Radiological complexity of nuclear facilities: an information complexity approach to workplace monitoring

Nuclear energy is crucial for achieving net-zero carbon emissions. A big challenge in the nuclear sector is ensuring the safety of radiation workers and the environment, while being cost-effective. Workplace monitoring is key to protecting workers from risks of ionising radiation. Traditional monitoring involves radiological surveillance via installed radiation monitors, continuously recording measurements like radiation fields and airborne particulate radioactivity concentrations, especially where sudden radiation changes could significantly impact workers. However, this approach struggles to detect incremental changes over a long period of time in the radiological measurements of the facility. To address this limitation, we propose abstracting a nuclear facility as a complex system. We then quantify the information complexity of the facility's radiological measurements using an entropic metric. Our findings indicate that the inferences and interpretations from our abstraction have a firm basis for interpretation and can enhance current workplace monitoring systems. We suggest the implementation of a radiological complexity-based alarm system to complement existing radiation level-based systems. The abstraction synthesized here is independent of the type of nuclear facility, and hence is a general approach to workplace monitoring at a nuclear facility.

Development and establishment of a parallel plate ionization chamber as a transfer standard for measurement of dose to tissue in beta radiation fields

A parallel-plate ionization chamber (PPC) with a nominal volume of 8.16 cm³ was developed based on theoretically simulated design parameters. Its purpose is to serve as a transfer standard for dosimetry in a beta radiation field. The entrance window of the PPC consists of an aluminized Mylar sheet with a thickness of 1.4 mg/cm2. The collecting and guard electrodes are created by applying a graphite coating on a Poly Methyl Methacrylate (PMMA) substrate with a thickness of 5 mm. The nominal sheet resistance of the graphite-coated PMMA substrate was measured using a four-probe technique and found to be approximately 800 Ω per square (Ω/□). Dosimetric characterization of the PPC was performed in the ISO 6980 reference beta radiation field, utilizing 90Sr-90Y and 85Kr beta radiation sources. The assessment included studies on short-term stability, linearity, current-to-voltage characteristics, stabilization time, and leakage current. The PPC was calibrated and established as a transfer standard using the 'Extrapolation Ionization Chamber,' recognized as an absolute standard for dose to tissue in 90Sr-90Y and 85Kr beta sources within the laboratory. The calibration coefficient of the PPC indicates an energy dependence of 0.6 % for 90Sr-90Y and 85Kr beta sources.

Measurement of energy and directional distribution of neutron ambient dose equivalent for the 7Li(p,n)7Be reaction

Double differential neutron fluence distributions were measured in the 7Li(p,n)7Be reaction for proton beam energies 7, 9 and 12 MeV. Seven liquid scintillator based detectors were employed to measure neutron fluence distributions using the Time of Flight technique. Neutron ambient dose equivalents were determined from the measured fluence distribution using ICRP (International Commission on Radiological Protection) recommended fluence to dose equivalent conversion coefficients. Neutron dose equivalents were also measured using a conventional BF3 detector based REM counter. Ambient dose equivalent measured by the REM counter is found to be in agreement with that determined from the neutron fluence spectra within their uncertainties. Angular distributions of the ambient dose equivalents were also determined from the measured fluence distributions at different angles.

Proton induced activation studies in the carbon steel composites

The number of accelerator installations has increased significantly in the last decade and requirements are consistently increasing. In these facilities neutrons and high energy charge particle induced reactions are possible with the metallic enclosures made up of natural Fe or steel composites used as structural components or shielding materials. Present study aims to generate a dose rate profile of the induced activations and quantify the induced radionuclide concentrations in the low carbon steel composites. A comparison of the radionuclide concentrations generated in the metallic Fe and SS-304 composite is also presented for a judicious material selection to minimise the radiation concerns.

