Radiation Environment and Medicine 2024 Vol.13, No.2 60–64

Note

Performance Test of Improved Commercially Available Tritium
Enrichment System: Toward Rapid and High Efficiency Enrichment
Naofumi Akata1*, Kazusa Okada 2, Nao Otashiro2, Haruka Kuwata3,
Khemruthai Kheamsiri3, Kaho Ohno2, Yukiko Yoshinaka1,
Ryohei Yamada1 and Masahiro Tanaka4
Institute of Radiation Emergency Medicine, Hirosaki University, 66-1 Honcho, Hirosaki, Aomori 036-8564, Japan
2
Hirosaki University School of Health Sciences, 66-1 Honcho, Hirosaki, Aomori 036-8564, Japan3
Hirosaki University Graduate School of Health Sciences, 66-1 Honcho, Hirosaki, Aomori 036-8564, Japan
4National Institute f or Fusion Science, National Institute of Natural Sciences, 322-6 Oroshi-cho, Toki, Gif u 509-5292, Japan
1

Received 26 October, 2023; revised 31 January, 2024; accepted 13 February, 2024

A commercially available tritium enrichment system was improved to provide rapid and highefficiency enrichment. Two smaller tanks of double-glazed glass were installed to realize better
cooling of sample water at 15 °C. The improved system kept the sample water in the tanks cooler
than in the large tanks of the original design. The tritium enrichment factor ranged from 5.24 to
5.50 with the mean value (±standard deviation) of 5.40 ± 0.10 and those values were higher thanobserved for operation before the improvement. The results obtained with the improved systemwere maintained at a high tritium enrichment factor.
Key words: tritium, enrichment system, high efficiency

1. Introduction
Tritium ( 3H; T 1/2 = 12.3 y) is the only radioisotope ofhydrogen and it decays to 3He. Sources of environmental
tritium are natural and artificial. Various reports can befound in the literature which summarize the properties
and behaviors of tritium1-4). Most of the naturally sourced
tritium is produced by the interaction of nitrogen (14N)
and oxygen (16O) atoms with cosmic rays in the upper
atmosphere, and its production rate has been estimatedas 0.25 atoms/cm2/s3), with the global tritium annual
radioactivity amount of approximately 72 1015 Bq/y4).
*Naofumi Akata: Institute of Radiation Emergency Medicine, Hirosaki
University, 66-1 Honcho, Hirosaki, Aomori 036-8564, Japan
E-mail:akata@hirosaki-u.ac.jp
https://doi.org/10.51083/radiatenvironmed.13.2_60
Copyright © 2024 by Hirosaki University. All rights reserved.

On the other hand, there are several sources for artificialtritium. Atmospheric nuclear weapon testing from the1950s to the early 1960s released huge amounts of tritium
into the atmosphere in the northern hemisphere, andapproximately 1.86×1020 Bq of tritium was released from1945 to 19855). Normal operations of nuclear facilities
also release tritium to the surrounding environment, andthe annual average discharge rate to the atmosphereworldwide were estimated to be 11.7 ×1015 Bq from 1998to 20025). Many researchers around the world reported
high tritium concentrations in precipitation6, 7). However,by 1996, it was reported that the concentrations had
returned to the natural background level7).
Since the Fukushima Dai-ichi Nuclear Power Plant(FDNPP) accident of March 2011, huge amountsof cont a mina t ed wa t er ha v e been produced indecontamination and decommissioning work. AlthoughNaofumi Akata et al. / Radiation Environment and Medicine 2024 Vol.13, No.2 60–64

