Analysis of purification in radioactively contaminated ocean water near the Fukushima nuclear accident site

The nuclear‐contaminated water in the seawater near the site of the Fukushima nuclear power plant (NPP) accident is being investigated for treating the radioactive material. One of the most important considerations in the treatment is the management of the vast aquatic area of the oceanic scale. There are two methods in the application of osmosis and filtration for the modeling. There is the molecule quantity by the water volume where the list of transition of quantities is shown, where it decreases to 10% from the reversed osmosis method and to 0.01% from the filtration method in 9 days. In the filtrations, the discharge variations in the sea are described as the maximum and minimum values within 100 square velocities. A design for the general radioactive contaminated seawater treatment facility is introduced.


| INTRODUCTION
It is important to protect humans from exposure to hazardous radiation in the wastewater near the site of the Fukushima nuclear accident.3][4] Once the contaminated water from Fukushima enters the Pacific Ocean, the seawater can spread all over the seas and oceans on Earth, although the time taken to reach that stage is reportedly varied.Therefore, it is not only a local concern but also a global problem that requires a significant solution.In the food chain, the minute radioactive material is consumed by plankton living in the aquatic ecosystem, which is then further transferred to higher levels in the food chain, such as to the tuna or the whale.
One of the most important considerations in the treatment of radioactively contaminated seawater is the management of the vast aquatic area of the oceanic scale.Figure 1 shows the water treatments implemented at the Fukushima accident site, so far.The list in Table 1 shows sites directly affected by the Fukushima contamination material through the oceanic currents. 5However, the other oceans-Atlantic, Indian, Southern (Antarctic), and Arctic-are also affected by the dumped contaminated seawater due to their interconnectivity.Hence, the radiation levels in the seawater are expected to gradually increase.The radioactivity decreases because of the radioactive decay depending on the half-life of each nuclide.In the treatment process, the handling method is very important.Carrying facilities, such as ships, use the filtration method.In local regions, carbon treatment or ion exchange methods could be used.In wider areas, ships equipped with filtration systems driven by towboats could be used.
The Japanese government made a process for releasing the radioactively contaminated water after treatments into the Pacific Ocean. 6,7International Atomic Energy Agency will investigate the radiological characteristics of the treated water and its assessment, to ensure the residents for protecting the environment.It is pressing ahead with plans to dump the water in starting 2023 and continuing for the next 30 years.Japan would like to release through a pipeline connecting 1 km from the coast.However, there are many opposites between domestic fishermen and neighboring countries.
There are several methods that can be used to clean up the contaminated water.Here, the size of the area under management, in this case, the massive scale of the environment affected, should be considered.One of the most unique characteristics is the vast area of the affected contaminated regions.There are two ways to study the application of osmosis and filtration in the modeling of the methods.These methods can effectively be combined to clean up seawater where a particular nuclide is prevalent.][16] Dynamic investigations are very important in the study, because the half-life could offset the radioactivity of the isotopes of interest.It is also necessary to reduce the natural life of hazardous radioactive material through seawater treatment.Hence, the time-based management is considered along with the area-based method, to thus use the "Time-Space" treatment.The "Time" is calculated by the dynamic method.The "Space" is considered to be the carrying vehicles, such as the scavenger ships, whose characteristics include fast navigation speed and wide management range.Therefore, filtration and osmosis are better options for "Space" consideration, because ship-based equipment with a towboat is easily available and effective.
Following the Japanese government, the accident site in Fukushima has been managed by the construction of large walls which implement three actions 17 : ◆ To develop the technology for impermeable walls by constructing the ice wall ◆ To establish the technology to control the groundwater level ◆ To operate impermeable walls as the ice wall for long periods.
However, just controlling the radioactively contaminated water does not construe effective management.Figure 1B shows the water treatment facility in which the water flows in the direction of arrow lines. 18The Multinuclide Removal Equipment (Advanced Liquid Processing System) is employed for the removal of radioactive material at the Fukushima Daiichi Nuclear Power Station.However, it is to be noted that the water tanks therein are full and need to be dumped into the sea.In addition, contaminated water continues to be present around the Fukushima Bay area since the time of the | 3311 accident.Hence, the water discarded into the sea should be investigated to understand the effect of the contaminated water.

