| Excore detectors are located at a distance from the core adjacent to (or in) the primary shield. The neutron flux decreases roughly exponentially as the distance between the neutron source and the excore detector increases, and the neutron flux arriving at the detector becomes a small fraction the neutron flux at the core. Therefore, it is difficult to get detailed information on the central flux distortion using the excore detector. The purpose of this thesis is to study the degree to which use of incore detectors is better than excore detectors by determining Axial Offset (AO) in transient states.;Neutron flux was calculated by nodal methods. The change of the neutron flux by control rod movements were solved numerically with the GEAR method. The xenon concentration and samarium concentration were calculated analytically. The change of the neutron flux in the fuel burnup transient was calculated with the cross section data interpolating the macro cross sections, which were calculated using the LEOPARD code. The excore detector response was calculated by the point kernel method and the diffusion kernel method, and incore detector response was assumed that this response was proportional to the averaged nodal flux.;The results showed that incore AO has less than 8 percent error of reference AO, which was calculated from all nodal flux, in most cases, but excore AO showed larger percent error of the reference AO in most cases than the incore AO. From all results, the incore AO error to the reference AO was about 20 percent less than the excore AO error to the reference AO. The excore AO did not respond more quickly to the change of the neutron flux than the incore AO in the fast transients, but except for the fast transient, the excore AO followed to the reference AO as the incore AO did. |
