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   Table of Contents - Current issue
April-June 2021
Volume 44 | Issue 2
Page Nos. 59-119

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ICRP Recommendations: Fit for purpose p. 59
DD Rao
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Radiological aspects during cutting and removal of L-08 coolant channel from the core of 540 MWe TAPS-4 nuclear reactor p. 61
Durgaprasad Dakinedi, S Adhya, SK Pal, K Venkataramana
The pressurized heavy-water reactors (PHWR) consist of a low-pressure horizontal reactor vessel, calandria, containing heavy water as moderator. The calandria is pierced by a large number of coolant tubes (also called pressure tubes [PTs], 392 in 540 MWe PHWR), which contains fuel bundles, and through which pressurized heavy-water coolant circulates. During biennial shut down in 2017, in-service inspection of coolant channels in Tarapur atomic power station-4 (TAPS-4) had been carried out and after the review of results of inspection, it was recommended by various groups of experts that channel L-08 should be removed for postirradiation examination at Bhabha Atomic Research Center (BARC). Before the channel removal job, one special shielding flask was designed to shift the removed channel to BARC. The integrity test of special shielding flask was carried out by safely placing cobalt-60 (source strength 851000 MBq) capsule source inside the shielding flask with the help of cranking unit mechanism followed by dose rate mapping on the outer surface of the flask. To establish the hydrogen pickup rates in L-08 PT, sliver samples were collected and separately sent to BARC. Four metallic sliver samples were obtained at four different distances from north E-face. The activity content present in each sliver sample was also estimated. The maximum activity estimated was 2313.24 MBq. Subsequently, L-08 coolant channel was cut from both sides using a chipless tool. Jobs involving heavy water (D2O) collection work were carried out with a ventilated plastic suit. Derived air concentration (DAC) of tritium at the work location was maintained below 1DAC during the entire activity. Particulate DAC was found below the detectable limit. Floor contamination checks and floor decontamination were conducted at regular intervals to avoid buildup of contamination. As a result of such high-quality radiological safety measures, only 25 workers, out of 270 radiation workers, have received a cumulative dose of more than 3 mSv in direct reading dosimeter with a maximum individual dose of 8.45 mSv and maximum individual uptake of 0.39 GBq/m3. Job was completed with a total collective dose of 324.35P-mSv which is 14.5% lower than estimated. This article highlights some of the critical tasks involved in the cutting and the removal of irradiated coolant channel from the core of 540 Mwe TAPS-4 reactor which is a first of kind activity in nature.
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Distribution of natural and artificial radioactivity concentration in soils of two districts (Ballia and Deoria) of Uttar Pradesh, India p. 67
Deepak Kumar, YP Gautam, AK Sharma, Vineet Kumar, AR Tripathi, S Kumar, J Kumar, IV Saradhi, A Vinod Kumar
This paper presents the activity concentrations of naturally occurring radionuclide 226Ra, 232Th, and 40K and the anthropogenic radionuclide, 137Cs in soil samples collected from Ballia and Deoria district of Uttar Pradesh, India. The mean activity concentrations of radionuclides in 43 soil samples from the two districts were measured using HPGe gamma spectrometry system. The activity level in soil samples varied from 23 to 50 Bq/kg with a mean of 30 Bq/kg for 226Ra, 30–74 Bq/kg with a mean of 47 Bq/kg for 232Th, 287–728 Bq/kg with a mean of 466 Bq/kg for 40K, and ≤0.1–1.4 Bq/kg with a mean of 0.4 Bq/kg for137Cs. The mean activity of naturally occurring 226Ra and 232Th is comparable with the international values reported by UNSCEAR while concentration of 40K is slightly higher. 137Cs activity is found to be comparable with the activities reported at other parts of India. Correlation of 226Ra and 40K activity with 232Th activity was observed as 0.85 and 0.75, respectively. A positive correlation (0.71) between 40K and 137Cs was found in the present study. The absorbed gamma dose rates in air were in the range of 44.6–98.3 nGy/h with a mean of 63.4 nGy/h, while the annual effective dose rates were observed in the range of 54.7–120.6 μSv/y with a mean of 77.8 μSv/y. The average value of radium equivalent activity in soil was 136.9 Bq/kg. This study provides a baseline data of natural radioactivity and 137Cs activity in soils of these two districts.
