H.S. Kushwaha

Wire-mesh capped deposition sensors: Novel passive tool for coarse fraction flux estimation of radon thoron progeny in indoor environments

Deposition-based (222)Rn and (220)Rn progeny sensors act as unique, passive tools for determining the long time-averaged progeny deposition fluxes in the environment. The use of these deposition sensors as progeny concentration monitors was demonstrated in typical indoor environments as conceptually superior alternatives to gas-based indirect monitoring methods. In the present work, the dependency of these deposition monitors on various environmental parameters is minimized by capping the deposition sensor with a suitable wire mesh. These wire-mesh capped deposition sensors measure the coarse fraction deposition flux, which is less dependent on the change in environmental parameters like ventilation rate and turbulence. The calibration of these wire-mesh capped coarse fraction progeny sensors was carried out by laboratory controlled experiments. These sensors were deployed both in indoor and in occupational environments having widely different ventilation rates. The obtained coarse fraction deposition velocities were fairly constant in these environments, which further confirmed that the signal on the wire-mesh capped sensors show the least dependency on the change in environmental parameters. This technique has the potential to serve as a passive particle sizer in the general context of nanoparticles using progeny species as surrogates. On the whole, there exists a strong case for developing a passive system that responds only to coarse fraction for providing alternative tools for dosimetry and environmental fine particle research.

Effect of Coolant Inventories and Parallel Loop Interconnections on the Natural Circulation in Various Heat Transport Systems of a Nuclear Power Plant during Station Blackout

Provision of passive means to reactor core decay heat removal enhances the nuclear power plant (NPP) safety and availability. In the earlier Indian pressurised heavy water reactors (IPHWRs), like the 220u2009MWe and the 540u2009MWe, crash cooldown from the steam generators (SGs) is resorted to mitigate consequences of station blackout (SBO). In the 700u2009MWe PHWR currently being designed an additional passive decay heat removal (PDHR) system is also incorporated to condense the steam generated in the boilers during a SBO. The sustainability of natural circulation in the various heat transport systems (i.e., primary heat transport (PHT), SGs, and PDHRs) under station blackout depends on the corresponding systems coolant inventories and the coolant circuit configurations (i.e., parallel paths and interconnections). On the primary side, the interconnection between the two primary loops plays an important role to sustain the natural circulation heat removal. On the secondary side, the steam lines interconnections and the initial inventory in the SGs prior to cooldown, that is, hooking up of the PDHRs are very important. This paper attempts to open up discussions on the concept and the core issues associated with passive systems which can provide continued heat sink during such accident scenarios. The discussions would include the criteria for design, and performance of such concepts already implemented and proposes schemes to be implemented in the proposed 700u2009MWe IPHWR. The designer feedbacks generated, and critical examination of performance analysis results for the added passive system to the existing generation II & III reactors will help ascertaining that these safety systems/inventories in fact perform in sustaining decay heat removal and augmenting safety.

A Survey on the Quality Assurance Procedures Used in Intensity Modulated Radiation Therapy (IMRT) at Indian Hospitals

A national survey to obtain information about the Quality Assurance (QA) procedures and methods being followed at Indian radiotherapy centers for intensity modulated radiation therapy (IMRT) was conducted. A questionnaire containing parameters relevant to IMRT QA was evolved to collect the information pertaining to the QA of IMRT delivery system, QA of IMRT treatment planning system, and patient specific IMRT QA. The questionnaire was circulated to 40 hospitals in the country and responses of 31 centers were received. Survey results showed that 71% centers are having adequate machine specifi c IMRT QA programme, 19% centers have inadequate machine specific IMRT QA programme and 9% centers have irrelevant machine specific IMRT QA programme. No specific answer for question of QA tests of TPS specific to IMRT were received from the user. Almost all the centers have programme of setup verification of the patient by means of EPID/DRR/OBI. However, 91% of centers could not provide any information about the QA methodology of the devices used for setup verification. For patient specific dosimetric QA, almost all the hospitals have the program of pre-treatment dose verification using calibrated ionization chambers of sensitive volumes in the range of 0.01 to 0.65 cc. Dosimetric verification is performed by combining dose from all gantry angles to a single gantry angle. Two dimensional (2D) dosimetry systems such as radiographic and radiochromic films, 2D array of ionization chambers/ semiconductor diodes and EPID are also used in patient specific dosimetry verifications. Majority of the centers (about 48%) accept the plan with 3% dose difference and 3 mm dose to distance agreement criteria with gamma index less than unity. However, a number of other acceptance criteria specific to institution and tumor site are being also followed. This survey reveals that a variety of IMRT QA program is being followed at the Indian hospitals. This study has brought into focus the need to evolve a national protocol for IMRT QA so that treatment outcomes of all the IMRT centers of country can be compared.

