Once spent nuclear fuels (SNFs) are removed from a reactor, they are cooled in pools for several years. This is followed by dry interim storage, which can last many decades. Understanding how the SNF behaves under these conditions and performing the corresponding safety assessments is a fundamental part of licensing storage facilities. In this paper, new models incorporated into the DIONISIO fuel performance code to simulate the behavior of SNF under storage conditions are described. Starting from a normal operational power history, the code can be used to analyze the evolution of fuel rod behavior across different storage scenarios, including extended periods in the pool followed by a dry storage period. Transition phases between reactor operation and pool storage are also accounted for. The thermal, mechanical and chemical models used in each case, along with the assumptions made, are detailed and validated with experimental measurements when they are available. Additionally, a benchmark case is simulated and the results are compared against those from other computational tools to assess performance and accuracy. The results demonstrate that the implemented models are capable of reliably simulating the behavior of fuel rods during storage conditions.

Background: Electroporation (EP), in which pulsed electric fields permeabilize cell membranes, is widely used in biomedical and food-processing applications, including electrochemotherapy, irreversible electroporation (IRE), and gene electrotransfer (GET). Optimizing EP protocols is critical to maximize therapeutic efficacy while minimizing unintended tissue damage.Methods: We introduce a theoretical framework for EP protocol optimization based on the spatiotemporal trajectories of ablation size, electroporation threshold, and pH-induced tissue damage. The framework analyzes how the time gradient of the electric field, derived from first principles, governs the evolution and interaction of these trajectories. The approach is evaluated using in silico and in vitro potato models and applied in vivo to GET protocols using a dorsal skinfold chamber model.Results: The time gradient of the electric field was found to govern all three trajectories, and their interaction determined protocol efficiency. Within the proposed framework, the entire ablation-size trajectory could be reconstructed from a single measurement obtained at the final pulse, eliminating the need to experimentally track the EP threshold trajectory. In the absence of pH effects, ablation size increased logarithmically with pulse number, while the EP threshold decayed exponentially. When pH-induced damage was included, ablation size increased logarithmically, whereas damage increased linearly. Combining these trends enabled the identification of a critical pulse number that maximizes the difference between ablation size and pH-induced damage.Conclusion: This trajectory-based framework provides a unified description of EP dynamics and a first-principles-based method for optimizing pulse number across EP-based protocols. Joint consideration of ablation, threshold, and damage trajectories can guide the design of safer and more effective EP treatments.

Las condiciones de tensión y temperatura a las que se somete a la vaina de un combustible nuclear gastado durante el almacenamiento en seco hacen que el hidrógeno ingresado durante el período de operación pueda precipitar en forma de hidruros orientados radialmente, lo cual puede degradar significativamente las propiedades mecánicas de la vaina. En este trabajo se presenta la implementación de un modelo computacional para simular el fenómeno de reorientación de hidruros, con el objetivo de integrarlo al módulo de almacenamiento en seco del código DIONISIO. El modelo fue validado mediante experimentos propios, así como también con experimentos disponibles en la literatura. En general, se obtuvo un buen acuerdo entre los resultados medidos y simulados.

En combustibles nucleares basados en dióxido de uranio (UO2), la fisión del isótopo U-235 genera una amplia variedad de productos de fisión, comúnmente clasificados en actínidos, volátiles e inertes. Estos subproductos se distribuyen dentro de la pastilla de UO2 según los perfiles de flujo neutrónico térmico y rápido. En el marco del desarrollo del código de combustible DIONISIO, se está incorporando un nuevo módulo denominado PerfEECC-FP, que simula la formación y evolución de los principales productos de fisión mediante la resolución de las ecuaciones de Bateman. Para ello, se emplean secciones eficaces precisas, extraídas de bibliotecas nucleares optimizadas para distintos tipos de reactores. A diferencia de códigos especializados como ORIGEN, la propuesta en DIONISIO busca modelar la generación de productos de fisión con dependencia espacial explícita, considerando tanto el radio de la pastilla como su posición axial en la pila combustible. Se propone en este trabajo la inclusión de cadenas isotópicas de interés —Xe-135, Cs-137, I-131, Sr-90 y Mo-99— y la evaluación de su evolución temporal comparándola con simulaciones realizadas con el código ORIGEN.

