ORIGINAL ARTICLE
Year : 2022 | Volume
: 45 | Issue : 2 | Page : 76--80
Studies on the contribution of the aquatic water body to the tritium flux in the atmosphere near the discharge point of Kakrapar Gujarat Site, India
Chetan P Joshi1, AK Patra1, DP Nankar1, IV Saradhi2, A Vinod Kumar2,
1 Environmental Survey Laboratory (Environmental Studies Section, Environmental Monitoring and Assessment Division, Bhabha Atomic Research Centre), Surat, Gujarat, India
2 Environmental Monitoring and Assessment Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
Correspondence Address:
Chetan P Joshi
Environmental Survey Laboratory (Environmental Studies Section, Environmental Monitoring and Assessment Division, Bhabha Atomic Research Centre), Surat, Gujarat
India
Abstract
The contribution of the aquatic water body to the tritium (3H) flux in the atmosphere near the discharge point of Kakrapar Gujarat Site has been assessed by collecting and analyzing the 3H activity in the air moisture and in the water sample near the aquatic discharge point. The observed air 3H activity near the discharge point was in the range of ≤0.20–19.8 Bq/m3, whereas the predicted 3H activity at the same location due to the atmospheric release through stack varied from 0.10 to 0.15 Bq/m3. The range of water 3H activity through the discharge point varied from ≤10 to 3482 Bq/l. The 3H flux (water to air transfer) was estimated and found to be in the range of ≤5.90E+01 – 2.05E+04 Bq/m2/s. The observation shows that during radioactive aquatic releases, there is an increase in the 3H activity levels in the water vapor near the aquatic discharge point. The observed 3H activity levels in air samples were extremely low to contribute any additional dose to the member of the public as compared to the public dose obtained from natural background sources.
How to cite this article:
Joshi CP, Patra A K, Nankar D P, Saradhi I V, Kumar A V. Studies on the contribution of the aquatic water body to the tritium flux in the atmosphere near the discharge point of Kakrapar Gujarat Site, India.Radiat Prot Environ 2022;45:76-80
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How to cite this URL:
Joshi CP, Patra A K, Nankar D P, Saradhi I V, Kumar A V. Studies on the contribution of the aquatic water body to the tritium flux in the atmosphere near the discharge point of Kakrapar Gujarat Site, India. Radiat Prot Environ [serial online] 2022 [cited 2023 Mar 24 ];45:76-80
Available from: https://www.rpe.org.in/text.asp?2022/45/2/76/364557 |
Full Text
Introduction
Radioactive liquid waste containing fission products and activation products is generated during the operation and maintenance of pressurized heavy-water reactors (PHWRs). In general, after proper treatment (processing and dilution), low-level liquid waste is disposed into the nearby waterbody through a discharge point as per the approved guideline given by the regulatory authority (Atomic Energy Regulatory Board).
In the atmospheric environment, tritium (3H) comes mainly in the form of tritiated water vapor (HTO). This HTO gets incorporated into the hydrosphere. There is also a minor pathway, in which 3H gets transferred between surface water and atmosphere.[1] 3H flux (Bq/m2/s) near water–atmosphere interface depends on 3H exchange. It is governed by a gradient of concentration at the water–atmosphere interface.[2]
Ciffroy et al. (2006)[3] developed a dynamic model to simulate doses from routine releases in freshwater. Horton et al. (1971) demonstrated that HTO and H2O have different evaporate rates.[4] Horton et al. reported two approaches used to calculate 3H evaporation from water or soil.[4] The first one considers that the emission of 3H is proportional to water evaporation and the second approach is consideration of each isotope follows its own concentration gradient. Taschner et al. observed that HTO and H2O had very different evaporation properties.[5] The river model from NCRP (1996) represents advection and dispersion processes driven by down-river currents, as well as radionuclide losses due to radioactive decay and sedimentation.[6]
A systematic study was undertaken to measure the 3H activity in atmospheric air moisture and water samples from discharge points during the low-level radioactivity discharge occasions. An attempt was made to calculate the 3H flux (Bq/m2/s) from water to atmosphere near the low-level radioactivity discharge point of the aquatic system (Moticher Lake) of Kakrapar Gujarat Site.
Materials and Methods
Site description
This study was performed at Kakrapar Gujarat Site where two PHWRs (220 MWe each), are operating since the year 1994 and two units of PHWR's (700 MWe) are under the advanced stage of construction. This site is situated on the southern bank of Moticher Lake, which is about 85 km away from the Arabian Sea toward the East of Surat, Gujarat state, India (latitude – 21° 14' N and longitude – 73° 22' E).
Atmospheric air moisture and water sample collection
Air moisture samples were collected using the moisture condensation method from discharge points at different distances such as 10m (BD1), 20m (BD2), 30m (BD3), 50m (BD4), 100m (BD5), and 500m (Intake). At the same time, water samples were also collected from the discharge point. The ambient met parameters were also measured.
Tritium analysis in atmospheric air moisture and water sample
Using a known volume of condensate moisture/water sample and Packard make Ultima Gold scintillation cocktail, the sample is prepared. 3H activity was measured in Tri-Carb 3170 LSA (Parso and Cook, 1994).[7] Based on the count rate, 3H activity was calculated. The background CPM of Tri-Carb 3170 LSA was 2.0 cpm, and the counting efficiency for 3H was about 22%. The minimum detectable levels obtained for the air moisture sample and water samples were 0.20 Bq/m3 or 10 Bq/l, respectively.
