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論文

An Investigation of the microstructure and phase composition of the Zr bearing metallic debris in a bypass channel of a BWR fuel after the exothermic reaction in the CLADS-MADE-04 test

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。

論文

Ten years of Fukushima Dai-ichi post-accident research on the degradation phenomenology of the BWR core components

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:1 パーセンタイル:32.89(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.

論文

Raman investigation of the CLADS-MADE-02 test debris to confirm the mechanism of the volatile and non-volatile boron compounds formation

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$$_{4}$$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.

論文

A BWR control blade degradation observed in situ during a CLADS-MADE-02 test under Fukushima Dai-Ichi Unit 3 postulated conditions

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:2 パーセンタイル:47.54(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.

論文

Features of a BWR neutron absorber melt relocation in an oxidative environment during the CLADS-MADE-02 test

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.

論文

Comparison of the observed Fukushima Dai-ichi Unit 2 debris with simulated debris from the CLADS-MADE-01 control blade degradation test

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:9 パーセンタイル:82.73(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.

論文

On the degradation progression of a BWR control blade under high-temperature steam-starved conditions

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.

論文

New research programme of JAEA/CLADS to reduce the knowledge gaps revealed after an accident at Fukushima-1; Introduction of boiling water reactor mock-up assembly degradation test programme

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:10 パーセンタイル:66.42(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.

論文

Raman characterization of the simulated control blade debris to understand the boric compounds transformations during severe accidents

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 B$$_{4}$$C degradation during the beginning phase of a severe accident until approximately 1873 K is described. A sequence of material interactions of B$$_{4}$$C with stainless steel resulted in partial transformation of B$$_{4}$$C 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.

論文

Characterization of the Fukushima Dai-ichi Unit 2 sediments / debris based on the on-site video investigations in comparison to the debris obtained after integral CLADS-MADE-01 test

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.

論文

Features of a control blade degradation observed ${it in situ}$ during severe accidents in boiling water reactors

Pshenichnikov, 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:13 パーセンタイル:85.03(Nuclear Science & Technology)

In the present paper new results using ${it in situ}$ 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 B$$_{4}$$C granules prevented direct steam attack of residual B$$_{4}$$C. 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.

論文

Heterogeneity of BWR control blade degradation under steam-starved conditions

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 B$$_{4}$$C 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 B$$_{4}$$C inside being severely damaged by melting to survive at 1475$$^{circ}$$C and protect B$$_{4}$$C from direct contact with steam.

論文

The Behaviour of materials in case of solidified absorber melt - oxidized BWR channel box interaction revealed after CLADS-MADE-01 test

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.

論文

High temperature oxidation test of simulated BWR fuel bundle in steam-starved conditions

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$$_{2}$$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-H$$_{2}$$O/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。

口頭

Specifications of CLADS test facilities for fuel degradation simulation

Pshenichnikov, A.; 山崎 宰春; 永江 勇二; 倉田 正輝

no journal, , 

Japan Atomic Energy Agency (JAEA) has to establish the scientific basis for the decommissioning of the Boiled Water Reactors (BWR) at Fukushima Daiichi Nuclear Power Station and provide the information on the nuclear fuel behavior during the nuclear accidents. To address these problems JAEA has developed several test facilities which combine unique features for the R&D related to Severe Accident (SA) propagation behavior for BWRs. The technical data and main features of the facilities will be introduced to the International audience to give an understanding of JAEA research abilities and possible collaboration in the severe accidents research.

口頭

CLADS test facilities on BWR core material degradation

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/B$$_{4}$$C 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.

口頭

Focusing the test strategy of CLADS-MADE-01 and first results of the BWR control blade degradation test

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.

口頭

Consideration for modeling of Zry oxidation and hydrogen uptake in steam-starved conditions

山崎 宰春; Pshenichnikov, A.; Pham, V. H.; 永江 勇二; 倉田 正輝

no journal, , 

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$$_{2}$$O/sec/rodという1rodあたりの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して用いられている。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1rodあたりの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、4本の燃料棒をチャンネルボックスで囲んだ試験体を用いて水蒸気枯渇条件に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。

口頭

シビアアクシデント時の燃料破損・溶融過程解析手法の高度化,1-4; ジルカロイ酸化/水素化モデルの整備

山崎 宰春; Pshenichnikov, A.; 永江 勇二; 倉田 正輝; 坂本 寛*; 徳島 二之*; 青見 雅樹*

no journal, , 

本研究では、被覆管の水蒸気が枯渇した条件での被覆管の酸化、及び水素吸蔵現象をモデル化することを目的とし、異なる2つの水蒸気供給速度による酸化/水素吸蔵挙動の違いに係るデータを取得した。これまで被覆管1本での酸化/水素吸蔵挙動を把握し、モデル化を進めているが、BWRではチャンネルボックスの酸化をモデルに考慮する必要があると考えられる。そこで、被覆管4本の周囲にチャンネルボックスを配置した試験体を用いて、1300$$^{circ}$$Cで酸化/水素吸蔵挙動試験を実施した。水蒸気供給量が少ない場合、試験体チャンネルボックス内上部にて酸化膜が減少するとともに水素吸蔵量が増加し、被覆管1本での試験で認められた酸化/水素吸蔵挙動と同じ傾向が見られた。

口頭

Status and first results of the BWR control blade degradation test under steam-starved conditions

Pshenichnikov, A.; 山崎 宰春; 永江 勇二; 倉田 正輝

no journal, , 

The present study is focused on the issue of a control blade degradation, which is the first step during BWR severe accidents. In particular problem of heterogeneous core degradation, boron behaviour, control blade liquefaction and melt relocation were analysed. Melt relocation features: onset, progress, candling, blockage formation and its subsequent melting was directly observed in situ using video cameras. Carefully tailored experimental conditions of the CLADS-MADE-01 test, which include preliminary oxidation, transient heating and long steam starvation phase, enabled successful reproducing of an accident scenario close to one that assumed to happen at Fukushima-1 Unit 2.

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