Pin-by-pin power reconstruction method using expansion in pseudo-harmonics

Highlights: • Pin-by- pin power reconstruction uses 2D diffusion equation and two energy groups. • Homogeneous flux is obtained from expansion in pseudo-harmonics and nodal mean values. • The pseudo-harmonics expansion are the auto functions of the symmetric matrix associated with the leakage + removal operator. • The heterogeneous power is the product of the homogeneous power by the function of form. • The method exhibits good accuracy when compared to the reference solution. • The largest deviation found is of the order of 4.7% in a cell near the baffle/reflector region. - Abstract: A pin-by-pin power reconstruction method was developed using the expansion in eigenfunctions for the reconstruction of neutron flux distribution in a homogeneous fuel assembly. The eigenfunctions used were the so-called pseudo-harmonics, which are eigenfunctions associated with the leakage plus removal operator of the neutron diffusion theory. The modulation technique was used to obtain the heterogeneous distribution of power density. In this technique, the power density homogeneous distribution, calculated with the reconstructed neutron flux is multiplied by a form function. This form function is obtained in the calculation of assembly homogenization. The results obtained by this method show good agreement between the reconstructed pin-by-pin power and that of the reference heterogeneous calculation, for the benchmark used. The largest deviation found was of the order of 4.7%, in a peripheral cell of a fuel element with the faces towards the region of the baffle/reflector.