Neutron Production Rate Research Articles

Study of inertial electrostatic confinement fusion using a finite-volume scheme for the one-dimensional Vlasov equation.

While the majority of fusion energy research is focused on magnetic confinement, there have been several alternative confinement methods aimed at the development of smaller and less expensive reactors. A number of these alternative reactors are based on a spherically convergent beam of recirculating ions and include designs such as inertial electrostatic confinement (IEC), multigrid IEC, and the periodically oscillating plasma sphere concept. Here, a fully time-dependent GPU-based Vlasov solver was developed in order to study these spherically convergent devices. This code solves the Vlasov equation for a spherically symmetric system using a finite-volume method with a modified flux to account for electrode transparency. The solver accounts for secondary electron emission, interactions between the charged particles, and collisional effects such as ionization and charge exchange. This code was used to investigate a system similar to the ion-injected device described by Hirsch (see [R. L. Hirsch, J. Appl. Phys. 38, 4522 (1967)10.1063/1.1709162]), who had reported a neutron production rate for deuterium-deuterium reactions in the range of 10^{6}to10^{7} neutrons per second, which was attributed to the formation of a virtual electrode structure near the center of the chamber. Attempts to reproduce this experiment [B. J. Egle, Ph.D. thesis, 2010] yielded similar fusion rates, though the majority of the reactions were found not to occur near the center of the chamber. The results of this Vlasov solver, considering only beam-beam and beam-background fusion reactions, show that beam-background reactions would be dominant in such an ion-injected device. This result is consistent with work by Baxter and Stuart, who proposed a simplified steady-state Boltzmann model. However, the result of both models are inconsistent with the experimental results, which indicate a higher neutron production rate, and an inverse pressure scaling trend. It is shown that the higher experimental rates may be explained by beam-target fusion between the ion beam and deuterium embedded on the inner surface of the cathode.

ASCOT simulations of 14 MeV neutron rates in W7-X: effect of magnetic configuration

Neutron production rates in fusion devices are determined not only by the kinetic profiles but also the fast ion slowing-down distributions. In this work, we investigate the effect of magnetic configuration on neutron production rates in future deuterium plasmas in the Wendelstein 7-X stellarator. The neutral beam injection, beam and triton slowing-down distributions, and the fusion reactivity are simulated with the ASCOT suite of codes. The results indicate that the magnetic configuration has only a small effect on the production of 2.45 MeV neutrons from thermonuclear and beam-target fusion. The 14.1 MeV neutron production rates were found to be between 1.49 × 1012 and , which is estimated to be sufficient for a time-resolved detection using a scintillating fiber detector, although only in high-performance discharges.

Evaluation of 3D printed buckyball-shaped cathodes of titanium and stainless-steel for IEC fusion system

An inertial electrostatic confinement (IEC) fusion device accelerates ions, such as deuterium (D) or tritium (T), to produce nuclear fusion and generate neutrons. The IEC's straightforward configuration consists of a concentric spherical transparent cathode at a negative bias surrounded by a grounded spherical anode. The effects of cathode properties on the neutron production rate (NPR) remain, to date, inadequately studied. This study aims to determine the impact of the cathode material on the NPR by investigating fusion reactions on the cathode surface. Two buckyball-shaped cathodes made of stainless steel (SS) and titanium (Ti), both of 5 cm diameter, fabricated by selective laser melting and 3D printing, are used for this investigation. A SS spherical chamber of 25 cm inner diameter is used as an anode in this experiment. A performance evaluation of surface fusion reaction in the IEC using SS and Ti grids is conducted by examining the NPR as a function of the applied voltage and grid currents at different gas pressures. So far, IEC with Ti and SS cathodes achieves NPRs of 2.32 and 1.41 × 107 n/s, respectively, at 5.6 kW (70 kV, 80 mA). The normalized NPRs (NPR/I-cathode) from IEC using SS and Ti cathodes are compared. The results demonstrate that fusion reaction occurs on the cathode surface, and fusion increases with the applied voltage. The measured NPR/I-cathode using the Ti cathode is higher than that of the SS cathode by factors of 1.36–1.64 across the 20–70 kV range. Moreover, fusion on the Ti cathode surface enhances the total NPR significantly compared to the SS cathode under the same conditions. The Ti's considerable ability to accumulate D ions and molecules compared with that of SS explains the difference of measured NPR results.

