Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Shi, W.*; 町田 昌彦; 山田 進; 吉田 亨*; 長谷川 幸弘*; 岡本 孝司*
Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 8 Pages, 2023/02
Clarifying hot spots of radioactive sources inside reactor building rooms based on monitoring air dose rates is one of the most essential steps in decommissioning of nuclear power plants. However, the attempt is regarded as a rather difficult task, because information obtained by air dose rate measurements is generally not enough to inversely estimate contaminated distribution among a tremendous number of potential distributions inside complex reactor building rooms as far as one uses the conventional ways. Then, in order to successfully perform the inverse estimations on source distributions even in such ill-posed circumstances, we suggest that a machine learning method, least absolute shrinkage and selection operator (LASSO) is a promising scheme. Subsequently, we construct a simple room model and employ Monte Carlo simulation code, Particle and Heavy Ion Transport Systems (PHITS) to numerically test feasibility of LASSO inverse estimation scheme. Consequently, we confirm high reconstruction performance of the LASSO scheme in successfully predicting radioactive source distributions. In addition, we carry out uncertainty analysis for the inverse estimation and derive an error function describing uncertainty of the inverse estimation as a useful error estimator. Finally, we find that additional use of spectral information in the measurements can significantly decrease the number of measurement points for the present inverse estimation. In conclusion, LASSO scheme is a quite useful way to explore radioactive hot spots toward the future decommissioning of nuclear power plants.
大平 早希; 飯田 芳久
Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 10 Pages, 2023/02
ニオブ-94(Nb-94)の鉱物への収着分配係数(
d)は、放射性廃棄物処分の安全評価において重要なパラメータの一つである。先行研究で、アルカリ条件下におけるNbのdは、Caの存在下で、Naの存在下よりも2桁高い値が報告されていた。本研究では、粘土鉱物へのNb収着に対するCaの影響を再検討するためにNb収着実験を行い、沈殿生成の有無を確認するためにブランクテストを行った。その結果、モンモリロナイトとイライトへのNb収着は、Ca濃度には依存せず、Ca存在下で得られたd値はCa非存在下での値と同じであることが分かった。鉱物表面での錯形成による収着を仮定した収着モデルを構築し、地球化学計算コードを用いて計算を行った。その結果、表面種X_ONb(OH)
とX_ONb(OH)
を用いたモデルにより、得られたデータの傾向を再現可能なことを確認した。
町田 昌彦; Shi, W.*; 山田 進; 宮村 浩子; 吉田 亨*; 長谷川 幸弘*; 岡本 孝司; 青木 勇斗; 伊藤 倫太郎; 山口 隆司; et al.
Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 11 Pages, 2023/02
In order to find radioactive hot spots inside reactor building rooms from structural data together with air dose rate measurement data, Least Absolute Shrinkage and Selection Operator (LASSO) has been recently suggested as a promising scheme. The scheme has been examined in simplified room models and its high estimation feasibility has been confirmed by employing Particle and Heavy Ion Transport code System (PHITS) as a radiation simulation code. In this paper, we apply the scheme to complex room models inside real reactor buildings. The target rooms are pool canal circulation system room and main circulation system room in Japan Materials Testing Reactor (JMTR) at Oarai area, Japan Atomic Energy Agency (JAEA). In these real rooms, we create STL format structural data based on Computer Aided Design (CAD) models made directly from their point group data measured by laser scanning devices, and we notice that the total number of their surface meshes in these real rooms reaches to the order of 1 million. Then, this order of the mesh number clearly indicates that one needs a simplified radiation simulation code considering only direct transmission of gamma ray as a radiation calculation instead of PHITS demanding high computational costs. By developing such a simplified code and customizing it to perform LASSO scheme, we consequently confirm that LASSO scheme driven by the simplified simulation can also successfully predict unknown radioactive hot spots on real structural models.
山田 一夫*; 東條 安匡*; 粟飯原 はるか; 富田 さゆり*; 洞 秀幸*; 渋谷 和俊*; 駒 義和; 五十嵐 豪*; 細川 佳史*; 丸山 一平*
Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 12 Pages, 2023/02
Experiments were conducted on mortar made from aggregates used in the Fukushima Daiichi NPP, which were dry carbonated and further cracks were introduced to reproduce the contamination history of the lower part of the turbine pit. The concrete was exposed to contaminated water after being in contact with seawater for one day due to the post-earthquake tsunami; Cs and Sr interacted differently with the constituent materials of the concrete and competitively adsorbed with ions in the seawater. The effects of various factors were quantitatively evaluated by experiment. Dry carbonation conditions enhanced infiltration but had a limited effect on cracking.
