Intense Neutron Research Articles

Fuel Cell Imaging with a Wolter Optics Neutron Microscope

Wolter optics promise to radically transform neutron imaging by improving the time resolution of the method by at least a factor 1,000 while providing spatial resolution of order a few micrometers [1]. These optics will enable neutron tomography of operating fuel cells with a time resolution of about a few minutes, which will provide unique insight into the water transport phenomena in membrane electrode assemblies of fuel cells and electrolyzers.Neutron imaging has played a critical role in understanding water transport in proton exchange membrane fuel cells and electrolyzers [2]. The primary limitation of the method is the inherent neutron source strength, which is about a billion times weaker than X-ray synchrotron sources. Additionally, neutrons are difficult to focus using refractive lenses so that neutron imaging beamlines heretofore can be described as pinhole cameras. In a pinhole camera, the best achievable spatial resolution (λg) is determined by the diameter of the pinhole (D ~1 cm), the pinhole-to-detector distance (L ~10 m), and the sample-to-detector distance (Z ~1 cm):λg = Z D / (L – Z) ~ Z D / LReturning to the source strength, the neutron fluence rate at the sample position scales as (D / L)2. This means that higher spatial resolution for finite sized objects requires sacrificing neutron intensity and incurring long exposure times. Typical measurements require about 20 minutes for a single two-dimension image of the water content in fuel cell for a spatial resolution of about 10 µm. Such time requirements preclude the use of tomography, which is required to understand the water content in real fuel cell components since the MEA cannot be considered to be planar at the few micrometer level.We will describe Wolter optics, and the optical system that will be first available in 2022. After the NCNR cold source upgrade is anticipated to yield a time resolution gain of about 10,000 compared to a pinhole camera. We will discuss our expected image acquisition and analysis procedures guided by ray tracing simulations.Figure 1. Proof of concept Wolter optics image of a fuel cell test section.[1] D. S. Hussey et al., “Design of a neutron microscope based on Wolter mirrors,” Nucl. Instruments Methods Phys. Res. Sect. A Accel. Spectrometers, Detect. Assoc. Equip., vol. 987, no. October 2020, p. 164813, 2021.[2] T. A. Trabold, J. P. Owejan, J. J. Gagliardo, D. L. Jacobson, D. S. Hussey, and M. Arif, “Use of neutron imaging for proton exchange membrane fuel cell (PEMFC) performance analysis and design,” Handb. fuel cells, vol. 6, no. Table 1, 2010. Figure 1

Non-destructive investigation of the Kyathos (6th-4th centuries BCE) from the necropolis Volna 1 on the Taman Peninsula by neutron resonance capture and X-ray fluorescence analysis

<p>The method of Neutron Resonance Capture Analysis (NRCA) is currently being developed at the Frank Laboratory of Neutron Physics. The Analysis determines the elemental and isotope compositions of objects non-destructively, which makes it suitable measurement tools for artefacts without sampling. NRCA is based on the registration of neutron resonances in radiative capture and the measurement of the yield of reaction products in these resonances.<br />The potential of NRCA at the Intense Resonance Neutron Source facility is demonstrated on the investigation of a Kyathos (6th-4th centuries BCE) from the necropolis Volna 1 on the Taman Peninsula. In addition, X-ray analysis was applied to the same archeological object. The element composition determined by NRCA and XRF data is in agreement.</p>

Long term operation of the radiation-hard Hall probes system and the path toward a high performance hybrid magnetic field sensor