Methodology of tritium evaporation model
The evaporation of 3H from water to air is governed by a gradient of concentration at the water–atmosphere interface and such exchanges may be modeled by Fick's diffusion relationship (Sheppard et al., 2006).[2] When water 3H activity is relatively higher than the atmospheric 3H activity, then tritiated water will diffuse from the water to the atmosphere to some extent. The gradient of concentration corresponds to the activity at the lower side of the boundary layer and the 3H activity at the upper side of the boundary layer.
The flux (Bq/m2/s) may be expressed as
ΨHTO = Kexch (HTOwater _ HTOvapour) (1)
Where ΨHTO is the flux (Bq/m2/s), Kexch is exchange velocity (m/s), HTOwater is tritium activity in water (Bq/m3), HTOvapor is the tritium activity in air (Bq/m3).
Tritium exchange velocity
3H exchange velocity was measured by performing the experiment in an environmental chamber. In this study, a known volume of tritiated water was evaporated. A petri dish containing 100 ml of 3H free water was kept inside the chamber. At regular time intervals, the air moisture sample and the water kept in a petri dish were simultaneously collected and analyzed for 3H. The time interval was from 1 h to 24 h.
Results and Discussion
Prediction of tritium activity in air moisture samples
Meteorological data were collected from the tower-mounted system installed at Environmental Survey Laboratory (ESL), Kakrapar Gujarat Site. Gaseous effluents have radioactive elements that are released through a stack of height 100 m. Various meteorological parameters, water temperature, and discharge point flow rate are measured and tabulated in [Table 1]. In predicting the dispersion of released materials, site-specific joint frequency data for met parameters were used. The air 3H activity (Bq/m3) [Table 2] in the atmosphere was predicted using a double Gaussian atmospheric plume dispersion model, site-specific meteorological conditions, and the release rate (Bq/s). The site-specific dilution factor for the discharge point was observed to be 1.0E-08 s/m3. The predicted 3H activity near the discharge point due to the atmospheric release through the stack was found to be varying between 0.10 and 0.15 Bq/m3.{Table 1}{Table 2}
Tritium concentration in air moisture sample collected near the discharge point
Atmospheric air moisture samples were collected near the discharge point on seven different occasions. Out of the seven occasions, at one occasion, there was no aquatic release. 3H activity in air moisture measured near the discharge point was found to be in the range of ≤0.20–19.8 Bq/m3. 3H activity was observed to be in the decreasing trend with respect to distance from discharge point. Predicted 3H activity in the air moisture sample was below the detection limit of Tri-Carb 3170 LSA (0.2 Bq/m3) throughout all seven occasions. The observed air 3H activity is compared with the predicted atmospheric activity which was computed through Gaussian Plume Model (GPM). The factors affecting the observed 3H activity near the discharge point are atmospheric 3H release, aquatic 3H release, various met conditions, and releases from land and biota.
Tritium concentration in water sample collected from the discharge point
Water samples were collected from the discharge point on seven different occasions. The 3H activity in discharge point water samples is observed to be ≤10–3482 Bq/l. It is to be noted that the 3H activity in one occasion was observed to be below detection level (≤10 Bq/l) as no low-level radioactivity was discharged into the aquatic system for that occasion. It is always ensured that the releases are well within the limits specified by the regulatory body.
Calculation of tritium flux from water to atmosphere
An attempt was made to calculate 3H flux from water to atmosphere during the time of low-level radioactivity discharged into the aquatic system. It is to be noted that the enrichment of 3H in the atmosphere was observed near the discharge point during low-level radioactive release into the aquatic system. This is due to the process of natural evaporation of water. Variation of 3H activity in discharge water on 3H flux is shown in [Figure 1], and the correlation coefficient was observed to be 1.0. This is clearly observed that the 3H flux near the discharge point is significantly influenced by low-level radioactivity discharged into the aquatic system. Variation of 3H activity in air with respect to 3H activity in discharged water is shown in [Figure 2], and the correlation coefficient was observed to be 0.9. The site-specific evaporation rate was observed to be 0.01–0.033 mg/cm2/s. Exchange velocity of 3H was evaluated inside an environmental chamber, and the average exchange velocity was found 5.90E-03 m/s. The 3H flux was calculated and varied from ≤5.90E+01 to 2.05E+04 Bq/m2/s [Table 3].{Figure 1}{Figure 2}{Table 3}
Conclusions
An attempt was made to find out the 3H flux in the atmospheric environment near the discharge point of Kakrapar Gujarat Site due to the release of 3H in the aquatic environment. To carry out this study, site-specific weather data, water 3H activity at the discharge point, and measured 3H activity data were used. Site-specific 3H flux was calculated and varied from ≤5.90E+01 to 2.05E+04 Bq/m2/s. For further modeling, the role of wind speed and water flow needs to be studied more precisely. This estimation will be useful to review and evaluate the additional low-level burden of 3H on the atmospheric environment near the aquatic discharge point of the Nuclear power plant site.
Acknowledgments
The authors would like to thank Shri. S. K. Roy, Site Director, Kakrapar Site, Shri A. B. Deshmukh, Station Director, KAPS-1 and 2, and Shri. S. K. Deshmukh, CE (E and US), for their keen interest and encouragement. The assistance rendered by Smt. Padma Chaudhary, Shri M. K Chaudhary, Shri. J. J. Chaudhary, and all other ESL staff are thankfully acknowledged.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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