Multi-aspect characterization of low-temperature tempering behaviors in high-carbon martensite

Zhang, Y.*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡; Harjo, S.; 宮本 吾郎*; 古原 忠*

ISIJ International, 64(2), p.245 - 256, 2024/01

https://doi.org/10.2355/isijinternational.ISIJINT-2023-251

As-quenched martensite in carbon steels needs to be tempered to restore its ductility and toughness for practical applications. During tempering of martensite, microstructural evolutions induced by a series of reactions relevant to carbon diffusion is known to occur. In this study, multi-aspect characterization using advanced techniques such as in-situ neutron diffraction, transmission electron microscopy and three-dimensional atom probe tomography, was performed to investigate the changes in tetragonality, physical properties, microstructure and solute carbon content in high-carbon martensite, with an aim to clarify its low-temperature tempering behaviors. A binary alloy with a chemical composition of Fe-0.78 mass%C was austenitized and quenched to prepare the as-quenched martensite, followed by tempering in continuous heating at different heating rates. It was found that various reactions occurred sequentially during tempering, starting from the structure modulation generated by carbon clustering in the 0th stage, then followed by the precipitation of metastable -carbide particles on linear features in the 1st stage, towards the later decomposition of retained austenite and precipitation of cementite in the 2nd and 3rd stages, respectively. After analyzing the experimental results, the solute carbon content in martensite tempered under various conditions was found to be in good agreement with that estimated from the lattice volume expansion, whereas the evaluation based on the tetragonality might lead to some underestimation of the solute carbon content in martensite tempered at high temperatures.

Thinning behavior of solid boron carbide immersed in molten stainless steel for core disruptive accident of sodium-cooled fast reactor

江村 優軌; 高井 俊秀; 菊地 晋; 神山 健司; 山野 秀将; 横山 博紀*; 坂本 寛*

Journal of Nuclear Science and Technology, 10 Pages, 2023/00

https://doi.org/10.1080/00223131.2023.2287109

Boron carbide (BC)- stainless steel (SS) eutectic reaction behavior is one of the most important issues in the core disruptive accidents (CDAs) of sodium-cooled fast reactors (SFRs). In this study, the immersion experiments using BC pellets with molten SS were conducted to evaluate the CDA sequences such as contact event of solid BC with degraded core materials including SS at very high temperature. The immersion experiment aims at understanding the kinetic behavior of solid BC-liquid SS reaction based on the reduced thickness of BC pellet after the experiment in the temperature ranges from 1763 to 1943 K, which is higher than the temperature of solid BC-solid SS reaction. Based on the kinetic consideration of the reaction rate constants for solid BC-liquid SS reaction, it was found that similar temperature dependency was identified between solid BC-liquid SS and solid BC-solid SS. Besides, the reaction rate constants of solid BC-liquid SS were smaller than those of solid BC-solid SS extrapolated in higher temperature region by two or more orders of magnitude due to two different evaluation method for BC side/SS side. It was confirmed that this difference was reasonable through the consideration of previous reaction tests in solid-solid contact for BC side/SS side.

Advanced concepts in TRISO fuel

湊 和生; 小川 徹

Comprehensive Nuclear Materials, 2nd Edition, Vol.5, p.334 - 360, 2020/08

https://doi.org/10.1016/B978-0-12-803581-8.11688-1

高温ガス炉燃料として、微小燃料核を熱分解炭素及び炭化ケイ素で四重に被覆したTRISO被覆粒子燃料が開発されてきた。ここでは、TRISO被覆粒子燃料の高温での性能向上、核分裂生成物による被覆層腐食の抑制及び核分裂生成物の保持能力の向上、並びに高速中性子体系で使用できる燃料など、種々の先進的な被覆粒子燃料について、燃料概念,製造,検査方法,照射挙動等の結果を体系的にとりまとめた。2012年に刊行されたComprehensive Nuclear Materialsに掲載された同名論文の内容に、その後の研究開発の進展を加筆したものである。

Study on plutonium burner high temperature gas-cooled reactor in Japan; Introduction scenario, reactor safety and fabrication tests of the 3S-TRISO fuel

植田 祥平; 水田 直紀; 深谷 裕司; 後藤 実; 橘 幸男; 本田 真樹*; 齋木 洋平*; 高橋 昌史*; 大平 幸一*; 中野 正明*; et al.

