Development of procedures for local void fraction measurements

Abstract

AREVA operates a world-wide unique thermal hydraulic platform to ensure high safety standards in the nuclear industry. This platform is operated as an accredited test and inspection body according to ISO 17025 and 17020 to grant high and independently confirmed quality standards. The aim of the tests is to demonstrate the reliability of components and systems, mainly under operational or accidental conditions. In addition to that it is also the aim of the tests to increase the understanding of the fluid dynamic processes. Especially under operational conditions it is very difficult to gain local measurement data. As an example for AREVA’s strategy in the field of advanced two-phase flow measurement techniques, this paper gives an overview on the current activities regarding the development of these measurement procedures focused on the local void fraction measurements under two-phase flow conditions in an annulus. With increasing requirements with respect to the local resolution, the efforts for measurement techniques increase as well. For that purpose AREVA has built up a specific test loop to develop adequate measurement techniques and corresponding validation processes. This loop allows the adjustment of water/steam properties representative of operational and accident conditions of LWRs and has been used to develop a procedure to measure the void fraction distribution in an annulus representing the hydraulic diameter of a typical LWR core sub-channel by means of a gamma tomography system. This paper describes the process, which has been established to reach a reliable high special resolution measurement. Further steps planned to increase the validity of the measurement procedure will also be discussed.