A Model intercomparison of atmospheric Cs concentrations from the Fukushima Daiichi Nuclear Power Plant accident, phase III; Simulation with an identical source term and meteorological field at 1-km resolution

Sato, Yosuke*; Sekiyama, Tsuyoshi*; Fang, S.*; Kajino, Mizuo*; Qurel, A.*; Qulo, D.*; Kondo, Hiroaki*; Terada, Hiroaki; Kadowaki, Masanao; Takigawa, Masayuki*; et al.

Atmospheric Environment; X (Internet), 7, p.100086_1 - 100086_12, 2020/10

https://doi.org/10.1016/j.aeaoa.2020.100086

The third model intercomparison project for investigating the atmospheric behavior of Cs emitted during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident (FDNPP-MIP) was conducted. A finer horizontal grid spacing (1 km) was used than in the previous FDNPP-MIP. Nine of the models used in the previous FDNPP-MIP were also used, and all models used identical source terms and meteorological fields. Our analyses indicated that most of the observed high atmospheric Cs concentrations were well simulated, and the good performance of some models improved the performance of the multi-model ensemble. The analyses also confirmed that the use of a finer grid resolution resulted in the meteorological field near FDNPP being better reproduced. The good representation of the wind field resulted in the reasonable simulation of the narrow distribution of high deposition amount to the northwest of FDNPP and the reduction of the overestimation over the area to the south of FDNPP. In contrast, the performance of the models in simulating plumes observed over the Nakadori area, the northern part of Gunma, and the Tokyo metropolitan area was slightly worse.

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.

Preliminary analysis of sodium experimental apparatus PLANDTL-2 for development of evaluation method for thermal-hydraulics in reactor vessel of sodium fast reactor under decay heat removal system operation condition

Ono, Ayako; Tanaka, Masaaki; Miyake, Yasuhiro*; Hamase, Erina; Ezure, Toshiki

Mechanical Engineering Journal (Internet), 7(3), p.19-00546_1 - 19-00546_11, 2020/06

https://doi.org/10.1299/mej.19-00546

Fully natural circulation decay heat removal systems (DHRSs) are to be adopted for sodium fast reactors, which is a passive safety feature without any electrical pumps. It is required to grasp the thermal-hydraulic phenomena in the reactor vessel and evaluate the coolability of the core under the natural circulation not only for the normal operating condition but also for severe accident conditions. In this paper, the numerical results of the preliminary analysis for the sodium experimental condition with the PLANDTL-2 are discussed to establish an appropriate numerical models for the reactor core including the gap region among the subassemblies and the DHX. From these preliminary analyses, the characteristics of the thermal-hydraulics behavior in the PLANDTL-2 to be focused are extracted.

Decontamination simulation and future prediction of air dose rate in difficult to return zone in Fukushima Prefecture

Yamashita, Takuya; Sawada, Noriyoshi*

JAEA-Research 2019-010, 227 Pages, 2020/03

JAEA-Research-2019-010.pdf:21.44MB
JAEA-Research-2019-010(errata).pdf:0.5MB

In order to support the decontamination activities proceeded by the national government and municipalities in terms of technology, we have developed a simulation system "RESET" which predicts the effect of decontamination. We also developed a "two-component model" for the purpose of predicting long-term changes in the air dose rate. We use these tools to perform decontamination simulation and predictive analysis of the air dose rate after decontamination, and provide information to the national government and municipalities aiming for reconstruction. In this report, the verification result of the prediction methods implemented using actual measurement data obtained in the "Decontamination model demonstration project in difficult-to-return zone" and "Survey result on transition of air dose rate after decontamination model demonstration project" conducted by Ministry of the Environment. In addition, the decontamination simulation conducted for the entire difficult-to-return area and the results of future prediction of the air dose rate after decontamination are shown.

