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Matsu'ura T.,Geological Survey of Japan | Matsu'ura T.,Japan Nuclear Energy Safety Organization | Miyagi I.,Geological Survey of Japan | Furusawa A.,Geological Survey of Japan
Quaternary Research | Year: 2011

We detected late Pleistocene cummingtonite-bearing cryptotephras in loess deposits in NE Japan and correlated them with known tephras elsewhere by using major-element compositions of the cummingtonite. This is the first time cryptotephras have been identified by analysis of a crystal phase rather than glass shards. In central NE Japan, four cummingtonite-bearing tephras, the Ichihasama pumice, the Dokusawa tephra, the Naruko-Nisaka tephra, and the Adachi-Medeshima tephra, are present in late Pleistocene loess deposits. Because the cummingtonite chemistry of each tephra is different and characteristic, it is potentially a powerful tool for detecting and identifying cryptotephras. An unidentified cummingtonite-bearing cryptotephra previously reported to be present in the late Pleistocene loess deposits at Kesennuma (Pacific coast) did not correlate with any of the known cummingtonite-bearing tephras in central NE Japan, but instead with the Numazawa-Kanayama tephra (erupted from the Numazawa caldera, southern NE Japan), although Kesennuma is well beyond the previously reported area of the distribution of the Numazawa-Kanayama tephra. Three new cummingtonite-bearing cryptotephras in the mid and late Pleistocene loess deposits (estimated to be less than 82. ka, 100-200. ka, and ca. 250. ka) on the Isawa upland were also detected. © 2010 University of Washington. Source

Yamamoto T.,Japan Nuclear Energy Safety Organization
Journal of Nuclear Science and Technology | Year: 2012

Based on periodically performed radioactivity measurements on soil samples in the site of Fukushima Dai-Ichi Nuclear Power Station, activity ratios to 137Cs of fission product and heavy nuclides were obtained for Sr, Nb, Mo, Tc, Ru, Ag, Te, I, Ba, La, Pu, Am, and Cm isotopes. By exponentially fitting or averaging, the activity ratios at the core shutdown were estimated. Using correlations of activity ratios of 134Cs to 137Cs, and 238Pu to the sum of 239Pu and 240Pu against fuel burnup, burnup of the fuel sourcing the deposited activity of the soil was estimated. The activity ratios to 137Cs of each nuclide on the deposited activity were divided by those calculated on the fuel at the shutdown to obtain the deposited activity fraction of each nuclide as a relative value to 137Cs, which also corresponds to the deposited fraction of each element as a relative value to Cs. The obtained deposited fractions relative to Cs are the orders of 10 -4 to 10 -2 for Sr, 10 -5 to 10 -3 for Nb, 10 -2 to 10 -1 for Mo, 1 to 10 for I, 10 -3 to 10 -2for Ba, 10 -2 for La, 10 -6 to 10 -3 for Pu, 10 -6 to 10 -4 for Am, and 10 -7 to 10 -5 for Cm. The deposited fractions for Tc, Ag, and Te were not estimated due to the lack of the calculated inventories in the fuel for the relevant measured radioactive nuclides. © 2012 Atomic Energy Society of Japan. All rights reserved. Source

Matsu'ura T.,Japan Nuclear Energy Safety Organization | Furusawa A.,Geological Survey of Japan | Shimogama K.,Dia Consultants Co. | Goto N.,Chiyoda Corporation | Komatsubara J.,Geological Survey of Japan
Quaternary Geochronology | Year: 2014

We investigated late Quaternary deep-sea sequences of the C9001C cores (D/V Chikyu shakedown cruise) to refine the tephrostratigraphy and reconsider the marine terrace chronology along the Pacific coast of northern Honshu, Japan. We identified 16 concentrations (spikes) of glass shards (numbered G1-G16 from top to bottom), which correspond to 12 visible tephras and 4 non-visible tephras (cryptotephras). We correlated several spikes with known dated tephras: G1 with Towada-Ofudo (To-Of: last MIS 3, ≥32ka), G2 with Shikotsu-1 (Spfa-1: mid MIS 3, ≥42-44ka), G3 with Aso-4 (MIS 5b, 87ka), G4 with Toya (MIS 5d, 106ka), G9 with White Pumice (WP: mid MIS 7, 220ka), G12 or G13 with ODP794 2H-2-120 (mid MIS 8, 274-283ka), and G14 with Shiobara-Otawara (So-OT: mid MIS 9, 320ka). We classified spike G6 as a turbidite. The two lowest of these tephras, ODP794 2H-2-120 and So-OT, were assigned to MIS 7 in a previous age model on the basis of the first occurrence of Emiliania huxleyi. However, our tephra-based age model is consistent with the last occurrence of Proboscia curvirostris, and we assigned the core sediment corresponding to MIS 7 from a previously reported segment 55m long to a younger segment 22m long, and then verified that the sedimentation rate was constant through the core. We used the newly obtained age for the WP tephra, along with outcrop and borehole core evidence, to reconsider the marine terrace chronology in the Kamikita Plain. A marine terrace that was previously assigned to MIS 7 with a possible vertical fault offset was reinterpreted as two separate terraces, one correlated with MIS 7e or 7c and the other with MIS 9. Regional uplift rates based on the revised terrace chronology and shoreline angle elevations appear to have been fairly steady at 0.18-0.36m/ky during the late Quaternary. © 2014 The Authors. Source

Ueda Y.,Japan Nuclear Energy Safety Organization
Transactions of the Atomic Energy Society of Japan | Year: 2010

A special committee on "Research on the analysis methods for accident consequence of nuclear fuel facilities (NFFs) " was organized by the Atomic Energy Society of Japan (AESJ) under the entrustment of Japan Atomic Energy Agency (JAEA). The committee aims to research on the state-of-the-art consequence analysis method for probabilistic safety assessment (PSA) of NFFs, such as fuel reprocessing and fuel fabrication facilities. The objective of this research is to obtain the useful information related to establishing quantitative performance objectives and to risk-informed regulation through qualifying issues needed to be resolved for applying PSA to NFFs. The research activities of the committee were mainly focused on the analysis method of consequences for postulated accidents with potentially large consequences in NFFs, e.g. events of criticality, leakage of molten glass, hydrogen explosion, boiling of radioactive solution and fire (including rapid decomposition of TBP complexes), resulting in release of radioactive materials to the environment. The results of the research were summarized in a series of six reports. This report aims to provide common backgrounds of the events studied in order to promote the understanding of the other five technical reports and shows overviews of abnormal events postulated in a reprocessing plant and their features. ©Atomic Energy Society of Japan. Source

Yoshioka K.,Toshiba Corporation | Ando Y.,Japan Nuclear Energy Safety Organization
Journal of Nuclear Science and Technology | Year: 2010

We have developed a deterministic group constant generation method based on the calculation results of a continuous energy Monte Carlo technique. This method features multigroup scattering matrix generation via a weight-to-flux ratio. We performed both diffusion and transport core calculations with this set of multigroup constants generated by the proposed method, which we then validated by both a comparison with a conventional method and a critical experiment analysis. The developed method is particularly useful for innovative fuel and future core designs as Monte Carlo calculations are applicable to any heavy material and the geometrical heterogeneity thereof. ©Atomic Energy Society of Japan. Source

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