Optimization of target, moderator, and collimator in the accelerator-based boron neutron capture therapy system: A Monte Carlo study

The aim of this study was to optimize the target, moderator, and collimator (TMC) in a neutron beam generator for the accelerator-based BNCT (A-BNCT) system. The optimization employed the Monte Carlo Neutron and Photon (MCNP) simulation. The optimal geometry for the target was decided as the one with the highest neutron flux among nominates, which were called as angled, rib, and tube in this study. The moderator was optimized in terms of consisting material to produce appropriate neutron energy distribution for the treatment. The optimization of the collimator, which wrapped around the target, was carried out by deciding the material to effectively prevent the leakage radiations. As results, characteristic of the neutron beam from the optimized TMC was compared to the recommendation by the International Atomic Energy Agent (IAEA). The tube type target showed the highest neutron flux among nominates. The optimal material for the moderator and collimator were combination of Fluental (Al203+AlF3) with 60Ni filter and lead, respectively. The optimized TMC satisfied the IAEA recommendations such as the minimum production rate of epithermal neutrons from thermal neutrons: that was 2.5 times higher. The results can be used as source terms for shielding designs of treatment rooms.

Anode shape dependency of discharge characteristics and neutron yield of a linear type inertial electrostatic confinement fusion neutron source

AbstractA linear inertial electrostatic confinement fusion neutron source equipped with a cooling system for high power operation was developed and its discharge characteristics and neutron production performance were tested under a wide range of discharge conditions. Four different types of discharge anodes were prepared and the dependencies of the device performance on the anode shape were precisely investigated. A maximum neutron production rate of 3.4×106 n/s was achieved when the device was operated with single‐cylinder‐type anodes under a discharge voltage of 94 kV, a current of 20 mA, and a deuterium gas pressure of 0.5 Pa. By comparing the discharge characteristics and neutron generation rates under different anode shapes, we found that the larger inner diameter of the anode leads to longer effective gap length and lower operating pressure, which may result in relatively high fusion reaction rate observed with the single‐cylinder‐type anodes.

Optimization of target lifetime for production of 14 MeV neutrons

Two methods are examined for extending the life of tritium targets for production of 14 MeV neutrons by the 3H(2H,n)4He nuclear reaction. With thick film targets the neutron production rate decreases with time due to isotope exchange of tritium in the film with implanted deuterium. In this case, the target life is maximized by operating the target at elevated temperature where the implanted deuterium mixes by thermal diffusion throughout the entire thickness of the film. The number of neutrons obtained from a target is then proportional to the initial tritium content of the film. A novel thin-film target design was also developed and tested. With these thin-film targets, the incident deuterium is implanted through the tritide into the underlying substrate material. A thin permeation barrier layer between the tritide film and substrate, reduces the rate of tritium loss from the tritide film. Good thin-film target performance was achieved using W and Fe for the barrier and substrate materials respectively. Thin-film targets were fabricated and tested and shown to produce similar number of neutrons as thick-film targets while using only a small fraction of the amount of tritium.

Energetic deuterium-ion beams and neutron source driven by multiple-laser interaction with pitcher-catcher target

Multiple lasers interacting with a deuterated (D) pitcher-catcher target and neutron generation are investigated using two-dimensional hybrid particle-in-cell and Monte Carlo simulations. It is found that when multiple laser pulses are focused on the front surface of the pitcher layer, D+ ion acceleration by target normal sheath acceleration (TNSA) is enhanced by the interfering overlapped light fields and the resulting periodic target-surface structure. With three laser pulses each of 4.5 × 1019 W cm−2 intensity, 33 fs duration and ∼160 mJ energy, focusing at suitable angles on the pitcher layer, one can obtain 15 MeV D+ ions and ∼25% laser-to-D+ ions energy conversion efficiency. As the resulting high-energy-density D+ ions bombard the catcher layer, D-D fusion reactions are triggered. About 3.6 × 107 neutrons can be produced, with the maximum neutron production rate as high as 3.1 × 1036 m−3s−1, almost an order of magnitude higher than that from a single laser of the same total energy.

Ten years of cosmic muons observation with Borexino

The Borexino detector at Gran Sasso has now accumulated over ten years of continuous data which represent a magnificent opportunity to study the cosmic muon flux at a deep underground location. We present here a precision measurement of the flux and of the expected seasonal modulation. We present the correlation with the atmospheric temperature variations from global atmospheric models. We measure the correlation parameters and infer the kaon-to-pion ratio in the production of cosmic muons from high energy primaries. We also find evidence of a long term modulation that is not present in the atmospheric data and we investigate a possible positive correlation with the solar activity. Finally we observe a seasonal modulation of the production rate of cosmogenic neutrons that is in phase with the muon modulation but shows a surprisingly larger amplitude.

