Conceptual design and initial evaluation of a neutron flux gradient detector

Identification of the position of a localized neutron source, or that of local inhomogeneities in a multiplying or scattering medium (such as the presence of small, strong absorbers) is possible by measurement of the neutron flux in several spatial points, and applying an unfolding procedure. It was suggested earlier, and it was confirmed by both simulations and pilot measurements, that if, in addition to the usually measured scalar (angularly integrated) flux, the neutron current vector or its diffusion approximation (the flux gradient vector) is also considered, the efficiency and accuracy of the unfolding procedure is significantly enhanced. Therefore, in support of a recently started project, whose goal is to detect missing (replaced) fuel pins in a spent fuel assembly by non-intrusive methods, this idea is followed up. The development and use of a dedicated neutron detector for within-assembly measurements of the neutron scalar flux and its gradient are planned. The detector design is based on four small, fiber-mounted scintillation detector tips, arranged in a rectangular pattern. Such a detector is capable of measuring the two Cartesian components of the flux gradient vector in the horizontal plane. This paper presents an initial evaluation of the detector design, through Monte Carlo simulations in a hypothetical scenario

Identification of diversions in spent PWR fuel assemblies by PDET signatures using Artificial Neural Networks (ANNs)

Spent nuclear fuel represents the majority of materials placed under nuclear safeguards today and it requires to be inspected and verified regularly to promptly detect any illegal diversion. Research is ongoing both on the development of non-destructive assay instruments and methods for data analysis in order to enhance the verification accuracy and reduce the inspection time. In this paper, two models based on Artificial Neural Networks (ANNs) are studied to process measurements from the Partial Defect Tester (PDET) in spent fuel assemblies of Pressurized Water Reactors (PWRs), and thus to identify at different levels of detail whether nuclear fuel has been replaced with dummy pins or not. The first model provides an estimation of the percentage of replaced fuel pins within the inspected fuel assembly, while the second model determines the exact configuration of the replaced fuel pins. The two models are trained and tested using a dataset of Monte-Carlo simulated PDET responses for intact spent PWR fuel assemblies and a variety of hypothetical diversion scenarios. The first model classifies fuel assemblies according to the percentage of diverted fuel with a high accuracy (96.5%). The second model reconstructs the correct configuration for 57.5% of the fuel assemblies available in the dataset and still retrieves meaningful information of the diversion pattern in many of the misclassified cases

Is oropharyngoesophageal scintigraphy the method of choice for assessing dysphagia in systemic sclerosis? A single center experience

Objectives: To evaluate the performance of oropharyngoesophageal scintigraphy (OPES) in the assessment of dysphagia in patients with systemic sclerosis (SSc), and to compare OPES results with those of barium esophagogram. Methods: Adult SSc patients who underwent OPES for the assessment of dysphagia were enrolled. OPES was performed with both liquid and semisolid boluses and provided information regarding oropharyngeal transit time, esophageal transit time (ETT), oropharyngeal retention index (OPRI), esophageal retention index (ERI), and site of bolus retention. Barium esophagogram results were also collected. Results: Fifty-seven SSc patients (87.7% female, mean age 57.7 years) with dysphagia were enrolled. OPES identified at least one alteration in each patient and findings were generally worse for the semisolid bolus. Esophageal motility was widely impaired with 89.5% of patients with an increased semisolid ERI, and middle-lower esophagus was the most frequent site of bolus retention. However, oropharyngeal impairment was highlighted by widespread increased OPRI, especially in anti-topoisomerase I positivity. Older patients and with longer disease duration presented slower semisolid ETT (p = 0.029 and p = 0.002, respectively). Eleven patients with dysphagia had a negative barium esophagogram: all of them presented some alterations in OPES parameters. Conclusion: OPES revealed a marked SSc esophageal impairment, in terms of both slowed transit time and increased bolus retention, but also shed light on oropharyngeal swallowing alterations. OPES showed high sensitivity, being able to detect swallowing alterations in dysphagic patients with negative barium esophagogram. Therefore, the use of OPES for the assessment of SSc-related dysphagia in clinical practice should be promoted

Conjugation with angiopep2 as a strategy for the brain delivery of a mitochondriotropic inhibitor of the potassium channel Kv_1.3

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Covid-19 And Rheumatic Autoimmune Systemic Diseases: Role of Pre-Existing Lung Involvement and Ongoing Treatments

The Covid-19 pandemic may have a deleterious impact on patients with autoimmune systemic diseases (ASD) due to their deep immune-system alterations

Advanced non-destructive methods for criticality safety and safeguards of used nuclear fuel

The safeguards verification of spent nuclear fuel is one of the major concern for the safeguards community, as this material represents about 80% of all material placed under safeguards.This PhD thesis described the development of two passive non-destructive assay (NDA) techniques: the Self-Indication Neutron Resonance Densitometry (SINRD) and the Partial Defect Tester (PDET).The NDA methods were investigated with Monte Carlo simulations and the benchmark experiments for SINRD were performed at the GELINA facility of JRC-IRMM in Geel, Belgium.The results for the SINRD technique showed promising results for the direct quantification of 239Pu in spent fuel, and both techniques gave encouraging results for the detection of partial defects.Doctorat en Sciences de l'ingénieur et technologieinfo:eu-repo/semantics/nonPublishe