Nuclear Engineering and Design, 357, p.110419_1 - 110419_10, 2020/02

https://doi.org/10.1016/j.nucengdes.2019.110419

固有の安全性に優れ高効率なプルトニウムの利用が可能なプルトニウム燃焼高温ガス炉が提案されている。プルトニウム燃焼高温ガス炉に用いるセキュリティ強化型安全(3S-TRISO)燃料においては、イットリア安定化ジルコニア(YSZ)を不活性母材とするPuO-YSZ燃料核へ、遊離酸素ゲッターの特性を有する炭化ジルコニウム(ZrC)を直接被覆する。本論文では、プルトニウム燃焼高温ガス炉の成立性および3S-TRISO燃料の研究開発について報告する。

Study on eutectic melting behavior of control rod materials in core disruptive accidents of sodium-cooled fast reactor, 2; Effect of BC addition on thermophysical properties of austenitic stainless steel in a solid state

高井 俊秀; 古川 智弘; 山野 秀将

Proceedings of International Nuclear Fuel Cycle Conference / Light Water Reactor Fuel Performance Conference (Global/Top Fuel 2019) (USB Flash Drive), p.847 - 852, 2019/09

In a core disruptive accident scenario, boron carbide (BC) in control-rod will be predicted to react with stainless steel (SS) as structural material. Produced eutectic material of SS-BC is assumed to relocate widely in the core. To add a function of evaluating this liquefaction and relocation behavior to CDA analysis codes, it is indispensable to maintain the thermophysical properties database of SS-BC. In this report, density and specific heat of SS-7mass%BC in a solid state were obtained, and compared them with those of SS-5mass%BC obtained so far and literature value of SS. It is found that the density decreased while the specific heat increased, as BC concentration in the austenitic stainless steel increased. By addition of 7mass%-BC to 316L SS, the density was decreased by approximately 7% at 294K. On the other hand, specific heat was increased by approximately 21% at 294K.

Development of security and safety fuel for Pu-burner HTGR; Test and characterization for ZrC coating

植田 祥平; 相原 純; 後藤 実; 橘 幸男; 岡本 孝司*

Mechanical Engineering Journal (Internet), 5(5), p.18-00084_1 - 18-00084_9, 2018/10

https://doi.org/10.1299/mej.18-00084

プルトニウム燃焼高温ガス炉に用いるセキュリティ強化型安全(3S-TRISO)燃料においては、イットリア安定化ジルコニア(YSZ)を不活性母材とするPuO-YSZ燃料核へ、遊離酸素ゲッターの特性を有する炭化ジルコニウム(ZrC)を直接被覆する。2015年度より開始した模擬のYSZ粒子への臭化物化学蒸着法に基づくZrC被覆試験の結果、粒子装荷量100gの条件において被覆層厚さ約18から21mのZrC層の被覆に成功した。また、走査型電子顕微鏡(STEM)を通じて、臭化物法の原料ガスによるYSZ表面の劣化は観察されなかった。

Thermophysical properties of stainless steel containing 5mass%-BC in the solid phase

高井 俊秀; 古川 智弘; 山野 秀将

Proceedings of 2018 International Congress on Advances in Nuclear Power Plants (ICAPP 2018) (CD-ROM), p.1007 - 1013, 2018/04

This study describes estimation results of thermophysical properties of stainless steel containing 5mass% boron carbide (5mass%BC-SS) in the solid state. 5mass%BC-SS eutectic sample was synthesized using a hot press method. Homogeneity of the sample was evaluated by chemical composition analysis, metal structure observation, and micro X-ray diffraction (XRD). Specific gravity and specific heat were evaluated up to 1000C. These measurements proved that the specific gravity in our sample was lowered and the temperature dependence of the specific gravity, along with the elevation of temperature, became gradual compared to that of grade type 316L stainless steel (SUS316L) used as a reactor material by addition of BC. The specific heat became slightly higher than that of SUS316L by addition of BC and showed similar temperature dependence up to 800C.

