Due to the unavailability of nuclear fuel reprocessing and a permanent geologic repository in the United States, it has become increasingly essential for domestic nuclear reactors to have safe, secure, and efficient solutions for onsite long-term used nuclear fuel (UNF) storage. As existing UNF pools at reactor sites are approaching their capacity limits, dry storage facilities known as Independent Spent Fuel Storage Installations (ISFSI) has become an important option for utilities. Such systems are designed to passively reject decay heat during storage and transfer of UNF while maintaining thermal, structural and nuclear integrity.Dry storage of UNF discharged from the reactor typically takes place 5 to 10 years after they are stored in the spent fuel pools. However, if a reactor is scheduled to be decommissioned, it is desirable to move the UNF into dry storage as soon as possible after the reactor is shut down. One of the key factors that limit the transfer of UNF to dry storage is the heat load. To provide flexibility in loading operations, NUHOMS® MATRIX (HSM-MX) systems, which is a two-tiered staggered, high-density horizontal storage module (HSM), is designed to reduce the footprint of the current EOS-HSM to allow for greater storage capability on an ISFSI pad than that currently available and cooling times required to move the UNF to dry storage. HSM-MX systems offer a wide range of thermal capabilities, including the industry-leading heat load of 50 kW per dry shielded canister.This paper presents the design and optimization of HSM-MX based on a maximum heat load of 50 kW from 37 Pressurized Water Reactor (PWR) fuel assemblies. During the initial conceptual design process, the HSM-MX design was optimized using SolidWorks® Flow Simulation, an intuitive Computational Fluid Dynamics (CFD) tool embedded within SolidWorks® 3D, for quick evaluation of the thermal performance of various geometry designs. Then, the thermal performance of the optimized module is evaluated with a detailed CFD based modeling approach in ANSYS Fluent code.