Conversion factors bridging radioactive fission product distributions in the primary containment vessel of Fukushima Daiichi NPP and dose rates measured by the containment atmosphere monitoring system

Uchida, Shunsuke; Pellegrini, M.*; Naito, Masanori*

Nuclear Engineering and Design, 380, p.111303_1 - 111303_11, 2021/08

https://doi.org/10.1016/j.nucengdes.2021.111303

Multi-term FP analysis procedures were developed to determine FP distribution all over F1 not only for analyzing accident propagation but also for planning its decommissioning projects. They should be validated based on the measured FP data. One of the useful tools for their validation was application of the dose rate data monitored by the containment atmosphere monitoring system (CAMS). However, in order to compare the data with different characteristics and dimensional units, e.g., FP distribution (kg, Bq) and dose rate (Sv/h), application of the conversion factors bridging them would be effective and useful. In order to prepare speedy, easy-to-handle and tractable procedures to calculate radiation dose rates at the CAMS detector locations, dose rate conversion factors were determined for major source locations and major radionuclides. The dose rates could be easily calculated by multiplying FP amounts obtained with the multiterm FP analysis procedures by the conversion factors.

Review of Fukushima Daiichi Nuclear Power Station debris endstate location in OECD/NEA preparatory study on analysis of fuel debris (PreADES) project

Nakayoshi, Akira; Rempe, J. L.*; Barrachin, M.*; Bottomley, D.; Jacquemain, D.*; Journeau, C.*; Krasnov, V.; Lind, T.*; Lee, R.*; Marksberry, D.*; et al.

Nuclear Engineering and Design, 369, p.110857_1 - 110857_15, 2020/12

https://doi.org/10.1016/j.nucengdes.2020.110857

Much is still not known about the end-state of core materials in each of the units at Fukushima Daiichi Nuclear Power Station (Daiichi) that were operating on March 11, 2011. The Nuclear Energy Agency of the Organization for Economic Development has launched the Preparatory Study on Analysis of Fuel Debris (PreADES) project as a first step to reduce some of these uncertainties. As part of the PreADES Task 1, relevant information was reviewed to confirm the accuracy of graphical depictions of the debris endstates at the damaged Daiichi units, which provides a basis for suggesting future debris examinations. Two activities have been completed within the PreADES Task 1. First, relevant knowledge from severe accidents at the Three Mile Island Unit 2 and the Chernobyl Nuclear Power Plant Unit 4 was reviewed, along with results from prototypic tests and hot cell examinations, to glean insights that may inform future decommissioning activities at Daiichi. Second, the current debris endstate diagrams for the damaged reactors at Daiichi were reviewed to confirm that they incorporate relevant knowledge from plant observations and from severe accident code analyses of the BSAF (Benchmark Study of the Accident at Daiichi Nuclear Power Station) 1 and 2 projects. This paper highlights Task 1 insights, which have the potential to not only inform future Decontamination and Decommissioning activities at Daiichi, but also provide important perspectives for severe accident analyses and management, particularly regarding the long term management of a damaged nuclear site following a severe accident.

Overview and outcomes of the OECD/NEA benchmark study of the accident at the Fukushima Daiichi NPS (BSAF), Phase 2; Results of severe accident analyses for Unit 2

Sonnenkalb, M.*; Pellegrini, M.*; Herranz, L. E.*; Lind, T.*; Morreale, A. C.*; Kanda, Kenichi*; Tamaki, Hitoshi; Kim, S. I.*; Cousin, F.*; Fernandez Moguel, L.*; et al.

Nuclear Engineering and Design, 369, p.110840_1 - 110840_10, 2020/12

https://doi.org/10.1016/j.nucengdes.2020.110840

This is the second paper in a series of 3 in which results of severe accident analyses for Unit 2 of Fukushima Daiichi are presented, gained in Phase 2 of the OECD/NEA project "Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF)". Nine organizations of six countries submitted results of their calculated severe accident scenarios for Unit 2 of Fukushima Daiichi using different severe accident codes. The present paper describes the findings of the comparison of the participants' results for Unit 2 against each other and against plant data, the evaluation of the accident progression and the final status inside the reactors. Special focus is on reactor pressure vessel status, melt release and fission product behavior and release. Unit 2 specific aspects will be highlighted and points of consensus as well as remaining uncertainties and data needs will be summarized.

Main findings, remaining uncertainties and lessons learned from the OECD/NEA BSAF Project

Pellegrini, M.*; Herranz, L.*; Sonnenkalb, M.*; Lind, T.*; Maruyama, Yu; Gauntt, R.*; Bixler, N.*; Morreale, A.*; Dolganov, K.*; Sevon, T.*; et al.

Nuclear Technology, 206(9), p.1449 - 1463, 2020/09

https://doi.org/10.1080/00295450.2020.1724731

Modelling of multi-physics phenomena in fast reactor design; Safety and experimental validation

Ninokata, Hisashi*; Pellegrini, M.*; Kamide, Hideki; Ricotti, M.*

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Safe Technologies and Sustainable Scenarios (FR-13), Vol.2, p.151 - 166, 2015/04

http://www-pub.iaea.org/books/iaeabooks/10682/Fast-Reactors-and-Related-Fuel-Cycles-Safe-Technologies-and-Sustainable-Scenarios-FR13

The paper provides a cursory look at current approaches in numerical modeling and simulation of typical multi-physics phenomena of concern relevant to the sodium-cooled fast reactor design and safety. Emphasis is placed on the methods that are in practice and their verification and validation programs, including for those of fluid-structure thermal interactions due to thermal striping, thermodynamics of sodium-water chemical reactions, multi-component and multi-phase flows in the fuel degradation and core meltdown phases. Several of numerical simulations of these multi-physics phenomena are shown with verification and validation programs that employ not only separate-effect small-scale experiments of clean geometry but also for large-scale integral tests or mock-up experiments. The last part of this paper will be spent on discussions on more quantitative validation basis with identification of errors and/or uncertainties based on the Bayesian rule.

Assessment of core status of TEPCO's Fukushima Daiichi Nuclear Power Plants, 115; Integrated evaluation of fuel debris remaining inside the RPV and the PCV; Unit2

Yamashita, Takuya; Honda, Takeshi*; Mizokami, Shinya*; Nozaki, Kenichiro*; Suzuki, Hiroyuki*; Pellegrini, M.*; Sakai, Takeshi*

no journal, , 

no abstracts in English

Assessment of core status of TEPCO's Fukushima Daiichi Nuclear Power Plants, 114; Integrated evaluation of fuel debris remaining inside the RPV and the PCV; Unit1

Sakai, Takeshi*; Mizokami, Shinya*; Honda, Takeshi*; Nozaki, Kenichiro*; Yamashita, Takuya; Pellegrini, M.*; Suzuki, Hiroyuki*

no journal, , 

no abstracts in English