Plasma and Fusion Research: Regular Articles

Volume 11, 2405017 (2016)

A New Pretreatment Technique for Environmental Tritium
Analysis with Microwave Heating Method∗)
Naofumi AKATA1,2) , Masahiro TANAKA1,2) , Sadatsugu TAKAYAMA1) , Hideki KAKIUCHI3) ,Toshiya TAMARI4) and Saburo SANO5)
1)

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, JapanSOKENDAI (The Graduate University for Advanced Studies), 322-6 Oroshi-cho, Toki 509-5292, Japan
3)
Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Aomori 039-3212, Japan
4)
Kyushu Environmental Evaluation Association, 1-10-1 Matsukadai, Higashi-ku, Fukuoka 813-0004, Japan5)
National Institute of Advanced Industrial Science and Technology, 2266-98 Anagahora, Shimoshidami,Moriyama, Nagoya 463-8560, Japan2)(Received 26 November 2015 / Accepted 13 January 2016)
The conventional method for FWT and OBT analysis is a liquid scintillation counting method after freezedrying and combustion of the sample. However, pretreatment for FWT and OBT analysis are complicated andtime consuming processes over weeks. Thus, we propose the application of microwave heating technique tosave time and eﬀort of the pretreatment of plant samples for FWT analysis. To understand the behavior of thecombustion and drying of organic samples, we conducted TG/DTA analysis of pine needle samples. It is foundthat the sample has to be heated up to 100 - 110 ◦ C for complete drying under N2 gas flow condition. Then, wetried the water recovery from fresh pine needle samples by the multi-mode microwave heating system. As aresults, it was provided to good recovery yield achieved more than 97% under these experimental conditions.
This result shows more preferable for the pretreatment of organic samples by microwave irradiation method thanthe conventional method.
c 2016 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords: Tritium analysis, FWT, OBT, microwave, pretreatment
DOI: 10.1585/pfr.11.2405017

1. Introduction
Tritium (3 H) is a radioisotope of hydrogen and it decays to Helium-3 with a half-life of 12.3 y. Most of natural tritium is produced by nuclear reaction of nitrogenand oxygen atoms with cosmic rays in the stratosphere.
Nuclear weapons testing in the atmosphere released large
amounts of anthropogenic tritium into the environment.
Nuclear facilities are also releasing tritium into the environment [1]. In the future, nuclear fusion reactors will havea large inventory of tritium as fuel [2]. Although tritium asfuel is burned in the core plasma and contained in the facility, small amounts of tritium will be released as gaseous
exhaust and drain water into the environment.
The deuterium plasma experiment is being planned to
produce higher performance plasma using the Large Helical Device (LHD) of the National Institute for Fusion
Science (NIFS) [3]. In the experiments, a small amountof tritium will be produced by the D(d, p)T reaction in D
plasma. Therefore, it is important to understand the tritium concentration in environmental samples for radiation
safety and environmental impact assessment [4]. Tritiumin environmental organic samples usually consists of freeauthor’s e-mail: akata.naofumi@lhd.nifs.ac.jp∗) This article is based on the presentation at the 25th International Toki
Conference (ITC25).

water tritium (FWT) and organically bound tritium (OBT).
The FWT exists as HTO form, and its behavior is similar tonatural water. On the other hand, OBT is tritium bounded
to organic molecules (or carbon). The OBT has a longer biological half-life and higher incorporation to organic materials than the FWT [5]. The conventional method for FWTand OBT analysis is a liquid scintillation counting method
after freeze-drying and combustion of the sample as summarized in MEXT report [6]. However, pretreatment operation for FWT and OBT analysis are complicated and time
consuming processes over weeks. Therefore, it is necessary to develop the simple and quick technique.
It is well known that microwave irradiation technique
is useful and convenient. Microwave irradiation to materials is a new comer for our civilization with a history of
only half century. The microwave heating has the dielectricloss, magnetic loss, joule heating, and so on with respects
to the kind of materials, for example with the dielectricmaterials, magnetic materials, metal powder, and so on.
It clearly suggests that the energy transfer mechanism in
microwave heating is quite diﬀerent from the traditional
heating process. In particular, microwave heating has thecharacteristic of volumetric heating in materials.
Thus, we propose the application of microwave heating technique to save time and eﬀort of the pretreatment of2405017-1

