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The time-dependent neutron diffusion equation approximates the neutronic power evolution inside a nuclear reactor core. Applying a Galerkin finite element method for the spatial discretization of these equations leads to a stiff semi-discrete system of ordinary differential equations. For time discretization, an implicit scheme is used, which implies solving a large and sparse linear system of equations for each time step. The GMRES method is used to solve these systems because of its fast convergence when a suitable preconditioner is provided. This work explores several matrix-free strategies based on different updated preconditioners, which are constructed by low-rank updates of a given initial preconditioner. They are two tuned preconditioners based on the bad and good Broyden's methods, initially developed for nonlinear equations and optimization problems, and spectral preconditioners. The efficiency of the resulting preconditioners under study is closely related to the selection of the subspace used to construct the update. Our numerical results show the effectiveness of these methodologies in terms of CPU time and storage for different nuclear benchmark transients, even if the initial preconditioner is not good enough. [ABSTRACT FROM AUTHOR]

For several years, reports have been published about fluctuations in measured radioactive decay time-series and in some instances linked to astrophysical as well as classical environmental influences. Anomalous behaviors of radioactive decay measurement and measurement of capacitance inside and outside a modified Faraday cage were documented by our group in previous work. In the present report, we present an in-depth analysis of our measurement with regard to possible correlations with space weather, i.e. the geomagnetic activity (GMA) and cosmic-ray activity (CRA). Our analysis revealed that the decay and capacitance time-series are statistically significantly correlated with GMA and CRA when specific conditions are met. The conditions are explained in detail and an outlook is given on how to further investigate this important finding. Our discovery is relevant for all researchers investigating radioactive decay measurements since they point out that the space weather condition during the measurement is relevant for partially explaining the observed variability. [ABSTRACT FROM AUTHOR]

The simplified spherical harmonics equations are a useful approximation to the stationary neutron transport equation. The eigenvalue problem associated with them is a challenging problem from the computational point of view. In this work, we take advantage of the block structure of the involved matrices to propose the block inverse-free preconditioned Arnoldi method as an efficient method to solve this eigenvalue problem. For the spatial discretization, a continuous Galerkin finite element method implemented with a matrix-free technique is used to keep reasonable memory demands. A multilevel initialization using linear shape functions in the finite element method is proposed to improve the method convergence. This initialization only takes a small percentage of the total computational time. The proposed eigenvalue solver is compared to the standard power iteration method, the Krylov-Schur method and the generalized Davidson method. The numerical results show that it reduces the computational time to solve the eigenvalue problem. [ABSTRACT FROM AUTHOR]

The one-dimensional two-fluid model approach has been traditionally used in thermal-hydraulics codes for the analysis of transients and accidents in water–cooled nuclear power plants. This paper investigates the performance of RELAP5/MOD3 predicting vertical upward bubbly flow at low velocity conditions. For bubbly flow and vertical pipes, this code applies the drift-velocity approach, showing important discrepancies with the experiments compared. Then, we use a classical formulation of the drag coefficient approach to evaluate the performance of both approaches. This is based on the critical Weber criteria and includes several assumptions for the calculation of the interfacial area and bubble size that are evaluated in this work. A more accurate drag coefficient approach is proposed and implemented in RELAP5/MOD3. Instead of using the Weber criteria, the bubble size distribution is directly considered. This allows the calculation of the interfacial area directly from the definition of Sauter mean diameter of a distribution. The results show that only the proposed approach was able to predict all the flow characteristics, in particular the bubble size and interfacial area concentration. Finally, the computational results are analyzed and validated with cross-section area average measurements of void fraction, dispersed phase velocity, bubble size, and interfacial area concentration. [ABSTRACT FROM AUTHOR]

222Rn is a naturally occurring gas created from the decay of 226Ra. The long-term health risk of breathing radon is lung cancer. One particular place where indoor radon concentrations can exceed national guidelines is in wastewater treatment plants (WWTPs) where treatment processes may contribute to ambient airborne concentrations. The aim of this paper was to study the radon concentration decrease after the application of corrective measures in a Spanish WWTP. According to first measures, air radon concentration exceeded International Commission Radiologica1 Protection (ICRP) normative (recommends intervention between 400 and 1000 Bq m-3). Therefore, the WWTP improved mechanical forced ventilation to lower occupational exposure. This measure allowed to increase the administrative controls, since the limitation of workers access to the plant changed from 2 h d-1 (considering a maximum permissible dose of 20 mSv y-1 averaged over 5 y) to 7 h d-1. [ABSTRACT FROM AUTHOR]

