Development and validation of the three-dimensional dynamic code—KIKO3D

A three-dimensional reactor dynamics program—KIKO3D—for coupled neutron kinetics and thermohydraulics calculation of VVER type pressurized water reactor cores has been developed and benchmarked. For solution of the time dependent neutronic equations, a nodal method was used. Concerning the geometry, the symmetries of the nodes, and the concrete form of the neutronic equations to be solved inside the nodes (transport or diffusion equation), the method is general enough, only the linear anisotropy of neutron flux on the node boundaries is utilized. Generalized response matrices for the time dependent problem are introduced which can be derived also from the response matrix of the stationary problem. The so obtained time dependent matrix equations show similar structure to the non-discretized equations. Therefore, the Improved Quasi Static factorization of the time dependent matrix equations can be carried out in the usual way, leading to the point kinetic and the shape function equations. In the KIKO3D code, this general nodal method was applied for the special case of rectangular and hexagonal homogenized nodes in which the diffusion equation is to be solved. In this special case, the traditional response matrices of the stationary problem and the generalized matrices necessary for the time dependent problem can be obtained by analytical formulas. The accuracy of the introduced approximations has been validated against rectangular and hexagonal benchmark problems.