島田 太郎; 行川 正和*; 三輪 一爾; 武田 聖司
Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 8 Pages, 2023/02
廃止措置段階に発生する可能性のある事故においては、解体作業中にフィルタ等へ蓄積した粉じんが一挙に環境に放出され地表に沈着した放射性粉じんが降雨に伴う地表流とともに傾斜の下流へ移動し、窪地に蓄積することも想定される。降雨や地形、表面の被覆状態などの条件によって変動する核種の移動量と公衆の被ばく線量を評価するコードの開発を進めている。その評価にあたっては必要な評価パラメータの設定方法を整備する必要がある。そこで、地表面に沈着した粉じんの傾斜面上の流下を模擬した室内降雨試験を実施して、核種移動量評価に必要なパラメータ値を廃止措置段階で想定される劣化状態を含めて取得し、その設定方法を検討した。被覆表面と表面を流れる水との抵抗量を示す等価粗度係数が既知の平滑なアスファルトをもとに得られた劣化アスファルトと平滑なコンクリートの等価粗度係数は文献で得られた値の範囲に収まった。しかし劣化コンクリートの等価粗度係数は、想定と異なり平滑なアスファルトよりもやや低い値となった。これは本試験では地表流による浮遊と雨滴衝撃による浮遊を同時に評価しているため、雨滴衝撃による浮遊のばらつきの影響によるものと考えられる。また、3Dスキャナで各表面の凹凸を点群として取得し表面粗さを評価したところ、等価粗度係数との相関が示唆され、実際の適用の際に利用できる可能性が示された。
鈴木 政浩; 町田 昌彦; 伊藤 倫太郎; 川端 邦明; 山口 隆司; 岡本 孝司
no journal, ,
福島第一原子力発電所の廃炉措置において、1号機から3号機の現場では高線量エリアが多々あることから、安全に効率的な作業を進めるには、まずは現場の空間線量率低減が必須である。原子力機構では、今回その解決策として、LASSO法を用いた逆解析手法を原子力現場に適用したプロトタイプシステムを開発している。限定された空間線量率の計測点から線源の特定を可能とし、特定された線源分布から空間線量率の算出・推定ができるものである。また、その線源対策として遮へい、除染を行った際、線量率変化を可視化で理解できるように最新のVR等の可視化媒体により作業現場の状況が分かるようなシステム開発を進めている。本報告では、本プロジェクトの全体概要と主要な成果を紹介する。
青木 勇斗; 伊藤 倫太郎; 北村 哲浩; 町田 昌彦; 鈴木 政浩; 大森 崇純; 谷口 達郎; 井手 広史
no journal, ,
Prior to the full-scale implementation of fuel debris removal operations in decommissioning of Fukushima Daiichi Nuclear Power Plants (1F), it is crucial to improve the on-site environment in order to safely and efficiently construct access routes inside reactor buildings. Among various improvement operations, it is one of the most essential activities to identify distributions of scattered radioactive sources based on the on-site structural data and air dose rate measurement data. In order to meet the demands, we now develop a prototype system enabling to inversely predict radioactive source distributions from air dose rate measurement data and structural data. In order to evaluate this system, a blind test was conducted in a real reactor building, JMTR in JAEA Oarai area. The test results reveal that if we cooperatively use two structural datasets, i.e., detailed and simplified structural datasets, then we can successfully reproduce radioactive source distributions and air dose rate fields inside the target room. These results suggest that the prototype system is promising in the future decommissioning in 1F.
鈴木 政浩; 青木 勇斗; 町田 昌彦; 伊藤 倫太郎; 川端 邦明; 山口 隆司; 岡本 孝司
no journal, ,
In this paper, we overview the R&D project and present key results obtained since last fiscal year. Particularly, we show that the core scheme of the protype system, i.e., LASSO scheme to inversely estimate hot spots actually works in Pool-canal circular operation (PCO) room of JMTR selected as a test field prior to applying it to 1F. In addition to the scheme verification, the present status of measurement technique developments is also presented. Their all results suggest that the project is successful, and furthermore, it is expected that this system is applicable to the future operations to improve the radiation environments inside 1F buildings.