Intercomparison of numerical atmospheric dispersion prediction models for emergency response to emissions of radionuclides with limited source information in the Fukushima Dai-ichi Nuclear Power Plant accident

Iwasaki, Toshiki*; Sekiyama, Tsuyoshi*; Nakajima, Teruyuki*; Watanabe, Akira*; Suzuki, Yasushi*; Kondo, Hiroaki*; Morino, Yu*; Terada, Hiroaki; Nagai, Haruyasu; Takigawa, Masayuki*; et al.

Atmospheric Environment, 214, p.116830_1 - 116830_11, 2019/10

https://doi.org/10.1016/j.atmosenv.2019.116830

The utilization of numerical atmospheric dispersion prediction (NDP) models for accidental discharge of radioactive substances was recommended by a working group of the Meteorological Society of Japan. This paper is to validate the recommendation through NDP model intercomparison in the accidental release from the Fukushima Dai-ichi Nuclear Power Plant in 2011. Emission intensity is assumed to be constant during the whole forecast period for the worst-case scenario unless time sequence of emission is available. We expect to utilize forecasts of surface air contaminations for preventions of inhalations of radioactive substances, and column-integrated amounts for mitigation of radiation exposure associated with wet deposition. Although NDP forecasts have ensemble spread, they commonly figure out relative risk in space and time. They are of great benefit to disseminating effective warnings to public without failure. The multi-model ensemble technique may be effective to improve the reliability.

International challenge to model the long-range transport of radioxenon released from medical isotope production to six Comprehensive Nuclear-Test-Ban Treaty monitoring stations

Maurer, C.*; Bar, J.*; Kusmierczyk-Michulec, J.*; Crawford, A.*; Eslinger, P. W.*; Seibert, P.*; Orr, B.*; Philipp, A.*; Ross, O.*; Generoso, S.*; et al.

Journal of Environmental Radioactivity, 192, p.667 - 686, 2018/12

https://doi.org/10.1016/j.jenvrad.2018.01.030

It is very important to understand the impact for CTBT stations caused by radioxenon emitted from medical isotope production facilities for detection of underground nuclear tests. Predictions of the impact on six CTBT radionuclide stations in the Southern Hemisphere of radioxenon emitted from the medical isotope production facility in Australia were carried out by participants from ten nations using ATM (Atmospheric Transport Modeling) based on the emission data of radioxenon from this facility, as part of study on impact of radioxenon emitted from medical isotope production facilities on CTBT radionuclide stations.

A New detector system for the measurement of high-energy prompt -rays for low-energy neutron induced fission

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Lguillon, R.*; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; Ache, M.*; Astier, A.*; et al.

Nuclear Instruments and Methods in Physics Research A, 906, p.88 - 96, 2018/10

https://doi.org/10.1016/j.nima.2018.07.055

We have developed a new setup to measure prompt fission -ray spectra in neutron induced fission up to energies sufficient to reveal the structure associated with giant dipole resonances of fission fragments. The setup consists of multi-wire proportional counters, to detect both fission fragments in coincidence, and two large volume (101.6 mm in diameter and 127.0 mm in length) LaBr(Ce) scintillators, to measure the -rays. The setup was used to obtain the prompt fission -ray spectrum for thermal neutron induced fission of U at the PF1B cold-neutron beam facility of the Institut Laue-Langevin, Grenoble, France. We have successfully measured the -ray spectrum up to energies of about 20 MeV, what extends the currently known -ray spectrum limit to higher energies by approximately a factor of two.

Measurement of high-energy prompt -rays from neutron induced fission of U-235

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Lguillon, R.; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; Astier, A.*; Pollitt, A.*; et al.

EPJ Web of Conferences, 146, p.04036_1 - 04036_4, 2017/09

https://doi.org/10.1051/epjconf/201714604036

The measurement of the prompt fission -ray spectrum (PFGS) is quite important to study the de-excitation process of neutron-rich fission fragments as well as to generate data required to design a generation-IV reactors. The PFGS measured for spontaneous fission of Cf shows a broad hump at energies more than 8 MeV. This is interpreted as a giant dipole resonance (GDR) of the fragments centered around 15 MeV. To understand how the GDR is populated in the fission process, one needs to measure the PFGS for the reactions with the mass yields different from the spontaneous fission of Cf, such as (n,f). The measurements of the PFGS for (n,f), however, are limited less than 9 MeV even in the recent experiment. This prompts us to make a new measurement to extend the know PFGS up to 20 MeV. The measurement has been carried out at the PF1B beam line of Institut Laue-Langevin. In this contribution we will present the results obtained the measurement.