Examination of I and Cs releases during late phase of Fukushima Daiichi NPP accident by using I/Cs ratio of source terms evaluated reversely by WSPEEDI code with environmental monitoring data

日高 昭秀; 横山 裕也

Journal of Nuclear Science and Technology, 54(8), p.819 - 829, 2017/08

AA2016-0500.pdf:0.44MB

https://doi.org/10.1080/00223131.2017.1323691

福島第一原子力発電所事故の評価では、炉内事象と環境モニタリング測定との結びつきの議論が重要であるが、事故から6年近く経過した現在でも、両者の事象を統合的に扱った研究は必ずしも進んでいない。WSPEEDIコードと環境モニタリングデータから逆算で詳細化されたI/Cs比に基づき、福島事故後期における原子炉建家等の地下汚染水からの気液分配に基づくI放出量を再評価するとともに、これまで検討が行われなかったCs放出挙動に関して化学形や放出機構等について検討した。原子炉建屋等の地下汚染水からのI放出量に関する再評価では、全ソースタームに対する地下汚染水からのI放出の寄与分は約10%となった。また、3/213/23及び3/303/31のI放出量に対するCs放出量の超過は、炉心冷却水がわずかに不足したことに伴う炉心温度の再上昇により、制御材を起源として生成するCsBOの放出でほぼ説明できる見通しを得た。

Development of security and safety fuel for Pu-burner HTGR, 5; Test and characterization for ZrC coating

植田 祥平; 相原 純; 後藤 実; 橘 幸男; 岡本 孝司*

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 4 Pages, 2017/07

プルトニウム燃焼高温ガス炉に用いるセキュリティ強化型安全(3S-TRISO)燃料においては、イットリア安定化ジルコニア(YSZ)を不活性母材とするPuO-YSZ燃料核へ、遊離酸素ゲッターの特性を有する炭化ジルコニウム(ZrC)を直接被覆する。2015年度より開始した模擬のYSZ粒子への臭化物化学蒸着法に基づくZrC被覆試験の結果、粒子装荷量100gの条件において被覆層厚さ約18から21mのZrC層の被覆に成功した。また、走査型電子顕微鏡(STEM)を通じて、臭化物法の原料ガスによるYSZ表面の劣化は観察されなかった。

Thermal stability of deep-level defects in high-purity semi-insulating 4H-SiC substrate studied by admittance spectroscopy

岩本 直也*; Azarov, A.*; 大島 武; Moe, A. M. M.*; Svensson, B. G.*

Materials Science Forum, 858, p.357 - 360, 2016/05

https://doi.org/10.4028/www.scientific.net/MSF.858.357

Thermal stability of deep level defects in high purity semi-insulating (HPSI) 4H-Silicon Carbide (SiC) substrates was studied. The samples were annealed from 700 to 1700 C, and Schottky barrier diodes (SBDs) were fabricated on the samples. The SBDs were characterized by current-voltage, capacitance-voltage and admittance spectroscopy measurements. The forward current of SBDs increased substantially with the increase of annealing temperature, while the reverse leakage current remained below 10 A. The capacitance of the samples annealed at 1400 and 1500 C was essentially zero at bias voltages between 0 and 10 V, but after 1600 and 1700 C annealing, the capacitance increased and started to respond to the bias voltage. The net hole concentrations in the 1600 and 1700 C annealed substrates were estimated to be 0.5110 and 1410 /cm, respectively. From admittance spectroscopy, five defect levels were detected. Defect peaks relating to boron acceptors increased although defect peaks with deep levels decreased with increasing annealing temperature. Therefore, it can be concluded that deep levels which act as compensation centers for boron acceptors dissociate by high temperature annealing, and as a results, hole concentration increases.