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Pshenichnikov, A.; Zubekhina, B.; 多木 寛; Pham, V. H.
Proceedings of International Topical Workshop on Fukushima-Daiichi Decommissioning Research 2024 (FDR2024) (Internet), 4 Pages, 2024/10
The CLADS-MADE-05 is the next test in the series of large-scale tests performed in JAEA with a purpose of understanding of mock-up assembly degradation and melt propagation behaviour accompanied by Cs and B containing aerosol release. A possibility of Cs and B aerosols interactions in RPV and formation of a new Cs bearing contaminating phase has been shown. This paper analyses the data on aerosol behaviour of Cs and B bearing aerosols when they interact in the gas line, and concentrates on the phenomenon of possible reactions on the liquid-liquid and liquid-gas interface when aerosols are interacting during the large-scale bundle degradation test.
Pshenichnikov, A.; Zubekhina, B.
Journal of Nuclear Materials, 597, p.155136_1 - 155136_12, 2024/08
被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)A high radiation dose rate under the shield plugs of the Units 2 and 3 reactors at the Fukushima Dai-Ichi Nuclear Power Station (1F), raised an important question on volatile radioactive Cs migration, adsorption and retention on various structural materials during the accident. The high dose rate interferes with decommissioning work. The purpose of this study is to present basic knowledge on contamination mechanisms of a BWR reactor structural materials and post-accident debris by Cs compounds to help decommissioning companies consider the ways of decontamination and debris handling during 1F debris retrieval.
Pshenichnikov, A.; 永江 勇二
Nuclear Engineering and Design, 415, p.112729_1 - 112729_16, 2023/12
被引用回数：0 パーセンタイル：0.00(Nuclear Science & Technology)The paper presents the results of a CLADS-MADE-03 BWR mock-up assembly degradation in high-temperature steam under a transient heating rate of 1 K/s, which are the assumed accident conditions for the beginning of the accident at the Unit 1 of the Fukushima Dai-Ichi Nuclear Power Station. In situ video investigations of the control blade provided visual evidences for the features of the control blade melt relocation. Based on the results, factors like an increase in the amount of core liquefied materials due to change of the melt composition, subsequent change in melt relocation features because of liquid/solid material ratio within the melt and B release and transport by aerosol formation were specially emphasized.
Pshenichnikov, A.; 倉田 正輝; 永江 勇二
Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR2022) (Internet), 4 Pages, 2022/10
CLADS-MADE-04は、下部コア領域での溶融伝播挙動の理解を目的としたシリーズの次のテストである。この寄稿では、電子プローブ マイクロアナライザー(EPMA)によって調査された金属破片の微細構造を含む試験後分析の最近の結果について説明する。テスト中、制御棒ブレードの溶融は、比較的ゆっくりと(数cm/分)急激な強い熱放出の波で発生し、最も高温の領域から、劣化しつつある制御棒ブレードとチャネルボックスに沿って下方に広がり、ジルカロイ-4で作られた壁を消費した。サンプル支持板にも大きな損傷が発生した。このような金属リッチ破片の微細構造の調査により、強化された局所コア劣化のメカニズムを理解できるようになる。EPMAによる相同定を徹底した上で、放熱性が高く周囲への拡散の可能性があることを確認する必要がある。Fe-B共晶デブリとZr-Fe共晶デブリの違いについて概説する。これは、下部炉心プレートのメルトスルーと、下部プレナムへのZr-Fe溶融材料の進行の可能性を理解するために特に重要である。
Pshenichnikov, A.; 柴田 裕樹; 山下 拓哉; 永江 勇二; 倉田 正輝
Journal of Nuclear Science and Technology, 59(3), p.267 - 291, 2022/03
被引用回数：3 パーセンタイル：35.51(Nuclear Science & Technology)The paper reviews the results of the JAEA and some International activities over the last ten years of research on the understanding of the core components melting and debris formation in boiling water reactors.
