Development of In-situ Radioactivity Inspection System for Radioactive Waste
and Decontamination System using Micro-algae
Sujung Min1, Dohyung Kim1 ,Woyoung Kim1, Sheunghyun Ha1, San Chae1, Unjang Lee1, Seung-Yop Lee2 , ,ORIONENC Co., Ltd.

#305, 37, Seongsui-ro 22-gil, Seongdong-gu, Seoul, 133-832, Korea1,
Department of Mechanical Engineering, Sogang University

35, Baekbeom-ro, Mapo-gu, Seoul, Republic of Korea2

Key words; Decommissioning, Microalgae, Inspection, Decontamination, Radioactivity, Bioremediation

AbstractIn 2011, Fukushima nuclear power plant accident in Japan caused contamination of lakes and rivers due toradioactive materials released. The conventional decontamination methods using chemical precipitation and ion
exchange can lower the radioactive concentration of contaminated water to a certain level. However, it isdifficult to purify the large amount of contaminated water to a level lower than the very low level due totechnical and economic reasons. Microalgae have recently been applied for the removal of the water-soluble
radioactive materials as well as bio-energy and high-value material resource. In this study, we develop a small
prototype of radioactivity measuring device using NaI(Tl) scintillator with photomultiplier tube in order tomeasure radioactivity in the decontamination system, which is based on semi-permeable membrane containing
radionuclide-removing microalgae into radioactive contaminated water.
1. Introduction
When the Fukushima nuclear power plant accident
occurred, the enormous quantities of water were used
to cool the reactors. Indeed, it was estimated thatapproximately 250,000 tons of water were used by
mid-January 2012 to cool down the nuclear reactors[1]. The general decontamination methods for theremoval of radionuclides in radioactive contaminatedwater are mostly chemical precipitation and ion
exchange, but they are costly and/or ineffective forlow concentrations with significant large volume.
Also, it is a time-consuming and costly process todispose a large amount of radioactive waste
generated in the dismantling of nuclear power plants.
The cost of the decontamination system developed by
Areva (Paris, France) and Kurion (CA,US) is around
US $660 million, and 2,000 cubic meters of thegenerated radioactive sludge should be preserved in
new long-term storages by 10 months after theaccident.
Thus, the development of an effective andeconomical method for removing the nuclide fromwidespread contamination in aquatic ecosystems has
become an important issue. Biosorption andphytoremediation using various biomasses havebeen considered as alternatives to the toxic metal
removal process using chemical reagents [2-4].
Biological remediation technologies become aninteresting alternative to reduce radioactive releases
in aqueous effluents or to clean-up contaminatedwater. Lee et al. [4] reported that microalgae
Chlorella vulgaris removes effectively radioactive
cesium and strontium in contaminated water. They
also discovered that biosorption of strontium induces
SrCO3 by photosynthetic biomimeralization.
In this paper, we introduce the outline of thedevelopment of the radioactivity decontamination
system and inspection system using and the NaI(Tl)detector for the performance test and semi-permeable
membranecontaining
radionuclide-removing
microalgae into radioactive contaminated water.
2. System Design
2-1 Decontamination procedures
Figure 1 shows the principle of removal ofradioactive nuclides by injecting semi-permeable6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanmembrane
containing
radionuclide-removing
microalgae into radioactive contaminated water.

performance, the microbial collection rate, and themaintenance period of microalgae are compared andevaluated for various candidate methods. Thesemethods are decontamination by adding adecontamination container to polluted water
environment, by passing contaminated water throughdecontamination vessel, and etc.

Fig. 1. Principle of removal of radionuclides using
the microalgae and semi-permeable membrane
In this study, firstly, microalgae with adsorption
capacity for a specific radionuclide are selected.
Previous studies have shown that various microalgae
have biosorption property for radioactive cesium andstrontium in water. Among various microalgae, theoptimal microalgae are selected through theadsorption performance tests for the radioactive
species Cs-137, Sr-90 and the like. Figure 2 shows across-sectioned HRTEM image of C. vulgaris cellswith strontium and conceptual model for a microalgal
absorption [4].

Fig. 3. A simple diagram of the post-treatment
system.

Fig. 2. A cross-sectioned HRTEM image of C.
vulgaris cells and conceptual model for a microalgal
absorption and surface- carbonating process [4].
Secondly, an optimal culture method capable ofmass production of the selected microalgae
efficiently is selected. There are two types of culture
methods: Open and closed type. A culture system isconstructed by selecting a culture method thatminimizes the energy and nutrients to be used for
microalgae cultivation while maximizing the use of
CO2.
Thirdly, a decontamination method with optimum
decontamination performance is selected by applying
a certain amount of cultured microalgae toradioactive contaminated water. The decontamination

Fourthly, after the decontamination is completed,the post-treatment method is selected for thebulkiness of the used microalgae. The usedmicroalgae adsorbing radionuclides in radioactive
contaminated water can be regarded as secondary
radioactive waste. The contaminated microalgae,
which have retained moisture, are reduced in volume
and weight through post-treatment.
Figure 3 shows a simple diagram of thepost-treatment system. The optimal post-treatment
method is selected in consideration of the volume
reduction rate, incidental waste generation rate,post-treatment time, cost and etc.
2-2. Selection of microalgae

