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Matsuba, Kenichi; Isozaki, Mikio; Kamiyama, Kenji; Tobita, Yoshiharu; Suzuki, Toru
International Electronic Journal of Nuclear Safety and Simulation (Internet), 4(4), p.272 - 277, 2013/12
In order to develop an evaluation method of the distance for fragmentation of molten core material discharged into the lower sodium plenum during core disruptive accidents (CDAs) in sodium cooled fast reactors, fundamental experiments were conducted using a high-density melt and water as simulants for the molten fuel and coolant, respectively. The melt was discharged into a water pool through a nozzle (inner diameter: from 30 mm to 150 mm) under a simulated CDA condition where a liquid-liquid direct contact is maintained between the melt and water. The present results showed that measured distances for fragmentation were limited to approximately 10 percent of predictions by the existing representative correlation, and that vapor expansion with pressure buildup near the melt could facilitate the fragmentation and thus contribute to the reduction of the distance for fragmentation. Through the fundamental experiments, useful knowledge was obtained for the future development of an evaluation method.
Matsuba, Kenichi; Isozaki, Mikio; Kamiyama, Kenji; Tobita, Yoshiharu; Suzuki, Toru
Proceedings of International Symposium on Symbiotic Nuclear Power Systems for 21st Century (ISSNP 2013) (CD-ROM), 6 Pages, 2013/11
In order to develop an evaluation method of the distance for fragmentation of molten core material discharged into the lower sodium plenum during core disruptive accidents (CDAs) in sodium cooled fast reactors, fundamental experiments were conducted using a high-density melt and water as simulants for the molten fuel and coolant, respectively. The melt was discharged into a water pool through a nozzle (inner diameter: from 30 mm to 150 mm) under a simulated CDA condition where a liquid-liquid direct contact is maintained between the melt and water. The present results showed that measured distances for fragmentation were limited to approximately 10 percent of predictions by the existing representative correlation, and that vapor expansion near the melt could facilitate the fragmentation and thus contribute to the reduction of the distance for fragmentation. Through the fundamental experiments, useful knowledge was obtained for the future development of an evaluation method.
Sato, Ikken; Tobita, Yoshiharu; Yamano, Hidemasa
Proceedings of 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8) (CD-ROM), 12 Pages, 2010/10
As part of Level-2 PSA methodology development for sodium cooled fast reactors (SFR), event trees for the initiating phase (IP) of Anticipated Transient Without Scram (ATWS) are constructed. ULOF (Unprotected Loss of Flow), UTOP (Unprotected Transient Overpower) and ULOHS (Unprotected Loss of Heat Sink) are selected as typical and important accident categories. Based on the state-of-the-art knowledge, the headings of these event trees are selected so that dominant factors in accident consequences can be represented appropriately. For each of the headings, available information for judgment are reviewed and integrated as database for Level-2 PSA. It is clarified that the headings of ULOF, for which experimental database and evaluation models have been reasonably established, can be commonly applied to certain part of the different accident categories. While, some points specific for UTOP and ULOHS are identified. ULOHS, in which significant heat up of the primary system is expected before start of the core disruption, necessitates an additional event tree before the core disruption providing various boundary conditions for the core disruption process.
Matsuba, Kenichi; Isozaki, Mikio; Kamiyama, Kenji; Tobita, Yoshiharu
no journal, ,
In order to develop an evaluation method of the distance for fragmentation (debris formation) of molten core material discharged into the lower sodium plenum during core disruptive accidents in sodium-cooled fast reactors, a fundamental experiment was carried out, in which molten alloy (melt) and water were employed to simulate liquid-liquid direct between molten core material and sodium. Experimental results show that measured distances for fragmentation of melt column tended to increase with the increase of discharge diameter. However, the measured distances were approximately 10% lower than predictions by the existing representative correlation. Based on the results of this fundamental experiment, it was understood that the distance for fragmentation can be significantly reduced in conditions where liquid-liquid direct is established and thus vapor formation occurs intensively.
Tagami, Hirotaka; Cheng, S.; Tobita, Yoshiharu; Guo, L.*; Zhang, B.*; Morita, Koji*
no journal, ,
no abstracts in English
Tagami, Hirotaka; Tobita, Yoshiharu; Cheng, S.; Guo, L.*; Zhang, B.*; Morita, Koji*
no journal, ,
no abstracts in English
Matsuba, Kenichi; Isozaki, Mikio; Kamiyama, Kenji; Tobita, Yoshiharu
no journal, ,
In order to develop an evaluation method of the distance for fragmentation (debris formation) of molten core material discharged into the lower sodium plenum during core disruptive accidents in sodium-cooled fast reactors, the dependency of the distance for fragmentation on the discharge conditions was discussed based on the results of a fundamental experiment using a molten alloy and water.
