.P. was detected by the F.P. detector.Subsequently various investigations and analyses were performed to elucidate and to assess this incident. It was established as a result that fuel melting had occurred in two fuel subassemblies, M-098 and M-127.Inspection of the lower plenum and study of the analytical model indicated that one of the two Zr segments originally installed on the conical flow guide had become loose and had partially blocked the inlet nozzles of four subassemblies adjacent to each other. To prevent recurrence of similar trouble, the remaining Zr segments on the conical flow guide were removed, and a malfunction detection analyzer was installed in the instrumentation and safety system.Preoperational tests are now under way, with the Enrico Fermi Atomic Power Plant scheduled to be restored to full power operation in February 1970.This report outlines the fuel melting incident and the subsequent repairs and modifications brought upon the reactor.