the contaminated water has been treated by passing it
through the multi-nuclide processing system (ALPS),
small amounts of radionuclides, especially tritium which
is not removed using ALPS are still present 8). Thistreated water is being stored in tanks on site; however,these tanks will soon become full. In response to this, theJapanese government approved a plan on 13 April 2021 torelease the stored treated water including mainly tritiumfrom the site to the Pacific Ocean9). In the future, tritium
monitoring will be conducted by the Tokyo ElectricalPower Company Holdings, the Ministry of Environment,
the Fukushima Prefecture government, and others.
Regarding the marine environmental monitoring for
ALPS treated water to be conducted by the Japanese
government, the lower detection limit target for tritium
was set at 0.1 Bq/L each for seawater and tissue
free water tritium (TFWT), while organically boundtritium (OBT) of aquatic organisms was set at 0.5 Bq/
L-combustion water10).
In general, low level tritium concentration inenvironmental water samples is measured using large
vials of 145 mL and a low background liquid scintillation
counter (LSC) for 1,000 min with a minimum detection
limit of approximately 0.3 Bq/L11). To detect less than
0.3 Bq/L of tritium in water samples, tritium has to beenriched using an additional procedure. In Japan, a tritium
enrichment system using a solid polymer electrolysis(SPE) membrane is commonly used, which has lessdanger of explosion due to the separation of the exhausted
H2 and O2 during the tritium enrichment12). It has beenreported that it is possible to detect tritium concentrationsof approximately 0.04 Bq/L using a procedure in which
800 mL of sample water is concentrated using this device
for approximately 3 days and measured using LSC for
1000 min13-16). For safe and rapid tritium monitoring in
the marine environment, a higher-performance tritium
enrichment system is needed. It has been reported thatelectrolysis of a water sample under low temperature
conditions is effective in obtaining a high separation
coefficient17). Akata et al.18) took on the challenge to gethigh performance enrichment with a low volume sampleof 500 mL under the cooling condition using double glass
reservoirs equipped with a cooling water circulation
device. They obtained a tritium enrichment factor of 5.00
which is higher than normally obtained. However, there
is still ample room for improvement for such points as
the size of the tanks in the SPE setup. It is important also
to shorten the time to obtain analytical results on thereleased concentrations of tritium to dispel rumors aboutdamage to the marine environment. This paper reportson the performance improvement of the commerciallyavailable system to make it faster and more efficient.

61

Fig. 1. Schematic diagram of the commercially available electrolytic
apparatus “TRIPURE®” with the solid polymer electrolysis (SPE).

Fig. 2. Improved SPE system with small double-glazed glass tanks
connected to the cooling water circulator.

2. Experimental
2.1. Overview of apparatus
In this study, the “Tripure” (XZ001, De Nora Permelec Ltd.
Japan) was improved which is a commercially available
SPE membrane electrical tritium enrichment system(Fig. 1). Its details have been reported previously12, 18).
Briefly, it consists of two water tanks with Peltier typeelectrical coolers, the electrolysis cell and a DC power
supply. The electrolysis cell is composed of an SPE
membrane made of fluorocarbon resin, a porous anode
made of porous Ti coated with iridium oxide and a porous
cathode made of SUS316. The electrolysis was started
at a constant current of 50 A until the water volume was62

Naofumi Akata et al. / Radiation Environment and Medicine 2024 Vol.13, No.2 60–64

Fig. 3. Sample water temperature and volume during the cooled and poorly cooled enrichment experiments.
The vertical dashed line indicates the 22 h time limit for switching to the lower applied current.

reduced to approximately 100 mL and then electrolysis
was done at 20 A to reach the top of the water levelsensor and get a volume of about 52 mL12). Akata et al.18)
reported that a somewhat higher efficiency was observed
when the same size of tanks (approximately 1,000 mL pertank) which were made of double-glazed glass were usedin place of the single-glaze glass tanks that had no gap
to allow cooling water to be circulated for better cooling(Tripure-1). It seems that the enrichment factor depends
on the performance of the electrolytic membrane. In
other words, the cooling efficiency of the sample water isdetermined by the contact area between the cooling area
and the sample water. Then, an additional improvement
was realized. Two smaller tanks (approximately 360
mL per tank) of double-glazed glass were installed forbetter cooling of sample water. Figure 2 shows theimproved enrichment system (Tripure-2). The coolingwater temperature of the circulator (CCA-1110, EYELA,Japan) was set at 15 C which was considered to be thelaboratory temperature. The sample water temperature
was determined using a thermo recorder (TR71nw, T&D,Japan).
2.2. Calculation of tritium enrichment factor
The relationship between tritium concentration in sample
water and water volume during electrolysis is defined by
the following equation,
β

