Long-term test of online measuring concentration of borate in the stand-by liquid control system of Isar 1 NPP

In BWR plants a boron injection system, called stand-by liquid control system, is installed if the sub-critical state is not reached with adequate certainty by inserting the control blades. This system has a storage tank which contains a certain amount of boron as sodium pentaborate. While the volume may be monitored by observing the fill level in the tank, there is no similar simple procedure to continuously survey the concentration with sufficient sensitivity. The procedure presented is aiming at identifying a method which also enables continuous monitoring of the concentration with appropriate accuracy. (orig.)