Calculation of the thermohydraulic parameters of a core comprised of unjacketed fuel assemblies

Abstract

A computer program for calculating the thermohydraulic parameters of a core with jacketless fuel assemblies as a single mass of fuel elements is developed on the basis of the Kedr program for the channelwise computation. The Kedr-A program algorithm employs the principle of decomposition (partition) to the computed region of the core (1/12th part). The computational space is divided into a definite number of subregions -symmetry elements with repeatable geometric structure of the lattice of fuel elements and other structural components of the core. The thermohydraulic parameters of the cells in each section of the core are calculated iteratively over the symmetry elements of the jacket-less fuel assemblies of 1/12th part of the core of a nuclear reactor with water coolant. The symmetry elements are interrelated by the conditions at the boundaries connecting theses regions. The computational algorithm is checked by comparing with experimental data on the mixing of the coolant obtained on a technological stand consisting seven jacketless fuel assemblies.The thermohydraulic parameters of fuel assemblies are now calculated by the channel-wise method [1][2][3][4], where the entire fuel assembly with rod-shaped fuel elements is divided into parallel channels (cells). Differential equations expressing the balance of mass, momentum, and energy taking account of the mass, moment, and heat flow through the conventional boundaries separating neighboring cells are written for each channel. The velocity, pressure, and enthalpy of the coolant in the cells of the fuel assemblies are determined in each computational layer by numerically solving the system of differential balance equations.There are no difficulties in calculating the thermohydraulic parameters of the reactor core consisting of fuel assemblies with rod-shaped fuel elements in a full-metal jacket; the calculation is performed using the tested method of [5] -core is treated as a system of parallel channels (fuel assemblies) united by common inflow and outflow collectors. The heat-engineering reliability of the core consisting of jacketless fuel assemblies [6] is evaluated by a different method [7]. The fuel assembly with the high energy release is selected, and the heat-engineering reliability for this assembly is calculated by a program written for the channel-wise method. The remaining part of the core is separated into a conventional macro cell with which the chosen fuel assembly interacts through the conventional boundary.There are objective reasons for using a simplified approach to evaluate the heat-engineering reliability of a core consisting of jacketless fuel assemblies. The domestic computer programs written for the channel-wise computational method [3,7] were developed for single fuel assemblies, for which the number of computational cells does not exceed 1000. In the calculation of a core as a single array of fuel elements, the number cells increases to 100,000. As a result of the increase in the number of cells, the computing time increases considerably...