Sodium Fast Reactor Power Monitoring and Clad Failure Detection using Adonis System

On sodium fast reactors, power is usually measured by heat balance on water to vapor heat exchangers which is correlated with the ex-core neutron flux measurements. The ex-core neutron power measurement is done by fission chambers (five on the French SFR Phnix reactor) with several activity ranges settled at the bottom of the primary vessel to cover the whole neutron flux range of more than 11 decades. This measurement instantly estimates the neutron power but induces some shift problems. The clad failure detection is done by gamma measurement on argon cover gas sampling and neutron measurement on primary sodium sample. This work deals with the use of gamma spectrometry for fourth generation SFR power monitoring and clad failure detection. Usually gamma spectrometers could not manage on-line application but recent improvements in this research field may improve it. The Adonis digital signal processing prototype gives a time function response and is able to do spectrometry measurement with metrological grade under high gamma flux impinging the HPGe detector, with also high and fast activity transient. Previous works on Pressurized Water Reactors (PWR) show that gamma emitter concentration in primary coolant is also directly correlated with reactor neutron power. On SFR, the use of short decay period gamma emitters as the 20F and 23Ne tagging agent will allow a very fast response system without thermal hydraulic distortion effects. The study is divided in two parts. First part deals with a simulation study based on physical calculations and MCNP simulations to predict sensor signal as a function of neutron power. The second part is an experimental test under preparation at the French SFR Phnix. Measuring activation and fission products contained in primary sodium, the adaptive Adonis system set on primary coolant sample could be an innovating neutron power monitoring and clad failure detection system for SFR