비금속 소재 열화 거동에 대한 열 및 방사선 영향성 평가

Abstract

Purpose: This paper evaluates the effects of heat and gamma radiation on the degradation behavior of fluoroelastomer under the normal and the Design-Basis Event (DBE) environments of a nuclear power plant. Methods: Accelerated thermal radiation aging and Loss-of-Coolant Accident (LOCA) tests were performed to simulate normal and DBE environments, respectively. Mechanical and thermal degradation caused by heat and radiation were measured by tensile test and thermogravimetric analysis. Molecular structure analysis was conducted through Fourier transformed infrared (FT-IR) spectroscopy. Results: The mechanical properties were not changed significantly in pre-aging, normal operating conditions. But radiation of the DBE accident environment significantly affected the mechanical properties of fluoroelastomer and molecular structures, such as C = O formation. Conclusion: The changes in mechanical properties were caused by increased crosslink density. The crosslink density increased due to chemical bonds that were scissioned by irradiation, resulting in the formation of free radicals. FT-IR results showed that C = O and C-O bonds were increased with increasing doses of gamma radiation. Because of the unstable molecular structure generated by reactions between free radicals and scissioned molecular and oxidized chemical bonds, polymeric materials were hardened and decreased in thermal stability as gamma radiation doses increased.