Tf Vf
Vf
― = ( ――― )Ti ViVi(1)where T i and T f are initial and final tritium concentrations,and V i and V f are initial and final water volumes,
respectively. β is the separation factor of tritium. The
separation factor β is influenced mainly by the isotope

fractionation due to evaporation, the inside pressure of theelectrolytical cell, and the vapor pressure of sample water
during electrolysis. So, it is common to determine anapparent separation factor βa experimentally. The tritium
enrichment factor Z T is defined using the followingequation.
1)
βaTf Vf (1- ―ZT = ― = ( ― )T i Vi(2)

In general, operation time of electrolytic enrichment
technique of tritium depends on the initial water volume
and electric current value. Total enrichment time from500 mL was less than 28 h. The D2O reagent (SigmaAldrich, USA) was diluted using pure water to prepare thesecondary tritium standard solution-A which was 4.14 ±0.09 Bq/L (n = 5) for determining the tritium enrichment
factor.
2.3. Tritium measurement
The water sample (50 mL) was mixed with 50 mLof a liquid scintillation cocktail (Ultima Gold LLT,PerkinElmer, USA) in a 145 mL low diffusion polyethylene
vial with an inner Teflon coating. Tritium concentration
was measured using a low background liquid scintillation
counter (LSC-LB5, Nippon RayTech, Japan) for 1,000 min(50 min ×10 repeats ×2 cycles). Counting efficiency wasdetermined using secondary tritium standard solution-Bof 118.17 ± 0.39 Bq/L (reference date: 9 September 2020)
produced by D2O reagent (Sigma-Aldrich, USA)16). The
minimum detection level was calculated as approximately
0.3 Bq/L.

Naofumi Akata et al. / Radiation Environment and Medicine 2024 Vol.13, No.2 60–64
Table 1. The estimated tritium enrichment factor of the un-cooling andcooled enrichment experiments
NumberUn-cooling experiment

Cooling experiment

123
45

4.55
4.35
4.86

5.50
5.43
5.38
5.24
5.42

Ave. ( S.D.)

4.59

0.26

5.40

0.10

3. Results and discussion
3.1. Cooling ef fect using small tanks
Figure 3 shows the sample water temperature andwater volume during the enrichment process using theimproved enrichment system. Until the volume reachedabout 100 mL, the average water temperature using
the cooling water circulator was 27.2 C and lower than
the average water temperature of 42.8 C in the poorly
cooled experiment. The average water temperature wasapproximately 15 C lower. The Tripure-2 effectively
cooled the sample water in the tanks.
3.2. Evaluation of tritium enrichment factor ZT
The tritium enrichment factor Z T was determined threetimes for un-cooling experiment and five times for thecooling experiment. Table 1 summarizes the values ofZ T. Although tritium enrichment factor using Tripure-2
under un-cooling condition ranged from 4.35 to 4.86 withmean value ( standard deviation) of 4.59 0.26 (n =3). On the other hand, tritium enrichment factor usingsame system under cooling condition by cooling water
circulator (15 C) ranged from 5.24 to 5.50 with meanvalue (± standard deviation) of 5.40 ± 0.10 (n = 5). These
data points suggested that the enrichment process wasreasonably stable under the cooling condition with thewater circulator providing cooling water in the gap of
the double-glazed glass. Akata et al.18) reported that atritium enrichment factor of 5.00 was gotten under thecooling condition using almost the same volume of tanks(approximately 1,000 mL per tank) and this was higher
than Z T for normal operation. The Tripure-2 which had
small tanks and water cooling in the gap provided higher
efficiency than Tripure-1 and the previously reported
improved system18). It seemed that the smaller size ofthe tanks was effective for increasing the contact time
between the sample water and tanks, thereby keepingthe water temperature lower. Therefore, it was presumed
that the high enrichment factor was obtained in a shortenrichment time using a small initial volume of sample
water. The minimum detection level using the Tripure-2
at an initial volume of 500 mL and LSC counting time of63

