In NSRR, pulse operation is performed by rapid withdrawals of three transient control rods at low power or high power critical. Under combined pulse operation mode, the pulse operation follows a high power operation up to 10 MW (for several seconds) which is controlled by a bank operation of regulating control rods. During the high power operation, the transient control rods are irregularly inserted into the core to prepare for the pulse operation at the end of the run. Partial or full insertion of the transient rod causes so called shadowing effect, that is, neutronic instruments located closer to the deeply inserted rod indicates lower reactor power than the others. The shadowing effects on the neutronic instruments are evaluated by three-dimensional neutron diffusion calculation of NSRR. (author).