Performance Characteristics of Newly Modified CaSO4:Dy based Indigenous Thermoluminescent Dosimeters for Environmental Radiation Monitoring

Environmental gamma radiation monitoring around the nuclear installations in India is being carried out for over three decades. This programme was essentially based on powder based Thermoluminescent Dosimeters (TLDs) using naturally occurring calcium fluoride (Fluorite) powder. Being powder based, it was labor intensive and to cater to the increasing demand for monitoring new stations, it was necessary to go for automatic TLD reader system. This was achieved by modifying the TLD cards suitably and using the automated PC based TLD badge TLD reader system indigenously developed and being used for personal dosimetry in India. This paper discusses the modifications that were carried out to make the TLDs suitable for environmental gamma monitoring using TLDs. Performance characterisation of the TLDs like accuracy, precision and energy dependence etc were carried out to see the efficacy of the system for use in the environmental gamma radiation monitoring. In addition, inter-comparison with the existing TLD system, both deployed simultaneously in the field was also carried out. It was found that the new TLD exhibit the accuracy of 89–96 % of the various delivered doses in the laboratory while the precision was observed to be within 4% for all the doses delivered. The gamma radiation levels as measured using two TLD systems were found to match very well with each other. The paper also discusses the results.

AEROSOL STUDIES IN A NUCLEAR AEROSOL TEST FACILITY UNDER DIFFERENT TURBULENCE CONDITIONS

Abstract An experimental nuclear aerosol test facility has been built at the Bhabha Atomic Research Centre for validating the aerosol behavior computer codes used in nuclear reactor safety assessment. Its essential components are the 10-m3 stainless steel test vessel, plasma torch aerosol generator, and aerosol instrumentation to study the aerosol characteristics. Studies have been conducted with metal/metal oxide aerosols in dry environments under varying turbulence conditions and the results have been compared with the predictions of NAUA (Mod 5) code. The code predictions were found to differ from the experimental observations. To explain the differences under calm conditions, a gravity-induced spatial stratification model was formulated and solved. It was found that NAUA prediction agrees fairly well with the depletion of total airborne mass given by this model. In the presence of turbulence, the code overestimated the airborne concentrations. This is attributed to the noninclusion of particle removal by inertial impaction. Accordingly, the deposition velocity formula used in the code was modified based on the Crump-Seinfeld approach. With this modification, the results of airborne mass depletion agreed quite well with the measured data. On the whole, the study provides validated modifications in the NAUA (Mod 5) code to include turbulence effects and a formulation of gravity-induced stratification of aerosols under calm conditions.

Environmental Radiation Measurements And Comprehensive Impact Assessment Around A Nuclear Power Plant Site In Kaiga, India

This paper presents the results of environmental monitoring of Kaiga site and impact assessment due to the operation of two PHWR type reactors. Measurements of radionuclides were carried out in atmospheric, terrestrial and aquatic environmental compartments using state-of art techniques and radiological impact due to external exposure, ingestion, inhalation and skin absorption pathways to individual member of public evaluated. A hypothetical case of OBT intake through contamination of crops due to tritium is also considered. The paper also presents the results of estimation of Site Specific Transfer Factors required for the impact assessment modeling. The parameters required for dose evaluation and respective uncertainties for each parameter were attributed. The dose distribution was estimated using parameter uncertainty analysis from all the pathways and for all the major radionuclides. Dose distribution was found to be lognormal and ranges from 0.2 — 5.8 μSv.a-1 (at 95% Confidence) with a mean value of 1.1 μSv.a-1 in the year 2006. Since the upper limit of 95% confidence level is below the regulatory limit, violation of the limit is highly unlikely. Statistical analysis of 137Cs concentration in soil and sediment samples indicate that there is no build up of 137Cs in the environment as compared to pre-operational value (p<0.001).

Environmental Gamma Radiation Monitoring Around Nuclear Power Stations in India, an Indian Scenario

There are 17 operating nuclear power reactors in India at 6 sites with an installed capacity of approximately 4120 MWe of electricity. Apart from two reactors in Tarapur Atomic Power Station (TAPS), which use enriched uranium and are based on boiling water reactor (BWR) technology, all the other reactors at various power stations use natural uranium as fuel, are moderated and cooled by heavy water and are Pressurised Heavy Water Reactors (PHWR). Environs of all the power stations in India are monitored for gamma radiation on regular basis using Thermoluminescent Dosimeters (TLDs). The gamma radiation levels thus measured are regularly compared with the pre-operational levels. The data generated for all the stations during the past years was subjected to various analyses like comparison of the annual levels with those during the pre operational levels, distribution studies, regressions with the possible contributors etc. This paper discusses the environmental gamma radiation levels based on the analyses of all data generated for all the power stations during the years up to 2005. Comparisons of the annual radiation levels with those during the pre operational data indicates that none of the stations show any increase in the environmental gamma radiation levels.