Experimental study on secondary droplets produced during liquid jet impingement onto a horizon solid surface

Zhan, Y.*; Kuwata, Yusuke*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi

Experimental Thermal and Fluid Science, 120, p.110249_1 - 110249_12, 2021/01

https://doi.org/10.1016/j.expthermflusci.2020.110249

Using natural systems evidence to test models of transformation of montmorillonite

Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio

Applied Clay Science, 195, p.105741_1 - 105741_11, 2020/09

https://doi.org/10.1016/j.clay.2020.105741

Safety functions for the clay buffer in a repository for high-level radioactive waste (HLW) are fulfilled if the presence of montmorillonite with high swelling capacity and low permeability is maintained in the long-term. The transformation of montmorillonite to the non-swelling mineral likely illite is addressed in most safety assessments by using simple semi-empirical kinetic models, but this approach contrasts with more complex reactive-transport simulations. In the present study, reactive-transport simulations are compared with simple semi-empirical kinetic models. Results suggest that reactive-transport simulations err on the side of conservatism, but may produce unrealistic estimates of illitization. This comparison demonstrates that reactive-transport models may be carefully applied to simulate the long-term evolution of near field environment for HLW disposal.

Application of photoluminescence microspectroscopy; A Study on transfer of uranyl and europium ions on dry silica gel plate

Kusaka, Ryoji; Watanabe, Masayuki

Journal of Nuclear Science and Technology, 57(9), p.1046 - 1050, 2020/09

https://doi.org/10.1080/00223131.2020.1755734

A Linear Equation of characteristic time profile of power in subcritical quasi-steady state

Yamane, Yuichi

Journal of Nuclear Science and Technology, 57(8), p.926 - 931, 2020/08

https://doi.org/10.1080/00223131.2020.1736682

An equation of power in subcritical quasi-steady state has been derived based on one-point kinetics equations for the purpose of utilizing it for the development of timely reactivity estimation from complicated time profile of neutron count rate. It linearly relates power, , to a new variable , which is a function of time differential of the power. It has been confirmed by using one-point kinetics code, AGNES, that the calculated points () are perfectly in a line described by the new equation and that points () calculated from transient subcritical experiments by using TRACY made a line with a slope indicated by the new equation.

Seven-year temporal variation of caesium-137 discharge inventory from the port of Fukushima Daiichi Nuclear Power Plant; Continuous monthly estimation of caesium-137 discharge in the period from April 2011 to June 2018

Machida, Masahiko; Yamada, Susumu; Iwata, Ayako; Otosaka, Shigeyoshi; Kobayashi, Takuya; Watanabe, Masahisa; Funasaka, Hideyuki; Morita, Takami*

Journal of Nuclear Science and Technology, 57(8), p.939 - 950, 2020/08

https://doi.org/10.1080/00223131.2020.1740809

After direct discharges of highly contaminated water of the Fukushima Daiichi Nuclear Power Plant (1F) from April to May 2011, Kanda suggested that relatively small amounts of run-off of radionuclides from the 1F port into the Fukushima coastal region subsequently continued by his estimation method. However, the estimation period was limited to up to September 2012. Therefore, this paper estimates the discharge inventory up to June 2018. In the missing period, the Japanese government and Tokyo Electric Power Company Holdings have continued efforts to stop the discharge, and consequently, the radionuclide concentration in seawater inside the 1F port has gradually diminished. We show the monthly discharge inventory of Cs up to June 2018 by two methods, i.e., Kanda method partially improved by the authors and a more sophisticated method using Voronoi tessellation reflecting the increase in the number of monitoring points inside the 1 F port. The results show that the former always yields overestimated results compared with the latter, but the ratio of the former to the latter is less than one order of magnitude. Using these results, we evaluate the impact of the discharge inventory from the 1F port into the coastal area and radiation dose upon fish ingestion.

