13：30
15：30

芦澤 宏明
<材料系>

Pornphatdet
audom
Thanataon
<材料系>

Aluminum nitride (AlN) ceramics have excellent properties such as high thermal conductivity, low thermal expansion, and low dielectric constant. They have been expected to be a promising material for corrosion and magneto-hydrodynamic (MHD) barrier in future fusion reactors. However, studies on neutron irradiation effects of AlN ceramics have been very few. In this study, commercially available AlN ceramics (random orientation) and highly oriented AlN ceramics fabricated under the strong magnetic field were neutron-irradiated, and their defects formation were evaluated from the viewpoint of neutron fluence and irradiation temperature. Furthemore their recovery behaviors by thermal annealing were also discussed to provide useful experimental data and to obtain systematic and valuable results for fusion applications.
The effect of neutron irradiation on lattice swelling was found to depend on neutron fluence and irradiation temperature differently, which lead to different recovery behavior. The defects development from point defects to large-scale dislocations with increasing neutron fluence from lower than 2 x 10²⁴ n/m² (E > 0.1 MeV) to higher fluence was pointed out. The lattice expansion switched from isotropic, where a and b crystal axis expanded in a similar percentage with c-axis, to anisotropic, where c-axis was significantly larger expanded. On the other hand, the higher irradiation temperature caused defects recovery and combination related to the shrinkage of the structure. The recovery behavior in length change was found to be different for specimens irradiated under lower and higher fluence. The AlN specimens with oriented crystal structure showed the apparent expansion along the c-axis, which was dominantly recovered after annealing.
The different types of defects also affected the hardness of the specimens. All specimens were hardened after irradiation, where the specimen without dislocation loops had a higher hardness. In contrast, the existence of dislocations caused reduction in hardness and the weakness of the surface that the indentation quickly generated cracks during the test. Furthermore change of color and transparency of the specimens after irradiation and under annealing were observed.

柴　茂樹
<融合理工学系>

最尤推定−期待値最大化法及びベイズの公式から導かれる最大事後確率推定法を用いた核燃料物質のパッシブγ線断層撮影技術を開発した。モックアップ燃料集合体の実測データ等を用いてパッシブγ線源分布の再構成をおこない高速かつ高精度の同技術の有効性を検証し妥当性を確認した。次に、本技術を原子力発電所事故で発生した燃料デブリが保管されている収納缶の断層撮影に適用した結果、可視化の難しい収納缶中央部においても燃料デブリ分布が得られることを明らかにした。さらに、本技術を用いた保障措置における検認技術を提案し、欠損燃料棒を含むBWR使用済燃料集合体内のパッシブγ線源分布の再構成画像から、画像解析により欠損燃料棒を識別できることを明らかにした。

舩山 成彦

再生可能エネルギー(再エネ)と原子力が連携した低炭素電力システムにおいて、再エネ由来の変動電力の負荷平準化が必要である。酸化カルシウム(CaO)は高い蓄熱密度を有し、安価であり、この負荷平準化に寄与する熱化学エネルギー貯蔵材料として期待される。本研究では負荷平準化に応用できる高性能なCaO化学蓄熱材料の開発を目的とした。単体CaO材料は熱伝導率が低く、熱化学反応中に体積変化及び凝集塊形成が発生し、蓄熱・熱出力応答の高速化と繰り返し耐久性向上が克服すべき課題であった。本研究ではこれらの課題を解決するために化学的に安定で高い熱伝導率を持つ高強度多孔性炭化ケイ素担体を導入した新規複合CaO材料に着目し、実験室規模の充填層反応器を用いて複合材料の蓄熱性能を実験的に検討した。炭化ケイ素フォーム及びハニカムを用いた複合CaO材料では単体CaO材料と比べ熱出力速度が向上し、さらに材料の体積変化及び凝集塊形成が抑制され、本材料の課題の克服が達成された。また充填層反応器の数値解析から、熱出力速度を最大化する多孔性担体の最適気孔率が示された。本研究より原子力を含む低炭素電力システムにおいて、本化学蓄熱材料は負荷平準化に貢献できることが明らかにされた。

Batsaikhan
Munkhbat
<機械系>

On March 11^th, 2011, a strong earthquake and huge tsunami occurred in Japan. The natural catastrophe caused major damage to the Fukushima Daiichi Nuclear Power Plant (1F), which led to core meltdown in unit 1-3 reactors. Retrieval of the fuel debris remaining under turbid water, high radiation and dark environment in the Reactor Pressure Vessel and Primary Containment Vessel is one of the most difficult task in decommissioning work of 1F. Submersion method is considering as possible method to retrieve fuel debris because water can be shield from radiation. However, due to strong earthquake and tsunami, there are leakage points in the reactor vessels. To use submersion method, it is necessary to stop these water leakages. Moreover, fuel debris information is crucial to decide further decommissioning steps and strategies. Therefore, in this thesis, array ultrasonic technique considered as a suitable technique that can obtain water leakage and fuel debris information inside the Primary Containment Vessel where camera inspection is limited. Two-dimensional flow measurement technique developed and validated based on conventional Ultrasonic Velocity Profiler (UVP) method. The performance of the developed technique was tested and validated. Moreover, to visualize object shape that representing fuel debris, array ultrasonic measurement technique developed. As conclusion, it is confirmed that the ultrasonic technique allow us to predict water leakage and visualize objects that representing fuel debris.

Kurniawan
Anggi Budi
<融合理工学系>

The transport of confined fast ions could experience magnetic resonance upon drifting inside the actual tokamaks where magnetic field ripple is existed. In this work, the transport phenomenon of confined banana ion is numerically investigated in the frame of ripple resonance condition upon having toroidal precession in a time period of banana motion. The resonance condition is carefully investigated in both collision-less orbit and neoclassical diffusion using two orbit-following schemes, guiding-center approximation (GC) and full-orbit equation (FO). Eventually, the analytical solution of difference between FO and GC was developed to analyze the finite Larmor radius effect behind the difference. The averaged diffusion coefficient on the same flux surface was also developed to physically approach the result in a more realistic manner.

Nguyen
Hoang Hai
<融合理工学系>

CANDLE burning concept was proposed to solve the disadvantages of current nuclear reactor designs. Sodium is one of the options for the coolant of CANDLE burning reactor because sodium provides good heat-removal performance and sodium coolant technology is established widely for fast reactor technology. However, CANDLE burning reactor with sodium coolant may have lower neutron economy due to softer neutron spectrum and higher neutron leakage. The purpose of this study was to show a design concept of sodium cooled small CANDLE burning reactor whose reactor size was comparable to other sodium fast reactors by Monte Carlo method with high accuracy. In the study, a Monte Carlo based procedure was developed for the CANDLE burning analysis with high accuracy. The results of analyses using the code system showed that a small sodium cooled CANDLE burning concept was feasible. Based on the result, the optimization was performed for the sodium cooled CANDLE burning reactor. The optimization goal was to minimize the reactor core size with keeping the reactor power. The optimization was performed by utilizing better heat-removal performance of sodium coolant and the better neutron economy of lead-based reflectors compared to sodium reflector. This study showed the design concept of small sodium cooled CANDLE burning reactor whose reactor size was comparable to other sodium fast reactors by numerical analysis with high accuracy.