Avoiding blind spots during the physical start-up process of a reactor is an important step in ensuring the safe operation of the reactor. This article uses the Mont Carlo program to calculate the equivalent thermal neutron flux of MBIR, and provides an explanation of the placement of the detectors for the source range and power range. When only the neutron source is loaded into the core, the equivalent thermal neutron flux rate inside the heat shield ranges from 3.8E-2 to 7.0E-2 cm−2 · s−1, meeting the minimum detection requirement, During the full power operation phase, the equivalent thermal neutron flux rate in the heavy concrete area is from 5E+08 to 5E+09 cm−2 · s−1, which can meet the power range detection requirements.