Abstract Recent advancements in computer technology have led to an increased ability to solve complicated reactor problems, and as a result, there has been an interest in codes and methods that utilize whole-core transport in three-dimensional, large-scale, highly-heterogeneous configurations. Most current reactor benchmark problems are either small-scale or involve spatial homogenization (pin cell or full-assembly) for diffusion codes; therefore, new whole-core benchmark problems must be designed in order to validate whole-core transport methods. This study focuses on an PWR case, with a low leakage loading pattern and Gadolinium as a burnable absorber. In this paper, a detailed description of a new 3D whole-core numerical benchmark problem based on a 4-loop layout is presented with geometric, material and cross section specifications. A set of 2-group and 4-group region-wise neutron cross section libraries is generated using the lattice depletion code HELIOS, and an MCNP model is described for three configurations (all rods in, all rods out, power-shaping rods inserted). Eigenvalues are presented for the 2-group calculations of all three configurations, and detailed pin fission density results are presented for the power-shaping configuration.