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論文

An Analytical model to decompose mass transfer and chemical process contributions to molecular iodine release from aqueous phase under severe accident conditions

Zablackaite, G.; 塩津 弘之; 城戸 健太朗; 杉山 智之

Nuclear Engineering and Technology, 56(2), p.536 - 545, 2024/02

Radioactive iodine is a representative fission product to be quantified for the safety assessment of nuclear facilities. In integral severe accident analysis codes, the iodine behavior is usually described by a multi-physical model of iodine chemistry in aqueous phase under radiation field and mass transfer through gas-liquid interface. The focus of studies on iodine source term evaluations using the combination approach is usually put on the chemical aspect, but each contribution to the iodine amount released to the environment has not been decomposed so far. In this study, we attempted the decomposition by revising the two-film theory of molecular-iodine mass transfer. The model involves an effective overall mass transfer coefficient to consider the iodine chemistry. The decomposition was performed by regarding the coefficient as a product of two functions of pH and the overall mass transfer coefficient for molecular iodine. The procedure was applied to the EPICUR experiment and suppression chamber in BWR.

論文

Estimation for mass transfer coefficient under two-phase flow conditions using two gas components

南上 光太郎; 塩津 弘之; 丸山 結; 杉山 智之; 岡本 孝司*

Journal of Nuclear Science and Technology, 60(7), p.816 - 823, 2023/07

 被引用回数:0 パーセンタイル:0.01(Nuclear Science & Technology)

For proper source term evaluation, we constructed the theoretical model to estimate the mass transfer coefficient of gaseous iodine species under two-phase flow conditions, which complicates the direct experimental measurements. The mass transfer speed is determined by the product of the overall mass transfer coefficient and the interfacial area. By using the ratio of two gas components, the interfacial area, which is an important parameter that is difficult to measure, can be canceled out and the ratio of their overall mass transfer coefficients can be obtained. This ratio is expected to be equal to the ratio of their diffusion coefficients. Therefore, the unknown mass transfer coefficient such as iodine species can be estimated using the diffusion coefficients of two gas components and the reference mass transfer coefficient such as O$$_{2}$$. We carried out the experiments using the bubble column to confirm this relationship. From the results in this study, we confirmed that the ratio of the overall mass transfer coefficient was in good agreement with the ratio of diffusion coefficient under the bubbly flow conditions. Using this relationship confirmed in this study, we estimated the mass transfer coefficient of I$$_{2}$$, one of the iodine species.

論文

Numerical analysis for FP speciation in VERDON-2 experiment; Chemical re-vaporization of iodine in air ingress condition

塩津 弘之; 伊藤 裕人*; 杉山 智之; 丸山 結

Annals of Nuclear Energy, 163, p.108587_1 - 108587_9, 2021/12

 被引用回数:0 パーセンタイル:0.01(Nuclear Science & Technology)

In the late phase of severe accident in light water reactor nuclear power station, re-mobilization of fission products (FPs) has a significant impact on the source term because most portion of FPs is retained in reactor coolant system and/or containment vessel. Recently, VERDON-2 experiment showed noticeable re-vaporization, which was one of the re-mobilization phenomena, of iodine under air ingress condition, but this mechanism has not been identified yet. The present study numerically investigated the FPs behaviors in VERDON-2 experiment with the mechanistic FPs transport analysis code incorporating thermodynamic chemical equilibrium model in order to further understand nature for FPs behavior, especially iodine re-vaporization under air ingress condition. Consequently, this analysis reproduced the deposition profile of cesium, one of important FPs in the source term, along the thermal gradient tube (TGT) in the experiment, which revealed that cesium was transported as CsOH in early phase of FP release from fuel, and then formed Cs$$_{2}$$MoO$$_{4}$$ and Cs$$_{2}$$Te after the release of molybdenum and tellurium was activated. Regarding iodine as another important FP, formation of CsI was predicted in steam condition. The CsI was transported and partly deposited and condensed onto the TGTs and other components of the VERDON facility. Under the air ingress condition, the present analysis showed the agreement for iodine re-vaporization in the experiment and revealed its mechanism; the deposits of iodide were chemical re-vaporized as molecular iodine (I$$_{2}$$) gas by redox reaction with competitive elements such as molybdenum, chromium and tellurium.