Generation of map on natural environmental background absorbed dose rate in India

A systematic mapping of natural absorbed dose rate was carried out to assess the existing exposure situation in India. The mammoth nationwide survey covered the entire terrestrial region of the country comprising of 45127 sampling grids (grid size 36 km²) with more than 100,000 data points. The data was processed using Geographic Information System. This study is based on established national and international approaches to provide linkage with conventional geochemical mapping of soil. Majority (93%) of the absorbed dose rate data was collected using handheld radiation survey meters and remaining were measured using environmental Thermo Luminescent Dosimeters. The mean absorbed dose rate of the entire country including several mineralized regions, was found to be 96 ± 21 nGy/h. The median, Geometric Mean and Geometric Standard Deviation values of absorbed dose rate were 94, 94 and 1.2 nGy/h, respectively. Among the High Background Radiation Areas of the country, absorbed dose rate varied from 700 to 9562 nGy/h in Karunagappally area of Kollam district, Kerala. The absorbed dose rate in the present nationwide study is comparable with the global database.

Clinical outcome of anterior cruciate ligament reconstruction with modified transtibial and anteromedial portal

Arthroscopic ACL reconstruction is the current standard care of treatment for anterior cruciate ligament (ACL) injuries. Modified transtibial (mTT) and anteromedial portal (AMP) techniques aim at the anatomical placement of femoral tunnel. Controversy existed in the literature with regard to the outcome of these techniques. Hence, we designed a retrospective comparative study to analyse the clinical and functional outcomes of mTT and AMP techniques. We hypothesized that there would be no difference between the clinical and functional outcomes in mTT and AMP techniques. This retrospective observational study was conducted in consecutive patients who underwent arthroscopic ACL reconstruction using semitendinosus-gracilis (STG) quadrupled graft in our tertiary care centre with a minimum follow-up of two years. Out of 69 patients, 37 had undergone ACL reconstruction by mTT technique and remaining by AMP technique. All the patients were assessed clinically by anterior drawer, Lachman's, pivot shift and single-legged hop test. Lysholm Knee Scoring Scale and International Knee Documentation Committee (IKDC) subjective knee evaluation score were used for the functional status. Knee instability was assessed objectively by KT-1000 arthrometer. There was no statistically significant difference in baseline demographic characteristics between mTT and AMP groups. At the end of 2 years, no statistically significant difference was noted in the anterior drawer and Lachman's test. Though not significant, IKDC scores and Lysholm's scores showed a better outcome in the AMP group when compared to the mTT group. AMP group showed significantly better outcome with KT-1000 arthrometer. Based on the results obtained, we presume that overall both mTT and AMP have similar functional outcome. However, as AMP technique offers significantly improved subjective rotational stability on pivot shift test, better hop limb symmetry index and KT 1000 readings compared to mTT, we suggest AMP over mTT.

Bifocal Stabilisation of Acute Acromioclavicular Joint Dislocation using Suture Anchor and Temporary K-Wires: A Retrospective Analysis

Introduction

The acromioclavicular joint (ACJ) is a major link connecting the upper limb to the torso. The acromioclavicular and coracoclavicular (CC) ligaments help in stabilising the joint. We feel it is prudent to address both these ligament injuries, to achieve optimum result. This study was undertaken to analyse the results of a simple frugal surgical technique we used to deal with this injury considering stabilisation for both these ligaments.

Materials and methods

In this retrospective study, skeletally mature patients with Type III, IV or V ACJ dislocations who underwent open reduction and stabilisation of the joint with temporary K-wires, repair of the capsule and augmentation of CC ligaments with suture anchors were included. Clinico-radiological and functional outcome was evaluated. Functional assessment of the upper limb was analysed using the Disabilities of Arm, Shoulder, and Hand Score (DASH), Constant shoulder score (CSS) and Oxford shoulder score (OSS).

Results

Clinical and radiological evaluation of the 32 patients who had completed two years from the index surgery, was done. Out of the 37 patients included initially, five were lost in follow-up. Majority of the subjects included were males and type V was the most common injury. Mean pre-operative CC distance on the affected side was 13.92±4.94mm. In the immediate post-operative radiograph, it was 7.63±2.08mm and in the final follow- up was 9.36±2.75mm. Measurements were taken by two independent investigators and inter, and intra-observer reliability were analysed by Interclass correlation coefficient. Excellent functional outcome was noted despite the 1.81±1.50mm average loss of correction. At final follow-up, mean DASH score was 4.67±4.18, Oxford shoulder score was 44.06±2.44 and Constant shoulder score was 86.37±5.81. The severity of the injury had no significant effect on the functional outcome post our method of stabilisation and rehabilitation.

