  The question whether an annual modulation is observable during nuclear decay
rate measurements has long been the subject of research. One of the possible
explanations for the annual variations would be the effect of solar neutrinos,
the flux of which changes in correlation with the Earth-Sun distance. A decay
rate measurement with a $^{137}$Cs source and a HPGe detector is currently
being conducted 30 meters below the ground at J\'anossy Underground Research
Laboratory (Csilleb\'erc, Hungary). The laboratory is part of the Vesztergombi
High Energy Laboratory (VLAB), one of the TOP 50 research infrastructures in
Hungary. From October 2022 to March 2023, data of six months' worth has been
collected, and hence this is a new opportunity to check whether the annual
variation in decay rate can be observed. The laboratory, the experiment, the
data processing method, and the first results are presented in this study.
