New leak detection technique using ceramic humidity sensor for water reactors

Abstract

Leak-before-break (LBB) approach has been considered for its application to the main steam line (MSL) of Korean Next Generation Reactor (KNGR) — an advanced pressurized water reactor under development. Unlike the primary water leakage, the MSL leak detection must be based on principles other than radioactivity measurements. Among potential options that are being considered as indicators of leakage, it is believed that humidity at the proximity of the piping system is an effective one. A ceramic-based humidity sensor was developed, which can be qualified for LBB applications. The ceramic material, sintered and annealed MgCr 2O 4–TiO 2, is shown to increase its electrical conductivity upon water vapor adsorption without any negative impact due to gamma radiation over the entire temperature range of interest. In the plant applications, the sensor array can be positioned in the annulus between the piping and surrounding insulation. By the analysis of humidity distribution in the annulus, a leak rate of 1 l h −1 can be detected within an hour when the distance between two adjacent sensors does not exceed 1 m. In order to minimize the number of signal wires, the use of AC impedance technique is shown to be advantageous. In this paper, the results of the development and the performance characterization of ceramic humidity sensor for the LBB application to the MSL of KNGR are summarized.