Pshenichnikov, A.; 永江 勇二; 倉田 正輝
Proceedings of TopFuel 2021 (Internet), 12 Pages, 2021/10
The results of the several recent tests performed in JAEA/CLADS are outlined in this paper. However, particular point of this work is focused on the interesting effect that was found on the debris, that contained partially reacted B
C (control blade debris). A Raman investigation of the control blade metallic debris helped to refine the governing mechanism of the B-compounds formation and transport, which is probably specific mostly for BWRs due to unique bundle configuration and materials morphology. All these factors may directly influence the accident progression in BWR and influence the final debris properties.
Pshenichnikov, A.; 倉田 正輝; 永江 勇二
Journal of Nuclear Science and Technology, 58(9), p.1025 - 1037, 2021/09
被引用回数：4 パーセンタイル：45.28(Nuclear Science & Technology)The paper summarizes the results of the control blade degradation test CLADS-MADE-02 performed in JAEA. The test focused at the beginning phase of the accident at Fukushima Dai-Ichi (1F) Unit 3. The investigation provided important data, especially on the temperature history, exhaust gas measurement and in situ video of metallic debris formation and relocation to the colder elevations under the test scenario, which reproduced oxidizing conditions during the initial phase of the 1F Unit 3 reactor heat-up. Based on the test results, some decommissioning related conclusions concerning the formation of new B-rich phases containing Cr and Fe were made.
Pshenichnikov, A.; 永江 勇二; 倉田 正輝
Proceedings of 28th International Conference on Nuclear Engineering (ICONE 28) (Internet), 7 Pages, 2021/08
The work on the understanding of the accident progression at the Units of the Fukushima Dai-Ichi Nuclear Power Plant (1F) is ongoing. This contribution gives a part of detailed investigations of the control blade melt propagation downwards through the prototypic BWR bundle assembly during the CLADS-MADE-02 test, where the conditions of the 1F Unit 3 was simulated. Interesting features emerged in an oxidative environment.
Pshenichnikov, A.; 永江 勇二; 倉田 正輝
Journal of Nuclear Science and Technology, 58(4), p.416 - 425, 2021/04
被引用回数：14 パーセンタイル：82.90(Nuclear Science & Technology)The paper describes the attempt of comparison of the simulated test CLADS-MADE-01 debris with the observed in the Unit 2. Similarities between them allowed to make conclusions on their possible source. During the test under postulated 1F Unit 2 simulated conditions a complex behaviour of the test sample with formation of mostly three types of debris was observed. A possible mechanism of stone-like debris formation in 1F case is discussed. The results of this paper broaden our understanding of the metallic debris properties after core degradation for a special case of steam-starved conditions at 1F Unit 2.
Pshenichnikov, A.; 永江 勇二; 倉田 正輝
Mechanical Engineering Journal (Internet), 7(3), p.19-00503_1 - 19-00503_10, 2020/06
High-temperature control blade degradation tests simulating a beginning phase of a severe accident in BWRs has been comprehensively performed in Japan Atomic Energy Agency (JAEA). In the latest test, a mock-up of BWR bundle material has been investigated under postulated Fukushima Dai-Ichi (1F) Unit 2 accident conditions in a complex heating transient scenario including a phase of lack of available steam. The progress in control blade degradation was monitored with help of an in situ video and the detailed analysis of the solidified metallic melt, so-called metallic debris, was carried out by conventional SEM and XRD methods. These results indicated that the composition of the metallic debris at different elevations has been significantly changed due to the redistribution and relocation of steel elements under the influence of B and C, sometimes accompanied by a formation of high-melting-point layers. The results of this paper significantly contribute to the physical understanding of control blade degradation phenomenology during beginning phase of a core degradation for a special case of steam-starved conditions at 1F Unit 2.
