Molten Core Concrete Interaction and Development of Core Catcher (2) Thermal shock effects for advanced high temperature ceramics
公開日:
カテゴリ: 第11回
Hokkaido University マルタ シルベスター Marta ZIEMNICKA-SYLWESTER Hokkaido University 奈良林 直 Tadashi NARABAYASHI Member Hokkaido University ?千葉 豪 Go CHIBA Hokkaido University 辻 雅司 Masashi TSUJI Hokkaido University 久保田 祥 Sho KUBOTA 宮脇 大地 Daichi MIYAWAKI
1. Why advanced high temperature ceramics
It has been proven at least twice (by Chernobyl and Fukushima NPP) that reactor core can be melted in case of sever accident.. The temperature measurements form Chernobyl indicated that the basis under the melted debris reached 1600oC, which means that commercially used refractories are not able to ensure thermal protection and chemical stability at such temperature. For instance, much lower temperature causes severe damage in concrete just at 1000oC (Fig.1. A). Many spallations were formed due to chemical reactions and significantly deteriorated mechanical properties can be expected. Despite better chemical stability of Al2O3, or alumina-based materials such as basalt, formation of spinels, or other eutectics significantly reduce the melting point which become lower, than 1600??C. Fig.1 A) Microstructure of concrete exposed to 5h annealing at 1000oC, B) photo of basalt after thermite reaction The poor refractoriness of basal at high temperature causes that basalt was melted while exposed to thermite reaction (Fig.1B). Therefore, more advanced and higher thermal stability materials Contact: Marta Ziemnicka-Sylwester, ?§060-8628 Sapporo?AFaculty of Engineering?AHokkaido University E-mail: marta.zs@eng.hokudai.ac.jp A B spallation Melted area - 325 - ?U‘S?w Vol.8, No.3 (2009) 2have to be considered for surface part of the new design core catcher. Therefore, in this study four monolithic advanced ceramics: Al2O3, TiN, TiC and SiC (Fig.2) (30x10x5mm) were investigated under sever thermal shock caused by thermite reaction, as well as corrosion resistance. ?Q?DResults and discussion 2.1 Effect of thermal shock The best thermal shock resistance was observed in SiC (Fig.2), because only 16% of sample was broken (Table 1). Fig.2 Samples used for thermal shock evaluation: A) before test; B) after thermite reaction Table 1 Mass loss caused by thermal shock 2.2 Corrosion resistance Significant differences in formation of corrosion products were observed (Fig. 3). The most thick scale grew up on the surface of TiC (300?Em), smaller on TiN (200?Em). Different effects (formation of binary FeAlO3 oxide) were observed in Al2O3. The most remarkable corrosion resistance was observed in SiC, where only thin layer (about 10?Em) with reduced carbon and increased oxygen content was formed (Fig.4), however the SiO2 is characterized by higher than TiO2 melting point. Fig.3 The SEI of the reaction zone (from the surface) after thermal shock and corrosion test at 1000??C for 5h. Fig.4. The line profile of elements near the surface of SiC after thermal shock and corrosion test at 1000??C for 5h. Conclusions: The results indicated that among considered materials SiC revealed both the best thermal shock resistance as well as the best refractoriness and corrosion resistance at 1000oC. Thus, it is the most perspective material for thick coating which could cover the most exposed to melted debris surface of core catcher. ?iHachinohe, July 24th , 2014?j Al2O3 SiC TiN TiC Material Mass loss [%] Al2O3 51.4 (Peeling) TiC 41.0 TiN 51.3 SiC 16.11 TiN Al2O3 TiC SiC SiC TiC Al2O3 TiN A B SiC surface - 326 - “ “Molten Core Concrete Interaction and Development of Core Catcher (2) Thermal shock effects for advanced high temperature ceramics “ “マルタ シルベスター,Marta ZIEMNICKA-SYLWESTER ,奈良林 直,Tadashi NARABAYASHI ,千葉 豪,Go CHIBA, 辻 雅司,Masashi TSUJI ,久保田 祥,Sho KUBOTA , 宮脇 大地, Daichi MIYAWAKI
1. Why advanced high temperature ceramics
It has been proven at least twice (by Chernobyl and Fukushima NPP) that reactor core can be melted in case of sever accident.. The temperature measurements form Chernobyl indicated that the basis under the melted debris reached 1600oC, which means that commercially used refractories are not able to ensure thermal protection and chemical stability at such temperature. For instance, much lower temperature causes severe damage in concrete just at 1000oC (Fig.1. A). Many spallations were formed due to chemical reactions and significantly deteriorated mechanical properties can be expected. Despite better chemical stability of Al2O3, or alumina-based materials such as basalt, formation of spinels, or other eutectics significantly reduce the melting point which become lower, than 1600??C. Fig.1 A) Microstructure of concrete exposed to 5h annealing at 1000oC, B) photo of basalt after thermite reaction The poor refractoriness of basal at high temperature causes that basalt was melted while exposed to thermite reaction (Fig.1B). Therefore, more advanced and higher thermal stability materials Contact: Marta Ziemnicka-Sylwester, ?§060-8628 Sapporo?AFaculty of Engineering?AHokkaido University E-mail: marta.zs@eng.hokudai.ac.jp A B spallation Melted area - 325 - ?U‘S?w Vol.8, No.3 (2009) 2have to be considered for surface part of the new design core catcher. Therefore, in this study four monolithic advanced ceramics: Al2O3, TiN, TiC and SiC (Fig.2) (30x10x5mm) were investigated under sever thermal shock caused by thermite reaction, as well as corrosion resistance. ?Q?DResults and discussion 2.1 Effect of thermal shock The best thermal shock resistance was observed in SiC (Fig.2), because only 16% of sample was broken (Table 1). Fig.2 Samples used for thermal shock evaluation: A) before test; B) after thermite reaction Table 1 Mass loss caused by thermal shock 2.2 Corrosion resistance Significant differences in formation of corrosion products were observed (Fig. 3). The most thick scale grew up on the surface of TiC (300?Em), smaller on TiN (200?Em). Different effects (formation of binary FeAlO3 oxide) were observed in Al2O3. The most remarkable corrosion resistance was observed in SiC, where only thin layer (about 10?Em) with reduced carbon and increased oxygen content was formed (Fig.4), however the SiO2 is characterized by higher than TiO2 melting point. Fig.3 The SEI of the reaction zone (from the surface) after thermal shock and corrosion test at 1000??C for 5h. Fig.4. The line profile of elements near the surface of SiC after thermal shock and corrosion test at 1000??C for 5h. Conclusions: The results indicated that among considered materials SiC revealed both the best thermal shock resistance as well as the best refractoriness and corrosion resistance at 1000oC. Thus, it is the most perspective material for thick coating which could cover the most exposed to melted debris surface of core catcher. ?iHachinohe, July 24th , 2014?j Al2O3 SiC TiN TiC Material Mass loss [%] Al2O3 51.4 (Peeling) TiC 41.0 TiN 51.3 SiC 16.11 TiN Al2O3 TiC SiC SiC TiC Al2O3 TiN A B SiC surface - 326 - “ “Molten Core Concrete Interaction and Development of Core Catcher (2) Thermal shock effects for advanced high temperature ceramics “ “マルタ シルベスター,Marta ZIEMNICKA-SYLWESTER ,奈良林 直,Tadashi NARABAYASHI ,千葉 豪,Go CHIBA, 辻 雅司,Masashi TSUJI ,久保田 祥,Sho KUBOTA , 宮脇 大地, Daichi MIYAWAKI