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論文

Analysis of transport behaviors of cesium and iodine in VERDON-2 experiment for chemical model validation

塩津 弘之; 伊藤 裕人*; 石川 淳; 杉山 智之; 丸山 結

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 6 Pages, 2018/11

The VERDON-2 experiment for FPs transport in steam environment was analyzed with the mechanistic FPs transport code incorporating thermodynamic chemical equilibrium model in order to assess its predictive capability for transport behavior of key FPs, especially for highly volatile FPs such as Cs and I. The present analysis reproduced well the Cs deposition profile obtained from the experiment, which revealed that Cs was transported as CsOH in early phase of FP release from fuel, and then formed Cs$$_{2}$$MoO$$_{4}$$ after increasing Mo release. On the other hand, the deposition peak of I was predicted to appear at 720 K, which was significantly higher than the experimental result at 600 K. This discrepancy was potentially caused by the following two points: lack of the other stable species in thermodynamics database for thermodynamic chemical equilibrium model, or failure of chemical equilibrium assumption for iodide species.

報告書

CHEMKEq; 化学平衡論及び反応速度論の部分混合モデルに基づく化学組成評価コード(受託研究)

伊藤 裕人*; 塩津 弘之; 田中 洋一*; 西原 慧径*; 杉山 智之; 丸山 結

JAEA-Data/Code 2018-012, 42 Pages, 2018/10

JAEA-Data-Code-2018-012.pdf:4.93MB

原子力施設事故時において施設内を移行する核分裂生成物(FP)の化学組成は、比較的遅い反応の影響を受けることにより化学平衡を仮定して評価した組成とは異なる場合が想定される。そのため、反応速度を考慮した化学組成評価が求められる。一方で、原子力施設事故時の複雑な反応に関する反応速度の知見は現状では限られており、実機解析に適用できるデータベースの構築に至っていない。そこで、FP化学組成評価における反応速度による不確かさの低減のため、化学平衡論及び反応速度論の部分混合モデルに基づく化学組成評価コードCHEMKEqを開発した。このモデルは、系全体の質量保存則の下、前駆平衡と見なせる化学種を化学平衡論モデルにより評価し、その後の比較的遅い反応を反応速度論モデルにより解くものである。さらにCHEMKEqは、本混合モデルに加え一般的な化学平衡論モデル及び反応速度論モデルが使用可能であり、かつ、それらモデル計算に必要なデータベースを外部ファイル形式とすることで汎用性の高い化学組成評価コードとなっている。本報は、CHEMKEqコードの使用手引書であり、モデル, 解法, コードの構成とその計算例を記す。また付録には、CHEMKEqコードを使用する上で必要な情報をまとめる。

論文

Evaluation of chemical speciation of iodine and cesium considering fission product chemistry in reactor coolant system

石川 淳; Zheng, X.; 塩津 弘之; 杉山 智之; 丸山 結

Proceedings of Asian Symposium on Risk Assessment and Management 2018 (ASRAM 2018) (USB Flash Drive), 6 Pages, 2018/10

Japan Atomic Energy Agency is pursuing the development and application of the methodologies on fission product (FP) chemistry for source term analysis by using integrated severe accident analysis code THALES2/KICHE. Generally, specific chemical forms of iodine and cesium such as cesium iodide (CsI) and cesium hydroxide (CsOH) were assumed in the source term analysis for light water reactors using an integrated severe accident analysis code. The accident at the Fukushima Dai-ichi Nuclear Power Station leads possible chemical effects of B$$_{4}$$C control materials and atmosphere on chemical speciation of iodine and cesium such as cesium metaborate (CsBO$$_{2}$$) and hydrogen iodide (HI). The difference of chemical speciation affects not only the FP behavior in the reactor coolant system (RCS) and transport to containment but also pH value of the suppression pool water in the containment. The pH value is one of the influential factors on the release of gaseous iodine (I$$_{2}$$ and organic iodine) from containment liquid phase. In the present study, the improvement of the THALES2/KICHE code in terms of FP chemistry in RCS was performed and applied to source term analysis for severe accidents at a boil water reactor with Mark-I containment vessel. This paper discusses the chemical speciation of iodine and cesium, and FP behavior and transport to containment.

