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Journal Articles

$^{129}$ I/ $^{127}$ I and $^{14}$ C records in a modern coral from Rowley Shoals off northwestern Australia reflect the 20th-century human nuclear activities and ocean/atmosphere circulations

Mitsuguchi, Takehiro; Okabe, Nobuaki*; Yokoyama, Yusuke*; Yoneda, Minoru*; Shibata, Yasuyuki*; Fujita, Natsuko; Watanabe, Takahiro; Kokubu, Yoko

Journal of Environmental Radioactivity, 235-236, p.106593_1 - 106593_10, 2021/09

https://doi.org/10.1016/j.jenvrad.2021.106593

Times Cited Count：5 Percentile：35.21(Environmental Sciences)

For a contribution to developing the usage of iodine-129 ( $^{129}$ I) as a tracer of deep-seated fluid, $^{129}$ I/ $^{127}$ I and $^{14}$ C were measured for annual bands (AD 1931-1991) of a modern coral collected from Northwestern Australia; the measurements were performed using the JAEA-AMS-TONO-5MV for $^{129}$ I/ $^{127}$ I and an AMS facility of the University of Tokyo for $^{14}$ C. Results indicate that both $^{129}$ I/ $^{127}$ I and $^{14}$ C distinctly increase from 1950s. The $^{14}$ C increase can be ascribed to atmospheric nuclear tests, while the $^{129}$ I/ $^{127}$ I increase is due to nuclear-fuel reprocessing as well as atmospheric nuclear tests. These results are in good agreement with previous studies, indicating that the $^{129}$ I/ $^{127}$ I measurement by JAEA-AMS-TONO-5MV has been further developed.

JAEA Reports

Design and demonstration of the prototype nitrogen circulation refining system for nitride fuel fabrication (Contract research)

Iwasa, Toma; Takano, Masahide

JAEA-Technology 2020-024, 29 Pages, 2021/03

JAEA-Technology-2020-024.pdf:2.33MB

Partitioning and transmutation of minor actinides (MA) is an important issue to reduce volume and radio-toxicity of high-level radioactive wastes. In Nuclear Science Research Institute, we have been carrying out R&D on MA-bearing nitride fuel for accelerator driven system. In the actual nitride fuel fabrication process, a special nitrogen gas highly enriched with $^{15}$ N is required to avoid $^{14}$ C production from $^{14}$ N by (n,p) reaction in the fuel. For the economical use of such expensive gas, we need a nitrogen circulation refining system that can remove carbon monoxide (CO) evolved by carbothermic nitridation of oxides and can use the nitrogen gas in the closed system without loss. To develop the system, at first we listed up the performance requirements, and then designed and assembled a prototype system for laboratory-scale demonstration. The system consists of CO removal unit and circulation unit that can automatically keep the system pressure and the gas flow rate constant. As a result of demonstration on the nitridation of oxide, both units completely satisfy the requirements. We confirmed that the concept can be applied to the actual fuel fabrication with further additional function such as automatic hydrogen feed for the control of decarburization.

JAEA Reports

Survey of $^{15}$ N isotopic enrichment plant and its cost for nitride fuel fabrication (Contract research)

Takano, Masahide

JAEA-Review 2020-080, 24 Pages, 2021/03

JAEA-Review-2020-080.pdf:1.71MB

Nitride is one of the potential fuel forms for minor actinide transmutation by the accelerator driven system. However, to avoid the $^{14}$ C production from $^{14}$ N by (n, p) reaction in the fuel, the special N $_{2}$ gas highly enriched with $^{15}$ N is needed for the fuel fabrication. To realize the availability of such gas has been an important issue. In this report, the degree of $^{15}$ N enrichment and gas amount required for the fuel fabrication are shown first, and then among the existing isotopic enrichment methods, N $_{2}$ cryogenic distillation is found to be a promising method from the viewpoint of constructing a huge scale plant because of its non-hazardous feature. Some commercial plants for $^{18}$ O enrichment based on the similar method have already been operated in Japan. Its technology and components can be applied to the $^{15}$ N enrichment plant. Assuming the supply of $^{15}$ N $_{2}$ gas from a cryogenic distillation plant, a series of enrichment simulation is performed to evaluate the plant size as functions of targeted degree of enrichment and annual production. By using the simulation results, the basic specifications for plant components and equipment are designed. As a result, a huge plant for annual production of 1000 kg $^{15}$ N $_{2}$ gas with 99% enrichment is found to be technically feasible. The $^{15}$ N $_{2}$ gas production cost is also evaluated to be approximately 1/30 of the current distribution price. This survey shows the availability of $^{15}$ N $_{2}$ gas required for the nitride fuel fabrication in both technical and economic aspects.

Journal Articles

Impacts of C-uptake by plants on the spatial distribution of $^{14}$ C accumulated in vegetation around a nuclear facility; Application of a sophisticated land surface $^{14}$ C model to the Rokkasho reprocessing plant, Japan

Ota, Masakazu; Katata, Genki; Nagai, Haruyasu; Terada, Hiroaki

Journal of Environmental Radioactivity, 162-163, p.189 - 204, 2016/10

https://doi.org/10.1016/j.jenvrad.2016.05.032

Times Cited Count：7 Percentile：22.36(Environmental Sciences)

Impacts of plant C uptake on ( $^{14}$ C) distributions around a nuclear facility were investigated by a land surface $^{14}$ C model (SOLVEG-II). The simulation combined the SOLVEG-II with a mesoscale model and an dispersion model was applied to $^{14}$ CO $_{2}$ transfer at test operations of the Rokkasho reprocessing plant (RRP) in 2007. The calculated $^{14}$ C-specific activities in rice grains agreed with the observations. Numerical experiment of chronic $^{14}$ CO $_{2}$ release from the RRP showed that $^{14}$ C-specific activities of rice plants at harvest differed from the annual mean ones in the air, which was attributed to seasonal variations in atmospheric $^{14}$ CO $_{2}$ and plant growth. $^{14}$ C accumulation in plant significantly increased when $^{14}$ CO $_{2}$ releases were limited during daytime, compared with the results observed during nighttime, due to extensive $^{14}$ CO $_{2}$ uptake by daytime photosynthesis. These results indicated that plant growth and photosynthesis should be considered in predictions of ingestion dose of $^{14}$ C for long-term chronic and short-term diurnal releases of $^{14}$ CO $_{2}$ , respectively.