The paper reports a systematic assessment of the radiation-hard Hall probes (RHP) magnetic diagnostic system of the JET tokamak, which is based on InSb semiconductor thin films, and describes the path that lead to the proposal of an innovative magnetic probe concept. A relevant account of RHP operation during the recent deuterium–tritium experimental campaign is also provided, showing correct operation under ITER-like intense neutron flux. The period considered for the systematic assessment of the RHP system ranges from October 2009 to March 2021, during which the machine produced more than 19 000 pulses. The RHP system consists of six three-dimensional Hall probes, which have built-in recalibration capability, thanks to the presence of microsolenoids that produce a local known field during a tailored automatic pre-pulse calibration sequence, that can also be initiated manually. During pulses, the microsolenoids can also be used as inductive sensors as their signals are recorded as well. Moreover, the system provides temperature measurements at the location of the probes, which are continuously recorded too. The assessment demonstrates accurate long-term operation of the RHP system. All the diagnostic channels reliably provide pre-pulse calibration data and pulse signals and the original sensitivities of the Hall sensors are preserved. Integration considerations and a data fusion analysis lead to the proposal of a high performance, compact, broadband, hybrid field probe, consisting of the combination of an inductive coil and a Hall sensor, to be manufactured by means of the coil technology developed for ITER or an alternative concept with improved radiation-hardness. The hybrid probe is expected to deliver the advantages of both inductive and Hall sensing technologies, essentially in the same package size of a single ITER magnetic discrete probe. In particular, it would solve the problem of the drift of the integrator for long lasting burning plasma discharges. The signals produced by the coil and the Hall sensor, processed by means of a Luenberger–Kalman observer, provide a magnetic field measurement which is non-drifting and low-noise. For these reasons, the hybrid probe has been proposed as the potential primary magnetic diagnostic sensor for future burning plasma experiments and demonstration fusion power plants.

Comprehensive stainless steel neutron transport libraries validation

Stainless steel is an important material that is relied upon to perform consistently over time in the nuclear industry. The paper focuses on the validation of different stainless steel neutron transport libraries. The validation was performed by means of samples activation in different positions and also the measurement of the fast neutron spectrum in the energy range of 1–12 MeV using a scintillation stilbene detector. Stainless steel was used in the form of a block with a hole for the neutron source. The dosimetric reactions used for validations were 58Ni(n,p)58Co, 93Nb(n,2n)92mNb, 197Au(n,2n)196Au, 63Cu(n,g)64Cu, 197Au(n,g)198Au, 115In(n,ń)115m1In, 115In(n,g)116m1In, 55Mn(n,g)56Mn, and 181Ta(n,g)182Ta. The experimental data were compared with MCNP6.2 calculations employing ENDF/B-VIII.0, ENDF/B-VII.1, JEFF-3.3, JEFF-3.2, CENDL-3.1, JENDL-5 and INDEN transport libraries. These libraries were used for the simulation of the stainless steel block. The activation foils cross sections were taken from the IRDFF-II library. An intense standard neutron 252Cf(sf) source was placed in the centre of the stainless steel block. INDEN library is the best for the calculation of neutron flux in the range of 1–12 MeV. For the activation detectors placed at the various distances inside the block, the best library depends on the reaction studied.

Time series anomaly detection in power electronics signals with recurrent and ConvLSTM autoencoders

The anomalies in the high voltage converter modulator (HVCM) remain a major down time for the spallation neutron source facility, that delivers the most intense neutron beam in the world for scientific materials research. In this work, we propose neural network architectures based on Recurrent AutoEncoders (RAE) to detect anomalies ahead of time in the power signals coming from the HVCM. Bi-directional gated recurrent unit, bi-directional long-short term memory (LSTM), and convolutional LSTM (ConvLSTM) are developed, trained, and tested using real experimental signals from the HVCM module. The results show a good performance of the proposed RAE models, achieving precision up to 91%, recall up to 88%, false omission rate as low as 20% (i.e. 80% of the anomalies were detected), and area under the ROC curve up to 0.9. The three RAE models provide very comparable performance, with LSTM showing slightly better performance than GRU and ConvLSTM. The RAE models are benchmarked against other anomaly detection methods, including isolation forest, support vector machine, local outlier factor, feedforward and convolutional autoencoders, and others; showing a better performance. The results of this study demonstrate the promising potential of RAE in anomaly detection for real-world power systems, and for increasing the reliability of the HVCM modules in the spallation neutron source.