論文

Influence of chemical speciation in reactor cooling system on pH of suppression pool during BWR severe accident

塩津 弘之; 石川 淳; 杉山 智之; 丸山 結

Journal of Nuclear Science and Technology, 55(4), p.363 - 373, 2018/04

 被引用回数:1 パーセンタイル:74.25(Nuclear Science & Technology)

The influences of chemical speciation for Cs-I-Te-Mo-Sn-B-C-O-H system, simulating a state in the reactor cooling system (RCS) of BWR, on pH of the suppression chamber (S/C) water pool were analytically investigated with PHREEQC code. Major conditions were chosen on the basis of the outputs from a BWR severe accident analysis by THALES2 code and chemical thermodynamic analysis with VICTORIA2.0 code. The chemical thermodynamic analysis showed that the chemical speciation of important volatile FPs, Cs and I, was strongly influenced by Mo and B$$_{4}$$C control material. As a consequence, pH of the S/C water pool was predicted to range from approximately 6 to 10, depending on the fraction of volatile FPs transported from the RCS to the S/C water pool and the H$$_{2}$$/H$$_{2}$$O ratio associated with the oxygen potential. It was implied that the formation of volatile I species such as I$$_{2}$$ in the S/C water pool was larger by 3 orders at the lowest pH than that at the highest pH.

論文

Application of Bayesian approaches to nuclear reactor severe accident analysis

Zheng, X.; 玉置 等史; 塩津 弘之; 杉山 智之; 丸山 結

Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 11 Pages, 2017/11

Nuclear reactor severe accident simulation involves uncertainties, which may result from incompleteness of modeling of accident scenarios, selection of alternative models and unrealistic setting of parameters during the numerical simulation, etc. Both deterministic and probabilistic methods are required to reach reasonable estimation of risk for severe accidents. Computational codes are widely used for the deterministic accident simulations. Bayesian approaches, including both parametric and nonparametric, are applied to the simulation-based severe accident researches at Japan Atomic Energy Agency (JAEA). In the paper, an overview of these research activities is introduced: (1) Dirichlet process models, a nonparametric Bayesian approach, are applied to source term uncertainty and sensitivity analyses; (2) Gaussian process models are applied to the optimization for operations of severe accident countermeasures; (3) Nonparametric models, include models based on Dirichlet process and K-nearest neighbors algorithm, are built to predict the chemical forms of fission products. Simplified models are integrated into the integral severe accident code, THALES2/KICHE; (4) We have also launched the research of dynamic probabilistic risk assessment (DPRA), and because a great number of accident scenarios will be generated during DPRA, Bayesian approaches would be useful for the boosting of computational efficiency.

論文

Source term analysis considering B$$_{4}$$C/steel interaction and oxidation during severe accidents

石川 淳; 塩津 弘之; 杉山 智之; 丸山 結

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 7 Pages, 2017/07

The Japan Atomic Energy Agency (JAEA) is pursuing the development and application of the methodologies on fission product (FP) chemistry for source term analysis by using the integrated severe accident analysis code THALES2. In the present study, models for the eutectic interaction of boron carbide (B$$_{4}$$C) with steel and the B$$_{4}$$C oxidation were incorporated into THALES2 code and applied to the source term analyses for a boiling water reactor (BWR) with Mark-I containment vessel (CV). Two severe accident sequences with drywell (D/W) failure by overpressure initiated by loss of core coolant injection (TQUV sequence) and long-term station blackout (TB sequence) were selected as representative sequences. The analyses indicated that a much larger amount of species from the B$$_{4}$$C oxidation was produced in TB sequence than TQUV sequence. More than a half of carbon dioxide (CO$$_{2}$$) produced by the B$$_{4}$$C oxidation was predicted to dissolve into the water pool of the suppression chamber (S/C), which could largely influence pH of the water pool and consequent formation and release of volatile iodine species.