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:6 パーセンタイル:53.26(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

Study on depth profile of heavy ion irradiation effects in poly(tetrafluoroethylene-co-ethylene)

五輪 智子*; 塩津 智之*; 裏川 達也*; 岡 壽崇; 村上 健*; 大島 明博*; 濱 義昌*; 鷲尾 方一*

Radiation Physics and Chemistry, 80(2), p.264 - 267, 2011/02

 被引用回数:8 パーセンタイル:53.54(Chemistry, Physical)

高LET放射線である重粒子線をETFEに真空、及び大気中で照射した。ETFEに対する照射効果を重粒子線の進入深さの関数として評価した。重粒子線照射によって共役二重結合が生成し、その生成量分布はブラッグ曲線に非常によく似ていること、LETが高くなるほど、C=Cの二重結合の長さが長くなることがわかった。さらに、大気中照射においては、試料表面からの酸素分子の拡散により、C=O結合が増加することが明らかになった。

口頭

Study on depth profile of heavy ion irradiation effects in poly(tetrafluoroethylene-co-ethylene)

五輪 智子*; 塩津 智之*; 裏川 達也*; 岡 壽崇; 村上 健*; 大島 明博*; 濱 義昌*; 鷲尾 方一*

no journal, , 

Various heavy ion beams were irradiated to stacked ETFE films under vacuum and in ambient condition. After the ion irradiation, the depth profile of the irradiation effects due to the energy deposition was evaluated by measuring the absorption of each one of the films with ultraviolet-visible spectroscopy (UV-vis) and Fourier transform infrared spectroscopy (FT-IR). The effects of irradiation in ambient atmosphere were compared with that under vacuum condition.

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。

口頭

シビアアクシデント時の原子炉冷却系条件におけるセシウム及びヨウ素の気相化学反応に与えるホウ素の影響

三輪 周平; 塩津 弘之; 逢坂 正彦; 杉山 智之; 丸山 結

no journal, , 

シビアアクシデント時の原子炉冷却系条件におけるセシウム及びヨウ素の気相化学反応に与えるBWR制御材ホウ素の影響を評価するため、シビアアクシデント時の原子炉冷却系温度条件におけるヨウ化セシウムとホウ素化合物の移行実験を水蒸気及び水素雰囲気で実施した。その結果、これらの両雰囲気においてホウ素化合物との気相反応によりガス状のヨウ素化合物の生成が促進される可能性があることが分かった。

口頭

Experiments on iodine and cesium chemistry with focus on boron effects

三輪 周平; 塩津 弘之; 逢坂 正彦; 杉山 智之; 丸山 結

no journal, , 

シビアアクシデント時の原子炉冷却系条件におけるヨウ素及びセシウムの化学挙動に与えるBWR制御材ホウ素の影響を評価するため、シビアアクシデント時の原子炉冷却系温度条件におけるヨウ化セシウム蒸気種とホウ素蒸気種の気相反応を想定した加熱実験を実施した。この結果、ホウ素蒸気種との気相反応により、ガス状のヨウ素化合物の生成が促進される可能性があることが分かった。

