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J. Radiat. Prot. Res > Volume 46(1); 2021 > Article
Yim and Lee: Changes of Activity Concentration of Tritium in Water under the Air with Tritiated Water Vapor
Recently, controversy continues over the cause of occurrence of tritiated water, whose activity concentration was about 7.1×108 Bq·m−3, found in a nuclear power plant in Korea. The power plant claims that the tritiated water may have been produced by the absorption of the tritiated water vapor from the air, while some suspect that it may have leaked out from the other systems [1]. We cannot hastily determine the exact cause but we have investigated the possibility that water containing initially no tritium could be changed to tritiated water with high activity concentration of tritium when it is placed in the air containing tritiated water vapor.
It has been well known since the 1960s that tritium in the air containing tritiated vapor (HTO, T is tritium or 3H) is easily transferred in water. This phenomenon has been used early for sampling of tritium in the air (known as air bubbler) [24] and still used today. It is also applied to respiratory masks for removing tritiated water vapor these days [57].
The relationship between the molar concentrations of tritium and hydrogen in the tritiated vapor of the air and those in (liquid phase) water at equilibrium is expressed by Equation (1), reported by Sepall and Mason [8], as follows:
(1)
([T]/[H])vapor([T]/[H])water=α
where T is tritium, H is hydrogen, and α is the partition constant (or equilibrium constant) and is 0.91 at 20°C.
In the above equation, molar concentrations of tritium in vapor and water can be converted to the activity concentrations of tritium in vapor and water, respectively, by the following equation:
(2)
[T]=mV=Aλ×16.023×1023×1V=Sλ×16.023×1023
where m is the number of moles of tritium in vapor or water, V is the volume of vapor or water, A is the radioactivity of tritium in vapor or water, λ is the decay constant of tritium, 6.023×1023 is Avogadro’s number, and S is the activity concentration of tritium in vapor or water.
The activity concentration of tritium in the air and that in water at equilibrium are calculated by using above two equations and the result is shown in Fig. 1.
An air with activity concentration of 3,000 Bq·m−3 (release limit of tritium in air with tritiated water vapor in Korea [9]) equilibrates at 20°C with a water with activity concentration of 1.92×108 Bq·m−3. Also, at the same temperature, an air with activity concentration of 300,000 Bq·m−3 (derived concentration of tritium in air with tritiated water vapor in Korea [9]) equilibrates with a water with activity concentration of 1.92×1010 Bq·m−3.
When a 1 m3 of water with no tritium is placed in certain volume of air with 50% RH (relative humidity) at 20°C and tritiated vapor, the activity concentration of tritium in air and that in water at equilibrium after saturation by the water and tritiated water vapors are shown in Table 1.
When a 1 m3 of water with no tritium is placed in a volume of air with 50% RH at 20°C, containing tritium, the activity concentration of tritium in air and that in water at equilibrium are changed with the volume of air. When volumes of air with initial activity concentration of 3,000 Bq·m−3 are 10 m3, 100 m3, 1,000 m3, 5,000 m3, 10,000 m3, 15,000 m3, and 20,000 m3, respectively, the activity concentrations of tritium in air at equilibrium are reduced to 0.47 Bq·m−3, 4.7 Bq·m−3, 47 Bq·m−3, 230 Bq·m−3, 440 Bq·m−3, 640 Bq·m−3, and 820 Bq·m−3, respectively, and those in water increase to 3.0×104 Bq·m−3, 3.0×105 Bq·m−3, 3.0×106 Bq·m−3, 1.5×107 Bq·m−3, 2.8×107 Bq·m−3, 4.1×107 Bq·m−3, and 5.3×107 Bq·m−3, respectively. It indicates that the activity concentration of tritium in water placed in the air of 3,000 Bq·m−3 and 15,000 m3 could exceed the release limit of tritiated water in Korea (4×107 Bq·m−3) [9]. If the initial activity concentration of tritium in air is 300,000 Bq·m−3, the equilibrium activity concentration of tritium in water placed in the air of above 150 m3 exceeds the release limit of tritiated water.
Changes of the activity concentration of tritium in air and that in water at equilibrium with relative humidity at 20°C are shown in Table 2.
The lower the initial relative humidity of air, although the activity concentration of tritium is the same, the higher the activity concentration of tritium in air and that in water at equilibrium. The reason is that the lower the relative humidity, the more evaporation of water until it reaches the equilibrium and the volume of water decreases.
As described above, we briefly estimates the change of the activity concentration of tritium in water when the water is placed in the air containing tritiated water vapor. We have confirmed that water with initially no tritium could be changed to tritiated water with high activity concentration. At present, we are planning to conduct experiments to verify that this phenomenon occurs in the field.

Notes

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Author Contribution

Methodology: SP Yim, CK Lee. Investigation: SP Yim, CK Lee. Writing - original draft: SP Yim. Writing - review & editing: CK Lee.

References

1. Cho HH. Tritium in air of Wolsung power plant, 1,800 times, is that normal? [Internet]. Seoul, Korea, Media Today; 2021 [cited 2021 Mar 21]. Available from: http://www.mediatoday.co.kr/news/articleView.html?idxno=211538

2. Valentine AM. An investigation of a bubbler tritium sampler (Report No. LA-3916). Los Alamos, NM, Los Alamos Scientific Laboratory. 1968.

