Measurement of fragments of a wall-impinging liquid jet in a shallow pool

Horiguchi, Naoki; Yoshida, Hiroyuki; Kaneko, Akiko*; Abe, Yutaka*

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 6 Pages, 2022/10

For safety evaluation of nuclear reactors in severe accidents, it is important to estimate physical quantities of fragments generated from the molten fuel jet, which falls in a pool and breaks up. The evaluation method has been developed for the behavior as liquid jet with hydrodynamic interaction including fuel coolant interaction (FCI). In case of a shallow pool assumed in ex-vessel, the molten fuel jet is assumed to behave as wall-impinging liquid jet and to form liquid film flow spreading on the floor with/without fragmentation. In our research, focusing on hydrodynamic interaction and the transient 3-dimensional spreading on the floor, we have developed the evaluation method by numerical simulation using the two-phase flow simulation code with interface tracking method (TPFIT) developed by JAEA and, the experimental method using the 3D-LIF method in liquid-liquid system for the validation data. In our previous studies, we investigated the wall-impinging liquid jet behavior with fragmentation and observed that the liquid film flow had some characteristic parts transiently. Since it indicates that the quantities change depending on the parts and affect the safety evaluation, it is important to measure the quantities of the fragments generated from each part. This paper explains the measurement of the physical quantities of the fragments generated from each part of the wall-impinging liquid jet in a shallow pool for the validation of the numerical simulation. We conducted an experiment with the 3D-LIF method and segmented the experimental data based on the fragmentation point over the liquid film flow using the dispersed phase tracking method, developed by JAEA. Then, we measured the diameter and amount of the fragments from the segmented experimental data and investigated their changing trend.

A Comparative CFD exercise on bubble hydrodynamics using Euler-Euler and interface tracking approaches

Dehbi, A.*; Cheng, X.*; Liao, Y.*; Okagaki, Yuria; Pellegrini, M.*

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 15 Pages, 2022/03

Numerical simulation of two-phase flow in fuel assemblies with a spacer grid using a mechanistically based method

Ono, Ayako; Yamashita, Susumu; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 16 Pages, 2022/03

JAEA is developing the methodology to predict the critical heat flux based on a mechanism in order to reduce the cost for full mock-up test. The evaluation method based on a mechanism is expected to be able to predict in the wide range of parameter under the unexpected conditions including the severe accident. In this study, the JUPITER code developed by JAEA is examined to apply for the two-phase flow simulation of LWR fuel assembly with the spacer grid. The benchmark data of single-phase flow in the bundle with the spacers by KAERI were used to validate the simulation result by JUPITER. Moreover, the single-phase flow simulation was conducted by another simulation method, STAR-CCM+, as a supplemental analysis to consider the effect of the different simulation methods. Finally, the two-phase flow simulation for the bundle with the spacer was conducted by JUPITER. The effect of the spacer with a vane on the bubble behavior is discussed.

Numerical simulation of microparticles motion in two-phase bubbly flow

Yoshida, Hiroyuki; Uesawa, Shinichiro

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 7 Pages, 2020/08

https://doi.org/10.1115/ICONE2020-16393

Quantitative analysis method for radiation distribution in high radiation environment by gamma-ray image spectroscopy (Contract research); FY2018 Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development

Collaborative Laboratories for Advanced Decommissioning Science; Kyoto University*

JAEA-Review 2019-036, 65 Pages, 2020/03

JAEA-Review-2019-036.pdf:4.46MB

JAEA/CLADS, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Quantitative Analysis Method for Radiation Distribution in High Radiation Environment by Gamma-ray Image Spectroscopy". Electron-tracking Compton camera (ETCC) has been developed originally for nuclear gamma-ray astronomy, and also applied to medical use as a technology that greatly improves the resolution of conventional Compton camera by measuring three-dimensional tracking of electrons using a gaseous 3-dimensional position detector (so called Time Projection Chamber) in the first stage. In the present study, based on the ETCC that has been developed for medical use, we produce a prototype of light weight ETCC with the emphasis on the operability at the site, and evaluate its practicability by field tests.

