Chikako Iwaki

Study on the Interfacial Behavior and Thermal Characteristics in Liquid-Vapor Flow of the Supersonic Steam Injector

Supersonic steam injector is a passive jet pump which operates without rotating power source or machinery and it has high heat-transfer performance due to the direct contact condensation between supersonic steam flow and subcooled water jet at the mixing nozzle. Since the supersonic steam injector has a quite simple and compact structure, it has been considered to apply to the safety system for the Next-generation nuclear power plant. There are various researches about the formulation and modeling of operating, flow structure and heat transfer characteristics of both vapor and liquid flow. However, there are few models which are capable of evaluating heat and momentum exchange at the boundary layer between supersonic steam flow and water jet. Since heat and momentum exchange is considered to have a major impact to operating characteristics of a supersonic steam injector, it is necessary to formulate the model which simulates such complex phenomena at the boundary layer with high accuracy. The objective of the present study is to investigate the relation between the thermal characteristics and interfacial behavior between the flows to develop a model which is able to assess the heat and momentum transfer characteristic and the flow structure of the supersonic steam injector in detail. In the present study, a visible test section of water jet-centered supersonic steam injector was adopted to conduct visualization of the water jet with high speed video camera. In addition, special measurement instrumentations of temperature and pressure were applied to obtain radial distribution of temperature and pressure in the mixing nozzle of the injector. There were large velocity and temperature gaps between the water jet and the supersonic steam flow which indicated the existence of large momentum and heat exchange at the boundary layer of the flows. It was clarified that there was pressure gradient which was considered to stabilize the water jet in the mixing nozzle from calculation of radial distribution of total pressure gradient. From the visualization measurement, it was also clarified the existence of a complex wavy behavior on the surface of the water jet. The wave velocity was estimated by the image processing technique and the cross-correlation method. It was found that there was a relation between the wave velocity and heat transfer characteristics in the supersonic steam injector. It is suggested that the enthalpy ratio between the liquid subcool enthalpy and steam condensation enthalpy as well as the Jacob number between both flows could be an indication factor for the effect of the wavy behavior on the condensation.Copyright

Development of Hydrogen Treatment System in Severe Accident: Part 3 — Study of Reactant Diameter Effect on Hydrogen Treatment

1. 緒言 シビアアクシデント時の水素処理装置開発において、これまで球形に成型した金属酸化物を充填した反 応器の水素処理特性を試験してきたが、実機適用においては反応を阻害する要因の影響評価が必要であ る。そこで、反応阻害要因のうち最も重要と考えられる水蒸気の影響を評価するための試験を実施した。 また、水蒸気の影響を考慮した反応器評価モデルを作成し、積算水素処理量の予測精度を評価した。 2. 反応器特性試験および評価 2-1. 試験装置 試験装置は主に、水素、水蒸気及び窒素を所定の流量比で 混合する混合器、混合ガスの予熱器、反応器試験体より構成 される。反応器試験体として、内径 65.9mm、高さ 600mm の ステンレス管の内部にφ2.0mmの CuO を充填したものを使用 した。反応器内に熱電対を、反応器入口・出口に水素濃度計 を設置して水素処理量を算出した。 2-2. 試験結果 圧力 0.17MPa、ガス流量 62L/min、水蒸気濃度 33vol%で試 験した時の水素濃度の時系列変化を図1に示す。ガスが供給 されると金属酸化物と水素との反応が開始し、反応器試験体 出口水素濃度が 0vol%となった。別途計測した反応器内温度 分布から、入口部より金属酸化物は反応熱によって約 600°Cま で温度上昇し、高温域(反応域)が徐々に出口側へ移行する ことを確認している。出口近傍の金属酸化物の温度低下とと もに、約 9400 秒から出口水素濃度が上昇し(図1)、やがて 反応が終了した。ガス温度、水素及び水蒸気濃度をパラメー タとした試験を実施したところ、出口水素濃度及び金属酸化 物の最高温度はこれらの条件に大きく依存した。そこで水素 処理性能を評価するため反応終了までの積算水素処理量を計 算したところ、図2に示すように、相対湿度が低いほど、ま たガス温度が高いほど積算水素処理量は増加することがわか った。 2-3. 反応器評価モデル 質量保存式とエネルギー保存式を基礎式とし、水素処理速度式を組込んだ一次元の反応器評価モデルを、 水蒸気の影響を考慮して修正した反応速度式を用いて改良し、解析結果を試験結果と比較した。その結 果、積算水素処理量を誤差約 30%以下で予測することを確認した。 3. 結論 反応器の水素処理特性試験により、水蒸気混在の条件でも水素処理が可能であること、積算水素処理量は相対 湿度に依存することがわかった。また水蒸気の影響を評価可能な反応器評価モデルを作成し、水蒸気混在条件 における水素処理量予測の目途を得た。 なお、本件は経済産業省平成 28 年度発電用原子炉等安全策高度化技術基盤整備事業(シビアアクシデント時の水素処理システムの開 発に向けた基盤整備)の成果の一部である。 参考文献 [1]岩城ら、「シビアアクシデント時の水素処理システムの開発(5)」、日本原子力学会 2016 年春の大会、1I14 [2]香月ら、「過酸化金属による水素処理特性評価」、日本機械学会、第 21 回動力・エネルギー技術シンポジウム、E212(2016) [3]山田ら、「シビアアクシデント時の水素処理システムの開発(8)」、日本原子力学会 2017 年秋の大会(投稿中) Chikako Iwaki, Tsukasa Sugita, Akira Yamada, Motoshige Yagyu, Yoshiko Haruguchi and Masashi Tanabe TOSHIBA Corporation 図1 水素濃度及び水素処理速度の試験結果

