Three-dimensional pin power reconstruction for the axially heterogeneous region in BWR

A three-dimensional pin power reconstruction method was proposed and verified by applying to the axially heterogeneous region problem of the BWR core calculation. Because the production assembly calculation has been carried out by two-dimensional deterministic calculation methods like current coupling collision probability or the method of characteristics, it has been difficult to predict the detailed three-dimensional heterogeneous pin power distribution of the axially heterogeneous region. Consequently, only radial intranodal homogeneous power distributions have been considered, and axial intranodal homogeneous power distributions have not been considered in the estimation of linear-heat-generation-ratio at common BWR core calculations. For an axially heterogeneous region in which two different nodes are combined, the Monte Carlo calculation method can execute three-dimensional heterogeneous assembly calculation directly. By taking advantage of this point, we proposed a three-dimensional pin power reconstruction method. The present three-dimensional pin power reconstruction method was applied to the control-rod-tip (CRT) region problem in BWR. The validity of this method was verified from the result obtained, in which the relative bundle-averaged three-dimensional pin power distribution was improved about 5% of RMS over without three-dimensional pin power reconstruction method.