Study on the two-phase flow in simulated LWR fuel bundle by CFD code

Ono, Ayako; Yamashita, Susumu; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.666 - 677, 2019/08

An evaluation methodology of critical heat fluxes (CHFs) based on a mechanism for fuel assemblies in light water reactors (LWRs) is needed in order to design and evaluate the safety for the fuel assemblies in LWRs. In our study, the numerical simulation with surface-tracking will be applied for the two-phase flow in fuel assemblies in order to obtain the detail data relating to the size and velocity of bubbles in the subchannel, which is needed to predict the CHF based on the mechanism. In this study, the numerical simulation of two-phase flow in 44 bundle was implemented by using JUPITER in order to establish the evaluation method of the size and velocity of bubbles by the numerical simulation, which is the multi-physics simulation code and enable to track the gas-liquid surface. The simulation results are validated by the curve of flow regime for air-water under the adiabatic condition. The bubble and velocity of bubbles obtained by simulation results are analyzed.

Study of chemical etching conditions for alpha-particle detection and visualization using solid state nuclear track detectors

Yamada, Ryohei; Odagiri, Taiki*; Iwaoka, Kazuki*; Hosoda, Masahiro*; Tokonami, Shinji*

Radiation Environment and Medicine, 8(1), p.21 - 25, 2019/02

http://crss.hirosaki-u.ac.jp/rem_archive/radiation-environment-and-medicine-vol-8-no-1

We evaluate radon/thoron and its progeny concentration using passive-type monitors using CR-39 plates. After exposure, it is necessary to do chemical etching for CR-39 plates. In the present study, we considered shortening of chemical etching time for CR-39 and enlargement of the track diameter (i.e. etch pit diameter) aiming for introduction of automatic counting system in the future. Optimum conditions were determined by changing solution concentration, solution temperature and etching time. As a result, the optimized conditions (concentration, temperature and etching time) were determined to be 8 M NaOH solution, 75 degrees Celsius and 10 hours. This result of etching time showed that the chemical etching was completed in less than half of conventional etching time. Furthermore, it was suggested that shorter etching time would be possible if we do not consider the enlargement of conventional track diameter.

Electron-tracking Compton camera imaging of technetium-95m

Hatsukawa, Yuichi*; Hayakawa, Takehito*; Tsukada, Kazuaki; Hashimoto, Kazuyuki*; Sato, Tetsuya; Asai, Masato; Toyoshima, Atsushi; Tanimori, Toru*; Sonoda, Shinya*; Kabuki, Shigeto*; et al.

PLOS ONE (Internet), 13(12), p.e0208909_1 - e0208909_12, 2018/12

AA2018-0639.pdf:2.39MB

https://doi.org/10.1371/journal.pone.0208909

Imaging of Tc radioisotope was conducted using an electron tracking-Compton camera (ETCC). Tc emits 204, 582, and 835 keV rays, and was produced in the Mo(p,n)Tc reaction with a Mo-enriched target. The recycling of the Mo-enriched molybdenum trioxide was investigated, and the recycled yield of Mo was achieved to be 70% - 90%. The images were obtained with each of the three rays. Results showed that the spatial resolution increases with increasing -ray energy, and suggested that the ETCC with high-energy -ray emitters such as Tc is useful for the medical imaging of deep tissue and organs in the human body.

Numerical simulation of two-phase flow behavior in Venturi scrubber by interface tracking method

Horiguchi, Naoki; Yoshida, Hiroyuki; Abe, Yutaka*

Nuclear Engineering and Design, 310, p.580 - 586, 2016/12

https://doi.org/10.1016/j.nucengdes.2016.10.043

Fabrication of hard-coated optical absorbers with microstructured surfaces using etched ion tracks; Toward broadband ultra-low reflectance

Amemiya, Kuniaki*; Koshikawa, Hiroshi; Yamaki, Tetsuya; Maekawa, Yasunari; Shitomi, Hiroshi*; Numata, Takayuki*; Kinoshita, Kenichi*; Tanabe, Minoru*; Fukuda, Daiji*

Nuclear Instruments and Methods in Physics Research B, 356-357, p.154 - 159, 2015/08

https://doi.org/10.1016/j.nimb.2015.05.002

Broadband low reflectance materials have various applications in the field of optical energy management; however, materials with ultra-low reflectance (below 0.1%) have been considered as mechanically delicate. We have developed a novel hard-surface optical absorber with microstructured, diamond-like carbon coated ion tracks on CR-39 plastic substrate. The spectral reflectance of the first prototype was below 2% for wavelengths ranging from 400 nm to 1400 nm; moreover, the optical absorber had mechanically hard surface and exhibited temporal durability. Choosing the appropriate design of the surface structure and coating layer is likely to reduce the reflectance to the order of 0.1%. This technique yields easy-to-handle broadband ultra-low reflectance absorbers.