Pshenichnikov, A.; 倉田 正輝; Bottomley, D.; 佐藤 一憲; 永江 勇二; 山崎 宰春
Journal of Nuclear Science and Technology, 57(4), p.370 - 379, 2020/04
被引用回数：15 パーセンタイル：67.54(Nuclear Science & Technology)The new research and development programme of JAEA/CLADS tests complement the previous investigations related to BWR severe accidents. A series of tests aiming at closing the gaps in understanding of the Fukushima Daiichi degradation sequence at each unit. The paper emphasises the problem of control blade degradation, which influences the accident progression at an early stage and shows the approach for thorough investigation of this problem.
Pshenichnikov, A.; 永江 勇二; 倉田 正輝
Mechanical Engineering Journal (Internet), 7(2), p.19-00477_1 - 19-00477_8, 2020/04
In order to address the challenge of the future Fukushima Dai-Ichi Nuclear Power Station (1F) debris characterization a new Raman spectroscopy investigation of simulated debris obtained after two control blade degradation tests CLADS-MADE-01 and CLADS-MADE-02 has been performed. A mechanism of the BC degradation during the beginning phase of a severe accident until approximately 1873 K is described. A sequence of material interactions of BC with stainless steel resulted in partial transformation of BC granules into pure graphite, that later experienced oxidation with formation of COx gas. Especially this mechanism is active during melting phase in oxidative environment. At the same time boron was associated with formation of new Cr-B-containing solid phases in liquid melt, that continued relocation depleted by Cr and B, which resulted in redistribution of elements within the degrading reactor core. This knowledge would provide new insights for understanding of the absorber blade degradation mechanism under specific accident conditions close to 1F Unit 2 and Unit 3 reactors and especially would be helpful during potential characterization of metallic debris of 1F.
Pshenichnikov, A.; 倉田 正輝; 永江 勇二
第24回動力・エネルギー技術シンポジウム講演論文集(USB Flash Drive), 4 Pages, 2019/06
The new data from video investigation of the 1F Unit 2 pedestal debris performed by TEPCO was analysed. The debris features as derived from visual appearance on the video compared with the debris obtained after the CLADS-MADE-01 test. Some speculative conclusions concerning the properties and possible nature of the debris can be made.
during severe accidents in boiling water reactorsPshenichnikov, A.; 山崎 宰春; Bottomley, D.; 永江 勇二; 倉田 正輝
Journal of Nuclear Science and Technology, 56(5), p.440 - 453, 2019/05
被引用回数：19 パーセンタイル：86.74(Nuclear Science & Technology)In the present paper new results using video, are presented regarding BWR control blade degradation up to 1750 K at the beginning of a nuclear severe accident. Energy-dispersive X-ray spectrometry (EDS) mapping indicated stratification of the absorber blade melt with formation of a chromium and boride-enriched layer. High content-B- and C-containing material with increased melting temperature acted like a shielding and was found to prevent further relocation of control blade claddings. The interacted layers around the BC granules prevented direct steam attack of residual BC. The results provide new insights for understanding of the absorber blade degradation mechanism under reducing conditions specific to Fukushima Dai-Ichi Unit 2 resulting from prolonged steam starvation.
Pshenichnikov, A.; 山崎 宰春; 永江 勇二; 倉田 正輝
Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05
This paper presents recent results on high-temperature control blade degradation at the very beginning phase of a severe accident in BWRs. The large-scale experiment has been performed in JAEA-CLADS laboratory using Large-scale Equipment for Investigation of Severe Accidents in Nuclear reactors (LEISAN). A prototypic sequence of Fukushima Daiichi (1F) Unit 2 has been taken. It has been shown that due to specific conditions happened at Unit 2 the lack of available oxygen allowed metallic melt more flexibility for relocation and inhomogeneous redistribution of melt components due to specially recreated temperature gradient. Phase composition of remained BC control blade claddings at different elevations, and phase composition of melt has been investigated by complementary methods and have shown significant difference in elevations together with stratification of metallic components with origination of high melting point layers due to redistribution of steel components and involvement of B and C. It allowed absorber blade residuals with BC inside being severely damaged by melting to survive at 1475
C and protect BC from direct contact with steam.
