A project is underway to develop an advanced two-phase flow modeling capability for the highly-scalable high-performance CFD code NEK5000 . The goal of the project is to develop a new two-phase version of the NEK5000 code, named NEK-2P, to simulate the two-phase flow and heat transfer phenomena that occur in a Boiling Water Reactor (BWR) fuel bundle under various operating conditions. The NEK-2P two-phase flow models will follow the approach used for the Extended Boiling Framework [2, 3, 4] previously developed at Argonne, but will include more fundamental physical models of boiling phenomena and advanced numerical algorithms for improved computational accuracy, robustness, and computational speed. The NEK-2P code is being developed on the foundation of the NEK5000 CFD Code developed at Argonne which provides general high-fidelity single-phase flow modeling capabilities. The paper describes the model development strategy which has been adopted by the development team for the simulation of two-phase boiling flow phenomena typical for a BWR fuel bundle. This strategy includes the extension of NEK5000 solver to allow modeling of two-phase boiling flows, and the implementation of an Advanced Boiling Framework (ABF) using local inter-phase surface topology maps and topology- specific phenomenological models. Results of initial analyses of selected experiments focused on boiling flow in a pipe with heated wall are presented.