Survey on the radioactive substance in the coastal areas near Fukushima Prefecture in FY2019 (Contract research)

Misono, Toshiharu; Tsuruta, Tadahiko; Nakanishi, Takahiro; Sanada, Yukihisa; Shiribiki, Takehiko; Miyamoto, Kenji*; Urabe, Yoshimi*

JAEA-Research 2020-008, 166 Pages, 2020/10

JAEA-Research-2020-008.pdf:13.11MB
JAEA-Research-2020-008(errata).pdf:0.92MB

After the accident at TEPCO Fukushima Daiichi Nuclear Power Station (1F), marine monitoring survey on radioactive substances have been conducted with financially supported by the Nuclear Regulatory Agency from FY2019. Results obtain in the project in FY2019 are presented in this report. Based on scientific grounds, the concept necessary for "progress of sea area monitoring" was arranged for the future medium- to long-term investigation of radiocesium concentrations. As basic information of survey frequency revise, a seabed topography and sediment distribution survey was conducted, and an attempt was made to understand the relationship between the seabed topography and the grain size distribution of bottom sediment. A columnar core sample was collected in the coastal area and analyzed for radioactive cesium concentration. In order to understand the dynamics of radioactive cesium contained in suspended matter flowing in from a river, suspended solids was collected using a sediment trap and the concentration of radioactive cesium was measured. We re-analyzed the towed monitoring data that had been implemented since 2013, and tried to improve the accuracy of the radioactive cesium distribution estimation map in the coastal area.

Development of MIG2DF Version 2

Takai, Shizuka; Kimura, Hideo*; Uchikoshi, Emiko*; Munakata, Masahiro; Takeda, Seiji

JAEA-Data/Code 2020-007, 174 Pages, 2020/09

JAEA-Data-Code-2020-007.pdf:4.23MB

The MIG2DF computer code is a computer program that simulates groundwater flow and radionuclide transport in porous media for the safety assessment of radioactive waste disposal. The original version of MIG2DF was released in 1992. The original code employs a two-dimensional (vertical or horizontal cross-section, or an axisymmetric configuration) finite-element method to approximate the governing equations for density-dependent saturated-unsaturated groundwater flow and radionuclide transport. Meanwhile, for geological disposal of radioactive wastes, landscape evolution such as uplift and erosion needs to be assessed as a long-term geological and climate events, considering site conditions. In coastal areas, the impact to groundwater flow by change of salinity distribution to sea level change also needs to be considered. To deal with these events in the assessment, we have revised the original version of MIG2DF and developed the external program which enables MIG2DF to consider unsteady landscape evolution. In these developments, this report describes an upgrade of MIG2DF (Version 2) and presents the configuration, equations, methods, and verification. This reports also give the explanation external programs of MIG2DF: PASS-TRAC (the particle tracking code), PASS-PRE (the code for dataset preparation), and PASS-POST (the post-processing visualization system).

Unsteady natural convection in a cylindrical containment vessel (CIGMA) with external wall cooling; Numerical CFD simulation

Hamdani, A.; Abe, Satoshi; Ishigaki, Masahiro; Shibamoto, Yasuteru; Yonomoto, Taisuke

Energies (Internet), 13(14), p.3652_1 - 3652_22, 2020/07

https://doi.org/10.3390/en13143652

Method for groundwater monitoring on the disposal of radioactive waste

Murakami, Hiroaki; Iwatsuki, Teruki; Takeuchi, Ryuji; Nishiyama, Nariaki*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(1), p.22 - 33, 2020/06

https://doi.org/10.3327/jnuce.27.1_22

Geological disposal of radioactive waste requires the large amounts of fundamental technical knowledge throughout the project. Monitoring is carried out to collect site-relevant information for the creation of an environmental database, to assist in the decision-making process, etc. We summarized the current technical level and problems of the groundwater monitoring in the world. Through the research and technology development so far, the technologies have been developed for drilling borehole in the geological environment survey prior to monitoring and the selection of the monitoring site. However, the following technical developments are remaining issues: long-term operation method of monitoring equipment, retrieving method of monitoring equipment after long-term operation, transport method of backfill material for borehole sealing, technical basis for the sealing performance when the borehole-protective casing and strainer tube are left.