Potential of Thermal Neutrons to Correct Cosmic‐Ray Neutron Soil Moisture Content Measurements for Dynamic Biomass Effects

AbstractCosmic‐ray neutron sensors (CRNS) enable noninvasive determination of field‐scale soil moisture content by exploiting the dependence of the intensity of aboveground epithermal neutrons on the hydrogen contained in soil moisture. However, there are other hydrogen pools besides soil moisture (e.g., biomass). Therefore, these hydrogen pools should be considered for accurate soil moisture content measurements, especially when they are changing dynamically (e.g., arable crops, deforestation, and reforestation). In this study, we test four approaches for the correction of biomass effects on soil moisture content measurements with CRNS using experiments with three crops (sugar beet, winter wheat, and maize) based on high‐quality reference soil moisture: (a) site‐specific functions based on in‐situ measured biomass, (b) a generic approach, (c) the thermal‐to‐epithermal neutron ratio (Nr), and (d) the thermal neutron intensity. Bare soil calibration of the CRNS resulted in high root mean square errors (RMSEs) of 0.097, 0.041, and 0.019 m³/m³ between estimated and reference soil moisture content for sugar beet, winter wheat, and maize, respectively. Considering in‐situ measured biomass for correction reduced the RMSE to 0.015, 0.018, and 0.009 m³/m³. The consideration of thermal neutron intensity for correction was similarly accurate. We also explored the use of CRNS for biomass estimation and found that Nr only provided accurate biomass estimates for sugar beet. In contrast, we found significant site‐specific relationships between biomass and thermal neutron intensity for all three crops, suggesting that thermal neutron intensity can be used both to improve CRNS‐based soil moisture content measurements and to quantify crop biomass.

Radiation shielding analysis of the HI-STORM FW storage cask

This paper presents radiation shielding analysis of the HI-STORM FW storage cask designed by the Holtec International, Inc. for the Nuclear Power Plant Krsko Spent Fuel Dry Storage (SFDS) project. The first part of the analysis is addressing the problem of a particle source generation. For each spent fuel assembly (SFA) neutron and gamma source intensities and spectra were calculated using ORIGEN-S module of the SCALE 6.2.3 code package. The second part of the analysis is considering neutron and gamma dose rates calculation, for which hybrid shielding methodology based on Monte Carlo (MC) code MCNP6.2 and ADVANTG3.0.3 code was used. The dose rates for the reference case included the contributions of fuel neutron, fuel gamma, secondary gammas from (n, γ) reactions, as well as gammas from activated SFA hardware components due to Co-60 presence. Expectedly, the results have shown that the dose rates around the cask have nonuniform behavior due to a specific design of the cask. The heavy concrete body of the cask presents a good attenuator for all types of radiation, however, a considerable streaming through the top and bottom ventilation openings was noticed. It was also observed that an important role was played by the isotope Co-60 which emits two lines of high energy deep penetrating gammas. The convergence of dose rates and associated relative uncertainties during MC calculations have shown that significantly more histories were required for gamma calculations compared to neutron calculations. To investigate the impact of different SFA content in the casks on the dose rates, shielding analysis was made for 16 casks that will be loaded in the first campaign. For comparison, the calculations of a single HI-STORM FW cask were additionally performed using MAVRIC module of the SCALE 6.2.3 and the obtained differences in external dose rates of 20–30% are expected. The calculation cases showed the differences in casks doses due to different casks loading within loading plan criteria, reduction provided by heavy concrete in cask body (more important for gammas), importance of careful design of lower and upper casks openings to keep increase of dose rates, compared to closed configuration, within one order of magnitude, and compromise needed when describing details of intensity and spectrum of SFA sources. The increased calculation mesh density was used to show that selected discretization is appropriate, and the limited influence of storage pad thickness was demonstrated by performing calculation with thick concrete slab corresponding to Dry Storage Building (DSB) floor foundation thickness.