Monte Carlo radiation transport modelling of the current-biased kinetic inductance detector

Malins, A.; Machida, Masahiko; Vu, TheDang; Aizawa, Kazuya; Ishida, Takekazu*

Nuclear Instruments and Methods in Physics Research A, 953, p.163130_1 - 163130_7, 2020/02

https://doi.org/10.1016/j.nima.2019.163130

Summaries of research and development activities by using supercomputer system of JAEA in FY2018 (April 1, 2018 - March 31, 2019)

HPC Technology Promotion Office*

JAEA-Review 2019-017, 182 Pages, 2020/01

JAEA-Review-2019-017.pdf:11.11MB

Japan Atomic Energy Agency (JAEA) conducts research and development (R&D) in various fields related to nuclear power as a comprehensive institution of nuclear energy R&Ds, and utilizes computational science and technology in many activities. As shown in the fact that about 20 percent of papers published by JAEA are concerned with R&D using computational science, the supercomputer system of JAEA has become an important infrastructure to support computational science and technology. In FY2018, the system was used for R&D aiming to restore Fukushima (environmental recovery and nuclear installation decommissioning) as a priority issue, as well as for JAEA's major projects such as research and development of fast reactor cycle technology, research for safety improvement in the field of nuclear energy, and basic nuclear science and engineering research. This report presents a great number of R&D results accomplished by using the system in FY2018, as well as user support, operational records and overviews of the system, and so on.

Dosimetric dependence of ocular structures on eye size and shape for external radiation fields of electrons, photons, and neutrons

Furuta, Takuya; El Basha, D.*; Iyer, S. S. R.*; Correa Alfonso, C. M.*; Bolch, W. E.*

Journal of Radiological Protection, 39(3), p.825 - 837, 2019/09

https://doi.org/10.1088/1361-6498/ab2bcb

Despite large variation of human eye, only one computational eye model has been adopted in almost all the radiation transport simulation studies. We thus adopted a new scalable and deformable eye model and studied the radiation exposure by electrons, photons, and neutrons in the standard radiation fields such as AP, PA, RLAT, ROT, by using Monte Carlo radiation transport code PHITS. We computed the radiation exposure for 5 eye models (standard, large, small, myopic, hyperopic) and analyzed influence of absorbed dose in ocular structures on eye size and shape. Dose distribution of electrons is conformal and therefore the absorbed doses in ocular structures depend on the depth location of each ocular structure. We thus found a significant variation of the absorbed doses for each ocular structure for electron exposure due to change of the depth location affected by eye size and shape. On the other hand only small variation was observed for photons and neutrons exposures because of less conformal dose distribution of those particles.

CFD analysis of the CIGMA experiments on the heated JET injection into containment vessel with external surface cooling

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

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.5463 - 5479, 2019/08

Parametric analysis of bubble and dissolved gas behavior in primary coolant system of sodium-cooled fast reactors

Matsushita, Kentaro; Ito, Kei*; Ezure, Toshiki; Tanaka, Masaaki

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 9 Pages, 2019/05

A numerical simulation code named SYRENA has been developed in JAEA to analyze the behavior of entrained bubbles and dissolved gas in the primary coolant of sodium-cooled fast reactor (SFR). In the present study, a flow network model of SYRENA to a hypothetical pool type reactor was developed and the non-condensable gas behavior was investigated through the comparison with that in the loop type reactor. The effect of the dipped-plate (D/P) tentatively introduced into the pool-type reactor on the gas behavior was investigated through the parametric analyses about the sodium exchange flow rate through the D/P and the gas entrainment rate at the free surface. It was suggested that the increase in the exchange flow rate through the D/P doesn't always work to decrease the bubble volume in the primary coolant system.

Estimation method of systematic uncertainties in Monte Carlo particle transport simulation based on analysis of variance

Hashimoto, Shintaro; Sato, Tatsuhiko

Journal of Nuclear Science and Technology, 56(4), p.345 - 354, 2019/04

https://doi.org/10.1080/00223131.2019.1585989

Particle transport simulations based on the Monte Carlo method have been applied to shielding calculations. Estimation of not only statistical uncertainty related to the number of trials but also systematic one induced by unclear physical quantities is required to confirm the reliability of calculated results. In this study, we applied a method based on analysis of variance to shielding calculations. We proposed random- and three-condition methods. The first one determines randomly the value of the unclear quantity, while the second one uses only three values: the default value, upper and lower limits. The systematic uncertainty can be estimated adequately by the random-condition method, though it needs the large computational cost. The three-condition method can provide almost the same estimate as the random-condition method when the effect of the variation is monotonic. We found criterion to confirm convergence of the systematic uncertainty as the number of trials increases.