• New heat transfer correlation for sodium-to-sodium heat exchanger is proposed. • It is based on STELLA-1 experimental results. • Results are validated by STELLA-1 and JOYO experimental results. • Results show good agreement with the experimental results. Multiple studies have been conducted on the convective heat transfer of a liquid metal flow to present the correlations between the Nusselt and Péclet numbers. However, those correlations are considerably deviated from the experimental data obtained from steady-state tests of a sodium-to-sodium heat exchanger using the large-scale sodium thermal-hydraulic test facility STELLA-1. In this work, a new convective heat transfer correlation acquired through curve fitting with the STELLA-1 experimental results is proposed for a Péclet number range from 68 to 524. The newly proposed correlation was used in the SHXSA design code developed for designing a sodium-to-sodium heat exchanger by the Korea Atomic Energy Research Institute. The adequacy of the correlation was assessed by comparing the calculated results of the SHXSA code with the test results from STELLA-1. By using the proposed correlation, the average absolute deviations of the shell-side outlet temperature, tube-side outlet temperature, and heat transfer rate improved from 0.70% to 0.51%, 0.37% to 0.17%, and 1.61% to 0.82%, respectively. In the assessment with the experimental results of the JOYO sodium-to-sodium heat exchanger, the average absolute deviations of the shell-side outlet temperature, tube-side outlet temperature, and heat transfer rate were determined to be 0.27%, 0.54%, and 2.05%, respectively. The calculated results using the proposed correlation showed a satisfactory agreement with the experimental data from the STELLA-1 and JOYO facilities, and thus the proposed correlation is expected to be practically employed for designing a sodium-to-sodium heat exchanger. [ABSTRACT FROM AUTHOR]