Measurement uncertainty prediction of pressure tube sag measurement tool using two stage Monte Carlo simulation

PREssure Tube SAg Measurement (PRESAM) tool, is a measuring tool designed to measure the sag profile of horizontal coolant channels of Indian Pressurised Heavy Water Reactor (IPHWR). The 'tool' consists of a tool head, data acquisition, control system, its associated hardware accessories as well as control and data processing software. The tool-head has a specially designed Linear Variable Differential Transformer (LVDT) mounted at the centre of a reference beam forming the curvature sensor assembly. From the output of the LVDT in the sensor, local curvature of the pressure tube can be deduced during a sag measurement scan of the pressure tube. The measured LVDT data is numerically processed to generate sag profile of the pressure tube. Thus, the sag profile generation involves two stages, the first is the data acquisition stage which is followed by the data processing stage. There are many sources of uncertainties present in both the stages and these uncertainties contribute to the overall uncertainty in the generated sag profile. Moreover, due to limitations of working in radioactivity, only a single measurement scan is performed per coolant channel. Hence, the main objective of present study is to identify various sources of uncertainties, quantification of uncertainty, uncertainty propagation and representation of uncertainty in PRESAM tool measurements. Additionally since sag measurements are not repeated, a new approach for uncertainty estimation based on two stage Monte Carlo simulation has been proposed in this paper.