3. McConnon D. The use of water as a sampling medium for tritium oxide (Report No. BNWL-CC-547). Richland, WA, Battelle Northwest Laboratory. 1970.

4. Osborne RV. Sampling for tritiated water vapor. Proceedings of the 3rd International Congress of the International Radiation Protection Association. 1973 September 9–14. Washington, DC. 1428-1433.

5. Yim SP, Lim IC, Ahn GH, Seoul CW, Lee CK. Performance test of ice packed respirator for tritium removal. Proceeding of the 36th Annual Radioactive Waste Management Symposium (WM). 2010 March 7–11. Phoenix, AZ.

6. Shin JS, Lee JK. Wet-type tritium filter cartridge. KR Patent. 20-0472036. 2014.

7. Radiation Safety Team of Wolsung Nuclear Power Plant #2. Introduction to performance test on tritium respirator at Wolsung Nuclear Power Plant #2 [Internet]. Gyeongju Korea, Wolsung Nuclear Power Plant; 2013 [cited 2021 Mar 21]. Available from: https://www.kins.re.kr/nsic_info/nsic/2013/pdf/13_5.pdf

8. Sepall O, Mason SG. Vapor/liquid partition of tritium in tritiated water. Can J Chem. 1960;38:2024-2025.
crossref
9. Nuclear Safety and Security Commission. Standards for Radiation Protection (NSSC Notice No. 2014-034) [Internet]. Sejong, Korea, National Law Information Center; 2014 [cited 2021 Mar 21]. Available from: https://www.law.go.kr/LSW/admRulInfoP.do?admRulSeq=2100000006874&lsId=35174&chrClsCd=010202

Fig. 1
Activity concentration of tritium in air and that in water at equilibrium (20°C).
jrpr-2021-00045f1.jpg
Table 1
Activity Concentration of Tritium in Air and That in Water at Equilibriuma)
Initial activity concentration of tritium in air (Bq·m−3) Phase Activity concentration of tritium in air and that in water at equilibrium, 20°C (Bq·m−3)

Volume of air (m3)

10 100 1,000 5,000 10,000 15,000 20,000
1,000 Air 0.16 1.6 16 76 150 210 270
Water 1.0×104 1.0×105 1.0×106 4.8×106 9.3×106 1.4×107 1.8×107

3,000 Air 0.47 4.7 47 230 440 640 820
Water 3.0×104 3.0×105 3.0×106 1.4×107 2.8×107 4.1×107 5.3×107

10,000 Air 1.6 16 160 760 1,500 2,100 2,700
Water 1.0×105 1.0×106 1.0×107 4.8×107 9.3×107 1.4×108 1.8×108

30,000 Air 4.7 47 470 2,200 4,400 6,400 8,200
Water 3.0×105 3.0×106 3.0×107 1.4×108 2.8×108 4.1×108 5.3×108

100,000 Air 16 160 1,600 7,600 15,000 21,000 27,000
Water 1.0×106 1.0×107 1.0×108 4.6×108 9.3×108 1.4×109 1.8×109

300,000 Air 47 470 4,700 23,000 44,000 64,000 82,000
Water 3.0×106 3.0×107 3.0×108 1.4×109 2.8×109 4.1×109 5.3×109

a) Initial air of 50% relative humidity at 20°C, initial volume of water of 1 m3.

Table 2
Changes of Activity Concentration of Tritium in Air and That in Water at Equilibrium with RH at 20°Ca)
Volume of air (m3) Phase Activity concentration of tritium in air and that in water at equilibrium, 20°C (Bq·m−3)

Initial activity concentration of tritium in air

3,000 Bq·m−3 300,000 Bq·m−3


10% RH 50% RH 100% RH 10% RH 50% RH 100% RH
10 Air 0.47 0.47 0.47 47 47 47
Water 3.0×104 3.0×104 3.0×104 3.0×106 3.0×106 3.0×106

100 Air 4.7 4.7 4.7 470 470 470
Water 3.0×105 3.0×105 3.0×105 3.0×107 3.0×107 3.0×107

1,000 Air 47 47 46 4,700 4,700 4,600
Water 3.0×106 3.0×106 3.0×106 3.0×108 3.0×108 3.0×108

5,000 Air 240 230 220 23,000 23,000 22,000
Water 1.4×107 1.40×107 1.40×107 1.50×109 1.50×109 1.40×109

10,000 Air 470 440 410 47,000 44,000 40,000
Water 3.0×107 2.8×107 2.6×107 3.0×109 2.8×109 2.6×109

15,000 Air 700 640 570 70,000 64,000 57,000
Water 4.5×107 4.1×107 3.6×107 4.5×109 4.1×109 3.6×109

20,000 Air 940 820 720 94,000 82,000 72,000
Water 6.0×107 5.3×107 4.6×107 6.0×109 5.3×109 4.6×109

RH, relative humidity.

a) Initial volume of water of 1 m3.

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