[en] Purpose: To store radioactive gaseous wastes from reactor equipment in a storage tank without using any compresser or vacuum pump. Method: Gaseous wastes concentrated in radioactive gaseous waste processing device are introduced into a gas holder accommodating a cooled adsorbent (for example: activated carbon, molecular sieves and the like), in which they are adsorbed in the adsorbent. Then, the temperature of the gas holder is increased to subject gaseous wastes to desorption, and the gaseous wastes are compressed in the storage tank. According to the present invention, the interior of the system other than at the time of the gaseous waste sealing operation is substantially in an evacuated state, and therefore the present invention has such an effect that the leakage of radioactive gas to the outside of the system can be avoided. (Kamimura, M.)

[en] Object: To effectively attenuate low density radioactive rare gases and radioactive iodine contained in waste gases in a large airflow ventilation system to purify the waste gases before discharging into atmosphere. Structure: In discharging large airflow waste gases in a ventilation system in an atomic power plant through a chimney, the aforesaid waste gases are introduced into a liquefaction and distilling apparatus to separate into nitrogen and oxygen, which occupy a greater part thereof, and small quantities of oxygen or the like containing enriched rare gases and iodine, the former being discharged through the chimney directly, while the latter is sent to a delay device to attenuate the radioactivity before the discharge thereof through the chimney. (Kamimura, M.)

[en] A process-based model for "1"3"7Cs transfer in forest surface environments was developed to assess the dynamic behavior of Fukushima-derived "1"3"7Cs in a Japanese forest. The model simulation successfully reproduced the observed data from 3 year migration of "1"3"7Cs in the organic and mineral soil layers at a contaminated forest near Fukushima. The migration of "1"3"7Cs from the organic layer to the mineral soil was explained by the direct deposition pattern on the forest floor and the turnover of litter materials in the organic layer under certain ecological conditions. Long-term predictions indicated that more than 90% of the deposited "1"3"7Cs would remain within the top 5 cm of the soil for up to 30 years after the accident, suggesting that the forest acts as an effective long-term reservoir of "1"3"7Cs with limited transfer via the groundwater pathway. The model was also used to explore the potential impacts of soil organic matter (SOM) interactions on the mobility and bioavailability of "1"3"7Cs in the soil–plant system. The simulation results for hypothetical organic soils with modified parameters of "1"3"7Cs turnover revealed that the SOM-induced reduction of "1"3"7Cs adsorption elevates the fraction of dissolved "1"3"7Cs in the soil solution, thereby increasing the soil-to-plant transfer of "1"3"7Cs without substantially altering the fractional distribution of "1"3"7Cs in the soil. Slower fixation of "1"3"7Cs on the flayed edge site of clay minerals and enhanced mobilization of the clay-fixed "1"3"7Cs in organic-rich soils also appeared to elevate the soil-to-plant transfer of "1"3"7Cs by increasing the fraction of the soil-adsorbed (exchangeable) "1"3"7Cs. A substantial proportion (approximate 30%–60%) of "1"3"7Cs in these organic-rich soils was transferred to layers deeper than 5 cm decades later. These results suggested that SOM influences the behavior of "1"3"7Cs in forests over a prolonged period through alterations of adsorption and fixation in the soil. - Highlights: • Dynamics of Fukushima-derived "1"3"7Cs (Cs) in a forest was assessed by a new model • Initially high Cs releases from the organic layer were reproduced by rain leaching • Litter decomposition and fixation of Cs in soil controlled subsequent Cs dynamics • Bioavailability and mobility of Cs were significantly increased in organic soils • SOM-induced alteration of adsorption and fixation processes affected Cs dynamics

[en] Object: To enable reduction of cooling time, simplification of maintenance, and release of cooling gas outside system. Structure: In starting of the liquefaction and distillation apparatus, liquid nitrogen is introduced into the tower bottom of a rectification tower from a liquid nitrogen tank through a liquid nitrogen supply line to vaporize the liquid nitrogen with help of heat entered from outside and a heater. The vaporized nitrogen gas moves up while cooling the interior of the rectification tower and is guided by a vacuum pump from the top of tower toward the purifying gas line and low temperature heat exchanger and disharging into atmosphere. When the interior of the apparatus is sufficiently cooled in a manner as described above, the liquid nitrogen supply line is closed, the liquid nitrogen is fed to a condenser, and the waste gases containing the radioactive rare gases from the raw exhaust supply line are introduced into the rectification tower for entry of normal operation. (Kamimura, M.)