During the storage stage, spent nuclear fuels undergo different thermomechanical stresses that can compromise their integrity, given the long times involved. Experimental data on these processes is not abundant and, in many cases, only simulation codes are available to predict the evolution of these parameters due to the difficulties of carrying out representative experiments. In this work, we present new models added to the storage module of the DIONISIO fuel code, which allow the code to simulate the behaviour of the fuel in each of the storage stages. Models are presented to describe the decay heat as well as the pool and dry storage stages. All these models require validation, either with data measured in different repositories around the globe or with experiments designed to reproduce the storage conditions. This paper presents a selection of validations to ensure the reliability of the models developed within the module.

The multiplicity of interconnected physical phenomena in different parts of fusion reactors means that several and varied physics models need to be applied to perform advanced studies of the materials and components of such complex devices. In the case of the vacuum vessel wall, it is necessary to study the heat deposition due to the interaction with the neutron flux, together with the removal of this heat by the liquid coolant. To do this, in this paper we show the performance of a multiphysics system in which a deterministic neutron transport solver is coupled with temperature and fluid dynamics solvers. These solvers are modules of the Alya framework, a highly efficient parallel finite element code developed by the Barcelona Supercomputing Center. The module TEMPER solves the heat equation in the wall and the fluid, NASTIN solves the incompressible Navier-Stokes equations for the coolant, and NEUTRO solves the steady-state Boltzmann linear transport equation for neutronics.NEUTRO, the main focus of our work, is more recent than other Alya modules, and is in its validation stage. For this reason, we include the results of its performance, recent new features, and some comparisons with other neutronics solvers. Coupling these modules at the time-step level with a shared domain enables us to perform neutronics and thermohydraulic simulations in a single run without intermediate files or manual intervention. This capability contributes to computational efficiency, reduces potential error, and has not yet been demonstrated to the best of our knowledge in the nuclear fusion field.After showing the results and comparison for test cases, we display an example of coupled operation to analyze neutron flux, heat deposition, fluid dynamics, and heat dissipation in the inner poloidal segment comprising half of a 40-deg-angle toroidal portion of an ITER sector.

Electroporation (EP), the temporary or permanent permeabilization of the cell membrane induced by an electric field, is the basis of various applications in medicine and food processing. In EP-based protocol optimization in terms of pulse number, such as in electrochemotherapy (ECT), irreversible electroporation (IRE), and gene electrotransfer (GET), it is essential to reach an optimal dose-response, that is, the pulse dose that maximizes the electroporated tissue area while minimizing damage. Predicting the electroporated tissue area variation in time, i.e., its trajectory, requires measuring the EP threshold trajectory and understanding the interaction between both trajectories and the damaged tissue area trajectory. Here we introduce a new methodology, based on the analysis of the nonlinear dynamic interaction of the EP threshold and damaged tissue area trajectories, that shows that the EP threshold trajectory is the time gradient of the electric field. This allows predicting the electroporated area trajectory with a single electroporated area measurement at the last pulse, thus avoiding the need to measure the EP threshold trajectory, a rather cumbersome task. Also, it makes it possible to explain at the macroscopic level why the EP threshold trajectory has an approximate exponential time decrease while the EP threshold isoline trajectory, aka the electroporated tissue area trajectory, has an approximate logarithmic time increase. Further, it permits predicting an optimal dose response in terms of pulse number in an EP-based protocol, with a single electroporated tissue area measurement. Examples of its application to an in vitro vegetal model, and to an in vivo skinfold chamber shed new light on the nonlinear dynamic behavior of electroporated tissue area, EP threshold, and damaged tissue area trajectories, paving the way for optimal treatment planning in EP-based protocols.

In this paper, an efficient model (from a computational point of view) is implemented to evaluate the gaseous and solid swelling in nuclear fuels under irradiation conditions. The model contemplates the precipitation of fission gases as intragranular and intergranular bubbles in the form of two coupled systems. For the intragranular gas, the diffusion equation is solved taking into account the processes of gas production, as well as the nucleation, growth and destruction of bubbles. In the case of the intergranular gas, bubbles are considered to have a lenticular shape and grow due to diffusion-controlled vacancy absorption. The results obtained and their comparison with experimental data indicate that the model is capable of performing realistic simulations of the pellet swelling processes, both under constant power conditions and fast power transient conditions. After that, the model was coupled with a solid swelling model and a grain growth model in order to analyze its performance as a whole.