Operating Condition of Steam Injector as a Passive Cooling System at Severe Accident of Nuclear Power Plant

Steam injector (SI) is a passive jet pump which is driven by high-performance steam condensation onto water jet and it is expected to be active at severe accident of nuclear power plant with no electricity. SI is mainly consists of convergent-divergent nozzle. Supersonic steam flow condenses onto water jet in the mixing nozzle and mass, momentum, and energy of steam is transferred to water in the mixing nozzle. Condensed water jet is accelerated at the throat and kinetic energy is converted into pressure in the diffuser, which produces higher pressure than inlet steam pressure. It is easy to apply the SI to nuclear power plant since SI has quite simple and compact structures.The objectives of the present study are to clarify the mechanism of heat and momentum transfer in the mixing nozzle and to determine operating range of SI for practical use.A transparent test section is adopted to conduct visualization of the flow structure with a high-speed video camera as well as measurement of pressure distribution in mixing nozzle, throat, and diffuser with changing back pressure. Fundamental parameters change between operative and inoperative state of the injector were evaluated by measuring pressure and temperature distribution along axial direction of the test section. Discharge pressure as one of operating characteristics of the injector was also measured in changing back pressure by decreasing the opening ratio of the back pressure valve attached downstream of the test section.It was confirmed that discharge pressure increased and the injector became inoperative unsteadily with decreasing opening ratio of the back pressure valve just after it produced the maximum discharge pressure. In the present investigation, this maximum discharge pressure is evaluated as the operation limit of the injector. Furthermore, discharge pressure from diffuser, which is one of the indicators of operating performance as well as operating limit is predicted from inlet condition adopting one-dimensional analysis model proposed previously. By comparing analytical result with experimental data, as well as visualization of flow structure in throat and diffuser, physics model including two-phase flow structure with shock wave which was observed at throat and diffuser are discussed in order to predict injector’s operation with high accuracy.Copyright

