A method for the calculation of the neutron flux in one-group P3 approximation in a reactor polycell with multizone annular clusters is presented. The cluster central zone contains multizone fuel rods. The rod and cluster neutron fluxes are assumed to be azimuthally symmetrical. Four moments in the scattering function are taken into account. The CLUST code has been developed for computing the neutron fluxes in a reactor polycell. Its numerical results are compared with those of the other codes and appear to be in good agreement with them.