Fuel-failure detection system for Pakistan research reactor-1

Fuel-failure detection in nuclear reactors is important from the safety point of view. After the conversion and upgrading of Pakistan Research Reactor-I (PARR-I), it was decided to install a fuel-failure detection system to confirm the performance and integrity of the new fuel elements. The fuel-failure detection 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 that were installed at the outlet coolant pipe in the valve pit. The graphite blocks were enclosed in a lead shield and paraffin wax to reduce background due to gamma radiation and scattering neutrons. A window was provided in the paraffin wax to extract the neutron signal. A gamma spectrometry system including an HPGe detector was also used for determination of the isotopic concentration of fission products. The fuel-failure detection system was tested and calibrated at a miniature neutron source reactor (PARR-2) which provided the basis for alarm limits setting in the event of fuel failure