| METHODS
There are several ways to purify the contaminated water, 19 including osmosis and filtration.It is important to examine the behaviors of radioactive materials when applying these methods to seawater because of the vast size of the sea in front of the Fukushima region.Table 2 shows the list of major materials in the sea. 20-23

| Osmosis
The chemical equation to calculate osmotic pressure is 24 where π is the osmotic pressure, i is the van't Hoff index, C is the molar concentration, R is the ideal gas constant, and T is the absolute temperature.Therefore, the molecular quantity can be expressed as where, n is the mole number and V is the volume.Hence, where, w is the solute quantity and M is the mole quantity.Hence, Finally, we can conclude that Therefore, the initial radioactively contaminated water can be treated by simple calculations.The materials in the sea are indefinite due to the uncertainties in the quantity of the contaminated dumping water.Hence, normalized values that can show the trend of the radioactive material behaviors were used in the simulations, although it was not to show the exact quantity.Figure 2 shows the osmosis configuration and the mole quantity by the water volume. 25imulations were carried out by the Vensim 7.2 single precision code system, 26 used for the scientific and technological matters for the modeling of quantities.

| Filtration
Filtration has been previously proposed for radioactive seawater. 27Figure 3 shows the simplified filtering facility that could be operated by the ship operating over the sea which can be applied in the front of the Fukushima seashore.In addition, the method can be applied to clean up the wide areas of the Pacific Ocean as well as the Indian and Atlantic Oceans.The nuclide in the Fukushima region could migrate into other oceans by seawater currents.Hence, it is considerable to make use of the filtering method, if the marine radioactive level increases.This efficient machinery equipped on the ship is effective considering the characteristics of the radiation contaminations in which the contaminations are present at the molecular level.
Due to the uncertainty of the exact quantity, the materials in the sea are calculated as the normalized values.The microfiltration of about 0.1 ~10 μm size and the ultrafiltration of about 1 nm ~0.1 μm size are targeted materials to consider. 28From the theoretical viewpoint, Darcy's law is used as a phenomenological constitutive equation of the flow, 29,30 Q kA μ where Q (m 3 /s) is total discharge, k (m 2 ) is the intrinsic permeability of the medium, A (m 2 ) is the cross-sectional area to flow, (P b − P a ) is the pressure drop, μ (Pa•s) is the viscosity, and L (m) is the length over which the pressure drop is taking place.In relation to pressure, the incompressible flow of water can be written as, 31

Dp
where Dp is dynamic pressure (Pa), ρ is density (kg/m 3 ), and v is velocity (m/s), which is generated by a random number due to the variable characteristics of the sea velocity.Hence, the following relation is obtained as, Hence, the values of discharge nuclei are proportional to the square velocity of the seawater.Figure 4 is the modeling for the radiation filtering of contaminated seawater as (a) radioactive material and (b) discharge variation, where the velocity of RanVo is obtained by the random number samplings.Figure 5 shows the radioactivity of the fallout material in which the quantity is to decrease on an exponential scale.Figure 6 shows the discharge variations in the sea.Hence, the filtering rate is disadvantageous to the discharged values.The maximum and minimum values are within 100 square velocities.

| RESULTS AND DISCUSSION
There are two methods in the application of osmosis and filtration for the modeling.There is the molecular quantity by the water volume in Figure 2 where the normalized values decrease significantly in the initial time.In the filtrations, Figure 6 shows the discharge variations in the sea as the maximum and minimum values within 100 square velocities.Figure 7 shows the design for the general radioactive contaminated seawater treatment facility (GRCSTF), where the configuration of the floating dock with the towboat is present in Figure 8. Table 3 shows the list of transition of quantities where it decreases to 10% from the reversed osmosis method and to 0.01% from the filtration method in 9 days.Hence, the radioactive quantity decreases significantly over several days.In the process, according to Environmental Protection Agency, reverse osmosis can treat uranium, radium, gross alpha, and beta and is known as the Best Available Technology and Small System Compliance Technology for particles and photon emitters. 19Following the first step, iodine-131, cesium-137, and other larger-sized nuclei can be filtered from seawater.Furthermore, the combination of the above methods can provide the best solutions for the complete removal of hazardous materials.Therefore, filtration and osmosis are the methods in the "Space" consideration and the speed of the ship is the value in the "Time" consideration.Eventually, the scavenger ship is required to have the characteristics of fast speed and wide management range.

