Experimental validation of predominant radiative heat loss through a metal containment vessel of small modular reactors under normal operation

Abstract

This study provides a systematic experimental quantification of the competing heat transfer mechanisms—conduction, natural convection, and radiation—within a representative, scaled geometry of a small modular reactor (SMR) equipped with a metal containment vessel (MCV). An experimental apparatus was developed to replicate the thermal behavior of the pressurizer region in a water-cooled SMR, enabling the evaluation of insulation performance under various environmental conditions: vacuum (∼0.07 bar), and nitrogen, argon, and carbon dioxide at atmospheric pressure. Results show that radiative heat transfer is the primary mode of heat loss, accounting for 44% to 83% of total heat transfer depending on the gap conditions. The vacuum condition demonstrated the lowest heat loss, owing to the suppression of convective heat transfer and the predominance of conduction and radiation. In contrast, carbon dioxide produced the highest heat loss due to its strong infrared absorption characteristics, which enhance radiative heat transfer. These findings underscore the critical role of radiation in thermal management within MCV-equipped SMRs. To enhance thermal efficiency and protect vital components from thermal degradation, insulation strategies should prioritize mitigating radiative heat transfer. This study offers foundational benchmark data on the partitioning of heat loss mechanisms, providing assessment for numerical models (e.g., CFD, system codes) used to optimize thermal insulation, improve reactor performance, and ensure structural integrity. By providing this crucial experimental data for model assessment, it contributes to the advancement of next-generation SMR containment design.