Simultaneous measurement of energy spectrum and fluence of neutrons using a diamond detector

Due to the excellent radiation hardness and high–temperature endurance, diamond detectors are suitable for intense neutron measurements and promising for neutron diagnostics of scientific fusion devices. In the present work, simultaneous measurement of energy spectrum and fluence of neutrons using a diamond detector was realized for the first time. The absolute response matrix of the diamond detector was simulated based on detailed analysis of the nuclear reactions and the proper selection of nuclear reaction data. Neutron energy spectra as well as neutron fluences for 5.0, 5.5, 8.5, 9.5 and 10.5 MeV neutrons from d–d reaction were measured using the diamond detector based on the absolute response matrix. The measured neutron energy spectra and neutron fluences are reasonable compared with those detected using a EJ-309 liquid scintillator and a 238U fission chamber, respectively, which verifies the reliability of the present work. Furthermore, the energy spectrum and fluence of a 14.2 MeV d–t neutron source were also measured using the diamond detector. The present work demonstrates the ability of simultaneous measurement of energy spectrum and fluence as well as for both d–d and d–t neutrons using a diamond detector, which is of great significance for neutron diagnostics of scientific fusion devices.

A Review on DPA for computing radiation damage simulation

A Monte Carlo code is developed for the radiation damage in the metals which results from nuclear collisions that create energetic recoil atoms of the host material. The development of the simulation codes for the radiation damage method by neutrons and protons can be highly useful in technology of advanced nuclear systems and nuclear fusion reactors. The aim of this review is to investigate the impact of the radiation damage in the materials by the neutron and proton energy irradiation. The damage parameter used in the evaluation is displacement per atom (DPA) in material as a function of neutron and proton energy. For this purpose, there are some software codes used which are related to radiation damage because radiation damage can be measured as a function of DPA, which is one of the critical issues for high intensity beams, particularly, for protons and neutrons.

Practical considerations in developing nuclear detectors for tokamak harsh environments

Fusion tokamaks (FT) and hybrid fusion-fission reactors (HFFR) present harsh working conditions characterized by intense neutron and gamma fluxes (>1012 cm−2 s−1), high working temperatures (up to 600 °C) and corrosive environment. The breeding blanket region (BB) of these plants are resulting very hostile to the detectors used to monitor/measure fundamental nuclear parameters such as neutron/gamma fluxes and energy spectra, and tritium production. Presently no detectors are ready for being hosted in the harsh environment of the BB and R&D activity is needed to develop and test the candidate detectors. Some important lessons can be learned from past activities carried out in the EU and devoted to studying and realizing nuclear detector prototypes for the European Test Blanket Modules (TBM) of ITER. Amongst the other, these studies pointed out the need for intense neutron fields and calibration facilities closely reproducing the expected working environments to be used for reliable testing and calibration of the prototypes.Accurate simulation by Monte Carlo technique of the proposed detectors allows to mimic and foresee the response and performances of the detectors pointing out several fundamental and critical aspects on the physical response of the detector so helping in understanding the detectors response. This can help in selecting the best performing detector. The selection is based upon a multi-step procedure.The lesson learned for ITER-TBM can be helpful to study and develop nuclear detectors to be used in HFFR reactors and in next fusion machines like DEMO this because, despite the difference, the ITER-TBMs and the BB of fusion devices and HFFR reactors experience a number of similarities in terms of radiation level, temperature and nuclear quantities to be measured.In this paper, after discussing the requirements to be fulfilled by the nuclear detectors that must operate in the harsh environments we will discuss an example of detector development by considering the case of a self-power neutron detector (SPND) with chromium emitter studied and developed for ITER-TBM. The detailed Monte Carlo analysis is also reported and the many issues not yet solved are highlighted and the possible follow up to HFFR instrumentation discussed.

Activated Corrosion Products Evaluations for Occupational Dose Mitigation in Nuclear Fusion Facilities

Activated corrosion products generation in primary heat transfer systems of nuclear fusion facilities is a relevant radiological source term for occupation dose assessments. The formation of the Chalk River Undefined Deposit, already well known in nuclear fission power plants, represents a significant safety issue in fusion applications due to the intense high energy neutron fluences (about 14 MeV in Deuterium-Tritium operation). The activated corrosion products formation is a multi-physical problem. The combined synergy of activation, corrosion, dissolution, erosion, ejection, precipitation, and transport phenomena induces the contamination of coolant loop regions located outside the bio-shield, where scheduled worker operation might take place. The following manuscript shows how activated corrosion products are evaluated for the nuclear fusion power plant design under investigation by the Safety and Environment Work Package (WPSAE) of the Eurofusion Consortium (i.e., the European Demonstration power plant, EU-DEMO). The major issues in activated corrosion products estimations are here exposed and the main results for mass and activity inventories are briefly shown for some main Primary Heat Transfer Systems of EU-DEMO.