論文

Thermochemical analysis for cesium and iodine species and their impact on aqueous pH under severe accident conditions

塩津 弘之; 石川 淳; 丸山 結

Proceedings of 2015 International Workshop on Post-Fukushima Challenges on Severe Accident Mitigation and Research Collaboration (SAMRC 2015) (USB Flash Drive), 8 Pages, 2015/11

The effect of chemical species on solution pH in S/C pool was investigated on the basis of parametric analysis with the integral severe accident code, THALES2, after performing the thermochemical analysis for Cs-I-Mo-B-C-O-H systems under severe accident conditions of BWR. In the results of thermochemical calculation without B$$_{4}$$C oxidation, Cs mainly took a chemical species of Cs$$_{2}$$MoO$$_{4}$$(c, g) at oxidation condition and partially form CsOH(g) and Cs(g) above $$sim$$1500 K at the reducing condition owing to Mo reduction. In addition, B$$_{4}$$C oxidation resulted in formation of major Cs species of CsBO$$_{2}$$(g) above 1800 K at a wide range of H$$_{2}$$/H$$_{2}$$O ratio. However, Cs$$_{2}$$MoO$$_{4}$$(c) could be preferentially formed under a H$$_{2}$$O rich oxidizing condition with low concentration of B$$_{4}$$C below 1800 K. In case of I, although CsI was dominate species in various conditions, HI fraction was increased with increase of B$$_{4}$$C amount above 1500 K. Based on THALES2 analysis, 80$$sim$$90% of Cs was retain in S/C pool by large scrubbing effect, resulting in the change of apparent pH at each Cs and I species in range of 4.8$$sim$$8.0. Especially, the case with higher fraction of Cs$$_{2}$$MoO$$_{4}$$ and HI shows the lower pH, indicating importance of their fraction because of larger formation of volatile I species such as I$$_{2}$$ and CH$$_{3}$$I by the chemical reaction at lower pH.

論文

Radioactive Cs in the severely contaminated soils near the Fukushima Daiichi Nuclear Power Plant

金子 誠*; 岩田 孟; 塩津 弘之; 正木 翔太*; 川元 侑治*; 山崎 信哉*; 仲松 有紀*; 井元 純平*; 古木 元気*; 落合 朝須美*; et al.

Frontiers in Energy Research (Internet), 3, p.37_1 - 37_10, 2015/09

高線量土壌中の放射性Csは雲母鉱物などの層状ケイ酸塩鉱物に取り込まれていることを現地調査及び模擬実験により明らかにした。

論文

Effect of minerals on accumulation of Cs by fungus ${{it Saccaromyces cerevisiae}}$

大貫 敏彦; 坂本 文徳; 山崎 信哉*; 香西 直文; 塩津 弘之; 宇都宮 聡*; 渡辺 直子*; 小崎 完*

Journal of Environmental Radioactivity, 144, p.127 - 133, 2015/06

 被引用回数:7 パーセンタイル:65.56(Environmental Sciences)

酵母へのCsの吸着に関して、培地中に存在する鉱物の影響を調べた。その結果、鉱物の存在は酵母へのCsの濃集を阻害した。鉱物へのCsの分配係数を調べた、分配係数が大きな鉱物の存在により、酵母へ濃集したCs濃度は少なかった。この結果から、酵母は、鉱物と競合してCsを濃集している。

論文

Parametric study for impact of in-vessel chemical forms of cesium and iodine on source term and pH of aqueous phase

塩津 弘之; 石川 淳; 丸山 結

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

In order to evaluate the effect of chemical forms of Cs and I on source terms and solution pH in a severe accident of a BWR, parametric analysis was performed with an integral severe accident code, THALES2, developed by JAEA. In the present analysis, THALES2 code was modified to take into account CsOH, Cs$$_{2}$$MoO$$_{4}$$ and CsBO$$_{2}$$ as Cs chemical forms, and CsI and HI as I chemical forms. The severe accident sequence examined was similar to that occurred at unit 3 of the Fukushima Dai-ichi NPP. Due to the effective scrubbing, approximately 90% of the initial core inventory of Cs and I was predicted to be retained in the water pool of the suppression chamber, resulting in limited influence of Cs chemical form on Cs source term. On the other hand, the present analysis indicated that solution pH of the water pool was strongly affected by chemical forms of Cs and I. This outcome implies that chemical forms of Cs and I influence I source term since the formation of volatile I species such as I2 and organic iodine in the water pool depends strongly on solution pH.

