Electronic Devices Mohsen Ahmadnia 6 2 2017 http://www.dline.info/ed/fulltext/v6n2/edv6n2_1.pdf In this work, the fission chamber detector with 5 MW of power was tested in different locations of Tehran Research Reactor pool. If the detector was located at the distance of 1 meter from the eastern edge of the reactor and at the height of about 1.4 meters from the floor, it was the best location for detector counting but due to the different placements and displacements in western part of the reactor, it was not possible unfortunately. The dead time for 3 MW of power had been 1.67% which was the best result in comparison with Monte Carlo Code.