Pramilla D Sawant

Risk Assessment for Natural Uranium in Subsurface Water of Punjab State, India

ABSTRACT Traces of uranium were measured by laser fluorimeter in 235 subsurface water samples collected from four districts of Punjab state in India. The concentration of U in water samples ranged between <2–644 μg/L with a mean value of 73.1 μg/L. The radiological risk was observed to be in the range of 5.55 × 10−6–1.78 × 10−3 with a mean value of 2.03 × 10−4, which is around 22% more than the maximum acceptable level (l.67 × 10−4) as per guidelines of Indias Atomic Energy Regulatory Board. The mean of chemical toxicity risk, expressed as life time average daily dose (LADD) was worked out to be 5.56 μg/kg/day with a range of 0.15–48 μg/kg/day by considering a bodyweight of 51.5 ± 8.5 kg, water ingestion rate of 4.05 L/d, and life expectancy of 63.7 yrs for an adult Indian reference man and compared with the reference dose (4.53 μg/kg/day). The average exposure level of U was comparatively high and the chemical toxicity was expected to be more. The mean of hazard quotient (LADD/ RfD) for all four districts was found to be greater than 1, indicating that groundwater may not be suitable for consumption from a chemical toxicity point of view.

Application of alpha track registration technique for plutonium estimation in bioassay samples

Bioassay monitoring is carried out for occupational workers handling plutonium (Pu) in nuclear facilities. In India, presently Pu estimation in bioassay samples is done by alpha spectrometry. The minimum detectable activity (MDA) of alpha spectrometry is 0.5mBq for a counting period of 1 day. To reduce the load of sample counting on alpha spectrometry, an alternative method based on alpha track registration in solid state nuclear track detectors (SSNTDs) is developed in the present paper. For this purpose, few urine samples of normal subjects spiked with known amounts of Pu in the range of 0.5-5.5mBq were exposed to CR-39 SSNTDs. The total number of alpha tracks seen in the CR-39 films of the sample and the standard were used to calculate the amount of Pu in the sample. The results of alpha track registration technique were also compared with that obtained by the well-established alpha spectrometry and were found to agree well within +/-30%. The minimum amount of Pu that can be analyzed by this method is 0.18mBq for an exposure period of 45 days.

Creatinine as a normalization factor to estimate the representativeness of urine sample - Intra-subject and inter-subject variability studies

In-vitro bioassay monitoring generally involves analysis of overnight urine samples (~12 h) collected from radiation workers to estimate the excretion rate of radionuclides from the body. The unknown duration of sample collection (10-16 h) adds to the overall uncertainty in computation of internal dose. In order to minimize this, IAEA recommends measurement of specific gravity or creatinine excretion rate in urine. Creatinine is excreted at a steady rate with normally functioning kidneys therefore, can be used as a normalization factor to infer the duration of collection and/or dilution of the sample, if any. The present study reports the chemical procedure standardized and its application for the estimation of creatinine as well as creatinine co-efficient in normal healthy individuals. Observations indicate higher inter-subject variability and lower constancy in daily excretion of creatinine for the same subject. Thus creatinine excretion rate may not be a useful indicator for extrapolating to 24 h sample collection.

Technology to Harvest Uranium from Seawater and Its Estimation by Laser Fluorimetry

Abstract Process technology for extraction of uranium from seawater has been initiated in India on bench scale field trials and for this purpose special adsorbents have been synthesised by radiation grafting technique. These adsorbents are in the form of leaflets that provide efficient contact patterns with water body in the sea. However, it was observed that during the extraction of uranium from seawater/brine, a few transition elements like vanadium also got extracted by the adsorbents. The product elute solutions were then stored in large glass-lined mild steel tanks, which lead to the extraction of iron from the tanks into the solutions. The main challenge was to separate uranium from these transition elements and then estimate its concentration by laser fluorimetry (LF). This paper reports the radiochemical separation procedure standardised for determining the concentrations of uranium metal ions from lean solutions of seawater/brine and its estimation by LF.

Alpha source preparation of actinides by micro-precipitation

Alpha spectrometry is used for qualitative and quantitative analysis of actinides in biological and environmental samples. This technique requires a thin, homogenous and carrier-free deposit. Numerous methods for source preparation are electrolytic deposition, spontaneous deposition, micro-precipitation, direct evaporation, vacuum sublimation, etc. The most widely used method for preparation of actinides for alpha spectrometry is electro-deposition of actinides onto a stainless steel planchette. This procedure is time consuming, requires elaborate equipment and is expensive. Micro-precipitation method on the other hand is comparatively faster and more reliable. Thus, the present study was taken-up to optimize various parameters for rapid alpha source preparation of actinides by micro-precipitation method.

Methodology for estimation of phosphorus-32 in bioassay samples by Cerenkov counting

Bioassay is the preferred individual monitoring technique for radiation workers handling phosphorus-32 (32 P), a pure beta emitter (βmax = 1.71 MeV) with 14.3 day half-life. The method standardized at Bioassay Laboratory, Trombay and in use for this purpose includes estimation of 32 P in urine by coprecipitation with ammonium phosphomolybdate followed by gross beta counting. In this study, the feasibility of Cerenkov counting for detection of 32 P in bioassay samples was explored, and the results obtained were compared with the conventional gross beta technique.

Nasal swab reference levels for plutonium based on aerosol characteristics and breathing patterns of individuals

In plutonium (Pu) handling facilities, there is a potential for internal exposure of radiation workers along with external exposure. Nasal swabs (NS) taken rapidly, on site, help in not only providing an early estimate of internal dose due to inhalation of Pu but also in decision making for medical intervention. However, the Committed Effective Dose (CED) computed based on the observed NS activity and that estimated from bioassay measurements of individuals may vary significantly. One of the reasons would be the use of default particle size (5 µm) for computing the CED based on the activity on NS. Other parameters like breathing pattern and levels of exercise would also influence the NS reference activity level and hence their impact needs to be assessed. This study indicated that observed NS reference levels had a direct dependence on all these parameters and use of default parameters for evaluation of internal dose based on NS activity would result in large uncertainties in the dose assessment.

A rapid radio-bioassay method for strontium estimation in nuclear/radiological emergencies

Strontium (Sr) is a by-product of the nuclear fission of uranium and plutonium in nuclear reactors and nuclear weapons. It is an important radionuclide in spent nuclear fuel and radioactive waste and is considered as one of the most hazardous constituents of nuclear wastes. Also during a nuclear/radiological emergency, workers as well as members of the public may get internally contaminated with Sr. Hence, a truly rapid radio-bioassay method will be needed to screen a large number of people for assessment of internal contamination and facilitate decision making on subsequent medical intervention. The current precipitation method used at Bioassay Lab., BARC, Trombay is quite lengthy and laborious. Efforts are being made to optimize bioassay methods at BARC using solid extraction chromatography (SEC) technique for emergency response. The present work reports standardization of SEC using Sr-Spec (Sr-Specific, make Eichrom Technologies, Darien, Illinois, USA) resin for rapid estimation of Sr in urine samples. Adsorbed Sr is eluted from the resin using 0.05M HNO 3 , precipitated as carbonate and estimated using a low background gas flow Geiger-Muller counter (make ECIL, Hyderabad, India). The average recovery of stable Sr is ~80% and comparable to radioactive recovery observed in spiked samples. The minimum detectable activity (MDA) achieved by this technique is ~4 mBq/mL for 90 Sr that is well below the required generic emergency action level of 19 Bq for 20 mL urine sample. The advantage of this method is its simplicity, fast turnaround time and an increase in the sample throughput.