Soil-soil solution distribution coefficient (Kd) is an important parameter in radiation dose assessment models for the environmental transfer of radionuclides. Since Kd values vary with soil properties, development of their estimation method using some soil properties is useful. In this study, we estimated Kd values of radionickel using selected soil properties. We determined Kd values of Ni for 142 agricultural soil samples collected throughout Japan and measured such soil properties as pH, cation exchangeable capacity, exchangeable Ca, clay content, concentrations of major elements in soil, and concentrations of major elements in water soluble fractions. The relationship between the Kd of Ni and each soil property was calculated using Spearman's rank correlation test. Then, in order to estimate Kd values of Ni based on soil properties, we used the method which we developed in the previous study for strontium using multiple linear regression analysis. Our results showed that potassium concentration in soil and phosphorus concentration in water soluble fraction were the most important factors contributing to estimation of Kd values. Finally, a predictive expression including three selected variables was created to estimate Kd values of Ni. Predicted Kd values from the expression were in good agreement with observed Kd values.
An experimental study has been carried out to clarify the characteristics of boiling during downward flow in a vertical tube of an FBR steam generator, especially the relationship between the flow aspect and the heat transfer mode. The experiment was done using purified water under the following conditions: initial pressures of 11.2-13.4 MPa, an initial water temperature of 200°C, and water flow rates of 0.021-1.67 kg/s. The tube was heated by high-frequency induction current, where the time averaged heat flux can be estimated using an inverse solution from the measured temperatures at two points on three different positions along the tube wall and was then confirmed to agree with the measured heat flux on the outer surface within 20% accuracy. The surface temperature and heat flux on the inner tube are also estimated correctly using the inverse solution. It is found that the characteristics of heat transfer strongly depend on flow rate. At a high mass flow rate, a stable nucleate boiling occurs on a vertical tube wall with a clockwise cycle on the q-ΔT diagram for changes in heat flux in dq/dΔT>0 at any time. At a low mass flow rate, boiling on the wall induces changes from dq/dΔT>0 to dq/dΔT<0 during heating and returns from dq/dΔT<0 to dq/dΔT>0 during the reduction in heat. The counterclockwise cycle always appears in the transition boiling region in dq/dΔT<0, where nucleate boiling and film boiling coexist and the ratios of boiling areas are changing temporally and spatially.
Several new regulatory approaches have been introduced to Japanese nuclear safety regulations, in which a prescriptive and deterministic approach had traditionally predominated. However, the options of regulatory approaches that can possibly be applied to nuclear safety regulations as well as the methodology for selecting the options are not systematically defined. In this study, various regulatory approaches for nuclear power plants are categorized as prescriptive or nonprescriptive, outcome-based or process-based, and deterministic or risk-informed. 18 options of regulatory approaches are conceptually developed and the conditions for selecting the appropriate regulatory approaches are identified. Current issues on nuclear regulations regarding responsibilities, transparency, consensus standards and regulatory inspections are examined from the viewpoints of regulatory approaches to verify usefulness of the categorization and selection concept of regulatory approaches. Finally, some of the challenges at the transitional phase of regulatory approaches are discussed.
Hydrogen and nuclear energies are expected as excellent energy resources and are environmentally friendly owing to the absence of emission of carbon dioxide. Toshiba has been developing the high-temperature steam electrolysis technology using solid-oxide cells for hydrogen production by nuclear energy. This paper shows the possibility of hydrogen production by high-temperature steam electrolysis using nuclear energy, through examination of the system concept applied to a high-temperature gas cooling reactor, with review of the results of research and development in Toshiba in relation to development issues clarified from tha viewpoint of hydrogen production efficiency, hydrogen production cost, and development risk.
A solution irradiation method is proposed as a new production technique for 99Mo, which is the parent nuclide of 99mTc used as a radiopharmaceutical. In this new technique, an aqueous molybdenum solution is irradiated with neutrons in a nuclear reactor, and an efficient and low-cost 99Mo production method compared with conventional 99Mo production methods can be realized by using the 98Mo (n, γ) 99Mo reaction and a high-performance adsorbent for (n, γ) 99Mo. In the present research, some tests under unirradiation and gamma-ray irradiation were carried out using two kinds of aqueous molybdate solutions as candidates for the irradiation target of the new technique, and the corrosivity for structural materials, the chemical stability, the radiolysis, and the gamma heating of the solutions were investigated. As a result, it was found that the solutions are a promising target and that stainless steel can be used as the structural material of capsules and pipes.
In Japan, safety of nuclear facilities is regulated by the central government and local governments are responsible for protecting the local public. To operate nuclear facilities in local communities, local governments would conclude safety agreements with power companies. In recent years, local governments have used the safety agreements as excuse for delaying the operations of nuclear facilities. The legal basis of the safety agreements was questioned by some who considered that this was the cause of the stranded relationship between local governments and power companies, and in some cases, the interrupted nature of electricity supply. To understand the sources of this difficult relationship, safety agreements must be analyzed, although these documents may have undergone revisions, and various regulations may have changed. By analyzing the safety agreements and revisions, we found that the relationship between local governments and power companies gradually changed over time, which can be divided into the following 3 stages: (1) in the early 70s, the dawn stage when local governments groped with the situation of nuclear facilities built in their communities; (2) from late 70s to 90s, the stage when local governments demanded information, and (3) from late 90s to present, the stage when local governments demand information and trustworthiness. This paper shows the results of analyzing the relationship changes between local governments and power companies. We conclude that viewpoints of local governments on nuclear power evolve, as social responsibilities of power companies stipulated in safety agreements also evolve over time.
The Global Trade and Analysis Project (GTAP) is a widely used computable general equilibrium (CGE) model developed by Purdue University. Although the GTAP-E, an energy environmental version of the GTAP model, is useful for surveying the energy-economy-environment-trade linkage in economic policy analysis, it does not have the decomposed model of the electricity sector and its analyses are comparatively static. In this study, a recursive dynamic CGE model with a detailed electricity technology bundle with nuclear power generation including FR was developed based on the GTAP-E to evaluate the long-term socioeconomic effects of FR deployment. The capital stock changes caused by international investments and some dynamic constraints of the FR deployment and operation (e.g., load following capability and plutonium mass balance) were incorporated in the analyses. The long-term socioeconomic effects resulting from the deployment of economic competitive FR with innovative technologies can be assessed; the cumulative effects of the FR deployment on GDP calculated using this model costed over 40 trillion yen in Japan and 400 trillion yen worldwide, which were several times more than the cost of the effects calculated using the conventional cost-benefit analysis tool, because of ripple effects and energy substitutions among others.
A numerical simulation method has been developed to predict atmospheric flow and stack gas diffusion, considering the buildings and complex terrain located near and relatively far from a stack, respectively. The turbulence closure technique was used for flow calculation, some calculation grids on the ground near a stack were treated as buildings, and stack gas diffusion was predicted using the Lagrangian particle model. The calculated flow and stack gas diffusion results were compared with those obtained by wind tunnel experiments under actual terrain containing buildings. Effective stack height was estimated by comparing the surface concentration along the plume axis with those under a flat-plate condition, and it was apparent that the effective stack heights estimated by calculations were almost the same as those obtained by the wind tunnel experiment. Then, the effective dose and relative concentration of stack gas were calculated using the effective stack heights obtained by a numerical model. Almost the same effective dose and relative concentration were obtained when compared with those using the effective stack height obtained by wind tunnel experiment.