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, JapanIn the previous paper [4], C. vulgaris cultivated in
MBM and YPG media, respectively, were collectedby centrifugation and washed three times withNaHCO3 3mM. The viability of microalgaeinteracted with intense radioactive Sr-90 and Cs-137
was evaluated in different levels of radioactivesolutions for 6 days. As a result, their survivalpatterns were different from each other according tothe radiation effect on the organisms. With highradio-resistance, C. vulgaris has doubled its biomass
within 2 days in a malnutrition condition. Whencultured
underillumination,
uptakeofradio-strontium and radio-cesium by the microalgae
was observed with time after the addition of 90SrCl2and 137CsCl, and maximum removals of Sr-90 andCs-137 by C. vulgaris were ≥90% and 70% of thetotal Sr-90 and Cs-137, respectively. Both themicroalgal cultures containing C. vulgaris
demonstrated different efficiency for strontium
uptake. These results indicate that the removal rates
of strontium highly depend on microalgae strains.
The removal of radio-strontium by C. vulgaris wasvery fast in 24h, in which almost 80% of the aqueous
Sr-90 was removed from the solution. Even in
2,000Bq/ml radiation, the dissolved 90Sr decreased
quickly and the Sr-90 radioactivity was little detectedin solution after several days.
Living C. vulgaris had a potential to remove 90Sr tovery low concentrations in highly radioactive
conditions. The strontium trapped by C. vulgaris wasconfirmed as a carbonate solid phase, strontianite(SrCO3). The 90Sr bio-crystallization process that
becomes structurally denser by microalgae is very
important to effectively grasp soluble strontium ionsand to prevent 90Sr resolubilization later on [4].
2-3. Conceptual design of system
The whole batch system for treating radioactive
contaminated water was conceptually constructed byorganically linking a microalgae mass culture system,a decontamination system, and a post-treatment
system to be derived through the above-mentioned
four-step study. Figure 4 shows a conceptual diagramof a system for treating radioactive contaminatedwater using microalgae, following the steps.
Firstly, the microalgae mass culture systemproduces sufficient amounts of microalgae prior to
the use in the decontamination equipment. Secondly,
the microalgae mass obtained through the culture
system is applied to the decontamination system sothat the decontamination activity can be performed at
the actual site of radioactive contamination. Thirdly,
before the radioactive contaminated water enters thedecontamination equipment, the specific radioactivity
in the water is measured and it is determined whether
or not the contamination is necessary. Finally, thetreatedwater
after
passing
through thedecontamination system is measured for specificradioactivity before releasing it outside to determine
whether it is to be sufficiently decontaminated.
At this time, after the comparative tests of various
detectors, a detector to be used for radioactivity
measurement will be selected and applied to thesystem.

Fig. 4. Concept of radioactive contaminated water
treatment system using microalgae.

2-4. Development of radioactivity detection devicefor decontamination system using microalgae
For the radioactivity measurement before and after
the decontamination using microalgae, we developed
a prototype of a small liquid radioactivity (for gammanuclide) measurement equipment. The photograph ofthe prototype is shown in Figure 5. It has the capacityof 1000 ml and we plan to develop a large-scaleliquid radioactivity measuring device in the future.
The developed prototype is composed of radiation
detecting, shielding and analyzing parts. Lead blocksof 60mm were used to isolate from the effects ofexternal environmental radiation or artificial radiation.
A NaI(Tl) detector was used because the scintillation
light yield is high and the response to electrons andgamma rays is almost linear. Also, the nuclide
analyzer: 1024 channel MCA integrated with NaI(Tl)detector was used.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, JapanACKNOWLEDGMENTS
This work was supported by the Korea Institute ofEnergy Technology Evaluation and Planning(KETEP) and the Ministry of Trade, Industry &Energy (MOTIE) of the Republic of Korea (No.
20161520101210)

Fig. 5. Prototype of small liquid radioactivity (forgamma nuclide) measurement equipment using the3inch NaI(Tl) detector and 1,000ml marinelli beaker
Figure 6 shows the linear response of sensor withgamma radioactivity using 137Cs (0.662 MeV: 100,500, 1000Bq). The radioactivity increases withincreasing the linear velocity of the radiation, andthus the dose increases linearly.

Fig. 6. Test results using the NaI(Tl) detector(0.662MeV Cs-137 : 100, 500, 1000Bq)
In the tests, the ability to measure 1/10 of theradioactivity limit recommended by the World HealthOrganization (WHO) for water was verified byobserving the measurement of radioactivity from 1 to1000 units. The resolution of NaI(Tl) detector wascalculated to be about 8% at 0.662MeV of Cs-137.

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3. Conclusion
This paper develops a small prototype ofradioactivity measuring device using NaI(Tl)scintillator with photomultiplier tube for treating
radioactive contaminated water using microalgae insemi-permeable membranes. This microalgae-based
bioremediation with small radioactivity measuring
device covers large-scale extremely low level (or lowlevel) radioactive contaminated water.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan