Detector for the failed position of reactor core structures

Purpose: To reduce the size and decrease the operation cost of a detector for the failed position of fuel elements or control rods in an LMFBR type reactor. Constitution: This invention provides an improved tag gas method. Two by-pass ways are provided in parallel with a circulating path in communication to the plenum portion of a reactor. The first by-pass comprises a gas detector operated at a normal temperature and the second by-pass comprises a compressor, a concentrator and a gas analyzer in this order. If tag gases are leaked due to the failure in the fuel elements, they are at first detected by the gas detector in the first by-pass. Then, the compressor, the concentrator and the gas analyzer in the second by-pass are started in response to the operation of the gas detector. The failed position is accurately detected based on the detailed analysis carried out in the gas analyzer. (Ikeda, J.)