Conclusion

Bifocal fixation restores the multidirectional stability of the disrupted ACJ. Adequate radiological reduction, good functional outcome and simplicity of execution make this technique an undemanding one for use in regular practice.

Hydrogeochemical characterization and evaluation of subsurface water quality in the Proterozoic Cuddapah Basin, Andhra Pradesh, India

In the current survey, different hydrogeochemical processes governing the geochemistry of aquifers, the usefulness of groundwater for regular consumption, and agricultural purposes were evaluated around the Tummalapalle area. One hundred forty-four borehole locations were chosen to characterize the major physicochemical components of the aquifer water. The analysis results of pH inferred that the groundwater is nominally acidic to basic, and pH ranged from 6.6 to 8.4. The average concentrations of TDS, Ca²⁺, Mg²⁺, total hardness (TH), HCO₃^-, and total alkalinity (TA) are within the allowable limits of potable water quality as prescribed by the Bureau of Indian Standards (BIS) and WHO. However, the average concentrations of Na⁺, K⁺, Cl^-, and SO₄^2- were all below the permissible limit. All samples were analyzed with the help of Piper and Chadha charts to determine the dominant hydrogeochemical components of groundwater. The dominance of cations in groundwater in this region is in the sequence of Ca²⁺  > Na⁺  > Mg²⁺  > K⁺, followed by anions HCO₃^-  > Cl^-  > SO₄^2-. The Gibbs plot analysis suggested the predominance of rock aquifer interaction as the major hydrogeochemical process governing groundwater geochemistry in this region. The water quality index (WQI) of all groundwater samples in the Tummalapalle region was estimated, with 55% of the samples being potable grade. The different irrigation indices were analyzed for the groundwater samples to estimate their desirability for agriculture. The maximum number of water samples was found to be well-suited for cultivation.

STUDY OF EFFECTIVENESS OF SHELTERING FROM RADIATION EXPOSURE DUE TO ACCIDENTAL RELEASE OF RADIOACTIVITY

Sheltering is one of the important protective actions as a part of emergency response during the early phases of an accident-mostly precautionary in nature. Sheltering via structural shielding reduces the direct exposure from plume/cloud shine and ground shine doses as well as the airborne radioactivity concentration and hence inhalation dose. The present study was aimed at estimating the shielding factor in the case of Indian houses for external exposure pathways using the FLUKA Monte Carlo based radiation transport code. Furthermore, the dose reduction factor due to exposure from the inhalation pathway was estimated using an indoor aerosol model. These factors were assessed for the three major types of dwellings, and they provided important inputs for decision-making for sheltering or evacuation in case of any sudden release of radionuclides into the environment.

Dose distribution to a random walker moving in a two-dimensional surface around a radioactive source

BACKGROUND

Modeling of dose distribution of randomly moving population around a radioactive source is a complex problem.

OBJECTIVE

The objective is to develop a model and solution techniques to estimate radiation absorbed dose to the population randomly moving around a radioactive source.

METHODS

The problem is formulated using a second-order partial differential equation; different moments of the dose distribution function are defined related to physically realizable quantities, and solutions are obtained using standard moments methods. Alternatively, numerical simulations are performed to estimate the radiation doses using Monte Carlo approach for individual positions and random motions of the people around the source.

RESULTS

A good agreement is found between average doses obtained from moments method and numerical simulations. A typical application of this model to different exposure conditions shows that the average dose is highly dependent on the population density. The study results show that average dose decreases with increase in the population density and movement area of random walker.

SIGNIFICANCE

This mathematical model can be used as a rapid assessment tool by the emergency planners in resource optimization by providing quick estimates of likely exposures for triage and emergency response.

