Miniature fission chambers with integral coaxial mineral insulated cable assembly have been developed for Local Power Range Monitoring in the BWR power station at Tarapur. The detectors measure neutron flux at fixed locations within the core in the power range of reactor operation and provide alarm in case of power distribution anomaly. Performance tests in DC mode have shown that the detectors have a neutron sensitivity of 1×10 -17 A/nv and a gamma sensitivity of 2×10 -14 A/(R/h). A gradual burnup due to neutron flux limits the useful life of these devices to about 2 yr. However, by operating the detector in Campbelling mode, its operational life can be extended to six years.