Tatsuo Torii

Abstract. Temporal variations in the amount of radionuclides released into the atmosphere during the Fukushima Daiichi Nuclear Power Station (FNPS1) accident and their atmospheric and marine dispersion are essential to evaluate the environmental impacts and resultant radiological doses to the public. In this paper, we estimate the detailed atmospheric releases during the accident using a reverse estimation method which calculates the release rates of radionuclides by comparing measurements of air concentration of a radionuclide or its dose rate in the environment with the ones calculated by atmospheric and oceanic transport, dispersion and deposition models. The atmospheric and oceanic models used are WSPEEDI-II (Worldwide version of System for Prediction of Environmental Emergency Dose Information) and SEA-GEARN-FDM (Finite difference oceanic dispersion model), both developed by the authors. A sophisticated deposition scheme, which deals with dry and fog-water depositions, cloud condensation nuclei (CCN) activation, and subsequent wet scavenging due to mixed-phase cloud microphysics (in-cloud scavenging) for radioactive iodine gas (I2 and CH3I) and other particles (CsI, Cs, and Te), was incorporated into WSPEEDI-II to improve the surface deposition calculations. The results revealed that the major releases of radionuclides due to the FNPS1 accident occurred in the following periods during March 2011: the afternoon of 12 March due to the wet venting and hydrogen explosion at Unit 1, midnight of 14 March when the SRV (safety relief valve) was opened three times at Unit 2, the morning and night of 15 March, and the morning of 16 March. According to the simulation results, the highest radioactive contamination areas around FNPS1 were created from 15 to 16 March by complicated interactions among rainfall, plume movements, and the temporal variation of release rates. The simulation by WSPEEDI-II using the new source term reproduced the local and regional patterns of cumulative surface deposition of total 131I and 137Cs and air dose rate obtained by airborne surveys. The new source term was also tested using three atmospheric dispersion models (Modèle Lagrangien de Dispersion de Particules d'ordre zéro: MLDP0, Hybrid Single Particle Lagrangian Integrated Trajectory Model: HYSPLIT, and Met Office's Numerical Atmospheric-dispersion Modelling Environment: NAME) for regional and global calculations, and the calculated results showed good agreement with observed air concentration and surface deposition of 137Cs in eastern Japan.

Polarized infrared spectra of isotactic polypropylene (IPP),[Complex chemical formula]were measured in the region from 4000 to 80 cm−1. The normal vibrations of these three polymers were calculated for the infrared- and Raman-active A and E species, by the use of the GF-matrix method with the Urey—Bradley force field. The results show a fairly good agreement between the observed and calculated frequencies. The assignments of the absorption bands were given, and discussions were made on the vibrational modes of the bands characteristic of the isotactic helical structures. A computation program for calculating the characteristic values and vectors of a Hermitian matrix was presented. From the normal coordinate treatment applied to the threo- and erythro- model of di-isotactic polypropylene-1-d,[Complex chemical formula]it was found that the polymers prepared from trans- and cis-propylene-1-d, CHD, CH–CH3, have threo- and erythro-di-isotactic structures, respectively, suggesting cis-opening mechanism in the coordinated anionic polymerization [α-TiCl3–Al(C2H5)3 catalyst]. The absorption bands characteristic of crystalline IPP are also observed in the 1:1 mole mixture of IPP and IPP-1,1,2-d3, while these bands disappear in the copolymer with the same chemical composition. This fact shows that these characteristic bands arise from the intramolecular interactions in a helical molecule, and the sequence of a certain number of the same monomeric units in the helix is necessary for appearance of these bands. The 1152 and 975 cm−1 bands, which appear also in molten IPP and an ether-soluble fraction of a commercial polypropylene, are ascribed to the chemical structure of head-to-tail sequence of –CH2–CH(CH3)– units.

Increases of environmental gamma‐ray dose which seem to originate from lightning activity were observed around a nuclear facility in Japan. Dose increases measured by thermoluminescent dosimeters (TLDs) exposed during a period including a lightning flash were up to about 0.1 mGy. Dose rates indicated by environmental radiation monitors around the facility also increased transiently at that time. From pulse‐height analysis of an NaI(Tl) scintillation detector, the photon energy spectrum evaluated by spectral unfolding is continuous with energy up to several MeV, consistent with bremsstrahlung emission from energetic electrons. Furthermore, energy spectra of bremsstrahlung photons emitted from high‐energy electrons are obtained by Monte Carlo calculation. These results are discussed in conjunction with observation.

The ambient dose-rate and the deposition of radioactive cesium was measured by using helicopters in the whole area of Japan to investigate the influence of the radioactivity that discharged into the atmosphere due to the disaster of the Fukushima Daiichi NPP (Nuclear Power Plant), Tokyo Electric Power Company (TEPCO), occurred by the East Japan earthquake and tsunami on March 11, 2011. As a result, the deposition of radioactive cesium on the ground was obtained, and it was clarified that range of Cs spread had been almost limited from the southern part of Iwate Prefecture to Kanto areas. The variation distribution of the dose-rate in Japan was also revealed in this measurement.