Designs and neutronic characteristics of an epithermal neutron moderator at ambient temperature for neutron time-of-flight measurements

ABSTRACT Compact time-of-flight (TOF) measurement systems are desirable for easy installation in various facilities. To achieve such compact systems, one of the key considerations is the design of the neutron moderator. Therefore, systematic studies on moderators considering both neutron energy resolution and neutron intensity are important. In this paper, to design an epithermal neutron moderator at ambient temperature for short-distance TOF measurements, the neutron intensity and energy resolution of epithermal neutrons have been studied using the Monte Carlo simulation code PHITS with JENDL-4.0 for various types of moderators. The neutronic characteristics of a moderator comprising several components were evaluated. The relationships between the moderator dimensions and both the energy resolution and intensity of the epithermal neutrons were determined. From the obtained results, the appropriate high-resolution moderator designs for the short-distance TOF measurements were proposed.

Preliminary finite element analysis of the stainless-steel liner of the maintainable test cell concept of IFMIF-DONES

• New maintainable design concept in fusion related facility. • Preliminary mechanical finite element analysis of an unusual shaped vacuum vessel. • Pareto front tradespace study for stiffening structure optimal variants. The main purpose of IFMIF-DONES facility is to provide a neutron source for irradiating small specimens and producing experimental data of material properties for the construction of DEMO fusion power plant. The Test Cell (TC) of the DONES is a confined and well-shielded room, where the strong irradiation environment is created. The biological shielding of the TC mainly consists of several meters thick concrete walls and shielding plugs, and a stainless-steel liner. The TC liner and the concrete walls are actively cooled by water because of the high volumetric heating coming from nuclear reactions. Although, the TC is designed to be fully functional for the complete life span of the facility, still there is a very low probability of defect of the TC biological shielding due to their exposure of intense neutron and gamma irradiation. Therefore, the original TC configuration, which was a monolithic approach, had to be revised. Due to this reason, at the end of 2019 the project team has changed the TC concept from the monolithic design to the so-called Maintainable TC Concept (MTCC) design, which allows a maintenance possibility in case of unexpected damage.

The Feasibility of Passive Neutron Measurement for Dry Storage Safeguards Approach

This work investigates the feasibility of using passive neutron measurement in identifying the removal or diversion of spent nuclear fuels (SNFs) in dry cask storage. In particular, we adopted a tomographic approach to measure emitted neutrons along the cask’s periphery through a laboratory-scale demonstration. An Arktis S670e helium-4 (He-4) detector array was utilized to measure neutrons. A 1/10th model cask was also built to mock the TN-32 dry cask. The test bench was conducted with three <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">252</sup> Cf sources to exemplify different assembly loading configurations. The measured neutron intensity patterns were then used to create images that represent the different source configurations. Also, Monte Carlo N-Particle Transport (MCNP) simulation was carried out to intercompare the experimental results with computational ones. Here, we describe the details behind the proposed safeguards technique through laboratory-scale demonstrations and examine its potentials and limitations.

高強度中性子全散乱装置NOVAによる水素貯蔵材料の平均・局所構造解析

高強度中性子全散乱装置NOVAによる水素貯蔵材料の平均・局所構造解析

Understanding Plasma Dynamics of Argentina Nano Focus Machine Using the Lee Code

Argentina Nano Focus Machine is a small plasma focus machine used as an intense neutron source. To understand the working of its plasma dynamics, the Lee model code is used. The results obtained from the Lee code agree reasonably well with the experimental data in terms of the peak current, radial start time and the pinch duration. Additionally, this code also produces information such as the optimum neutron yield (6.2x104), maximum ion beam energy (1.2 J) and the dependence of these yields and various speeds on operating pressure. The resultant data is reliable and all the input that is required is just one experimental current waveform together with the actual machine and operating parameters.