Simulation study on radiation fields around targets to apply CR-39 for photo-neutron measurement in electron accelerator near the threshold energy

Photo-neutron production in electron accelerator near the threshold energy has been studied by Monte Carlo simulation using the FLUKA code. A pencil beam of 10 MeV electron was incident normally on W, Ta, Pb and Bi targets and a CR-39 detector attached to the target was used as scoring region. In the simulation, photon and neutron spectra, yield and their spatial distribution, fast neutron fluence above 100 keV, total dose and neutron dose deposition were estimated for these metallic targets. The photon emission was found to be forward peaked whereas the neutron emission was isotropic in nature. The photon yield was found to be 5 to 6 orders of magnitude higher than that of neutrons. In W and Ta, the photon yield is maximum for 1.5 mm thickness whereas for Pb and Bi, the photon yield is highest at 2 and 2.5 mm respectively. The total neutron yield was highest for W and lowest for Pb whereas highest number of fast neutrons above 100 keV was for W followed by Bi, Pb and Ta. Production of significant number of fast neutrons above 100 keV suggests the possibility of the use of CR-39 detector for measurement of these neutrons. The total dose deposition was found to be highest for Bi followed by Pb, Ta and W whereas the neutron dose equivalent was highest for W followed by Pb, Bi and Ta. This simulation study will be useful for neutron dosimetry, estimation of source term, implementation of CR-39 for measurement and other radiation protection aspects in the vicinity of an electron accelerator.

Application of multipoint dose rate measurement for radioactive inventory estimation in waste drums

Dose-to-Curie (DTC) conversion is a fast and simple method for quantification of radionuclide content in solid waste packages with a prior knowledge of waste matrix and radionuclide composition of the waste stream. A dose to curie conversion factor generated based on an assumed radioactivity distribution in the package is used for conversion of the measured dose rate to activity. The difference between the radionuclide distribution for drum from field and the assumed distribution is a major source of error in activity estimation using this technique. In this work, the systematic error of DTC method, due to the spatial variation of a single hot-spot in 200 L solid waste drum is subjected to systematic analysis using Monte-Carlo simulation. Data analysis was carried out with 1920 source locations within the drum and up to sixteen measurement points for dose rates around the drum. The span of error obtained for different configurations of detectors were compared to optimise the waste drum assay system. The general trends observed in simulation were found to be in good agreement with the experimental measurements done using a ¹³⁷Cs (318.2 MBq) standard source placed at selected locations. The results presented here clearly establish the advantage of multipoint dose rate measurement to improve the accuracy in activity estimation using DTC method.

Evaluation of influential correction factors applicable for absolute beta dosimetry of 85Kr, 90Sr-90Y and 106Ru-106Rh beta emitters

Extrapolation ionization chamber is normally used for absolute measurement of absorbed dose to tissue and in standardization of beta particle emitting sources in particular. However, in this technique, several correction factors are applied to the measured ionization current to evaluate the true value of the dose to the tissue from beta radiation. These correction factors are described in ISO 6980-2:2004. Out of these, ion recombination correction factor (k_sat) and ambient air density correction factor (k_ad) are evaluated experimentally during measurement of ionization current. Other significant correction factors are backscatter correction factor (k_ba), correction factor for perturbation in electron spectrum due to ionization chamber side wall scatter (k_pe), correction factor for difference in attenuation of beta spectrum due to change in ambience condition (k_abs) and correction factor for radial non-uniformity of dose inside detector volume (k_ra). Experimental evaluation of correction factors k_ba, k_pe and k_abs are not easily achievable. In the present work four significant correction factors k_ba, k_pe, k_abs and k_ra are derived theoretically by Monte Carlo particle transport simulation. These correction factors are evaluated for beta emission spectrum of ⁸⁵Kr, ⁹⁰Sr-⁹⁰Y and ¹⁰⁶Ru-¹⁰⁶Rh radioactive sources.

DEVELOPMENT OF NACL-BASED OPTICALLY STIMULATED LUMINESCENT PHOSPHORS FOR THE POSSIBLE APPLICATIONS IN DOSIMETRY

New highly sensitive optically stimulated luminescent phosphors with NaCl moiety and dopants Ca,Cu,P/Mg,Cu,P are developed. These phosphors show very high optically stimulated luminescence (OSL) sensitivity. The dose response for NaCl:Ca,Cu,P is linear up to 1.2 Gy and for NaCl:Mg,Cu,P is slightly sub linear from 0.2 Gy. These phosphors show 30% fading during first 4 and later signal gets stabilised with no further signal loss. These sensitive phosphors will find applications in radiation dosimetry using OSL.

