Fuel failure detection is important from the point of view of the safety of nuclear reactors. After the conversion and upgradation of Pakistan Research Reactor-1 (PARR-1), it was desired to install a fuel failure detection system to confirm the performance and integrity of the new fuel elements. The fuel failure detection system is based on monitoring of delayed neutrons emitted from fission products leaking into the primary coolant loop from the fuel. For this purpose two neutron detectors (BF3) were placed in the graphite moderator blocks which were installed at the outlet coolant pipe in the valve pit. The graphite blocks were enclosed in lead shield and polyethylene to reduce background due to gamma and neutrons. (author). 8 fig.