Measurement campaign at Tricastin 2 to optimize the radiochemical purification of PWR primary circuit

The CEA and EDF conducted a measurement campaign on Unit 2 of the Tricastin power plant in July 2003, during an innovative test on high flow rate (38 t/h) purification, during end of cycle shutdown. The aim of this campaign was two-fold: 1) Perform a functional qualification of the filter and demineralizer of the Chemical and Volume Control System for a flow rate of 38 t/h, 2). Obtain information on the dynamic behavior of the filter and of the mixed-bed ion exchange resin used by the operator, so as to optimize radioelement capture. To meet these objectives, the following measurements were made during end of cycle shutdown: - Chemical and radiochemical measurements upstream and downstream from the purification station of the CVCS circuit, thus allowing the purification factor to be estimated for active and inactive elements; - In situ gamma spectrometry with a CdZnTe detector on the filter and demineralizer in operation during shutdown, to check the integration of radioelements on these parts. The lengthwise profile of the 58Co in the resin column was thus obtained. - Separation between soluble/insoluble radioactive elements, obtained on primary water samples, - Monitoring of the primary circuit chemistry (including lithium and boron contents, redox potential), in order to accurately define the chemical form of the species present in the primary fluid. These measurements were used to check the proper design basis of the filter and demineralizer versus the 38 t/h flow rate, during the purification phase after the primary circuit had been oxygenated. Moreover, a specific and original experiment consisted in having primary water circulate on 4 lines each representing a miniature purification station (flat filter of 90 mm diameter and 350 cm3 of ion exchange resin, in a column 27,5 cm high). A longitudinal examination using gamma spectrometry gave an activity profile in the resin columns for the following elements: 58Co, 60Co, 59Fe, 54Mn, 124Sb and 110mAg. Different types of ion exchange resins were tested, as well as a mixed-bed resin initially loaded with nickel, so as to simulate a used column having undergone several end of cycle shutdowns. The results of this series of measurements are confronted to the theoretical previsions and to experimental studies on synthetic fluid. They provide very interesting and new information on the dynamic behavior of the filtering media used to purify CVCS primary circuits. (authors)