Boron doped zirconium–niobium alloy is employed for neutron reactivity control in advanced nuclear reactors. An accurate knowledge of the boron content and uncertainty associated with the measurement result is essential for reactivity calculations. In view of the refractory nature of the alloy, boron determination in these matrices is a challenging task for analytical chemists. Also due to non-availability of matrix-matched reference materials, direct solid analysis cannot be resorted to. With this in view, a simple and sensitive method based on potentiometric determination of boron as tetrafluoroborate with tetrafluoroborate ion selective electrode has been developed. After dissolving the sample, boron was quantitatively converted to BF₄^- with the addition of HF. Potential response was measured with Orion 9305 BN BF₄^- ion selective electrode. The response of the ion selective electrode was Nernstian in the range of 0.1–100.0 lg/g of boron in the solution. The method has been validated by two independent methods namely spectrophotometry and inductively coupled plasma-atomic emission spectrometry (ICP-AES). All identifiable sources of uncertainties in the methodology have been individually assessed. The combined uncertainty is calculated employing uncertainty propagation law. The expanded relative uncertainty in the measurement (coverage factor 2) is 6.50%.