Modeling fission spikes in nuclear fuel using a multigroup model of electronic energy transport

In fission based nuclear reactors the fuel is subject to an intense neutron environment that drives the fission chain reaction. Due to this process fission fragments are created with energies reaching 1 MeV/amu that lose energy primarily through inelastic interactions with the electronic structure producing electronic excitations. Subsequently, these excitations thermalize through electron-phonon interactions resulting in the formation of a high temperature thermal spike and associated pressure spike. This process promotes atomic mobility that is expected to evolve lattice defects, including the annealing of latent ion tracks. In this work, a multigroup model for electron energy transport is developed and applied to molecular dynamics simulations in the LAMMPS code to examine fission energy deposition and fission effects in nuclear fuel. This technique utilizes MCNP Monte Carlo electron transport calculations to determine the initial injection of fission energy. To provide a more predictive approach than semi-empirical two-temperature models, the electron-phonon interactions are defined to include multiphonon energy transfer as a function of atomic and electron temperature, and are evaluated from electronic structure calculations using the VASP density functional theory code and PHONON lattice dynamics code. Application of this model to fission energy deposition in uranium dioxide predicts ion track formation and fission enhanced atomic mobility behavior within reasonable agreement of experimental trends. Furthermore, simulations of fission fragment interactions with latent ion tracks demonstrate an annealing effect due to this enhanced mobility.

Investigating the role of S-shape guide in neutron guidance system with 241Am-Be source

Guides play a key role in concentrating the neutron beam and increasing the flux for a neutron guide system. In this research, the role of a radius of curvature and length parameters on neutron intensity on the sample for the S-shape guide has been investigated and the results have been analyzed for three different types of geometry. In this work, the Monte Carlo simulation method is used with McStas software. The results show that at a constant radius with increasing length, the guide moves more towards bending and passes neutrons with less energy. Conversely, at a constant length with increasing radius, the guide gradually deviates from the curved state and it leads directly to the straight guide, all of the neutron energy spectra passes. A radius of curvature of 70 m and a length of 4 m were chosen for the S-shaped guide due to the passage of a larger range of thermal neutron fluxes. The guide radius can lead to a cut-off wavelength for neutrons. This guide can also eliminate fast neutrons and gamma rays..

The magnetic structure of DyFeO3 revisited: Fe spin reorientation and Dy incommensurate magnetic order

High resolution and high intensity neutron powder diffraction is used to study the ground state magnetic order and the spin reorientation transition in the orthoferrite DyFeO3. The transition from the high temperature k = 0 Γ4 (G x A y F z ) to the low temperature Γ1 (A x G y C z ) type order of the Fe-sublattice is found at T SR = 73 K and does not show any thermal hysteresis. Below T N2 = 4 K the Dy-sublattice orders in an incommensurate magnetic structure with k = [0, 0, 0.028] while the Fe-sublattice keeps its commensurate Γ1 type order. DyFeO3 is the first orthoferrite RFeO3 to possess an incommensurate magnetic order of the rare earth sublattice under zero field conditions; an important piece of information neglected in the recent discussion of its multiferroic properties.

3D isotope density measurements by energy-resolved neutron imaging

Tools for three-dimensional elemental characterization are available on length scales ranging from individual atoms, using electrons as a probe, to micrometers with X-rays. However, for larger volumes up to millimeters or centimeters, quantitative measurements of elemental or isotope densities were hitherto only possible on the surface. Here, a novel quantitative elemental characterization method based on energy-resolved neutron imaging, utilizing the known neutron absorption cross sections with their ‘finger-print’ absorption resonance signatures, is demonstrated. Enabled by a pixilated time-of-flight neutron transmission detector installed at an intense short-pulsed spallation neutron source, for this demonstration 3.25 million state-of-the-art nuclear physics neutron transmission analyses were conducted to derive isotopic densities for five isotopes in 3D in a volume of 0.25 cm3. The tomographic reconstruction of the isotope densities provides elemental maps similar to X-ray microprobe maps for any cross section in the probed volume. The bulk isotopic density of a U-20Pu-10Zr-3Np-2Am nuclear transmutation fuel sample was measured, agrees well with mass-spectrometry and is evidence of the accuracy of the method.