Reactor core performance calculation method and device

In the present invention, compensation for power distribution in a reactor core and fuel rod power distribution in fuel a assemblies by a spectrum interference hysteresis effect between adjacent assemblies, a burnup degree distribution effect, and a control rod hysteresis effect can be calculated collectively, at a high accuracy in a short period of time using a nuclear constant given by calculation for burning of a single assembly. Namely, (1) spacial distribution of spectrum in a fuel node is determined only in the vicinity of an aimed node by using a known corrected one group model. As a result, the time for the calculation can be shortened. (2) the spectrum distribution and the spectrum hysteresis distribution in the aimed node are subjected to non-separation type development by analytic solution of diffusion equations. As a result, accuracy of calculation for the spectrum hysteresis effect is improved. (3) the distribution of the burnup degree in the fuel node is developed while being separated into attribution of gradient of high speed groups and attribution of distortion in spectrum. As a result, accuracy of burnup degree distribution effect can be improved. (I.S.)