Fuel failure detection device

In a fuel failure detection device of an FBR type reactor, a coolant sampling line and a sodium pot, an inert gas supply pipe for transferring nuclear fission products contained in coolants compulsorily to a cover gas, a transformation pipe for sending them to a radiation detector, a radiation detector and an inert gas returning pipe are disposed in an equipment always installed in reactor upper mechanisms situated just above a reactor core. Fission products released from a ruptured fuel pin into sodium coolants flow into an upper guide tube of a control rod, uprise in a sodium circulation tube and is then transported with no dilution to the radiation detector by a gas pressure and radioactivity concentration thereof is measured. Even in any of operation states such as during rated power operation or reactor shutdown of the nuclear reactor, fuel rupture and the magnitude of the rupture can be rapidly detected, failed fuels can be identified, and control rods can be inserted rapidly to the reactor core as required, thereby enabling to conduct reactor scram. (N.H.)