A new method for the localisation of gas leaker fuel subassemblies in fast breeder reactors.

• Gamma spectrometric analyses of cover gas activity. • Detection of gas leaker fuel subassembly in fast reactors by measurement of cover gas activity. • Identification of FPNG markers during reactor operation with gas leaker fuel subassembly. • Localisation of gas leaker fuel subassembly in fast reactors. In Fast Breeder Test Reactor, increase in reactor vessel cover gas (RVCG) activity was detected during reactor operation. However, delayed neutron detection system did not show increase in reading above background. Gamma spectrometric analyses of RVCG sample confirmed the presence of gas leaker fuel subassembly (GLFSA). Detection of 133mXe, 135mXe and 85Kr in RVCG are indicators for a fuel clad failure and the specific activity of 133Xe is observed to be three orders higher compared to baseline data. Reactor was operated after shuffling the suspected FSAs and RVCG samples were analysed to confirm the removal of GLFSA. Detection of 133Xe, 138Xe and 135mXe in the RVCG samples during short duration operation is an indicator for the presence of GLFSA in core. Comparison of specific activity of 133Xe, 138Xe, 135mXe and 87Kr with baseline data facilitates the localisation of the GLFSA in the absence of delayed neutron detection counts. [ABSTRACT FROM AUTHOR]