Pshenichnikov, A.; 倉田 正輝; 永江 勇二; 山崎 宰春
Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet), 4 Pages, 2019/05
The paper summarizes the first results of a thorough SEM investigation uncovering the process of channel box wall penetration by Fe-Cr-Ni-B containing melt. The preliminary oxidation of channel box is shown to play an important role on severe accident progression resulted in the suppression of channel box massive destruction. Only one small droplet came out to the other side of channel box. The mechanism of local beginning of oxide layer destruction with subsequent Zircaloy-4 channel box penetration is under discussion.
山崎 宰春; Pshenichnikov, A.; Pham, V. H.; 永江 勇二; 倉田 正輝; 徳島 二之*; 青見 雅樹*; 坂本 寛*
Proceedings of Annual Topical Meeting on Reactor Fuel Performance (TopFuel 2018) (Internet), 8 Pages, 2018/10
燃料集合体の酸化及び水素吸収はその後の事故進展挙動に影響を与えることから、PWR燃料集合体では、実効的な水蒸気流量としてg-H
O/sec/rodという単位が導入されており、事故進展評価の重要なパラメータといて用いられている。一方BWRにおいては、燃料集合体の構成がPWRとは異なることにより、PWRで用いられている規格化された水蒸気流量ではチャンネルボックスの内外での酸化及び水素吸収の差が正確に評価できない。そのため、PWRで用いられているg-HO/sec/rodという規格化された水蒸気流量に代わる、適切な評価パラメータがBWRでも必要である。そこで、ジルカロイの水蒸気枯渇条件での酸化及び水素吸収データを取得するため、実機を模擬したBWRバンドル試験体を用いて高温酸化試験を行なった。BWRにおける水蒸気流量を規格化するため、水蒸気流路断面積を考慮したパラメータを検討した。
Pshenichnikov, A.; 永江 勇二; 倉田 正輝
no journal, ,
One of the promising methods of debris characterization - a Raman spectroscopy was utilized for investigation of simulated debris obtained after two control blade degradation tests CLADS-MADE-01 and CLADS-MADE-02. New results allowed to refine a mechanism of the BC degradation during the beginning phase of a severe accident. A partial transformation of BC granules into pure graphite promotes formation of particular phases in the debris based on the oxidative or reducing environment. This knowledge would provide new insights for understanding of the absorber blade degradation mechanism under specific accident conditions close to 1F Unit 2 and Unit 3 reactors.
永江 勇二; 柴田 裕樹; Pshenichnikov, A.; 山崎 宰春; 倉田 正輝
no journal, ,
Two control blade degradation test facilities which were designed for the investigation of high temperature degradation of the nuclear reactor elements, have been set up in Tomioka-site. One was a test facility for small-scale samples and another one was test facility for large-scale samples. In situ video of the experiment and mass-spectrometric analysis of the output gases can be carried out during tests, and heating rate can be controlled up to 1 K/s. The working area of the large-scale facility consists of the isolated heating area 1.2 m height with the water cooled lower part to achieve the natural temperature gradient conditions as during severe accident. Steam rate in large-scale facilities can be controlled in the range of 15-100 g/min, and a test piece for the control blade degradation tests can be used to simulate a part of the control blade and fuel assembly. Chemical reaction between stainless steel/BC and Zry is affected by the oxide layer on Zry. The oxidation behavior depends on steel flow rate and tendency of control blade degradation possibly has threshold condition. According to pretest, critical condition for reaction between molten control rod and channel box can be recognized. Further analysis and tests in various steam rate will be conducted to evaluate the critical condition.
Pshenichnikov, A.; 山崎 宰春; 永江 勇二; 倉田 正輝
no journal, ,
Current presentation gives a deep analysis of the progression of the 1F accident at Unit 2. Based on that analysis the explanation of the strategy for a severe accident test program of JAEA-CLADS to contribute to understanding of accident progression at 1F Unit 2 is given. First result of CLADS-MADE-01 (BWR control blade degradation test) is presented.