Model inter-comparison of atmospheric Cs-137 from the Fukushima Daiichi Nuclear Power Plant accident

Kitayama, Kyo*; Morino, Yu*; Takigawa, Masayuki*; Nakajima, Teruyuki*; Hayami, Hiroshi*; Nagai, Haruyasu; Terada, Hiroaki; Saito, Kazuo*; Shimbori, Toshiki*; Kajino, Mizuo*; et al.

no journal, , 

For the evaluation of the validity and variability of atmospheric transport model results, we compared results of seven models submitted for the model inter-comparison project of Science Council of Japan to simulate Cs released from the Fukushima Daiichi Nuclear Power Plant. Model reproducibility was assessed with the observed hourly atmospheric concentrations of Cs in Tohoku and Kanto regions. Among nine plumes from 12 to 21 in March 2011, performance of the models was the best for the plume which dispersed over the Kanto region in 15 March. The models generally reproduced the observed Cs concentrations in plumes which widely spread inland of Tohoku or Kanto regions. By contrast, the models largely underestimated the observed Cs concentrations for the case which passed coastal areas of Japan. Ensemble average of seven models showed reasonable performance for most of plumes, and no individual models reproduced better than the ensemble average.

Model intercomparison study for atmospheric Cs from the Fukushima Daiichi Nuclear Power Plant Accident using identical input data

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qulo, D.*; et al.

no journal, , 

An intercomparison of atmospheric dispersion model targeting on the physical process of Cs released from the Fukushima Daiichi Nuclear Power Plant was conducted. Twelve atmospheric models participated in this project. To exclude the uncertainties of the model result due to the emission inventory and meteorological data, all models used the same emission and meteorological data. Concentration of Cs from the national suspended particle matter monitoring network and the deposition density by the aircraft were used for the comparison between results of the model and observation. Our analyses elucidated the figure of merit in space (FMS) of the model ensemble mean was improved from a previous model intercomparson about the accumulated deposition. The model ensemble mean captured approximately 36% of the observed high concentration. The inter-model spread of the capture rate was from 8% to 38%. It was originated from the difference in deposition and diffusion processes among the models.

Model intercomparison project for cesium (Cs) from the Fukushima Daiichi Nuclear Power Station Accident using identical meteorological data and source term

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qulo, D.*; et al.

no journal, , 

no abstracts in English

Measurement of high-energy prompt fission rays in U(n,f)

Ogawa, Tatsuhiko; Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Lguillon, R.*; Soldner, T.*; Hambsch, F.-J.*; Ache, M.*; Astier, A.*; et al.

no journal, , 

Measurement of -rays emitted from fission of actinide has been conducted for radiation transport analysis in reactors, safety of spent fuel, and fundamental nuclear physics. In earlier studies, -rays up to 8 MeV were measured because they are those emitted by fission fragments at excited states. According to some theoretical studies, however, some fission fragments have excitation energy up to 20 MeV and they emit -rays above 8 MeV. In this study, the -rays produced by fission of U induced by thermal neutrons were measured with LaBr scintillators at the high-flux reactor in the Institut Laue Langevin. The obtained -ray spectrum agreed with the earlier measurement below 8 MeV, forms a bump above 10 MeV, and smoothly continued up to 20 MeV. The measurement in this study clarified the -ray energy spectrum attributed to fission reactions up to 20 MeV in case of U(n,f).

Measurement of high-energy prompt fission -ray emission in U ()

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Lguillon, R.*; Ogawa, Tatsuhiko; Soldner, T.*; Kster, U.*; Hambsch, F.-J.*; Kawano, Toshihiko*; et al.

no journal, , 

Review of model intercomparison projects (MIPs) of atmospheric dispersion model for Cs emitted from Fukushima Daiichi Nuclear Power Plant; MIPs with identical source term and meteorological data

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kadowaki, Masanao; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; et al.

no journal, , 

Two Model Intercomparison of Projects (MIPs) of atmospheric dispersion model targeting on Cs released from Fukushima Daiichi Nuclear Power Plant (FDNPP) on March 2011 were conducted. Both MIPs were conducted using an identical source term of Cs, identical meteorological data, and the same horizontal grid resolution (3 km and 1 km) to exclude the uncertainties of the model originated from them. Our analyses indicated that most of the model well simulated the atmospheric Cs obtained from the operational aerosol sampling of the national suspended particle matter network. Our analyses also indicated that meteorological data were most critical for reproducing the atmospheric Cs events, and the extent of the horizontal diffusion and the deposition were critical if the meteorological field was reasonably simulated. The comparison of the results between the two MIPs elucidated that the fine grid resolution is required to simulate atmospheric Cs in the vicinity of FDNPP, but the use of the fine grid resolution does not always improve the performance of the models especially for areas distant from the FDNPP. The results of both MIPs elucidated that the good performance of some models improved the performance of the multimodel, highlighting the advantage of using a multimodel ensemble.