The absence of a long-term solution for the storage of spent nuclear fuel prompts utilities in the United States to establish on-site storage for used fuel. The challenges associated with placement of spent fuel in dry cask storage on the power plant’s Independent Spent Fuel Storage Installations (ISFSI’s) include aging management of the stainless steel canisters and monitoring for the possible onset of stress corrosion cracking (SCC). The San Onofre Nuclear Generating Station (SONGS) has initiated a test program to examine the effects of heat generation variations inside a test canister using an electric heater rather than spent fuel on the shell temperatures. The test helps in the evaluation of external environmental factors and shell temperature, and to monitor for SCC. This paper presents the computational fluid dynamics (CFD) modeling developed in support of the test to analyze the air natural circulation in the subgrade enclosure and within the test canister with the electrical heating. The thermal analysis is performed using ANSYS CFX and integrally simulates the flow behavior and heat transfer mechanisms both inside and outside the test canister. Comparison of results from different heat loads that represent the decay heat time-profile, sensitivity to the turbulence model, and modes of heat dissipation are discussed. The CFD results are also compared to in-situ temperature measurements to validate the analysis.