Characteristics of droplet evaporation on high-temperature porous surfaces for estimating cooling time of fuel debris
At the Fukushima Daiichi nuclear power station, fuel debris is cooled under immersion. However, under an unexpected significant drop in water level, the water comes into contact with fuel debris that possesses a porous structure. In this scenario, rapid cooling of the fuel debris is essential. Howev...
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| Language: | English |
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The Japan Society of Mechanical Engineers
2025-05-01
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| Series: | Mechanical Engineering Journal |
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| Online Access: | https://www.jstage.jst.go.jp/article/mej/12/4/12_24-00451/_pdf/-char/en |
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| author | Kohei YUKI Naoki HORIGUCHI Hiroyuki YOSHIDA Kazuhisa YUKI |
| author_facet | Kohei YUKI Naoki HORIGUCHI Hiroyuki YOSHIDA Kazuhisa YUKI |
| author_sort | Kohei YUKI |
| collection | DOAJ |
| description | At the Fukushima Daiichi nuclear power station, fuel debris is cooled under immersion. However, under an unexpected significant drop in water level, the water comes into contact with fuel debris that possesses a porous structure. In this scenario, rapid cooling of the fuel debris is essential. However, the cooling time has not been estimated, because the thermal behavior of high-temperature debris, including capillary phenomena, is not well understood. In the present study, the droplet evaporation characteristics on metallic porous media featuring pores smaller than 1 mm were investigated. To derive lifetime curves for droplets, the authors conducted experiments using 316L stainless steel and bronze porous materials with pore diameters of 1, 40, and 100 μm to establish droplet lifetime curves. The experimental findings indicate that the Leidenfrost phenomenon is mitigated on porous surfaces because the vapor escapes through the pores of the porous material. Further, as the temperature increases, an oxide film having a fine structure activates capillary action in bronze porous media. By contrast, a stainless-steel porous medium prevents capillary phenomena owing to its low wettability, inhibiting droplet absorption and dispersion into the pores. Consequently, if the fuel debris has similar characteristics to steel porous media, rapid cooling via the capillary action is unexpected. Finally, the cooling heat flux and cooling time of fuel debris are estimated according to experimental results. The estimation indicates that even in the case of stainless steel, the fuel debris can be cooled from 200 to 100 °C within 60 min under a low-decay heat condition. However, when the decay heat exceeds a certain value, the fuel debris cannot be cooled in either the stainless steel or bronze cases. Therefore, for risk management, the cooling system should be established for situations where the decay heat is substantial and simple spray cooling is not sufficient. |
| format | Article |
| id | doaj-art-ad693616087d487db5abae2cf32e73c7 |
| institution | OA Journals |
| issn | 2187-9745 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | The Japan Society of Mechanical Engineers |
| record_format | Article |
| series | Mechanical Engineering Journal |
| spelling | doaj-art-ad693616087d487db5abae2cf32e73c72025-08-20T01:59:34ZengThe Japan Society of Mechanical EngineersMechanical Engineering Journal2187-97452025-05-0112424-0045124-0045110.1299/mej.24-00451mejCharacteristics of droplet evaporation on high-temperature porous surfaces for estimating cooling time of fuel debrisKohei YUKI0Naoki HORIGUCHI1Hiroyuki YOSHIDA2Kazuhisa YUKI3Department of Mechanical Engineering, Tokyo University of Science-YamaguchiJapan Atomic Energy AgencyJapan Atomic Energy AgencyDepartment of Mechanical Engineering, Tokyo University of Science-YamaguchiAt the Fukushima Daiichi nuclear power station, fuel debris is cooled under immersion. However, under an unexpected significant drop in water level, the water comes into contact with fuel debris that possesses a porous structure. In this scenario, rapid cooling of the fuel debris is essential. However, the cooling time has not been estimated, because the thermal behavior of high-temperature debris, including capillary phenomena, is not well understood. In the present study, the droplet evaporation characteristics on metallic porous media featuring pores smaller than 1 mm were investigated. To derive lifetime curves for droplets, the authors conducted experiments using 316L stainless steel and bronze porous materials with pore diameters of 1, 40, and 100 μm to establish droplet lifetime curves. The experimental findings indicate that the Leidenfrost phenomenon is mitigated on porous surfaces because the vapor escapes through the pores of the porous material. Further, as the temperature increases, an oxide film having a fine structure activates capillary action in bronze porous media. By contrast, a stainless-steel porous medium prevents capillary phenomena owing to its low wettability, inhibiting droplet absorption and dispersion into the pores. Consequently, if the fuel debris has similar characteristics to steel porous media, rapid cooling via the capillary action is unexpected. Finally, the cooling heat flux and cooling time of fuel debris are estimated according to experimental results. The estimation indicates that even in the case of stainless steel, the fuel debris can be cooled from 200 to 100 °C within 60 min under a low-decay heat condition. However, when the decay heat exceeds a certain value, the fuel debris cannot be cooled in either the stainless steel or bronze cases. Therefore, for risk management, the cooling system should be established for situations where the decay heat is substantial and simple spray cooling is not sufficient.https://www.jstage.jst.go.jp/article/mej/12/4/12_24-00451/_pdf/-char/enfuel debrisporous mediadroplet evaporationleidenfrost phenomenoncapillary phenomenon |
| spellingShingle | Kohei YUKI Naoki HORIGUCHI Hiroyuki YOSHIDA Kazuhisa YUKI Characteristics of droplet evaporation on high-temperature porous surfaces for estimating cooling time of fuel debris Mechanical Engineering Journal fuel debris porous media droplet evaporation leidenfrost phenomenon capillary phenomenon |
| title | Characteristics of droplet evaporation on high-temperature porous surfaces for estimating cooling time of fuel debris |
| title_full | Characteristics of droplet evaporation on high-temperature porous surfaces for estimating cooling time of fuel debris |
| title_fullStr | Characteristics of droplet evaporation on high-temperature porous surfaces for estimating cooling time of fuel debris |
| title_full_unstemmed | Characteristics of droplet evaporation on high-temperature porous surfaces for estimating cooling time of fuel debris |
| title_short | Characteristics of droplet evaporation on high-temperature porous surfaces for estimating cooling time of fuel debris |
| title_sort | characteristics of droplet evaporation on high temperature porous surfaces for estimating cooling time of fuel debris |
| topic | fuel debris porous media droplet evaporation leidenfrost phenomenon capillary phenomenon |
| url | https://www.jstage.jst.go.jp/article/mej/12/4/12_24-00451/_pdf/-char/en |
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