c 2016 The Japan Society of Plasma
Science and Nuclear Fusion Research

Plasma and Fusion Research: Regular Articles

Volume 11, 2405017 (2016)

plant samples for FWT analysis. In this paper, we report
the preliminary result of endothermic and exothermic phenomena by using thermal analysis instrument and multimode microwave drying.

2. Materials and Method
2.1Samples

Fresh one-year-old pine needle samples were collected at our institute (35◦ 19’N, 137◦ 10’E) in June 2014.
Collected samples were sealed in water-vapor-tight laminate bag (AL-30L, Seisannipponsha, Japan) and was kept
in a refrigerator.

2.2

Thermal analysis

Thermal analysis is useful tool to evaluating the endothermic phenomena, exothermic phenomena and weightchange characteristics. Thermogravimetric Analysis (TG)observes the weight change in a sample with respect to thetemperature. Negative weight change means desorption ofvolatile components from the sample, and positive weightchange means absorption of gaseous components from thesurrounding atmosphere. On the other hands, Diﬀerential
Thermal Analysis (DTA) observes the temperature of sample as compared to the reference material. Positive andnegative peaks mean exothermic change and endothermicchange, respectively. In this study, TG/DTA analysis wasdone [7]. A few collected fresh pine needle samples were
cut into fragments with a few millimeter long. The cut
samples of approximately 30 mg was placed into Pt cup (φ:5 mm), and the TG and DTA of samples were measured byusing TG/DTA analyzer (EXSTAR6000, Seiko Instrument,Japan). The experimental conditions are as follows.
Atmosphere: N2 flow (100 cc min−1 ).
Heating rate: 5 ◦ C min−1 up to 150 ◦ C, 350 ◦ C and 600 ◦ C.

2.3

Fig. 1 Test furnace of 2.45 GHz magnetron system.

Fig. 2 Setup of quartz tube with pine needle samples in test furnace.

Microwave heating method

The multimode test furnace, as shown in Fig. 1, wasused for this present study [8]. This test furnace with avolume of 0.92 m3 is equipped with five magnetrons. Themagnetron generate 2.5 kW at 2.455 ± 0.030 GHz. Eachmagnetron has small diﬀerences in frequency and the beatof waves occurring in the chamber. In addition, twomode stirrers scatter the standing wave, easing the nonuniformity due to the standing wave.
The fresh pine needle sample (approximately 80 g)with silica wool (both side of sample) was placed in aquartz tube (50 mm φ, 500 mm in length). The silicone
rubber stopper with tygon tube was provided at each endof tube. We have installed this sample tube in test furnace.
The setup of sample tube shown in Fig. 2. N2 gas (2 Lmin−1 ) was supplied to front side of quartz tube throughthe tygon tube during the microwave irradiation. The tygon
tube connected rear position of quartz tube issued out of
the test furnace from the small port, glass trap cooled withliquid nitrogen and/or mixture of ice and salt connected for

FWT collection. And we measured absorption spectrum in
UV range using single-beam ultraviolet visible light spectrophotometer (ASUV-3100PC, Japan) to confirm the situation of recovered FWT (mixing of impurities).

3. Results and Discussion
Figure 3 show the TG/DTA curve of fresh pine needle samples. Decreasing of TG curve was initiated around50 ◦ C and terminated at 100 - 110 ◦ C, and it was almost flatfrom 110 to 250 ◦ C. In DTA curve, a negative peak wasrecognized at around 100 ◦ C which is endothermic change.
And, it was flat curve after 120 ◦ C. These phenomena are
typical trend of the dehydration reaction from the samples.
This results indicated that dehydration reaction happened
by heating, and was completed at 120 ◦ C. After that, TG
curve was gradually decreasing from 250 to 400 ◦ C. Then,DTA curve is almost flat. The decreasing trend of TG curve2405017-2

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Volume 11, 2405017 (2016)

Fig. 3 TG/DTA curve of pine needle samples with photo in the each temperature condition of samples.