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One year of 222Rn concentration at a typical rural site in South India p. 73
K Charan Kumar, Nagaraja Kamsali
The simultaneous measurements of atmospheric radon, ambient gamma radiations dose, and relevant meteorological parameters were carried out at the National Atmospheric Research Laboratory (NARL), Gadanki, India (13.459° N, 79.175° E) during June 2013–May 2014 are analyzed and presented. The results show that radon strongly correlates with temperature, relative humidity, and a weak correlation with air pressure, ambient gamma dose during fair weather days. Radon's well-defined monthly variability is observed, with the highest during winter and lowest during monsoon season. The fast Fourier transform analysis revealed a hidden memory in variations in radon activity with prominent peaks at 24 h and 12 h, indicating the influence of atmospheric stability on the abundance of radon in air. About 99% of radon activity lies below 70 Bq/m3 with a mean value of 11.81 ± 4.83 Bq/m3, and about 99% ambient gamma dose levels range from 140 to 240 nSv/h at NARL with a mean value of 192.17 ± 17.43 nSv/h. The ambient gamma dose levels are well within limits prescribed by the UNSCEAR.
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Long-term trends in gamma radiation monitoring at the multi-facility nuclear site, Kalpakkam, South-India p. 79
Deepu Radhakrishnan, M Boopathy, V Gopalakrishnan, PT Rakesh, S Chandrasekaran, CV Srinivas, R Venkatesan, B Venkatraman
In this work, the analysis of the long-term environmental radiation monitoring data collected within the Department of Atomic Energy site, Kalpakkam using gamma monitors such as GammaTRACERS (GTs) from 2013 to 2018 and Autonomous Gamma Dose Loggers (AGDLs) located in the site boundary at distances from 1.25 to 2.5 km from 2016 to 2018 are presented with respect to dose variation in different locations/wind sectors/seasons. The average background dose rates are in the range of 140–220 nGy/h except at a location (GT2) where a dose rate of 400 ± 20 nGy/h is found. It is observed that the detectors generally measure the normal background doses and at times slightly higher doses (above background) due to exposure to 41Ar plume during normal operations from Madras Atomic Power Stations. The monitors were categorized into four groups: Group 1 to Group 4. Dose rates higher than normal were observed in Group 1 detectors during winter and North-east monsoon seasons and in Group 3 and Group 4 detectors during summer and South-west monsoon seasons and during January to March months in Group 2 detectors. The gamma dose rates during 41Ar plume transit vary in the range of 600–900 nGy/h. The cumulative annual effective doses at the site boundary, analyzed from 2016 to 2018, due to normal operational releases varied from 11 μSv to 114 μSv in different sectors which is significantly lower compared to annual dose limit (1000 μSv) for public.
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Natural and fallout radioactivity mapping of Kakrapar Gujarat site, India p. 92
SS Wagh, AK Patra, IV Saradhi, A Vinod Kumar
This study presents the activity and outdoor gamma absorbed dose rates (terrestrial and cosmic) due to the naturally occurring (226Ra, 232Th, and 40K) and anthropogenic (137Cs) radionuclides around Kakrapar Gujarat site. The activity level (Bq/kg) in the soil ranged 5.7–48.4 for 226Ra, 9.7–28.0 for 232Th, 83.9–585.7 for 40K, and 0.2–4.6 for 137Cs, respectively. The mean concentration levels measured in Kakrapar soil from the naturally occurring radioisotopes are lower than the corresponding global average values. 137Cs activity in the soil is comparable with the preoperational period. The total effective dose rates in air outdoors ranged 17.2–78.1 μSv/y with the mean value of 32.8 μSv/y. The mean value of absorbed dose rate due to cosmic components was 37.5 nGy/h which is comparable to the worldwide reported values.
