Completion of "Joyo" Experimental Fast Reactor Upper Core Structure Replacement - Development of Fast Reactor Core Internal Equipment Replacement method -
In the "Joyo" experimental fast reactor of Japan Atomic Energy Agency, the upper core
structure was damaged due to an accident with the experimental equipment in the reactor vessel.
Under high radioactive atmosphere (with fuel loaded) and with the inert gas boundary of about
maximum of 160°C, the old upper core structure was extracted through a gap of millimeters by
remote control and was replaced with a new upper core structure. Such unprecedentedly difficult
operation was successfully completed after a prior study of the risks, design validation using a
full-scale mock-up and operational training. This replacement contributed to the development of
the fast reactor core internal equipment replacement method.
