Overview
Following the Great East Japan Earthquake in March 2011 and the subsequent Fukushima Daiichi Nuclear Power Plant accident, there have been concerns about the potential outflow of highly radioactive bottom sediments contaminated with cesium from agricultural reservoirs in surrounding areas.
Our proprietary SepaTech Microbubble System, based on a pressurized dissolution method, has shown promising potential for the removal of radioactive substances.
In December 2014, using the SepaTech system, we successfully removed over 70% of radioactive cesium from the bottom sediments of Kasamatsu Pond in Kawamata Town, Fukushima Prefecture.
This page outlines the methods and results of this case.
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Contents
・ Overview of the Reservoir and Pre-Operation Conditions
・ Treatment Method
・ Treatment Results
・ Photos of the Treatment Process
Reservoir Overview and Pre-Operation Conditions
Radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant fell onto pond surfaces, surrounding lands, and forests. Cesium deposited on pond surfaces settled into the bottom sediments, while cesium from surrounding areas was washed in by rain and accumulated on the sediment layer.
Finer soil particles, which are more prone to flow into ponds, tend to strongly adsorb cesium due to their surface properties. Additionally, fallen leaves and other debris settling in the pond also captured cesium.
・ Location : Kasamatsu Pond, Ogami, Kawamata Town, Fukushima Prefecture
・ Pond Capacity : 3500m^3
・ Estimated Contaminated Sediment Volume :
3500m^3pond capacity / 4 m embankment height * 0.1 m sediment layer = 87.5m^3
Treatment Method
For the purpose of removing radioactive cesium from sediments, we adopted a flotation separation method utilizing microbubbles.
Work Procedure:
- Preparation：Site setup, equipment installation, temporary facilities (tents, toilets), and surrounding cleaning.
- Preliminary Surveys：Sampling and analysis of sediments and water before, during, and after treatment.
- Microbubble Injection：
- Phase 1：Inject microbubbles to promote flotation of fine particles and organic matter.
- Phase 2：Apply jet water flow to further stir and lift sediments.
- Collection & Treatment：Collect floated sludge, dry it, pack it, and store it temporarily after concentration measurement.
- Safety Measures：Mandatory life jackets, masks, personal radiation monitoring, and surface contamination checks.
Treatment Results
We evaluated results by sampling sediments with a core sampler and measuring cesium concentrations.
At three test points (as shown in Figure 1), all locations showed a 70% or more reduction in radioactive cesium concentrations after treatment (average reduction: 77%).
Furthermore, radioactive cesium in pond water was below detection limits — indicating that the SepaTech Microbubble System prevented recontamination of pond water through sediment disturbance.
| Sampling Point | Before Treatment | After Treatment | ||
|---|---|---|---|---|
| ¹³⁴Cs | ¹³⁷Cs | ¹³⁴Cs | ¹³⁷Cs | |
| ① | 77.8 | 291 | 21.1 | 92.4 |
| ② | 106 | 437 | 20.7 | 106 |
| ③ | 29.1 | 67.3 | 10.6 > | 10.2 > |
| Stored Water | 9.78 > | 8.92 > | 8.51 > | 10.2 > |
（Note）>indicates below detection limit. Units: Bq/kg
SepaTech® operated for approximately 40 hours.
Currently, materials like zeolite, smectite, iron minerals, carbides, and layered double hydroxides are used as adsorbents for radioactive removal.
However, post-treatment disposal of these adsorbents remains a challenge.
Therefore, the SepaTech Microbubble System offers a significant advantage in cesium reduction and handling efficiency.