Observables of interest for the characterisation of Spent Nuclear Fuel

The characterisation of Spent Nuclear Fuel (SNF) in view of intermediate storage and final disposal is discussed. The main observables of interest that need to be determined are the decay heat, neutron and -ray emission spectra. In addition, the inventory of specific nuclides that are important for criticality safety analysis and to verify the fuel history has to be determined. Some of the observables such as the decay heat and neutron and -ray emission rate can be determined by Non-Destructive Analysis (NDA) methods. Unfortunately, this is not always possible especially during routine operation. Hence, a characterisation of SNF will rely on theoretical calculations combined with results of NDA methods. In this work the observables of interest, also referred to as source terms, are discussed based on theoretical calculations starting from fresh UO2 and MOX fuel. The irradiation conditions are representative for PWR. The Serpent code is used to define the nuclides which have an important contribution to the observables. The emphasis is on cooling times between 1 a and 1000 a.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Valve-sparing aortic root replacement using the reimplantation (David) technique:a systematic review and meta-analysis on survival and clinical outcome

BACKGROUND: Current guidelines recommend valve-sparing aortic root replacement (VSRR) procedures over valve replacement for the treatment of root aneurysm. The reimplantation technique seems to be the most widely used valve-sparing technique, with excellent outcomes in mostly single-center studies. The aim of this systematic review and meta-analysis is to present a comprehensive overview of clinical outcomes after VSRR with the reimplantation technique, and potential differences for bicuspid aortic valve (BAV) phenotype. METHODS: We conducted a systematic literature search of papers reporting outcomes after VSRR that were published since 2010. Studies solely reporting on acute aortic syndromes or congenital patients were excluded. Baseline characteristics were summarized using sample size weighting. Late outcomes were pooled using inverse variance weighting. Pooled Kaplan-Meier (KM) curves for time-to-event outcomes were generated. Further, a microsimulation model was developed to estimate life expectancy and risks of valve-related morbidity after surgery. RESULTS: Forty-four studies, with 7,878 patients, matched the inclusion criteria and were included for analysis. Mean age at operation was 50 years and almost 80% of patients were male. Pooled early mortality was 1.6% and the most common perioperative complication was chest re-exploration for bleeding (5.4%). Mean follow-up was 4.8±2.8 years. Linearized occurrence rates for aortic valve (AV) related complications such as endocarditis and stroke were below 0.3% patient-year. Overall survival was 99% and 89% at 1- and 10-year respectively. Freedom from reoperation was 99% and 91% after 1 and 10 years, respectively, with no difference between tricuspid and BAVs. CONCLUSIONS: This systematic review and meta-analysis shows excellent short- and long-term results of valve-sparing root replacement with the reimplantation technique in terms of survival, freedom from reoperation, and valve related complications with no difference between tricuspid and BAVs

Filgotinib for Treating Moderately to Severely Active Ulcerative Colitis:An Evidence Review Group Perspective of a NICE Single Technology Appraisal

The National Institute for Health and Care Excellence invited the manufacturer (Galapagos) of filgotinib (Jyseleca®), as part of the Single Technology Appraisal process, to submit evidence for the clinical effectiveness and cost effectiveness of filgotinib for treating moderately to severely active ulcerative colitis in adults who have had an inadequate response, loss of response or were intolerant to a previous biologic agent or conventional therapy. Kleijnen Systematic Reviews Ltd, in collaboration with Maastricht University Medical Centre+, was commissioned to act as the independent Evidence Review Group. This paper summarises the company submission, presents the Evidence Review Group’s critical review on the clinical and cost-effectiveness evidence in the company submission, highlights the key methodological considerations and describes the development of the National Institute for Health and Care Excellence guidance by the Appraisal Committee. The company submission included one relevant study for the comparison of filgotinib versus placebo: the SELECTION trial. As there was no head-to-head evidence with any of the comparators, the company performed two separate network meta-analyses, one for the biologic-naïve population and one for the biologic-experienced population, and for both the induction and maintenance phases. The Evidence Review Group questioned the validity of the maintenance network meta-analysis because it assumed all active treatments to be comparators in this phase, which is not in line with clinical practice. The economic analysis used a number of assumptions that introduced substantial uncertainty, which could not be fully explored, for instance, the assumption that a risk of loss of response would be independent of health state and constant over time. Company and Evidence Review Group results indicate that at its current price, and disregarding confidential discounts for comparators and subsequent treatments, filgotinib dominates some comparators (golimumab and adalimumab in the company base case, all but intravenous and subcutaneous vedolizumab in the Evidence Review Group’s base case) in the biologic-naïve population. In the biologic-experienced population, filgotinib dominates all comparators in both the company and the Evidence Review Group’s base case. Results should be interpreted with caution as some important uncertainties were not included in the modelling. These uncertainties were mostly centred around the maintenance network meta-analysis, loss of response, health-related quality-of-life estimates and modelling of dose escalation. The National Institute for Health and Care Excellence recommended filgotinib within its marketing authorisation, as an option for treating moderately to severely active ulcerative colitis in adults when conventional or biological treatment cannot be tolerated, or if the disease has not responded well enough or has stopped responding to these treatments, and if the company provides filgotinib according to the commercial arrangement.</p

