Sodium fast reactor power monitoring and clad failure detection using ADONIS system

This work deals with the use of gamma spectrometry for fourth generation Sodium Fast Reactor (SFR) power monitoring and clad failure detection. Usually, gamma spectrometers could not manage on-line applications in high count rate and fast activity variations but recent improvements in this research field may improve it. The ADONIS analyser for gamma spectrometry could met two needs of fourth generation SFR [1]. The ex-core neutron power measurement gives instant neutron power estimation but has some shift problems, mainly due to the burn-up phenomenon. High security margins are then set and so, the reactor can not work at its best thermodynamic efficiency. Previous works on Pressurized Water Reactors (PWR) show that gamma emitters concentration in primary coolant is also directly linked with reactor power ( 16 N power measurement) [7]. On SFR, the use of short decay period gamma emitters as the 20 F radionuclide will allow a fast power measurement with a direct correlation with the instant fission rate and without burn-up dependency. The second need is the clad failure detection improvement. The SFR clad failure detection is done by radiochemical and gamma measurements on argon cover gas and primary sodium samples. Gaseous fission products and delayed neutron fission products (only the 137 I and the 87 Br) are measured but lots of fission products (gamma emitters) are not measured nowadays on-line due to high sodium activity and its fast changes. This paper presents the experiment done at the French Phenix SFR of the CEA Marcoule and its analysis. Measuring activation and fission products contained in primary sodium coolant, the adaptive ADONIS gamma spectrometry system set on primary sodium coolant sample could be a new innovating power monitoring and clad failure detection system for future SFR.