The implemented models in TRAC-BF1 for the decay heat calculations are based on the 1971 American Nuclear Society (ANS) Standard or the 1979 ANS Standard if selected by the user. With the entry into force of the 1994 ANS Standard and the subsequent review, the TRAC-BF1 models were made completely obsolete, so a revision of the older models and the implementation of ANSI/ANS-5.1-2005 Standard in the code are required. In this paper, a novel numerical study is presented based on the analytical resolution of the decay heat equation which takes into account the number of reactor operation histories, the number of fissionable nuclides, and the number of groups per fissile. Moreover, this paper describes the influence of the short-term power histories on the total decay heat power calculation due to the high interest in the simulation of severe transients, such as Anticipated Transients without SCRAM, which cannot be ignored in nuclear safety analysis. [ABSTRACT FROM PUBLISHER]

Spectral preconditioners are based on the fact that the convergence rate of the Krylov subspace methods is improved if the eigenvalues of the smallest magnitude of the system matrix are ‘removed’. In this paper, two preconditioning strategies are studied to solve a set of linear systems associated with the numerical integration of the time-dependent neutron diffusion equation. Both strategies can be implemented using the matrix–vector product as the main operation and succeed at reducing the total number of iterations needed to solve the set of systems. [ABSTRACT FROM PUBLISHER]

In nuclear safety analysis, it is very important to be able to simulate the different transients that can occur in a nuclear power plant with a very high accuracy. Although the best estimate codes can simulate the transients and provide realistic system responses, the use of nonexactmodels, together with assumptions and estimations, is a source of uncertainties whichmust be properly evaluated. This paper describes a Rod Ejection Accident (REA) simulated using the coupled code RELAP5/PARCSv2.7 with a perturbation on the cross-sectional sets in order to determine the uncertainties in the macroscopic neutronic information. The procedure to performthe uncertainty and sensitivity (U&S) analysis is a sampling-based method which is easy to implement and allows different procedures for the sensitivity analyses despite its high computational time. DAKOTA-Jaguar software package is the selected toolkit for the U&S analysis presented in this paper. The size of the sampling is determined by applying the Wilks' formula for double tolerance limits with a 95% of uncertainty and with 95% of statistical confidence for the output variables. Each sample has a corresponding set of perturbations that will modify the cross-sectional sets used by PARCS. Finally, the intervals of tolerance of the output variables will be obtained by the use of nonparametric statistical methods. [ABSTRACT FROM AUTHOR]

In many developing countries, the access to safe drinking water is not available to all the population. As a response to these problems, AQUAPOT project developed a water treatment facility based on ultrafiltration (UF) technology able to be used in developing countries that are working in Ecuador and Mozambique. Up to now, the major problem detected in the field application of UF in drinking water production from surface water has been membrane fouling and its cleaning. To study the consequences that lack of cleaning and maintenance of the installation can have over the membranes, AQUAPOT has simulated fouling over UF membrane that suffered from an irreversible fouling after long term filtration of surface water. The experimental study included characterization of the foulant layer and chemicals test (under static and dynamic conditions) to remove membrane fouling, with moderate results for chemicals solutions tested. In this study, air bubbles are used as an alternative, cost effective and environmentally friendly membrane cleaning technique to remove severe fouling. This work describes the experimental procedure performed in the physico-chemical test with chemical solutions bubbled with air, and the main results obtained when comparing the permeability values before and after cleaning the membrane. [ABSTRACT FROM AUTHOR]

One method successfully employed to denoise digital images is the diffusive iterative filtering. An important point of this technique is the estimation of the stopping time of the diffusion process. In this paper, we propose a stopping time criterion based on the evolution of the negentropy of the 'noise signal' with the diffusion parameter. The nonlinear diffusive filter implemented with this stopping criterion is evaluated by using several noisy test images with different statistics. Assuming that images are corrupted by additive Gaussian noise, a statistical measure of the Gaussianity can be used to estimate the amount of noise removed from noisy images. In particular, the differential entropy function or, equivalently, the negentropy are robust measures of the Gaussianity. Because of computational complexity of the negentropy function, it is estimated by using an approximation of the negentropy introduced by Hyvärinen in the context of independent component analysis. [ABSTRACT FROM AUTHOR]

The main goal of the present paper is to quantify, in homogeneous and heterogeneous phantoms, the differences between experimentally measured dose distributions inside it, and those calculated by the simulation of different transport models using the Monte Carlo computer code MCNP. This objective has been achieved simulating the electron and photon transport in a water phantom irradiated by a Theratron 780 (MDS Nordion) 60Co radiotherapy unit, which has been realistically modeled, considering field sizes from 5 cm × 5 cm to 20 cm × 20 cm. The source description and characteristics of the incident beam have been slightly modified in order to study the results variations of these models. Different methodologies have also been applied to speed up the calculations with the aim of applying MCNP efficiently in radiotherapy treatment planning. [ABSTRACT FROM AUTHOR]