Experimental and analytical investigation of formation and cooling phenomena in high temperature debris bed

Hotta, Akitoshi*; Akiba, Miyuki*; Morita, Akinobu*; Konovalenko, A.*; Vilanueva, W.*; Bechta, S.*; Komlev, A.*; Thakre, S.*; Hoseyni, S. M.*; Skld, P.*; et al.

Journal of Nuclear Science and Technology, 57(4), p.353 - 369, 2020/04

https://doi.org/10.1080/00223131.2019.1691078

Improvements on evaluation functions of a probabilistic fracture mechanics analysis code for reactor pressure vessels

Lu, K.; Katsuyama, Jinya; Li, Y.

Journal of Pressure Vessel Technology, 142(2), p.021208_1 - 021208_11, 2020/04

https://doi.org/10.1115/1.4045512

A Study of a calibration technique for a newly developed thyroid monitor and its uncertainties due to body size for radioiodine measurements

Yoshitomi, Hiroshi; Nishino, Sho; Tanimura, Yoshihiko; Takahashi, Masa

Radiation Measurements, 133, p.106279_1 - 106279_6, 2020/04

https://doi.org/10.1016/j.radmeas.2020.106279

Uncertainty of the body size on the counting efficiency of a newly developed thyroid monitor was estimated by Monte Carlo simulations using several voxel phantoms. Overlying tissue thickness was a major impact factor on the counting efficiency. As a result, uncertainty related to the body size of the monitored subject was found to be 25%.

Development of database of dose reduction factor for reducing equivalent doses to the thyroid by implementing iodine thyroid blocking (Contract research)

Kimura, Masanori; Munakata, Masahiro; Hato, Shinji*; Kanno, Mitsuhiro*

JAEA-Data/Code 2020-002, 38 Pages, 2020/03

JAEA-Data-Code-2020-002.pdf:3.23MB

To consider the method of implementing urgent protective actions in a nuclear accident appropriately, the authors have been assessing the effects of reducing doses by taking urgent protective actions using a Level 3 Probabilistic Risk Assessment (PRA) code, the OSCAAR, developed by the JAEA. Iodine thyroid blocking is an effective urgent protective action to reduce equivalent doses to the thyroid due to inhalation of radioactive iodine. However, the timing of the administration of stable iodine (SI) is important to maximize the effectiveness for thyroidal blocking. Therefore, the careful consideration should be given to the most effective way of iodine thyroid blocking when preparing off-site emergency plans. In the present study, the authors developed a new metabolic model for thyroid by combining the respiratory tract model (Publ.66) and gastrointestinal tract model (Publ.30) of the ICRP with a metabolic model for thyroid (Johnson's model) in order to calculate the behavior of radioiodine and stable iodine in the body more realistically. The model is useful to evaluate the effect of the administration of SI for reducing equivalent doses to the thyroid depending on the its timing. We also calculated the reduction factor for equivalent doses to the thyroid in order to the thyroid by using the model, and then developed the its database for the OSCAAR. Consequently, the OSCAAR can evaluate the effectiveness for thyroidal blocking realistically and promptly.

Experimental research on pool scrubbing of particles of radioactive materials

Akiba, Miyuki*; Hotta, Akitoshi*; Abe, Yutaka*; Sun, Haomin

Nippon Genshiryoku Gakkai Wabun Rombunshi, 19(1), p.1 - 15, 2020/02

https://doi.org/10.3327/taesj.J18.042

Tests at three different scales were conducted in order to understand the mechanisms of pool scrubbing. In the small-scale separate effect test, high resolution two-phase flow measurement techniques such as a high-speed camera, wire mesh sensor and PIV were applied to capture the behaviors of a single bubble and two-phase flow structures. In the large-scale integral effect test, the dependence of the aerosol removal efficiency on submergence and pool temperature was measured under constant pressure and depressurized conditions. To clarify relationships between individual phenomena and combined phenomena observed in two tests, the mid-scale integral effect test was undertaken.

Fracture limit of high-burnup advanced fuel cladding tubes under loss-of-coolant accident conditions

Narukawa, Takafumi; Amaya, Masaki

Journal of Nuclear Science and Technology, 57(1), p.68 - 78, 2020/01

https://doi.org/10.1080/00223131.2019.1659873