Development of a model for the approximation of the neutron and photon flux in a BWR spent fuel assembly

This paper proposes a simplified model built with Matlab to compute an approximation of the neutron and photon flux in a BWR spent fuel assembly in a pond. Starting from a reduced number of Monte Carlo simulations, a set of transmission probabilities has been calculated. These values allow the estimation of the particle flux inside a fuel assembly placed in a generic storage rack. This calculation is possible provided the transmission probability has been calculated for the desired value of burnup and cooling time of the assemblies in the rack. The validity of the model has been tested first with a uniform pattern of the storage rack and finally with a generic configuration. Reference values from the equivalent Monte Carlo simulations show very good agreement and the relative error between the two measures is always within few percents. The main advantage of this simplified model is the great reduction of computational time required to perform the estimation and the fact that the basic idea behind the model can be applied to any fuel geometry and type of storage pond.JRC.E.8-Nuclear securit

Improved electronics for

Several non-destructive assays techniques have been developed for the measurement of fissile materials in the fields of dismantling, decommissioning, nuclear security, and nuclear safeguards. Among these techniques, neutron coincidence counting is based on the detection of time-correlated neutrons from induced and spontaneous fissions. 3He Tubes have been the primary choice for neutron coincidence counting due to their high detection efficiency, rather low sensitivity to gamma-rays and proven field reliability. This paper covers the implementation of a new electronic setup to a Canberra WM3400 neutron coincidence counter. First we describe the properties of the used detectors, with focus on the characteristics of the default electronics and highlight its limitations such as the high input capacitance, short shaping time and the necessity for selected tubes. We then propose the new electronic setup to overcome these limitations. This setup includes a dedicated preamp for every tube , the possibility to adjust for gain differences between the tubes and a better optimised shaping time for 3He detectors. We carried out measurements with the two electronic systems to compare their performances in terms of gamma-ray sensitivity, efficiency and die-away time. The gamma ray sensitivity was measured with calibrated 137Cs and a 60Co sources at the Laboratory for Nuclear Calibration of the Belgian Nuclear Research Centre with dose rates between 10 μSv/h and 50 mSv/h. Measurements with a 252Cf source were used to determine the die-away time of the system and the total measurement efficiency for the considered geometry. The measurements showed that, with the default electronics, neutron count-rates are already affected by gamma radiation at a dose rate of 10÷30 μSv/h. On the other hand the neutron coincidence counter equipped with the new electronics proved to be insensitive to gamma-radiation up to a dose rate of at least 20 mSv/h. The high-voltage set with the new electronics is lower than in the case of the default electronics and is within the range recommended by the tubes manufacturer. The die-away time was not affected by the used electronics. A reduction of about 20% in the neutron detection efficiency due to the used discriminator threshold was observed

Improved electronics for 3He based neutron counters

Several non-destructive assays techniques have been developed for the measurement of fissile materials in the fields of dismantling, decommissioning, nuclear security, and nuclear safeguards. Among these techniques, neutron coincidence counting is based on the detection of time-correlated neutrons from induced and spontaneous fissions. 3He Tubes have been the primary choice for neutron coincidence counting due to their high detection efficiency, rather low sensitivity to gamma-rays and proven field reliability. This paper covers the implementation of a new electronic setup to a Canberra WM3400 neutron coincidence counter. First we describe the properties of the used detectors, with focus on the characteristics of the default electronics and highlight its limitations such as the high input capacitance, short shaping time and the necessity for selected tubes. We then propose the new electronic setup to overcome these limitations. This setup includes a dedicated preamp for every tube , the possibility to adjust for gain differences between the tubes and a better optimised shaping time for 3He detectors. We carried out measurements with the two electronic systems to compare their performances in terms of gamma-ray sensitivity, efficiency and die-away time. The gamma ray sensitivity was measured with calibrated 137Cs and a 60Co sources at the Laboratory for Nuclear Calibration of the Belgian Nuclear Research Centre with dose rates between 10 μSv/h and 50 mSv/h. Measurements with a 252Cf source were used to determine the die-away time of the system and the total measurement efficiency for the considered geometry. The measurements showed that, with the default electronics, neutron count-rates are already affected by gamma radiation at a dose rate of 10÷30 μSv/h. On the other hand the neutron coincidence counter equipped with the new electronics proved to be insensitive to gamma-radiation up to a dose rate of at least 20 mSv/h. The high-voltage set with the new electronics is lower than in the case of the default electronics and is within the range recommended by the tubes manufacturer. The die-away time was not affected by the used electronics. A reduction of about 20% in the neutron detection efficiency due to the used discriminator threshold was observed