[en] The impacts of carbon uptake by plants on the spatial distribution of radiocarbon (¹⁴C) accumulated in vegetation around a nuclear facility were investigated by numerical simulations using a sophisticated land surface ¹⁴C model (SOLVEG-II). In the simulation, SOLVEG-II was combined with a mesoscale meteorological model and an atmospheric dispersion model. The model combination was applied to simulate the transfer of ¹⁴CO₂ and to assess the radiological impact of ¹⁴C accumulation in rice grains during test operations of the Rokkasho reprocessing plant (RRP), Japan, in 2007. The calculated ¹⁴C-specific activities in rice grains agreed with the observed activities in paddy fields around the RRP within a factor of four. The annual effective dose delivered from ¹⁴C in the rice grain was estimated to be less than 0.7 μSv, only 0.07% of the annual effective dose limit of 1 mSv for the public. Numerical experiments of hypothetical continuous atmospheric ¹⁴CO₂ release from the RRP showed that the ¹⁴C-specific activities of rice plants at harvest differed from the annual mean activities in the air. The difference was attributed to seasonal variations in the atmospheric ¹⁴CO₂ concentration and the growth of the rice plant. Accumulation of ¹⁴C in the rice plant significantly increased when ¹⁴CO₂ releases were limited during daytime hours, compared with the results observed during the nighttime. These results indicated that plant growth stages and diurnal photosynthesis should be considered in predictions of the ingestion dose of ¹⁴C for long-term chronic releases and short-term diurnal releases of ¹⁴CO₂, respectively. - Highlights: • Impact of plant C uptake on the spatial distribution of C-14 was investigated. • Growth stage affected C-14 accumulation in plants under continuous C-14 release. • Photosynthesis enhanced C-14 accumulation at diurnal intermittent C-14 releases. • These plant C uptakes should be included in dose estimations against C-14 releases.

[en] Purpose: To reduce the oxygen charging amount and recover hydrogen for reuse for adjusting stoichiometrical imbalance between hydrogen and oxygen upon recombining them and removing hydrogen in gaseous wastes. Constitution: In a gaseous waste processing device comprising a recombiner for reacting hydrogen and oxygen in gaseous wastes and a condensator for eliminating resulted water, a hydrogen gas purifying column is disposed to the downstream of the recombiner and the condensator thereby enabling to recover a hydrogen gas and eliminating the requirement for oxygen charging. Accordingly, since most of the hydrogen gas is recovered and can be recyclically used, the consumption of the hydrogen gas is substantially decreased. Further, since it is no more necessary to inject oxygen for attaining the stoichiometrical balance, oxygen is not consumed as usual. (Yoshihara, H.)

[en] Purpose: To easily form radioactive wastes pellets which are stable for a long period of time. Method: Inorganic binders comprising silica sol, lithium silicate or mixtures thereof are added to radioactive wastes and, depending on the requirements, curing promotors and/or water proofness improver to the inorganic binders are further mixed and the resultant mixture is hardened by press-molding them into a pellet shape. Since such binders are added and press-molded, it is possible to mold strong and long time durable pellets at a lower molding pressure than usual. (Takahashi, M.)

[en] Purpose: To obtain dense and stable solidification products. Constitution: Radioactive wastes resulted from nuclear power facilities are integrally solidified using a water-hardenable solidification material prepared by mixing a binder of water-hardenable inorganic compounds, aggregates, inorganic fluidizing material and dispersant. By adding the dispersant and inorganic fluidizing material to the solidification material, individual particles of the inorganic dispersant are dispersed and the fine particles in the binders are also dispersed and enter between the binders and the aggregates to improve the sliding between these particles. As a result, particles constituting the solidification material are uniformly dispersed in the water added to take a readily movable state. Accordingly, the solidification material is easily flowable on the surface of wastes to be processed upon packing of the solidification material and packed easily with no gaps in the container for the solidification material package. (Seki, T.)

[en] In order to predict the impact of atmospheric pollutants (gases and aerosols) to the terrestrial ecosystem, new schemes for calculating the processes of dry deposition of gases and aerosols, and water and carbon cycles in terrestrial ecosystems were implemented in the one-dimensional atmosphere-SOiL-VEGetation model, SOLVEG. We made performance tests at various vegetation areas to validate the newly developed schemes. In this report, the detail in each modeled process is described with an instruction how to use the modified SOLVEG. The framework of 'terrestrial ecosystem model' was developed for investigation of a change in water, energy, and carbon cycles associated with global warming and air pollution and its impact on terrestrial ecosystems. (author)

[en] In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with ¹³⁷Cs. However, ¹³⁷Cs transfer processes determining the tree contamination (particularly for stem wood, a prominent commercial resource) remain insufficiently understood. We propose a model (SOLVEG-R) for simulating dynamic behavior of ¹³⁷Cs in a forest tree-litter-soil system and applied it to contaminated forests of cedar plantation and natural oak stand in Fukushima to elucidate relative impact of distinct ¹³⁷Cs transfer processes determining the tree contamination. The transfer of ¹³⁷Cs to the trees occurred mostly ( > 99%) through surface uptake of ¹³⁷Cs trapped by needles and bark during the fallout. Root uptake of soil ¹³⁷Cs was several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, internal contamination of the trees proceeded through an enduring recycling (translocation) of ¹³⁷Cs absorbed on the tree surface. A significant surface uptake of ¹³⁷Cs through bark was suggested, contributing to 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining uptake occurred at needles) of the total uptake by the trees. It was suggested that the activity concentration of ¹³⁷Cs in stem wood of the trees at these sites are currently (as of 2021) decreasing by 3% per year, mainly through radioactive decay of ¹³⁷Cs and partly through dilution effect from tree growth. (author)