Nonreciprocal surface acoustic wave propagation via magneto-rotation coupling

Xu, M.*; Yamamoto, Kei; Puebla, J.*; Baumgaertl, K.*; Rana, B.*; Miura, Katsuya*; Takahashi, Hiromasa*; Grundler, D.*; Maekawa, Sadamichi*; Otani, Yoshichika*

Science Advances (Internet), 6(32), p.eabb1724_1 - eabb1724_4, 2020/08

https://doi.org/10.1126/sciadv.abb1724

Four-point-bend tests on high-burnup advanced fuel cladding tubes after exposure to simulated LOCA conditions

Narukawa, Takafumi; Amaya, Masaki

Journal of Nuclear Science and Technology, 57(7), p.782 - 791, 2020/07

https://doi.org/10.1080/00223131.2020.1724207

Key factors controlling radiocesium sorption and fixation in river sediments around the Fukushima Daiichi Nuclear Power Plant, 1; Insights from sediment properties and radiocesium distributions

Tachi, Yukio; Sato, Tomofumi*; Akagi, Yosuke*; Kawamura, Makoto*; Nakane, Hideji*; Terashima, Motoki; Fujiwara, Kenso; Iijima, Kazuki

Science of the Total Environment, 724, p.138098_1 - 138098_11, 2020/07

https://doi.org/10.1016/j.scitotenv.2020.138098

To understand and predict radiocesium transport behaviors in the environment, highly contaminated sediments from Ukedo and Odaka rivers around the Fukushima Daiichi Nuclear Power Plant were investigated systematically focusing on key factors controlling radiocesium sorption and fixation, including particle size, clay mineralogy and organic matter.

Chemical forms of uranium evaluated by thermodynamic calculation associated with distribution of core materials in the damaged reactor pressure vessel

Ikeuchi, Hirotomo; Yano, Kimihiko; Washiya, Tadahiro

Journal of Nuclear Science and Technology, 57(6), p.704 - 718, 2020/06

https://doi.org/10.1080/00223131.2020.1720844

To suggest efficient process of the fuel debris treatment after the retrieval from the Fukushima Daiichi Nuclear Power Plant (1F), thorough investigation is indispensable on potential source of U in the fuel debris. Estimation on the fuel debris accumulated in the reactor pressure vessel is specifically important due to its limited accessibility. The present study aims to estimate the chemical forms of U in the in-vessel fuel debris, especially in the minor phases such as metallic phases, by performing the thermodynamic calculation considering the material relocation and changing environment during the accident progression in the 1F Unit 2. Input conditions for the thermodynamic calculation such as composition, temperature, and oxygen amount were assumed mainly based on the results of severe accident analysis. The chemical form of U varied depending on the local amount of Fe and O. In regions of low steel content, the U-containing metallic phase was dominated by -(Zr,U)(O), while regions of high steel content were dominated by Fe(Zr,U) (Laves phase). A few percent of U was transferred to the metallic phases under reducing conditions, raising challenging issues on the chemical removal of nuclear material from fuel debris.

Atmospheric-dispersion database system that can immediately provide calculation results for various source term and meteorological conditions

Terada, Hiroaki; Nagai, Haruyasu; Tanaka, Atsunori*; Tsuzuki, Katsunori; Kadowaki, Masanao

Journal of Nuclear Science and Technology, 57(6), p.745 - 754, 2020/06

https://doi.org/10.1080/00223131.2019.1709994

We have estimated source term and analyzed processes of atmospheric dispersion of radioactive materials released during the Fukushima Daiichi Nuclear Power Station (FDNPS) accident by the Worldwide version of System for Environmental Emergency Dose Information. On the basis of this experience, we developed an dispersion calculation method that can respond to various needs in a nuclear emergency and provide useful information for emergency-response planning. By this method, if a release point is known, it is possible to immediately obtain the prediction results by applying provided source term to the database of dispersion-calculation results prepared in advance. With this function, it is easy to compare results by applying various source term with monitoring data, and to find out the optimum source term, which was applied for the source term estimation of the FDNPS accident. By performing this calculation with past meteorological-analysis data, it is possible to immediately get dispersion-calculation results for various source term and meteorological conditions. This database can be used for pre-accident planning, such as optimization of a monitoring plan and understanding of events to be supposed in considering emergency countermeasures.