LMFBR type reactor

Purpose: To secure the safety of an LMFBR type reactor when a fuel exchanger is shutdown at the time of exchanging fuels and shorten the effective height of a reactor vessel by providing a hole in predetermined area of a guide tube for the fuel exchanger to raw a coolant by convection therethrough. Constitution: The fuel exchanging guide tube for guiding a fuel exchanger through large and small rotation plugs of an LMFBR type reactor fuel vessel is adjusted so as to be coaxial with the desired spent fuel. When the fuel unit to be exchanged is sealed at the top due to the failure of a fuel exchange system in a state where the top is hanging above the surface of the coolant, elevational and horizontal temperature distributions are formed in the coolant due to the decay heat generated from the fuel. Since the coolant can flow through the hole formed at the predetermined position of the guide tube for the fuel exchanger, the guide tube is prevented therein from becoming an abnormally high temperature, and the safety can be consequently secured. (Sekiya, K.)