1,000 min was estimated to be approximately 0.056 Bq/
L which was lower than the value for normal “Tripure”
operation (0.065 Bq/L). The relatively uncertainty ofthis procedure was calculated approximately 8 %. Ueda
et al.13) reported that an enrichment factor of 7 to 8 wasobserved using 800 mL of water as the initial volume, andthe operation time was about 50 h. The operation time ofTripure-2 was approximately 28 h.
Tritium concentration level in natural water has beenreported elsewhere19-21). Recently, the most important
target among environmental media is the tritium
concentration in sea water and marine products. The
lower detection limit target for tritium was set at 0.1 Bq/
L for marine environment monitoring by the Japanese
government10). Monitoring data should be made available
to researchers as well as the general public as quickly as
possible. Here, if the minimum detection level of tritium
measurement is approximately 0.3 Bq/L, Z T has to be 3or higher. Additionally, high tritium enrichment factor
and stable enrichment operations are also important forgetting low uncertainty of tritium measurement.
4. Conclusion
The commercially available “Tripure” tritium enrichment
system was improved to achieve faster and higher
efficiency of enrichment. Two small tanks (approximately
360 mL per tank) of double-glazed glass were installed
for cooling of sample water at 15 °C by circulating water
through the gap of their double-glazed glass structure.
The improved system kept the sample water in the tanks
cooler than the normal system with polyethylene tanks
that had no gap cooling. The tritium enrichment factor ZT
ranged from 5.24 to 5.50 with the mean value (±standarddeviation) of 5.40 0.10. The improved system wasoperated stably at high ZT. For monitoring of the marine
environment, the improved system offered time savingsof about 24 h compared to the normal one and Tripure-1.
Acknowledgement
The authors acknowledge Dr. H. Kakiuchi (Institutefor Environmental Sciences, Japan) and Dr. H. Tazoe(Hirosaki University, Japan) for important discussions.
This work was partially performed with the support of theNIFS collaboration Research Program (NIFS22HDCF003)
and JSPS KAKENHI Grant numbers 17KK0015 and21H03607.
Conflict of interest disclosure
The authors declare that no conflict of interest exists.

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References

12.

Momoshima N, Nagao Y, Toyoshima T. Electrolytic enrichmentof tritium with solid polymer electrolyte for application toenvironmental measurements. Fusion Sci Technol. 2005;48:520–3.

13.

Ueda S, Hasegawa H, Kakiuchi H, Ochiai S, Akata N, Hisamatsu
S. Nuclear accident-derived 3H in river water of Fukushima
Prefecture during 2011–2014. J Environ Radioact. 2015;146:102–9.

14.

Akata N, Kakiuchi H, Tanaka M, Ishikawa Y, Kurita N, Furukawa
M, et al. Isotope and chemical composition of monthly precipitationcollected at Sapporo, northern part of Japan during 2015-2019.
Fusion Eng Des. 2021;168:112434.

15.

Kuwata H, Akata N, Okada K, Tanaka M, Tazoe H, Kurita N, etal. Monthly precipitation collected at Hirosaki, Japan: its tritium
concentration and chemical and stable isotope compositions.
Atmosphere. 2022;13:848.

16.

