The purposes of the exponential experiments are to obtain reactor physics parameters for determining the criticality conditions of a nuclear reactor, and to confirm the feasibility of a newly proposed reactor concept. When conducting the experiments and modifying various methodologies and reactor constants used in the calculations, a target reactor can be brought closer to realization. The final goal of the exponential experiments is to realize a subcritical steady-state reactor with an external neutron source, and to determine neutronics characteristics of the reactor by measuring spatial neutron flux distributions in a subcritical system. In this chapter, an experimental system is introduced for conducting exponential experiments using natural uranium and polyethylene reflector at KUCA. Moreover, theoretical preparation and experimental procedures are described to obtain the reactor physics parameters, including the multiplication factor, spatial decay constant, and material buckling using reaction rate distributions measured by neutron detectors.