口頭

Numerical analysis for fission product behavior in VERDON-2 experiment

塩津 弘之; 伊藤 裕人*; 杉山 智之; 丸山 結

no journal, , 

The VERDON-2 experiment for fission products (FPs) transport under steam condition was analyzed with the mechanistic FPs transport code based on thermodynamic chemical equilibrium model in order to understand their behavior, especially for Cs and I with high volatility. Furthermore, the chemical model was validated for improve source term evaluation method with consideration of chemistry. The present analysis reproduced well the Cs distribution obtained from the experiment, which revealed that Cs transported as CsOH in early phase of FP release from fuel, and then form Cs$$_{2}$$MoO$$_{4}$$ after Mo release. On the other hand, the I deposition peak was predicted at a higher temperature than experimental result, which was observed at 600 K in the experiment and at 720 K in the analysis. This discrepancy was potentially caused by following two points: lack of the other stable species in thermodynamics database for chemical equilibrium model, or failure of chemical equilibrium assumption for iodide species. These results suggest that FPs transport code with thermodynamic chemical equilibrium model can evaluate Cs behavior as CsOH and Cs$$_{2}$$MoO$$_{4}$$ species and not currently available on the evaluation for I behavior.

口頭

原子炉冷却系内FP化学を考慮したソースターム解析手法の構築

石川 淳; Zheng, X.; 塩津 弘之; 杉山 智之

no journal, , 

熱化学平衡計算コードCHEMKEqによる多ケース解析結果からなるデータベースと代替統計モデル(K近傍法)を活用したFP化学平衡組成計算モデルを構築し、シビアアクシデント総合解析コードTHALES2に導入した。BWRプラントのシビアアクシデント解析に適用した結果、従来評価では、工学的判断によりセシウム及びヨウ素の化学種としてCsI及びCsOHと仮定していたが、RCS内FP化学を考慮することによりCsI, CsBO$$_{2}$$やCs$$_{2}$$MoO$$_{4}$$の化学形として格納容器へ移行する可能性が示された。

口頭

Numerical analysis for fission product behavior in VERDON-2 experiment

塩津 弘之; 伊藤 裕人*; 杉山 智之; 丸山 結

no journal, , 

水蒸気雰囲気での大規模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を用いた解析を実施し、平衡論に基づいたCsおよびIに係る化学挙動予測機能の評価を行った。解析の結果、平衡論により高温領域での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や低温領域でのCs化学挙動では実験結果との定性的な一致が見られず、手法に課題があることが示された。

口頭

ホウ素含有水蒸気条件での非凝縮性ヨウ素の生成促進現象に対する化学平衡論解析

塩津 弘之; 三輪 周平; 逢坂 正彦; 杉山 智之; 丸山 結

no journal, , 

ホウ素含有水蒸気条件での非凝縮性ヨウ素の生成促進現象を明らかにすることを目的に、TeRRaを用いた高温化学反応実験の化学平衡論解析を実施した。その結果、高温領域におけるCsBO$$_{2}$$生成に伴う反応により非凝縮性ヨウ素の生成が促進された可能性があることが分かった。

口頭

シビアアクシデント時のセシウム, ヨウ素の化学挙動に与えるホウ素の影響

三輪 周平; 鈴木 恵理子; 塩津 弘之; 杉山 智之; 逢坂 正彦

no journal, , 

軽水炉シビアアクシデントにおいて原子炉内移行時のホウ素がセシウム, ヨウ素の化学挙動に与える影響を評価した。ホウ素は炉内高温領域に沈着してセシウムを捕集する可能性があること、気相中のセシウムとの反応により揮発性ヨウ素化合物を生成させること等、シビアアクシデント解析にて考慮すべきホウ素の影響を明らかにした。

口頭

Analysis of mass transfer effect on chemically produced iodine release from aqueous phase

Zablackaite, G.; 塩津 弘之; 城戸 健太朗; 杉山 智之

no journal, , 

To investigate the mass transfer effect on the overall iodine release to the environment, we propose a chemical-process-reduced mass transfer (CPR-MT) model for iodine that is based on two-film theory and includes an effective mass transfer coefficient ($$tilde{k}_{mt}$$). By formally decomposing $$tilde{k}_{mt}$$ into iodine chemistry and mass transfer contributions, we discuss their impact for a variety of severe accident conditions of nuclear power station.

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