The quality control of mammography units is necessary to reduce the dose imparted to women as much as possible. An accurate characterisation of the primary X-ray spectra is very useful for this purpose. Primary spectra can be obtained using Compton spectrometry techniques. In this work, a commercial spectrometer used to characterise a mammography X-ray tube has been simulated using the Monte Carlo method by means of the MCNP code. Using the developed model, a Response matrix is obtained. Owing to the fact that this matrix is ill-conditioned, the inversion is not a simple process. This problem has been solved using the truncated singular value decomposition method. Results obtained when this methodology was applied have been compared with theoretical X-ray spectra. [ABSTRACT FROM AUTHOR]

Mammographic phantom images are usually used to study the quality of images obtained by dedicated mammographic equipment. The digital image treatment techniques allow us to carry out an automatic analysis of the phantom image. In this work, some techniques of digital image processing are applied to compute a specific image quality index (IQI) for a mammographic phantom, namely CIRS model 11A version SP01. The algorithm designed analyses the phantom image by means of automatic detection of the number of microcalcifications, and the image resolution as the number of line pairs per millimetre. Then, the IQI is calculated from a scoring system. The manner in which the functioning conditions (kV and mAs) of the mammographic equipment and the preprocessing denoising method of the digital image affect the results for the IQI are also studied. [ABSTRACT FROM AUTHOR]

Breast screening programmes are the best weapon to fight against breast cancer. Nevertheless, despite the benefits, this practice supposes a radiological risk that cannot be forgotten. In order to calculate breast glandular doses, different MCNP- 4C2 models have been developed, simulating the exposure conditions. Radiological detriments have been transported from the population under study in the UNSCEAR 2000 to the Valencian Community, obtaining the detection-induced cancer ratio (DICR) for this population. [ABSTRACT FROM AUTHOR]

A Theratron 780 (MDS Nordion) 60Co radiotherapy unit has been simulated with the Monte Carlo code MCNP. The unit has been realistically modelled: the cylindrical source capsule and its housing, the rectangular collimator system, both the primary and secondary jaws and the air gaps between the components. Different collimator openings, ranging from 5 × 5 cm² to 20 × 20 cm² (narrow and broad beams) at a source-surface distance equal to 80 cm have been used during the study. In the present work, we have calculated spectra as a function of field size. A study of the variation of the electron contamination of the 60Co beam has also been performed. [ABSTRACT FROM AUTHOR]

Propolis obtained from honeybee hives has been used in folk medicine as an anti-inflammatory, anti-carcinogenic or immunomodulatory agent. In animal studies, the radioprotector effect of propolis has been attributed to its free-radical scavenging properties. The present study was carried out to show the protective properties of propolis extract against DNA damage induced by gamma irradiation. The evaluation of the radioprotective effect of propolis has been carried out by the analysis of chromosome aberration induction after several doses of gamma rays. The results of an analysis in the presence of ethanol extract of propolis (EEP) were compared with the dose-effect calibration curve for gamma-rays by analysis of chromosome aberrations without propolis, a decrease in the radiation-induced chromosome aberrations has been observed to be higher than 50% for all the doses. [ABSTRACT FROM AUTHOR]

A realistic characterisation of the primary beam is very important for the quality control of X-ray tubes. The most accurate technique to assess the actual photon spectrum is X-ray spectrometry. Some difficulties arising in the spectrum determination can be avoided using a Compton spectrometer. Simulation models are useful tools to know the effect of some operational parameters, such as collimation of primary beam, relative position of focus and detector, and the influence of shielding materials. A simulation model has been developed using the MCNP code, based on the Monte Carlo method, in order to reproduce a commercial Compton spectrometer. In this work, the model developed is applied to analyse the influence on measurements of shielding materials present in the spectrometer. [ABSTRACT FROM AUTHOR]

In this paper we formualte a master equation approach describing a D+T thermonuclear plasma in a lumped phase space. From the first moments of this master equation and performing the pass to the continuous limit the evolution equations for the expected phase space ion densities emerge. Also we have obtained the evolution equations of the equal time correlation and covariance functions. Finally we have deduced the hydrodynamic equations that arise from a master equation approach. [ABSTRACT FROM AUTHOR]

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Radioactive liquid wastes of low-medium activity level are generated in radio immune assay (RIA) laboratories, which are also potentially infectious because of the pathogens from patient blood. The most common way of managing these wastes consists of a temporal storage, for partial radioactivity decay, followed by management by an authorised company. The object of this work is to study the viability of treating radioactive liquid wastes coming from RIA using membrane techniques in order to reduce their volume, which would mean an improvement from the radiological point of view and a decrease in management costs. This paper describes the results of some experiments carried out with RIA real wastes, by means of processes such as ultrafiltration and reverse osmosis. It has been proved that waste volume can be significantly reduced, obtaining a treated liquid that is free of pathogens and organic matter and with an activity level around the environmental background. [ABSTRACT FROM AUTHOR]