Analysis of the leak-detection system for top welds of EBR-II fuel elements

An analysis of the leak detector used to check the top welds on EBR-II fuel elements was performed. Data were obtained to allow calculation of volumes of the metering chamber and test chamber at each station of the leak detector. These volumes and a mathematical model were used to calculate decrease in pressure with time for each station. Values for calibrated leaks and unknown leak rates were compared with calculated ones. The calculated results for the two calibrated leaks agreed with the observed pressure-time results for the two leaks. Results show that determining the volumes of each leak-detector station allows the leakrate sensitivity to be readily calculated for each station. One leak-detector station could not detect a minimum leak rate of 2 x 10/sup -4/ std cm/sup 3/ sec at 40 atm, which is the current specification. The other four stations could meet the specification. Suggestions are given for periodic calibration of the leak detectors as well as precautions that must be observed to achieve optimum sensitivity when operating the leak detector. (auth)