Realistic simulation of nuclear fuel performance requires not only validated models capable of describing the thermomechanical phenomena that take place within the fuel under irradiation conditions, but a detailed description of the thermal hydraulics of the channel surrounding the fuel rods, which provides the boundary conditions of the system. In this work, the main results and outlooks of coupling the thermal hydraulics code SubChanFlow with the fuel performance code DIONISIO are presented. To achieve this, an internal coupling was implemented, wherein DIONISIO is used as a master code controlling SubChanFlow as a thermal hydraulics subroutine replacing the simplified version already embedded in DIONISIO. Several tests were conducted to ensure the performance and quality of the coupling under normal operation conditions as a first approach. In addition, it was observed that the coupling demonstrated a significant improvement in the description of the cladding temperature and related variables, such as oxide thickness and hydrogen uptake, when compared with experimental data.

In this work, the main developments made by coupling the thermohydraulic code SubChanFlow with the fuel performance code DIONISIO are presented. To accomplished this, an internal coupling was made where DIONISIO is used as a master code controlling SubChanFlow as a thermohydraulic subroutine that replaced the default one. Several tests were carried out to ensure the performance and quality of the coupling. In addition, the coupling showed significant improvement in the cladding temperature description and related variables such as the oxide thickness and the fuel temperature when comparing with experimental data.

We study the dynamical Casimir effect in a double superconducting cavity in a circuit quantum electrodynamics architecture. Parameters in the quantum circuit are chosen in such a way the superconducting cavity can mimic a double cavity, formed by two perfectly conducting outer walls and a dielectric one, with arbitrary permittivity separating both halves. We undertake a spectral analysis of the cavity, showing that the spectrum varies significantly depending on the values of the susceptibility of the dielectric mirror and the relative lengths of both cavities. We study the creation of photons when the walls oscillate harmonically with a small amplitude. Furthermore, we explore the possibility of entangling two uncoupled cavities, starting from a symmetric double cavity and having both of its halves become uncoupled at a later given instant. We consider both cases: (i) when the field is initially in a vacuum state and (ii) the situation in which photon creation via the dynamical Casimir effect has already taken place. We show that the cavities become entangled in both cases but, in the latter, the quantum correlation between individual modes can be greatly increased at the cost of diminishing the entanglement between most pairs of modes.

We present a new module included in the DIONISIO 3.0 code, extending its capabilities to analyze experiments without irradiation in two-dimensional domains with axial symmetry and three-dimensional domains. The code can analyze any material and geometry subject to histories of variable temperature, pressure, composition of the atmosphere, etc. Based on the finite element method, the code can build simple geometries or read meshes adapting them to the specific case to be simulated. We compare the calculations of the module in different scenarios to analyze the behavior of rods and UO2 pellets. In the former, we used several ballooning experiments under constant pressure or temperature over diverse atmospheres. A description of the evolution of a crack in the cladding is included. In the latter, we use a thermal densification model included in the code to analyze the porosity behavior during re-sintering processes.

A simple method for the production of 99Mo is proposed involving the fission of 235U loaded onto commercially available activated carbon fibers. The maximum uranium loading that could be achieved on the material was 0.35 mg g−1. The dependence of the metal ion loading on pH showed that in the pH range 6–9, Mo was not significantly bound to the carbon surface, whereas all other metal species investigated were relatively strongly held. This finding suggests that it should be possible to devise a process based on this new target material providing five-day irradiation in a high neutron flux does not alter the surface properties of the carbon matrix.

We study the role of driving in an initial maximally entangled state evolving under the presence of a structured environment in a weak and strong regime. We focus on the enhancement and degradation of maximal Concurrence when the system is driven on and out of resonance for a general evolution, as well as the effect of adding a transverse coupling among the particles of the model. We further investigate the role of driving in the acquisition of a geometric phase for the maximally entangled state. As the model studied herein can be used to model experimental situations such as hybrid quantum classical systems feasible with current technologies, this knowledge can aid the search for physical setups that best retain quantum properties under dissipative dynamics.

We examined whether survivin acts as a constitutive and inducible radioresistance factor in pancreatic cancer cells. Using a quantitative TaqMan reverse transcription-polymerase chain reaction for survivin mRNA in five pancreatic cancer cell lines, we found an inverse relationship between survivin mRNA expression and radiosensitivity. PANC-1 cells, which had the highest survivin mRNA levels, were most resistant to X-irradiation; MIAPaCa-2 cells, which showed the least survivin mRNA expression, were the most sensitive to X-irradiation. Our results suggested that survivin could act as a constitutive radioresistance factor in pancreatic cancer cells. To determine whether radioresistance is enhanced by induction of survivin expression by irradiation, PANC-1 and MIAPaCa-2 cells were subjected to sublethal doses of X-irradiation followed by a lethal dose. Survivin mRNA expression was increased significantly in both PANC-1 and MIAPaCa-2 cell lines by pretreatment with a sublethal dose of X-irradiation, as was cell survival after exposure to the lethal dose. In this system, enzymatic caspase-3 activity was significantly suppressed in cells with acquired resistance. These results suggest that survivin also acts as an inducible radioresistance factor in pancreatic cancer cells. Survivin, then, appears to enhance radioresistance in pancreatic cancer cells; inhibition of survivin mRNA expression may improve the effectiveness of radiotherapy.

