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Imaizumi, Yuya; Yamada, Fumiaki; Arikawa, Mitsuhiro*; Yada, Hiroki; Fukano, Yoshitaka
Mechanical Engineering Journal (Internet), 5(4), p.18-00083_1 - 18-00083_11, 2018/08
A calculation program was developed to evaluate and discuss the effectiveness of the countermeasures such as sodium pump-up and siphon-breaking against the loss-of-reactor-level (LORL) where the coolant circulation path is lost in loop-type sodium-cooled fast reactors. Due to the non-negligible possibility obtained by probabilistic risk assessment (PRA), sodium leakages in two points both occurred in primary heat transport system (PHTS) was assumed in this study. In addition, the crack size was discussed and evaluated realistically, instead of the value that was assumed in the conventional studies. Representative sequences and leakage positions were chosen, and the sodium level transient in reactor vessel (RV) was calculated. The calculations were also conducted where the larger crack size was set for the second leakage, in order to investigate additional requirements to maintain the RV sodium level. The evaluation results clarified that the coolant circulation loop can be maintained even after the second leakage in PHTS, taking into account the effects by the countermeasures.
Yamada, Fumiaki; Imaizumi, Yuya; Nishimura, Masahiro; Fukano, Yoshitaka; Arikawa, Mitsuhiro*
Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 10 Pages, 2017/07
The loss-of-reactor-level (LORL) is one of the loss-of-heat-removal-system (LOHRS) of beyond-DBA (BDBA) severe accident. An evaluation method for the LORL which is caused by the coolant leakage in two positions of the primary heat transport system (PHTS) was developed for prototype JSFR which is loop-type sodium-cooled fast reactor. The secondary leakage in cold standby which occurred in different loop from that of the first leakage in rated power operation can lead LORL by excessive declining of the sodium level. Therefore, the sodium level behavior in RV was studied in a representative accident sequence by considering the sodium pumping up into RV, siphon-breaking to stop pumping out from RV and maintain the sodium level, and calculation programs for the transient sodium level in RV. The representative sequence with lowest sodium level was selected by considering combinations of possible leakage positions. As a result of the evaluation considering the countermeasures above, it was revealed that the LOHRS can be prevented by maintaining the sodium level for the operation of decay heat removal system, even in the leakages in two positions of PHTS which corresponds to BDBA.
Imaizumi, Yuya; Fukano, Yoshitaka
Proceedings of 2016 International Congress on Advances in Nuclear Power Plants (ICAPP 2016) (CD-ROM), p.357 - 363, 2016/04
SAS4A is the code which has been developed to analyze the initiation phase of the core-disruptive accident in SFRs. The code of which can be adopted in a safety licensing needs to be validated through the experimental results. In this study, the code was validated by the experimental results of CABRI project which was conducted in the framework of international collaboration. The selected three CABRI tests of this validation target were all conducted using annular fuel pellets with middle burn-up (6.4 at%). Severe conditions consisted of loss of flow (LOF) and transient overpower (TOP) was imposed in the tests to reproduce similar conditions when unprotected-loss-of-flow (ULOF) occurred in SFRs. The TOP were imposed when coolant temperature reached around the boiling point or several seconds after the cladding melting. The results of the SAS4A analyses agreed well with the CABRI results such as the timing of coolant boiling, voiding extension during the coolant boiling, and the relocation and refrozen behaviors of the molten fuel. Consequently, the coolant boiling and fuel relocation models of SAS4A were validated by these analyses.
Cs discharge rates after the Fukushima Dai-ichi Nuclear Power Plant accident from two distinct watershed simulation modelsKitamura, Akihiro; Imaizumi, Yoshitaka*; Yamaguchi, Masaaki; Yui, Mikazu; Suzuki, Noriyuki*; Hayashi, Seiji*
Kankyo Hoshano Josen Gakkai-Shi, 2(3), p.185 - 192, 2014/09
Annual discharge rates of radioactive cesium through selected rivers due to the Fukushima Dai-ichi Nuclear Power Plant accident were simulated by two different watershed models. One is the Soil and Cesium Transport, SACT, model which was developed by Japan Atomic Energy Agency and the other one is the Grid-Catchment Integrated Modeling System, G-CIEMS, which was developed by National Institute of Environmental Studies. We choose the Abukuma, the Ukedo, and the Niida rivers for the present study. Comparative results showed that while components and assumptions adopted in two models differ, both methods predicted the same order of magnitude estimates.
Fukano, Yoshitaka; Imaizumi, Yuya; Yoshioka, Naonori*; Akahori, Hisashi*
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Imaizumi, Yuya; Fukano, Yoshitaka
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The test result of EFM1 in the CABRI in-pile experiment which was conducted as an internationally collaborated project was analyzed by SAS4A code. The code was developed for the analysis of initiation phase of core disruptive accident. In the EFM1 test, transient overpower was imposed after the cladding melting and coolant boiling which was due to the previously imposed loss of flow. The behavior of large relocation and refreezing of the molten fuel which was caused by the heating peak after the fuel melting was one of the important point in the analysis. As a result, good agreements were observed between the results of experiment and analysis such as timings of coolant boiling, extension of boiling area and behavior of molten fuel motion.
Imaizumi, Yuya; Fukano, Yoshitaka
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Mori, Takero; Sotsu, Masutake; Imaizumi, Yuya; Yoshimura, Kazuo; Fukano, Yoshitaka
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Imaizumi, Yuya; Yamada, Fumiaki; Nishimura, Masahiro; Mori, Takero; Fukano, Yoshitaka
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no abstracts in English