論文

Effects of CeO$$_{2}$$ nanoparticles on microbial metabolism

正木 翔太*; 塩津 弘之; 大貫 敏彦; 坂本 文徳; 宇都宮 聡*

Chemical Geology, 391, p.33 - 41, 2015/01

 被引用回数:4 パーセンタイル:75.72(Geochemistry & Geophysics)

酵母はCe酸化物ナノ粒子の存在により特異な有機物を排出した。Ceナノ粒子は酵母の生育への直接的な影響はないものの、グリコシシス酵素を排出した。このことから、Ceナノ粒子は酵母の代謝を変化させることが分かった。

口頭

Mechanism and crystallochemical signature of nano-particle formation by microorganisms

塩津 弘之; Giang, M.*; 仲松 有紀*; 大貫 敏彦; 宇都宮 聡*

no journal, , 

We investigated to understand the effect of pH, coexistent REEs and the functional group of cells surfaces on the crystal chemistry of biogenic nanoparticle formation. These nano-particles were characterized as phosphate containing a series of REEs. The nano-particles at pH 3 had monazite structure, while the particles forming at pH 4 and 5 were amorphous. REE phosphate inorganically synthesized at room temperature revealed crystalline structure (monazite, xenotime or habdophane) depending on the element. Additional inorganic model experiments using the CMC, Ln resin and Cellulose Phosphate, which have the functional groups similar to cell surfaces, demonstrated that the nano-particles precipitated without structure. Based on these data it is suggested that adsorption to the functional groups on the cell surfaces constrain the shape and structure of nanoparticles.

口頭

生体鉱物化における生物由来ナノ粒子の形態制御

塩津 弘之; Jiang, M.*; 仲松 有紀*; 大貫 敏彦; 宇都宮 聡*

no journal, , 

高レベル放射性廃棄物の処分には地層処分が検討されているが、長期貯蔵後の人工バリア崩壊と地下水の浸入によって高レベル放射性廃棄物の変質が起きた場合、放射性核種の放出が予想される。一方で、地下環境中には多様な微生物が普遍的に存在しており、微生物-放射性核種間相互作用が放射性物質の移行挙動を支配する要因の一つであると考えられ、核種移行モデルの構築にはその詳細なメカニズム解明が必須である。本研究では、複数Ln存在系で微生物(酵母)への吸着実験を行い、酵母への元素分配傾向を定量的に示し、各パラメーターの影響を解明することを目的とした。結果、pH3では溶液中で生成したLnPO$$_{4}$$が細胞表面に吸着し、pH4, 5ではLnが静電吸着したサイトで鉱物化が進むことが明らかになった。また、Lnの静電吸着は、monazite結晶構造生成を阻害することが示唆された。さらに生体鉱物化における軽Lnの優先的な分配は、溶解度積に支配されていると考えられる。

口頭

Formation of rare earth phosphate nano-particles by microorganisms

塩津 弘之; Jiang, M.*; 仲松 有紀*; 大貫 敏彦; 宇都宮 聡*

no journal, , 

We investigated to understand the effect of pH, coexistent REEs and the functional group of cells surfaces on the crystal chemistry of biogenic nanoparticle formation. These nano-particles were characterized as phosphate containing a series of REEs. The nano-particles at pH3 had monazite structure, while the particles forming at pH4 and 5 were amorphous. REE phosphate inorganically synthesized at room temperature revealed crystalline structure (monazite, xenotime or habdophane) depending on the element. Additional inorganic model experiments using the CMC, Ln resin and Cellulose Phosphate, which have the functional groups similar to cell surfaces, demonstrated that the nano-particles precipitated without structure. Based on these data it is suggested that adsorption to the functional groups on the cell surfaces constrain the shape and structure of nanoparticles.

