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柳田 栄造*; 近藤 健太*; 坂東 洋太*; 出来 真斗*; 牧野 高紘; 大島 武; 小野田 忍; 直井 美貴*; 富田 卓朗*
no journal, ,
これまでに、閾値エネルギー密度を超えるフェムト秒レーザーをSiC基板へ照射すると、室温において比抵抗が急激に低下することを明らかにしている。また、その比抵抗の温度依存性は不純物の活性化エネルギーED1, ED2の二成分で表すことができるモデルを示している。今回、不純物活性化エネルギーの照射レーザーエネルギー密度依存性を求めた。その結果、照射フルエンス5.8J/cm以下では、50meV程度のED1および150200meVのED2が得られた。一方、照射フルエンス8.7J/cm以上ではED2が消失し、新たに数meVのED2'が得られた。ED2'に起因する電気伝導度も照射フルエンスの増加に伴い増加する傾向を示しており、ED2'といった新たな不純物の増加がフェムト秒レーザー照射領域におけるキャリアを大きく増加させ、急激な比抵抗の低下に寄与していると結論できた。
坂東 大都*; 佐々木 凌太郎*; 福田 貴斉*; 山路 哲史*; 山下 拓哉
no journal, ,
As one of the three tasks of "Project of Decommissioning, Contaminated Water and Treated Water Management (Development of Analysis and Estimation Technologies for Characterization of Fuel Debris) (Development of Estimation Technologies of RPV Damaged Condition, etc.)", this study presents evaluation of the fuel debris behavior below the damaged RPV lower head boundary of Fukushima Daiichi Nuclear Power Station (1F) Unit-2. The focus of the study is to evaluate the debris behavior at the time of / after the failure of the RPV boundary. It is expected to provide more comprehensive understanding of the precedingly obtained muon image, which seemed to indicate that a large amount of highly-dense materials distributed between the RPV lower head and the thermal insulation structures just below the RPV. The Moving Particle Semi-implicit (MPS) method is being developed to evaluate the fuel debris behavior in/under the actual plant geometry and conditions. The melt behavior analysis code, based on the MPS method, is being developed to analyze the following two debris behaviors. Firstly, the debris discharge behavior from penetration tube structures is analyzed. The solidified debris blocks are represented by rigid bodies, using the Passively Moving Solid (PMS) model with consideration of decay heat of the oxidic fuel debris. The relocations of the oxidic debris involving melting of the surrounding metallic debris and the penetration tube wall structure are analyzed. Secondly, the melt behavior on / through the multi-layered thermal insulation structures below the RPV is analyzed. The discharged melt from the RPV boundary may freeze on the insulation plate, depending on the thermal condition in the pedestal and the discharged melt history.