Filgotinib for Treating Moderately to Severely Active Ulcerative Colitis:An Evidence Review Group Perspective of a NICE Single Technology Appraisal

The National Institute for Health and Care Excellence invited the manufacturer (Galapagos) of filgotinib (Jyseleca®), as part of the Single Technology Appraisal process, to submit evidence for the clinical effectiveness and cost effectiveness of filgotinib for treating moderately to severely active ulcerative colitis in adults who have had an inadequate response, loss of response or were intolerant to a previous biologic agent or conventional therapy. Kleijnen Systematic Reviews Ltd, in collaboration with Maastricht University Medical Centre+, was commissioned to act as the independent Evidence Review Group. This paper summarises the company submission, presents the Evidence Review Group’s critical review on the clinical and cost-effectiveness evidence in the company submission, highlights the key methodological considerations and describes the development of the National Institute for Health and Care Excellence guidance by the Appraisal Committee. The company submission included one relevant study for the comparison of filgotinib versus placebo: the SELECTION trial. As there was no head-to-head evidence with any of the comparators, the company performed two separate network meta-analyses, one for the biologic-naïve population and one for the biologic-experienced population, and for both the induction and maintenance phases. The Evidence Review Group questioned the validity of the maintenance network meta-analysis because it assumed all active treatments to be comparators in this phase, which is not in line with clinical practice. The economic analysis used a number of assumptions that introduced substantial uncertainty, which could not be fully explored, for instance, the assumption that a risk of loss of response would be independent of health state and constant over time. Company and Evidence Review Group results indicate that at its current price, and disregarding confidential discounts for comparators and subsequent treatments, filgotinib dominates some comparators (golimumab and adalimumab in the company base case, all but intravenous and subcutaneous vedolizumab in the Evidence Review Group’s base case) in the biologic-naïve population. In the biologic-experienced population, filgotinib dominates all comparators in both the company and the Evidence Review Group’s base case. Results should be interpreted with caution as some important uncertainties were not included in the modelling. These uncertainties were mostly centred around the maintenance network meta-analysis, loss of response, health-related quality-of-life estimates and modelling of dose escalation. The National Institute for Health and Care Excellence recommended filgotinib within its marketing authorisation, as an option for treating moderately to severely active ulcerative colitis in adults when conventional or biological treatment cannot be tolerated, or if the disease has not responded well enough or has stopped responding to these treatments, and if the company provides filgotinib according to the commercial arrangement.</p

A non-destructive method to determine the neutron production rate of a sample of spent nuclear fuel under standard controlled area conditions

A method to determine the neutron production rate of a sample of spent nuclear fuel by means of non-destructive analysis conducted under controlled-area conditions is described, validated and demonstrated. A standard neutron well-counter designed for routine nuclear safeguards applications is applied. The method relies on a transfer procedure that is adapted to the hot-cell facilities at the laboratory for high and medium level activity of the SCK CEN. The sample transfer and measurement procedures are described together with results of Monte Carlo simulations. Experiments with radionuclide sources were carried out at the Joint Research Centre to test the procedures and to determine the performance characteristics of the detection device. Finally, measurements of a segment of a spent nuclear fuel rod were carried out at the SCK CEN to validate and demonstrate the method.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Blind Benchmark Exercise for Spent Nuclear Fuel Decay Heat

The decay heat rate of five spent nuclear fuel assemblies of the pressurized water reactor type were measured by calorimetry at the interim storage for spent nuclear fuel in Sweden. Calculations of the decay heat rate of the five assemblies were performed by 20 organizations using different codes and nuclear data libraries resulting in 31 results for each assembly, spanning most of the current state-of-the-art practice. The calculations were based on a selected subset of information, such as reactor operating history and fuel assembly properties. The relative difference between the measured and average calculated decay heat rate ranged from 0.6% to 3.3% for the five assemblies. The standard deviation of these relative differences ranged from 1.9% to 2.4%

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals &lt;1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Simulations à l'échelle atomique du comportement des gaz nobles dans le dioxyde d'uranium

