Sensitivity study of accident scenarios on MCCI for Fukushima Daiichi unit-1 by MELCOR

Takumi Noju, Akifumi Yamaji, Kiyoshi Matsumoto, Xin Li

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

At Fukushima Daiichi Nuclear Power Plant unit 1 (1F1), it is expected that molten corium-concrete interaction (MCCI) occurred in a significant scale. large uncertainty in progression of the accident is inevitable due to lack of information (measurements) such as the timings of RPV depressurization and RPV failure (discharge of debris from RPV) and the RPV failure mode. Furthermore, significant uncertainties exist in the calculated results even with a set of well-defined boundary conditions among different severe accident analysis codes such as MAAP and MELCOR. Hence, this study aims influences of scenario uncertainties and modeling uncertainties in predicting the late phase of the 1F1 accident, where MCCI is expected to have occurred using MELCOR2.1. Two depressurization scenarios (early depressurization with steam relief valve failure and late depressurization with main steam line failure) and two RPV failure modes (penetration tube failure and RPV lower head rupture) on the subsequent MCCI are considered. Analyses with MELCOR indicated that different cases led to different debris compositions (metals and oxides) and amount on the basemat floor and led to differences in the radial ablation depths, while axial ablation depths showed negligible differences among different cases. However, in all cases, MCCI did not terminate 140 hours after the reactor scram. Sensitivity studies have been carried out with and without the presence of external water injection and parametric study with some of the parameters involved in MELCOR simulation relevant to MCCI. The results showed that the concrete ablation in the radial direction was suppressed by external water injection. However, the axial ablation was enhanced, indicating necessity to further investigate modeling of MCCI in MELCOR2.1.

Original languageEnglish
Title of host publication2017 International Congress on Advances in Nuclear Power Plants, ICAPP 2017 - A New Paradigm in Nuclear Power Safety, Proceedings
PublisherInternational Congress on Advances in Nuclear Power Plants, ICAPP
ISBN (Electronic)9784890471676
Publication statusPublished - 2017 Jan 1
Event2017 International Congress on Advances in Nuclear Power Plants: A New Paradigm in Nuclear Power Safety, ICAPP 2017 - Fukui and Kyoto, Japan
Duration: 2017 Apr 242017 Apr 28

Other

Other2017 International Congress on Advances in Nuclear Power Plants: A New Paradigm in Nuclear Power Safety, ICAPP 2017
CountryJapan
CityFukui and Kyoto
Period17/4/2417/4/28

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Nuclear Energy and Engineering

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    Noju, T., Yamaji, A., Matsumoto, K., & Li, X. (2017). Sensitivity study of accident scenarios on MCCI for Fukushima Daiichi unit-1 by MELCOR. In 2017 International Congress on Advances in Nuclear Power Plants, ICAPP 2017 - A New Paradigm in Nuclear Power Safety, Proceedings International Congress on Advances in Nuclear Power Plants, ICAPP.