Akata N, Iwata C, Nakada M, Kato A, Okada K, Kuwata H, et al.
Tritium concentration in monthly precipitation near the fusion
test facility in Japan before and after the deuterium plasma
experiment. Radiat Prot Dosim. 2022;198:976–84.

17.

Uematsu K, Yamazaki H, Sato M. Tritium enrichment byelectrolysis using solid polymer electrolyte. Radioisotopes.
1996;45:375–7. (in Japanese)

18.

Akata N, Iwata C, Kato A, Tanaka M, Tazoe H, Shima N, et al.
Low-volume electrolytic enrichment for tritium measurement
using improved solid polymer electrolyte system at NIFS and its
application. Radiat Environ Med. 2020;9:93–7.

1.

Okada S and Momoshima N. Overview of tritium: characteristics,
sources and problems. Health Phys. 1993;65:595–609.

2.

Momoshima N. Tritium in the environment. Radiat Prot Dosim.
2022;198:896–903.

3.

United Nations Scientific Committee on the Effects of AtomicRadiation. Sources and Effects of Ionizing Radiation, Volume I:
Source; UNSCEAR 2000 Report to the General Assembly with
Scientific Annexes. New York, NY, USA; United Nations: 2000.

4.

Akata N, Tanaka M, Iwata C, Kato A, Nakada M, Kovács T, et al.
Isotope composition and chemical species of monthly precipitationcollected at the site of a fusion test facility in Japan. Int J Environ
Res Pub Health. 2019;16:3883.

5.

United Nations Scientific Committee on the Effects of AtomicRadiation. Sources and Effects of Ionizing Radiation; UNSCEAR
2008 Report to General Assembly with Scientific Annexes Volume
I. New York, NY, USA; United Nations: 2010.

6.

Morishima H, Kawai H, Koga T, Niwa T. The trends of globaltritium precipitations. J Radiat Res. 1985;26:283–312.

7.

Araguas AL, Danesi P, Froehlich K, Rozanski K. Global
monitoring of the isotopic composition of precipitation. J Radioanal
Nucl Chem. 1996;205:189–200.

8.

Yamanishi T, Kakiuchi H, Tauchi H, Yamamoto T, Yamamoto T.
Discussions on tritiated water treatment for Fukushima Daiichi
Nuclear Power Station. Fusion Sci Technol. 2020;76:430–8.

19.

Liu Y, Yuan J, Du D, Sun B, Ti X. Monitoring long-term ecologicalimpacts from release of Fukushima radiation water into ocean.
Geogr Sustain. 2021;2:95–8.

Hasegawa H, Ueda S, Akata N, Kakiuchi H, Hisamatsu S. Tritium
activity concentrations and residence times of groundwatercollected in Rokkasho, Japan. Radiat Prot Dosim. 2015;167:201–5.

20.

Minist r y of En v ironment. W it h rega rd t o t he ma rine
environmental monitoring for ALPS treated water to be conductedby the Japanese government (Proposal of monitoring plan for
Reiwa-4 FY), https://www.env.go.jp/content/900544130.pdf.
Accessed 11 March 2023 (in Japanese)

Akata N, Tanaka M, Kato H, Yamanishi H, Kakiuchi H, Hayashi
H, et al. Long-term monitoring of tritium concentration inenvironmental water samples collected at Tono Area, Japan.
Plasma Fusion Res. 2016;11:1305032.

21.

Gusyev MA, Morgenstern U, Nishihara T, Hayashi T, Akata N,
Ichiyanagi K, et al. Evaluating anthropogenic and environmental
tritium effects using precipitation and Hokkaido snowpack at
selected coastal locations in Asia. Sci Total Environ. 2019;659:1307–
21.

9.

10.

11.

Akata N, Kakiuchi H, Shima N, Iyogi T, Momoshima N, Hisamatsu
S. Tritium concentrations in the atmospheric environment atRokkasho, Japan before the final testing of the spent nuclear fuelreprocessing plant. J Environ Radioact. 2011;102:837–42.