The STEREO experiment (Search for Sterile Reactor Neutrino Oscillations) investigates the possible oscillation of neutrinos from a nuclear reactor into light so-called sterile neutrinos. It is located at the Institut Laue–Langevin (ILL) in Grenoble, France. The experiment started operating and taking data in November 2016. Detector Measuring principle The STEREO detector is placed at a distance of 10 m away from the research reactor at the ILL. The research reactor has a thermal power of 58 MW. STEREO is supposed to measure the neutrino flux and spectrum near the reactor. To be able to detect the neutrinos radiated from the reactor, the detector is filled up with 1800 litres of organic liquid scintillator which is doped with gadolinium. Inside the scintillator neutrinos are captured via the process of inverse beta decay In this process a positron is produced. When the positron moves through the scintillator a light signal is produced, which is detected by the 48 photomultiplier tubes (PMTs) placed at the top of the detector cells. The capturing of the neutron which is also produced during the inverse beta decay produces a second coincidence signal. The expected distance between the oscillation maximum and minimum of light sterile neutrinos is about 2 m. To see the oscillation the detector is divided into 6 separate detector cells, which each measure the energy spectrum of the detected neutrinos. By comparing the measured spectra a possible oscillation could be discovered (see Figure 2). The STEREO experiment detects neutrinos per day. Detector shielding Neutrinos only interact weakly. Therefore, neutrino detectors such as STEREO need to be very sensitive and need a good shielding from additional background signals to be able to detect neutrinos precisely. To achieve this high sensitivity the 6 inner detector cells are surrounded by a liquid scintillator (without gadolinium) which acts as a "Gamma-Catcher" detecting in- and outgoing gamma radiation. This significantly increases the detection efficiency as well as the energy resolution of the detector. A cherenkov detector filled with water is placed on top of the detector to detect cosmic muons which are produced in the atmosphere and would otherwise act as a large background source. To shield the detector from radioactive sources coming from surrounding experiments it is surrounded and shielded by many layers (65 t) of mostly lead and polyethylene but also iron, steel and B_4C. Motivation Although neutrino oscillation is a phenomenon that is quite well understood