Table 1 Summary of condition and results of microwave heating
experiment.

means desorption of volatile components from the sample.
It is diﬃcult to get oxidation reaction under the N2 gas flow
condition. The heated pine needle samples of 350 ◦ C is not
more green color than that of 150 ◦ C. It seems that negative
weight change from 250 to 400 ◦ C is desorption of volatilecomponents from the sample. Afterwards, we did not findthe clear trend to 600 ◦ C.
Based on TG/DTA analysis, we carried out the microwave heating experiments using big size multimode test
furnace. We have conducted three experiments in whichmicrowave outputs are 0.5, 1.0 and 2.5 kw. Experiment
time was decided by microwave output power. After microwave heating experiments, the dried pine needle samples were re-dried by oven dryer for calculating the recovery yield of FWT. Summary of experimental conditions
and its results are shown in Table 1. Recovery yield ofexperiment-1, 2 and 3 are 93%, 97% and 83%, respectively. Experiment-3 was worst recovery yield in which
the microwave output power was highest. In experiment-3,FWT as water vapor was suddenly flowing from the tube
to the cold trap and the rear position of cold trap became

Fig. 4 Sample and recovered water condition after microwave
experiment.

hot by heated water vapor. This results indicated that one
step liquid nitrogen cold trap system could not collect allwater vapor. The color condition of the dried pine needle samples and the recovered FWT water were shown inFig. 4. The sample color of Experiment-1was similar to150 ◦ C heated pine needle color of TG/DTA analysis. The
color of recovered water was almost transparent. On theother hands, the sample color of Experiment-3 was black
as if carbonized at high temperature. The recovered water was brown. These results suggested that experimental
condition of Experiment-1 and Experiment-2 were better
than Experiment-3. Next, we measured absorption spectrum in UV range of recovered water to confirm the water
quality (organic content in recovered water). The resultsof absorption spectrum were shown in Fig. 5. We confirmed the absorption peak in UV range (vicinity 300 nm)

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Volume 11, 2405017 (2016)

4. SummaryFig. 5 Absorption spectrum of recovered water (FWT).

at each of the experimental conditions. It is well known
that UV-Vis absorption for pure water is hardly observed
at 250 nm or more. Therefore, the absorption of more than
250 nm are based on organic materials. The content of organic matter in FWT was depend on microwave output
power. This results indicated that the pine needle tissue
had been destroyed by microwave energy, and desorbed
volatile components has been collected by liquid nitrogencold trap with FWT (water vapor). The recovered water
was purified by atmospheric distillation with addition ofKMnO4 . There were no marked absorption peak in UV
range (250 - 300 nm) by single or double operation. We
were required about 4 hours for single distillation operation. The microwave irradiation method for FWT recovery
was preferable for saving the pretreatment time. Next step,
we have plan to design the FWT recovery system fromplant samples using microwave irradiation technique.

We conducted TG/DTA analysis of pine needle samples to evaluating the endothermic phenomena, exothermic
phenomena and weight change characteristics. It is foundthat the sample has to be heated up to 100 - 110 ◦ C for
complete drying under N2 gas flow condition. Next, wetried the water recovery from fresh pine needle samples
by the multi-mode microwave test furnace. The recovery
yield achieved more than 97% under these experimental
conditions (microwave output: 1.0 kw, time: 30 min, N2flow: 2 L min−1 ). This results indicated that sample drying and water recovering technique using microwave irradiation is useful to save the time than the conventional
method. We will try to design the microwave irradiation
system for FWT recovery from the plant samples based onthese preliminary results.

Acknowledgments
This work was supported by JSPS KAKENHI Grant
Number 26340032.
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[6] MEXT, Radioactivity Measurement, Series No.9 (2002).
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