The Validation of the 4S Safety Analysis Code for Loss of Offsite Power Event

The 4S (Super-Safe, Small and Simple) reactor is a small fast reactor which has been developed by Toshiba Corporation in cooperation with Central Research Institute of Electric Power Industries (CRIEPI). The 4S system design of the 30MWt version is completed and the licensing activities have commenced. In licensing activities, safety analyses are performed by using Toshiba self-developed safety analysis code SAEMKON (Safety Analysis for Energy, Motion, Kinetics, One dimensional Flow-Network) which is a kind of one dimensional flow network code. To satisfy the regulations of U.S. Nuclear Regulatory Commission, the code verification and validation (VV Separate Effects Test (SET) phase, Integral Effects Test (IET) phase and Applicability Demonstration phase (confirm that SAEMKON has the capability to analyze particular events).In SET phase, the analysis results of the important phenomena should be evaluated with using theoretical solutions, other validated computer programs, experimental results, standard problems with known solutions, or published data and correlations. The important phenomena of LOSP are selected by PIRT (Phenomena Identification and Ranking Tables) and the phenomena are classified into 5 types. To validate the code with 5 types of phenomena, various evaluations have been performed with comparison to data of test and published paper.In IET phase, the test data of EBR-II (Experimental Breeder Reactor-II) are used and the capability of the code to simulate natural circulation behavior of the plant is confirmed.The applicability demonstration has been also planned by using a CFD 4S full scale model.In this paper, these validation results of the 4S safety analysis code for LOSP are described.Copyright

Development of Technologies on Innovative-Simplified Nuclear Power Plant Using High-Efficiency Steam Injectors: Part 11—Visualization Study on the Start-Up of the Steam Injector

The Steam Injector is the superior system to pump the fluid without rotating machine. Because the water column is surrounded by the saturated steam, very high heat transfer is also expected with direct condensation. The inside of the Steam Injector is very complicated. To improve the efficiency of the Steam Injector, the water column behavior inside the Injector is visualized using the Dynamic PIV system. Dynamic PIV system consists of the high-speed camera and lasers. In this study, 384 x 180 pixel resolution with 30,000 fps camera is used to visualize the flow. For the illumination CW green laser with 300 mW is applied. To view inside the Injector, relay lens system is set at the Injector wall. Very high speed water column during the starting up of Steam Injector had been clearly visualized with 30,000 fps. The wave velocity on the water column had been analyzed using PIV technique. The instability of the water column is also detected. (authors)

Development of Technologies on Innovative-Simplified Nuclear Power Plant Using High-Efficiency Steam Injectors: Part 12—Evaluations of Spatial Distributions of Flow and Heat Transfer in Steam Injector

Next-generation nuclear reactor systems have been under development aiming at simplified system and improvement of safety and credibility. One of the innovative technologies is the supersonic steam injector, which has been investigated as one of the most important component of the next-generation nuclear reactor. The steam injector has functions of a passive pump without large motor or turbo-machinery and a high efficiency heat exchanger. The performances of the supersonic steam injector as a pump and a heat exchanger are dependent on direct contact condensation phenomena between a supersonic steam and a sub-cooled water jet. In previous studies of the steam injector, there are studies about the operating characteristics of steam injector and about the direct contact condensation between static water pool and steam in atmosphere. However, there is a little study about the turbulent heat transfer and flow behavior under the great shear stress. In order to examine the heat transfer and flow behavior in supersonic steam injector, it is necessary to measure the spatial temperature distribution and velocity in detail. The present study, visible transparent supersonic steam injector is used to obtain the axial pressure distributions in the supersonic steam injector, as well as high speed visual observation of water jet and steam interface. The experiments are conducted with and without non-condensable gas. The experimental results of the interfacial flow behavior between steam and water jet are obtained. It is experimentally clarified that an entrainment exists on the water jet surface. It is also clarified that discharge pressure is depended on the steam supply pressure, the inlet water flow rate, the throat diameter and non-condensable flow rate. Finally a heat flux is estimated about 19MW/m2 without non-condensable gas condition in steam.Copyright

Effect of Non-Condensable Gas on Steam Injector

Next-generation reactor systems have been under development aiming at simplified system and improvement of safety and credibility. A steam injector has a function of a passive pump without large motor or turbo-machinery, and has been investigated as one of the most important component of the next-generation reactor. Its performance as a pump is depends on direct contact condensation phenomena between a supersonic steam and a sub-cooled water jet. Although non-condensable gases are well known for reducing heat transfer, the effect of the non-condensable gas on the condensation of supersonic steam on high-speed water jet has not been cleared. The present paper reports the results of an experimental study of condensation of supersonic steam around turbulent water jet with model steam injector made by transparent plastic. The visual observation carried out by using high-speed camera. The non-condensable gas effect on the pump performance and flow characteristics are clarified by the image processing technique for the jet shape and gas-liquid interface behavior.Copyright