Implementation of three gamma measuring stations on the Colentec loop in Cadarache for the on line observation of the clogging phenomena in Steam Generator

The Tube Support Plate blockage, also named clogging, is a complex phenomenon that can occur in the steam generator of Pressurized Water Reactors. This deposit of iron oxides, that can reduce the coolant flux and constraint the primary tubes, could have significant consequences on heat exchanges and the integrity of the primary tubes. Since 2014, an experimental program carried out jointly by CEA-EDF, has been performed on a representative dedicated equipment, the COLENTEC loop at Cadarache. The physico-chemical properties of the deposit formed (chemical composition, thickness...) were determined at the end of each experimental campaign lead at thermohydraulic and chemical stable conditions. ...In order to determine the influence on clogging of parameters such as the chemistry, the temperature, the pressure in an on line process and without performing separate experimental campaigns, a method of measurement on radioactive tracer, the gamma emitter 59 Fe, has been studied by our laboratory.First, a modelization with a monte carlo code, MCNP, has been carried out with the geometrical configuration of the Tube Support Plate zone of COLENTEC in order to determine the most adapted measuring station. These calculations had shown that a 30% efficiency, high purity, germanium detector, with a specific collimation would be able to detect the accumulation of 59 Fe in the Tube Support Plate of COLENTEC.Then, in order to improve and ensure those important online measurements, our laboratory has proposed the installation of two additional measuring stations. One will be dedicated to a second on-line measurement, with a gamma detector of the same type, but positioned on a section of the loop remote from the previous area, to verify that there is no significant secondary deposit evolution elsewhere on the circuit. The last additional gamma measurement station will consist of a low background system able to carry out 59 Fe concentration measurements of liquid samples taken from the loop during the test.This paper presents the context of this experiment and then focuses on the spectrometry measuring stations, modelizations and tests.