Study of optically stimulated luminescence and calculation of trapping parameters of K2Ca2(SO4)3:Eu nanophosphor

K₂Ca₂(SO₄)₃:Eu nanophosphor was synthesized by chemical coprecipitation method and annealed at different temperatures from 400 to 900 °C. The nanophosphor annealed at 600 °C showed cubic structure with crystallite size ~25 nm. TEM shows morphology of K₂Ca₂(SO₄)₃:Eu nanophosphor was in the form of nanorods having diameter ~20 nm and length of ~100-200 nm. These samples were irradiated with gamma radiation for the doses varying from 10 mGy to 10 kGy and their Thermoluminescence (TL) and continuous-wave optically stimulated luminescence (CW-OSL) have been studied. CW-OSL response was found to be maximal for the sample annealed at 600 °C. The TL glow curve of the nanophosphor apparently showed a major peak at around 160 °C accompanied by three low intensity peaks at ~75, 215 and 285 °C. The traps responsible for all the TL peaks in K₂Ca₂(SO₄)₃:Eu were also found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response suggested that the traps associated with low temperature peaks are responsible for fast decay and the traps associated with the higher temperature peaks are responsible for slow decay of the OSL signal. OSL response showed linear behavior up to 1 kGy and saturated with further increase in the gamma dose. The wide OSL response makes studied K₂Ca₂(SO₄)₃:Eu nanophosphor a good candidate for high dose measurement.

DOSE ASSESSMENT FOR ATMOSPHERIC DISCHARGE OF LONG-LIVED RADIONUCLIDES IN NUCLEAR POWER PLANT DECOMMISSIONING

Decommissioning of nuclear power plants is a multistage process involving complex operations like radiological characterization, decontamination and dismantling of plant equipment, demolition of structures, and processing and disposal of waste. Radioactive effluents released into the environment may result in exposure of population through various exposure pathways. The present study estimates the public dose due to atmospheric discharge of important radionuclides during proposed decommissioning activities of Indian Pressurized Heavy Water Reactors. This study shows that major dose contributing radionuclides are 60Co followed by 94Nb, 134Cs, 154Eu, 152Eu, 133Ba, 99Tc, 93Mo and 41Ca. It is found that infant dose is higher than adult dose and major fraction of total dose (~98%) is through ground shine and ingestion; other pathways such as inhalation and plume shine contribute only a small fraction. This study will be helpful in carrying out radiological impact assessment for decommissioning operations which is an important regulatory requirement.

Determination of calibration matrix for HPGe-based in vivo monitoring system for estimation of 241Am in lungs and liver

The detection of internal contamination may be carried out by direct or indirect methods. The lung counting technique using an array of High Purity Germanium (HPGe) detectors is one of such direct detection methods. It is known from the literature that the estimation of activity by organ counting can lead to erroneous results if an amount of activity is possessed by an adjacent organ. In the case of HPGe-based lung monitoring, the estimation could be misleading if the activity is possessed by the liver, which is a proximal organ. In such cases the measured activity should be modified using cross-talk coefficients which account for the contribution from adjacent organs. The determination of cross-talk coefficients for ²⁴¹Am was carried out by placing the detectors over inactive lungs of an Lawrence Livermore National Laboratory phantom when the source activity was contained in the liver and vice versa. A calibration matrix was formulated with calibration coefficients as diagonal elements and cross-talk coefficients as off-diagonal elements. The measured activities may be modified by matrix multiplication with the inverse of the calibration matrix to nullify the contribution from adjacent organs. The current work has empirically determined the fitting equations which relate calibration and cross-talk coefficients for lungs and liver measurement geometries with muscle-equivalent chest wall thickness (MEQ-CWT) values. The values of these coefficients were determined for an average MEQ-CWT of 1.77 cm for lungs and 1.33 cm for liver. The calculations showed that the activity contribution from liver to lungs was 29% higher than that of lungs to liver. A verification exercise was conducted to demonstrate this method. For the given calibration source, the percent overestimation was reduced for lung activity, while the liver activity was slightly underestimated. In the case of old exposure follow-up monitoring cases, the ²⁴¹Am activity built up in liver could interfere with the lung monitoring results and this method using the calibration matrix may be used for estimation of more accurate results.