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Thermoluminescence and optically stimulated luminescence studies of Indian soils for its application in retrospective dosimetry p. 98
SN Menon, Sonal Y Kadam
Optically stimulated luminescence (OSL) of quartz obtained from ceramics, concrete, and soil has been studied extensively for its use in retrospective dosimetry. The OSL properties of quartz separated from surface soil of different parts of India were investigated for its application as a retrospective dosimeter. Different parameters such as recuperation, recycling ratio, equivalent dose plateau, and relevant to single-aliquot regenerative protocol were investigated. The dose recovery tests were also performed. These studies show that the soil samples can be used for dose evaluation during any radiation accident.
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Estimation of surface layer scaling parameters using SODAR for the coastal site of Tarapur p. 103
Vedesh Krishnacharya Varakhedkar, Sanjay Vasudev Vanave, Aramana Baburajan, IV Saradhi
This report presents the directional dependence of surface scaling parameters, namely, roughness length and corresponding friction velocity, for neutral category at the Tarapur coastal site. The average roughness length of the lowest value of 0.5 m in the west (W) direction and the highest value of 0.885 m in the N direction has been observed and average friction velocity of the lowest value 0.39 m/s in the W direction and the highest value 0.73 m/s in the NW direction was observed for 2019. Sector average turbulent kinetic energy was estimated to be 1.413 m2/s2 and its dissipation rate as 0.33 m2/s3 for the 10 m elevation from the surface. Surface drag coefficient for the 10 m height was 0.0229 for the smooth ocean surface and 0.0255 for the land surface was observed for the Tarapur coastal site.
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Dosimetric evaluation of analytic anisotropic algorithm and Acuros XB algorithm using in-house developed heterogeneous thorax phantom and homogeneous slab phantom for stereotactic body radiation therapy technique p. 110
Swati Dubey, Priyusha Bagdare, Sanjay Ghosh
To perform patient-specific quality assurance (QA), the accuracy of the dose calculation algorithm is vital, especially in the lung cancer stereotactic body radiation therapy (SBRT). The present study is based on the evaluation of two widely used algorithms, analytical anisotropic algorithm (AAA) and Acuros XB (AXB) inside the in-house developed heterogeneous thorax phantom (HTP) and a homogeneous slab phantom (HSP) simultaneously. To evaluate dosimetric differences between the two algorithms, point dose measurement was performed for pretreatment QA plans of 35 lung cancer patients by keeping the same monitor units and beam angles as those for the actual patient treatment. The dose was calculated on the Eclipse treatment planning system inside both the medium by using both AAA and AXB algorithms. Plans were delivered on the Edge linear accelerator (LA) (Varian Medical Systems, Palo Alto, CA, USA), and measurements were taken by using a 0.01 cc ion chamber and DOSE1 electrometer. Statistical analysis was performed on the observed data set, and percentage (%) variations between the measured and planned doses were calculated and analyzed. The mean % variations between the measured and planned doses inside HTP for all QA plans were found to be 2.61 (standard deviation [SD]: 0.66) and 2.19 (SD: 0.64) for AAA and AXB algorithms, respectively. Whereas, inside HSP, it was found to be 1.79 (SD: 0.74) and 1.64 (SD: 0.70) for AAA and AXB algorithms, respectively. The mean % difference between the measured dose and the planned dose was derived to be statistically significant for HTP, however, it was found to be statistically insignificant inside the HSP at P < 0.01. The Pearson's correlation coefficient test showed a strong positive correlation between the measured dose and the planned dose for both AAA and AXB inside HTP as well for HSP. The results obtained from this study showed that as the actual patient body is heterogeneous, thus to get more realistic results, patient-specific QA must be performed inside the heterogeneous phantom instead of homogeneous. Moreover, in the homogeneous medium, both the algorithms predict the dose efficiently, however, in heterogeneous medium, AAA over/under predicts the dose, whereas AXB shows good concurrence with measurements.
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ICRU report 95 – Operational quantities for external radiation exposure p. 116
C Sneha
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