Nuclear fuel performance is highly affected by the behaviour of fission gases, particularlyat elevated burnups, where large amounts of gas are produced and canpotentially be released. The importance of fission gas release was the motivationfor large efforts, both experimentally and theoretically, in order to increase ourunderstanding of the different steps of the process, and to continuously improveour models.Extensions to higher burnups, together with the growing interest in novel typesof fuels such as inert matrix fuels envisaged for the transmutation of minor actinides,make that one is still looking for a permanently better modelling, basedon a physical understanding and description of all stages of the release mechanism.Computer simulations are nowadays envisaged in order to provide a betterdescription and understanding of atomic-scale processes such as diffusion, but evenin order to gain insight on specific processes that are inaccessible by experimentalmeans, such as the fuel behaviour during thermal spikes.In the present work simulation techniques based on empirical potentials havebeen used, focusing in a first stage on pure uranium dioxide. The behaviour ofpoint defects was at the core of this part, but also the estimation of elastic andmelting properties.Then, in a second stage, the study has been extended to the behaviour of heliumand xenon. For helium, the diffusion in different domains of stoichiometrywas considered. The simulations enabled to determine the diffusion coefficient andthe migration mechanism, using both molecular dynamics and static calculationtechniques. Xenon behaviour has been investigated with the additional intentionto model the behaviour of small intragranular bubbles, particularly their interactionwith thermal spikes accompanying the recoil of fission fragments. For thatpurpose, a simplified description of these events has been proposed, which opensperspectives for further work./Les performances du combustible nucléaire sont fortement affectées par le comportementdes gaz de fission, et ce particulièrement lorsqu’un taux d’épuisementélevé est atteint, puisque d’importantes quantités de gaz sont alors produiteset peuvent potentiellement être relâchées. Les enjeux, entre autre économiques,liés au relâchement de gaz de fission ont donné lieu à d’importants efforts, tantsur le plan expérimental que théorique, afin d’accroître notre compréhension desdifférentes étapes du processus, et d’améliorer sans cesse les mod`eles. Les extensionsà des taux d’épuisements encore plus élevés ainsi que l’intérêt croissant pourde nouveaux types de combustible tels que les matrices inertes, envisages en vuede la transmutation des actinides mineures, font qu’à l’heure actuelle, le besoinpermanent d’une meilleure modélisation, basée sur une compréhension et une descriptionphysique des différentes étapes du processus de relâchement de gaz defission, est toujours de mise.Les simulations par ordinateur ont ainsi été considérée comme un nouvel anglede recherche sur les processus élémentaires se produisant à l’échelle atomique, à lafois afin d’obtenir une meilleure compréhension de processus tels que la diffusionatomique ;mais aussi afin d’avoir accès à certains processus qui ne sont pas observablespar des voies expérimentales, tels que la le comportement du combustiblelors de pointes thermiques.Dans ce travail, deux techniques, basées sur l’utilisation de potentiels interatomiquesempiriques, ont permis d’étudier le dioxyde d’uranium, dans un premiertemps en l’absence d’impuretés. Cette partie était principalement centrée sur lecomportement des défauts ponctuels, mais a aussi concerné différentes propriétésélastiques, ainsi que le processus de fusion du composé.Ensuite l’étude a été étendue aux comportements de l’hélium de du xénon. Pource qui a trait à l’hélium, la diffusion dans différents domaines de stoechiométriea été considérée. Les simulations ont permis de déterminer le coefficient de diffusionainsi que le mécanisme de migration lui-même. Quant au xénon, outre lespropriétés de diffusion, l’intention fut de se diriger vers la modélisation des petitesbulles intragranulaires, et plus précisément vers leur interaction avec les pointesthermiques, créées lors du recul des fragments de fission. Une description simplifiée de ce processus a été proposée, qui offre de nouvelles perspectives dans cedomaine.Doctorat en Sciences de l'ingénieurinfo:eu-repo/semantics/nonPublishe

Application of time-periodic stochastic subspace identification on operating wind turbine rotor data

The stochastic subspace identification (SSI) algorithm is a robust-working method to identify mode shapes, eigenfrequencies and damping ratios from response time histories of linear time-invariant systems (LTI), which are operated under random excitation. In case of rotating substructures, e.g. wind turbine rotors, the periodic responses contain participation of several higher harmonics of the rotor speed. For such timeperiodic systems the modal analysis can be described by characteristic exponents called Floquet multipliers, which postulate periodic modal deformation except for the total amplitude (determined by damping ratio) after one period of revolution. The presented periodically expanded subspace algorithm (SSI-LTP) projects the system response from one period to the next. The algorithm is applied to the evaluation of simulated and experimental rotor blade deformation data of a wind turbine operating at different wind and rotor speeds, which were measured with a commercially available optical rotor blade deformation measurement system

In-pile Xe diffusion coefficient in UO2 determined from the modeling of intragranular bubble growth and destruction under irradiation

Intragranular bubbles grow in the nuclear fuel by diffusion and precipitation of fission gases, mainly xenon; and are ultimately destroyed, under irradiation, by fission fragments. This article will attempt to determine the in-pile bubble distributions taking into account the evolution of the concentration profile around a bubble during its growth and the destruction process by fission fragments. From these distributions a relation between the bubble mean radius and the diffusion coefficient of xenon can be established, allowing the determination, from experimental measurements of intragranular bubble sizes, of the in-pile Xe diffusion coefficient in UO2. The estimated activation energy (0.9 eV) is about one order of magnitude lower than the widely used value of 3.9 eV determined from out-of-pile experiments. This effect can be attributed to the presence of point defects created by the irradiation. © 2007 Elsevier B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe