Static Modal Analysis of the Current-To-Flux Subcriticality Monitor for Accelerator-Driven Systems

With Accelerator-Driven Systems (ADS), the incineration of large quantities of minor actinides is envisaged by coupling a particle accelerator to a subcritical core. Despite the subcritical operation of the core, a monitoring tool is indispensable in an ADS for both safety and operational purposes. Several experimental techniques are under investigation today within the European FP7 project FREYA (Fast Reactor Experiments for hYbrid Applications) at the VENUS facility at SCK CEN, where the lead fast zero-power VENUS-F core is coupled to the GENEPI-3C deuteron accelerator. The proposed monitoring concept combines an initial reactivity determination, e.g. by the pulsed neutron source technique, a long-Term relative reactivity monitor, by the current-To-flux (CTF) technique, and an interim cross-checking, by the source jerk technique. In this paper the CTF technique is presented as a candidate for continuous reactivity monitoring. Static modal analysis is applied to evaluate the point kinetics relationship between accelerator source neutrons and the neutron flux. As a first test case, the zero-power VENUS-F SC1 core is considered. Spatial correction on the CTF monitor is evaluated by measurement results for the control rods worth at different detector positions. Good agreement between the modal and experimental spatial correction factor (SCF) is found with 9 modes. Limited SCF are found in the VENUS-F reflector, far away from the perturbation. Modal analysis is envisaged for the monitoring of burn-up in demonstrator ADS like MYRRHA.