Our team at CEA/Irfu is working with ASNR to study the possibility of using neutron noise measurements, i.e., stochastic variations in neutron flux, to estimate the reactivity of subcritical nuclear systems. The aim is to propose this technique for online measurement of the reactivity of the corium at Fukushima Daiichi during future decommissioning operations. The thesis work will focus on evaluating a solution based on Micromegas-type neutron detectors (nBLM detectors) developed by IRFU, which are adapted to the extreme gamma radiation expected in the vicinity of the Fukushima Daiichi corium. The student will participate in experiments at nuclear research facilities in Europe and the United States to test this technical solution and measure neutron noise for a wide range of reactivities. He/she will be responsible for analyzing the data and evaluating the various inversion methods used to estimate reactivity from neutron noise measurements.