The aging degradation and lifetime assessment of a domestic class 1E Ethylene-Propylene-Diene-Monomer (EPDM), which is a popular insulating elastomer for electrical cables in the nuclear power plants, were studied for equipment qualification verification under the Loss of Coolant Accident (LOCA) con...
The aging degradation and lifetime assessment of a domestic class 1E Ethylene-Propylene-Diene-Monomer (EPDM), which is a popular insulating elastomer for electrical cables in the nuclear power plants, were studied for equipment qualification verification under the Loss of Coolant Accident (LOCA) conditions. The specimens were acceleratively aged, underwent a LOCA environment, as well as tested mechanically, thermo-gravimetrically, and spectroscopically according to the American Society of the Testing of Materials (ASTM) procedures. The tensile test results revealed that the elongation at break gradually decreased with an increasing aging temperature. The lifetime of EPDM aged isothermally at $140^{\circ}C$ was 1,316 hours and reduced to 1,120 hours after experiencing the severe accident test. The activation energies of the elongation reduction were $1.10{\pm}0.196$ eV and $0.93{\pm}0.191$ eV before and after the LOCA condition, respectively. The TGA test results also showed that the activation energy of the aging decomposition decreased from 1.35 eV to 1.02 eV after undergoing the LOCA environment. Although the mechanical property changes were discernibly observed during the aging process, along with the LOCA simulation, the FT-IR analysis showed that the spectroscopic peaks and their intensities did not alter significantly. Therefore, it can be concluded that the degradation of the domestic class 1E EPDM due to aging can be tolerable, even in severe accident conditions such as LOCA, and thus it qualifies as a suitable insulating material for electrical cables in the nuclear power plants.
The aging degradation and lifetime assessment of a domestic class 1E Ethylene-Propylene-Diene-Monomer (EPDM), which is a popular insulating elastomer for electrical cables in the nuclear power plants, were studied for equipment qualification verification under the Loss of Coolant Accident (LOCA) conditions. The specimens were acceleratively aged, underwent a LOCA environment, as well as tested mechanically, thermo-gravimetrically, and spectroscopically according to the American Society of the Testing of Materials (ASTM) procedures. The tensile test results revealed that the elongation at break gradually decreased with an increasing aging temperature. The lifetime of EPDM aged isothermally at $140^{\circ}C$ was 1,316 hours and reduced to 1,120 hours after experiencing the severe accident test. The activation energies of the elongation reduction were $1.10{\pm}0.196$ eV and $0.93{\pm}0.191$ eV before and after the LOCA condition, respectively. The TGA test results also showed that the activation energy of the aging decomposition decreased from 1.35 eV to 1.02 eV after undergoing the LOCA environment. Although the mechanical property changes were discernibly observed during the aging process, along with the LOCA simulation, the FT-IR analysis showed that the spectroscopic peaks and their intensities did not alter significantly. Therefore, it can be concluded that the degradation of the domestic class 1E EPDM due to aging can be tolerable, even in severe accident conditions such as LOCA, and thus it qualifies as a suitable insulating material for electrical cables in the nuclear power plants.
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제안 방법
First, tensile test specimens were prepared and accelerative aging temperatures were determined to be 140ºC, 155ºC, and 170ºC after careful examination of its thermo-physical properties.
Tensile tests were carried out by a universal testing machine (model 5582, Instron Co.) in order to measure the elongation of the aged specimens.
The aging decomposition of the EPDM was examined through weight loss measurement using a Thermo-Gravimetric Apparatus (TGA). Current analysis followed the procedure proposed and described in ISO 11358 and ASTM E1641-04 [15]:
On the other hand, information on the decomposition kinetics due to aging can be provided by a Thermo-Gravimetric Analyzer (TGA) test.The specimens that experienced the LOCA condition were also tensile-tested or thermo-gravimetrically analyzed in order to examine the elongation or the decomposition and to compare the results before and after the LOCA test. Finally, Fourier Transformed Infra-Red (FT-IR) spectroscopic analyses analyzed the micro-structural changes of the aged specimens.
Therefore, in this study, experimental investigation was carried out in order to evaluate the aging degradation and lifetime of a domestic class 1E EPDM both with and without undergoing LOCA environment. Specimens were supplied by L domestic company.
이론/모형
The LOCA test was conducted following IEEE-383 [4] in the test facility at the Korea Institute of Machinery and Manufacturing (KIMM) in Daejeon, South Korea. A schematic diagram of the LOCA-MSLB (Main Steam Line Break) test loop is shown in Fig.
성능/효과
After experiencing the LOCA environment, the lifetime of the EPDM was reduced to 1,120 hours while the activation energy of the elongation reduction decreased to 0.93 ± 0.191 eV.
Based on these experimental findings, it is confirmed that not only the aging of EPDM, but also the experience of a severe accident environment such as LOCA, can considerably reduce the mechanical and thermal integrity, as well as the lifetime, of the elastomer. On the other hand, it was also found that the short period accident experience did not significantly influence the aging degradation as its aging temperature is higher.
In the polymer industry, it is believed that the elastomer is no longer serviceable when its elongation at break reaches 50% or 60% of the initial elongation of the intact materials [19]. In this study, for a conservative approach, 60% elongation at break was chosen to be the lifetime of EPDM. According to the definition, the lifetime of EPDM isothermally aged at 140ºC is 1,316 hours, which is then reduced to 1,120 hours after experiencing the LOCA environment.
Through this study it can be concluded that the aging degradation of the domestic class 1E EPDM can be tolerable, even in accident conditions, such as LOCA and, therefore, it is a suitable and qualified insulating material for electrical cables in nuclear power plants.
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