口頭

多様なセシウム汚染廃棄物の中間・最終処分安全評価のための機関連携による多角的研究,10; Cs移行への微生物活性の影響

大貫 敏彦; 坂本 文徳; 香西 直文; 山崎 信哉*; 塩津 弘之; 宇都宮 聡*

no journal, , 

放射性Csの移行への微生物の活性の影響を酵母を用いて調べた。その結果、微生物の活性がある状態でのCs取り込み量は休眠状態よりも大きかった。さらに、培地中に鉱物を添加することにより取り込み量の減少が見られた。したがって、酵母は活性条件では鉱物などと競合しながら細胞内にCsを取り込む。

口頭

ソースターム及び液相pHに及ぼすセシウム及びヨウ素化学形の影響

塩津 弘之; 丸山 結; 石川 淳

no journal, , 

シビアアクシデント総合解析コードTHALES2を用い、燃料から放出されるセシウム及びヨウ素の化学形がセシウムのソースタームに与える影響を検討した。合わせて、揮発性ヨウ素の生成に多大な影響を及ぼす液相pHの変化を評価した。従来の研究を参考にして、セシウムの化学形としてCsOH, CsBO$$_{2}$$及びCs$$_{2}$$MoO$$_{4}$$、ヨウ素の化学形としてCsI及びHIを考慮した。解析の結果、セシウムの化学形はセシウムのソースタームに大きな影響を及ぼさないことが示唆された。また、化学組成によって、大量のヨウ素が溶解しているサプレッションチャンバーの液相pHが大きく低下し、ヨウ素のソースタームが増大する可能性があることがわかった。

口頭

Development and application of methodologies for source term analysis

丸山 結; 石川 淳; Zheng, X.; 城戸 健太朗; 松本 俊慶; 塩津 弘之; 伊藤 裕人; 玉置 等史

no journal, , 

An integral code system for severe accident analysis in light water reactors, THALES2/KICHE, has been developed at Japan Atomic Energy Agency (JAEA). The core melt progression and the transportation of radioactive materials within reactor coolant system (RCS) and containment vessel (CV) are analyzed with THALES2 code in conjunction with KICHE code for the iodine reaction kinetics in aqueous phase. The applications of THALES2/KICHE code have been made in various analytical studies for severe accident progression, including analyses for the accident at the Fukushima Daiichi Nuclear Power Plant (1F) in order to obtain technical knowledge on the source term into the environment and the core damage state.

口頭

VICTORIAコードを用いたB$$_{4}$$C制御材のFP化学に与える影響に関する解析

塩津 弘之; 石川 淳; 丸山 結

no journal, , 

熱化学平衡計算が可能なシビアアクシデント時放射性物質移行挙動解析コードVICTORIAにB$$_{4}$$Cに関連する化学種及びそれらの熱化学データを追加し、原子炉冷却系内におけるFP(Cs及びI)の化学形や移行挙動に与えるB$$_{4}$$C制御材の影響を解析した。解析の結果、B$$_{4}$$Cが存在する系の場合、より安定なCsの化学形であるCsBO$$_{2}$$の生成に伴い、B$$_{4}$$Cが存在しない系において支配的であったCsOH及びCs$$_{2}$$MoO$$_{4}$$の生成割合が減少することが示された。Iの化学種に関しては、高温領域においてCsIの生成割合が減少するとともにHIの有意が見られた。

口頭

ソースターム評価手法の高度化に向けたFP化学挙動の評価,2; Cs及びIの再蒸発挙動に与えるBの影響に係わる解析的検討

塩津 弘之; 石川 淳; 伊藤 裕人; 杉山 智之; 丸山 結

no journal, , 

Cs及びIの再蒸発挙動に与えるBの影響評価実験を対象とした熱力学平衡計算に基づいた解析により、コードの予測性能評価並びにB$$_{2}$$O$$_{3}$$存在下でのCs及びIの再蒸発に係る化学反応機構の検討を行い、B蒸気種によってI移行が促進されることを解析的に示した。

口頭

シビアアクシデントにおけるCs及びIの化学挙動評価手法に関する検討

塩津 弘之; 伊藤 裕人*; 石川 淳; 杉山 智之; 丸山 結

no journal, , 

照射済み燃料からのFP放出・移行挙動実験であるVERDON-2実験について化学平衡を仮定するFP移行挙動評価コードVICTORIA2.0による解析を実施し、平衡論によりCs化学挙動を定性的に評価できることを明らかにした。一方でIはその移行量を過小評価しており、手法に課題があることが示された。

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