| CONCLUSIONS
7][8] The important conclusions of this study are as follows: • The radioactive contamination was investigated.
• The Fukushima nuclear accident is the modeling case.• Environmental significance of the nuclear accident is solved effectively.• Oceanic treatment for nuclear disasters is studied in a vast area.
In this work, one of the most important considerations in the treatment of radioactively contaminated seawater is the management of the vast aquatic area of the oceanic scale.Two methods in the application of osmosis and filtration are modeled.The molecule quantity by the water volume is analyzed where the normalized values decrease significantly in the early time.In the filtrations, the discharge variations in the sea are described.
It is imaginable to avoid wastewater dumping into the sea.There are other methods for treating contaminated water where the evaporation of unclean water could be an option.However, the facility needs to be sealed completely to prevent leakage of radioactive material into the atmosphere.Therefore, the liquid contaminants should not be changed to the other phases such as gas.Additionally, it is expensive to construct an evaporation facility considering the environmental hazards.Hence, simpler and cheaper construction methods are needed.
In addition, the Japanese government has discussed the freezing of the contaminated underground water, although it has been dismissed as an option to treat the radioactively contaminated water which will enter the sea through the Pacific Ocean currents.We can think and construct a gathering lake instead of dumping the contaminated water into the sea.The soils in the Fukushima accident site are contaminated currently.Therefore, the newly made artificial lake should be made water-proof such that the water will not be absorbed into the underground soil and the upper opening is sealed.
The gathered water will be then treated by the above methods.
The responsible role of the government in disaster control could increase significantly through reasonable and wise management.Furthermore, international cooperation with other countries also can aid the government.The skill and technology of radioactive material treatment can solve important nuclear issues of the world.For example, this water treatment could be applied to the Chernobyl case, which is located far from the sea.The underwater contamination treatment could be applied to this site using the above methods.
In addition, the conventional safety systems of the nuclear power plants (NPPs) can be improved by this GRCSTF in which the integrity of the plant system could be increased as the postaccident protection system.The multiple-barrier system in the NPPs can be modified considering this incident after the severe accident of the core melting case, where the GRCSTF is added to the nuclear safety systems.Furthermore, natural ecological self-restoration could be possible, because the above two systems focus on natural recovery without changing seawater quality at the molecular level.Hence, the nuclear system can be much more reliable and acceptable to the public, as nuclear accidents can be treated systematically within a comparatively shorter time.
It is also thinkable of some dilemmas such as a tripartite evolutionary game model where a dilemma is related by government, society, and company for the natural disaster. 32Hence, it is needed to make the evolutionary stabilization by the social management which could give a lesson in solving the Fukushima disaster.Furthermore, the consideration of shipping during the COVID-19 epidemic era could reduce carbon emissions. 33So, if one does not use nuclear energy, the Fukushima accident would not happen.However, the cheap price of nuclear energy could not contribute the society for the economic growth.One more dilemma is the evolutionary game for inland shipping pollution where the government controls with interested groups together. 34In this case, the sincere minds of the stakeholder are necessary to treat the marine disaster.

1
The Fukushima accident site (A) geological site and (B) water treatment facility.T A B L E 1 List of Fukushima site-induced currents in the Pacific Ocean.

T A B L E 2 2
List of major materials in the sea.Mole quantity by the water volume.(A) Osmosis configuration, (B) Modeling, and (C) Simulations.

F I G U R E 3 4
Configuration of radiation filtering of contaminated sea water.Modeling for the radiation filtering of contaminated sea water.(A) Radioactive material and (b) discharge variation.F I G U R E 5 The result of radioactivity of fallout material in the sea.F I G U R E 6 The result of discharge variation in the sea.

F I G U R E 7
Design for the general radioactive contaminated seawater treatment facility (GRCSTF).F I G U R E 8 Design for the floating dock type with the towboat.T A B L E 3 List of transition of quantity.