We present significant improvements and validations of a deterministic neutron transport code (NEUTRO) dedicated to solving the Boltzmann Transport Equation. The code is integrated as a module in the Alya software package developed by the Barcelona Supercomputing Center which uses the Discrete Ordinates Method on angular coordinates, multi-group for energy discretization and FEM on unstructured meshes to treat special complex domains. The anisotropy of the scattering medium is introduced into the scattering kernel using real base expressions for spherical harmonics. In order to build the total cross-section and the respective group matrix for the elastic cross-section, we use the NJOY code. We test the solver using different geometries, orders of integration for the angular discretization and number of energy groups. Finally, we compare our results against benchmarks obtained from an NEA database that reported measurements of leakage spectra of several materials.

When zirconium-based materials are subjected to irradiation, dimensional changes occur due to irradiation creep and growth. Predicting the behavior of these phenomena is necessary to determine the maximum time of operation required to avoid possible mechanical problems, such as buckling of sheaths, cracks, sheath-cooling channel contact, etc. In this work, a model to evaluate the irradiation growth based on the evolution of microstructural defects such as dislocations and point defects is presented. Preliminary results obtained are in good agreement with experimental data. In addition, the model was incorporated as a new subroutine within the nuclear fuel code DIONISIO and some comparisons with experimental data and previous models in DIONISIO are presented.

Various numerical models are developed that seek to reproduce, in a simulation instance, the formation and evolution of cracks in the claddings of nuclear fuel elements. The algorithms are based on the cohesive zone method within the finite element framework. When applied to simulations involving fracture mechanics, cohesive elements have various advantages, such as not needing to know the stress state in advance, representing the nucleation of the crack, and being able to reproduce the contact between the crack surfaces after fracture, with numerous application examples for ductile materials, including metals. The models developed were included in the DIONISIO 3.0 nuclear fuel code and compared with analytical test cases, controlled tests of nuclear materials, and a large set of experimental exercises with rods subjected to steep power ramps where breakages are caused due to contact with the pellets. Similarly, these new models were used in controlled experiments where the conditions of an accident type such as a loss-of-coolant accident are reproduced, analyzing the variation of the thermohydraulic, thermomechanical, and structural parameters of a rod.

A model to evaluate the nuclear fuel pellets densification under the combined effects of temperature and irradiation has been formerly elaborated and subjected to several separate tests which were exposed in a previous work of this team. The model considers the point defects diffusion to and from the lattice defects and the interaction between the fission fragments and the fabrication pores to give a microscopic description of the densification process. The model was recently included as a subroutine of the fuel performance code DIONISIO 3.0 and a new module, DIONISIO-FEM, was developed to simulate the sole effect of temperature during re-sintering tests. These incorporations have allowed a more detailed and precise description of the processes that take place in the fuel pellets during densification proving a very good agreement with the experimental data obtained in the open literature. (C) 2020 Elsevier Ltd. All rights reserved.

The geometric phase can be used as a fruitful venue of investigation to infer features of the quantum systems. Its application can reach new theoretical frontiers and imply innovative and challenging experimental proposals. Herein, we take advantage of the geometric phase to sense the corrections induced while a neutral particle travels at constant velocity in front of an imperfect sheet in quantum vacuum. As it is already known, two bodies in relative motion at constant velocity experience a quantum contactless dissipative force, known as quantum friction. This force has eluded experimental detection so far due to its small magnitude and short range. However, we give details of an innovative experiment designed to track traces of the quantum friction by measuring the velocity dependence of corrections to the geometric phase. We notice that the environmentally induced corrections can be decomposed in different contributions: corrections induced by the presence of the dielectric sheet and the motion of the particle in quantum vacuum. As the geometric phase accumulates over time, its correction becomes relevant at a relative short timescale, while the system still preserves purity. The experimentally viable scheme presented would be the first one in tracking traces of quantum friction through the study of decoherence effects on a NV center in diamond.