A hybrid continuous energy and multi-group Monte Carlo method

This paper investigates mixing multi-group (MG) and continuous energy (CE) representation of cross-sections depending on location of a particle in a Monte Carlo neutronic eigenvalue calculations in 1D and 2D PWR test cases with UOX and MOX fuel. Different population normalisation needs to be applied to CE and MG region to account for the difference in criticality between CE and MG representation. This normalisation procedure requires a neutron production rate ratio between CE and MG region to be known a priori. A resonance correction in energy spectrum during transition of a particle between the MG and CE region was developed based on the equivalence resonance treatment theory. With these, it was shown that it is possible to accelerate total calculation time, while introducing only a moderate error below 1% in the fission rate distribution. The magnitude of acceleration is heavily dependent on the relative size of CE and MG zones.

2-D Evaluation of Bred Tritium Using Neutron Imaging Plate

Tritium breeding performance of a fusion blanket is a key parameter for the self-sufficient fueling of a fusion reactor, and thus designed to validate the performance of a neutronics experiment. Measuring the 2-D distribution of bred tritium is challenging via conventional methods such as $\beta $ -ray counting from an irradiated lithium sample using a liquid scintillation counter (LSC) and a single-crystal diamond detector with a thin 6LiF film, because they are point detectors which require many measurements. In this article, 2-D distribution of the low quantity produced tritium was evaluated with a neutron imaging plate (NIP) with a Gd convertor by estimating the loss of neutrons via a capture reaction by Li. Deuterium–deuterium (DD) fusion neutrons were generated using a compact fusion device at an average neutron production rate of $1.5 \times 10 ^{5}$ n/s by applying high voltages. A neutron image with “shadows” projected by thermal neutron capture reactions of 6Li(n, $\alpha$ ) and 10B(n, $\alpha$ ) was successfully obtained. The experimentally evaluated values were confirmed to be consistent with the total number of capture reactions calculated using a neutron transport code. The results suggest that the approach could be a facile method for the 2-D evaluation of bred tritium.

New source design will increase ultracold neutron production rate

Physicists propose a design for a next-generation source of ultracold neutrons which can produce a high current of ultracold neutrons.

An iterative fission matrix scheme for calculating steady-state power and critical control rod position in a TRIGA reactor

Although Monte Carlo simulations are the most accurate representation of nuclear reactor cores, they can be computationally expensive. This computational expense can prohibit the use of Monte Carlo in situations that require sequences of neutronics calculations, such as accounting for temperature feedback. In the present work, we demonstrate a fission matrix methodology to calculate the fission source in the Penn State Breazeale Reactor while accounting for control rod movement and fuel temperature feedback. A fission matrix A, represents the rate of fission neutron production in a reactor core, where the aij entry of the matrix is equal to the neutrons produced in cell i per neutron born from cell j. The fission source distribution and multiplication factor keff are the principle eigenvector and principle eigenvalue, respectively, of the fission matrix. Given a varied core temperature distribution, a new fission matrix can be obtained by interpolating from a database of pre-calculated fission matrices. This approach shows promise in accurately and quickly calculating the reactivity and fission source distributions for a system with an arbitrary temperature distribution. In the present work, the largest resulting relative error of the calculated power distribution per pin was 1.52% compared to a Serpent criticality simulation, and all calculated eigenvalues were within 50 pcm, which corresponds to 0.1–0.4 cm of rod insertion depending on whether rods are inserted in the center or edge of the core. In contrast, the critical rod position varies by 13.49 cm for the cases considered (0–650 kW). The present database is composed of data from 78 Monte Carlo calculations, but enables subsequent neutronics calculations to be done in a fraction of a second. Future work would be to implement correction factors for neighboring temperature differences in three-dimensional models, incorporate xenon feedback, and investigate ways to decrease database size.

Preliminary results of a miniature cylindrical inertial electrostatic confinement fusion device equipped with inductively coupled plasma generator

In this paper a cylindrical neutron generator based on inertial electrostatic confinement is designed and constructed. This miniature sized linear neutron generator is equipped with an inductively coupled plasma generator as the pre-ionization system. The preliminary neutron counting results by a 3He detector indicated linear correlation between the discharge current and Neutron Production Rate (NPR) at fixed voltages. The pre-ionization helps to increase the discharge current at fixed pressures therefore the charge exchange reactions does not increase by this method. Primary results represent NPR of 105 n/s at −40 kV cathode voltage that could be increased between 107 to 108 n/s by increment of this voltage up to −80 kV and cathode cooling considerations.

Preliminary Results of Neutron Transport in Blanket Module by MCNP with Profile Analysis Using Imaging Plate

Measurement of neutron flux and energy spectrum profile inside the blanket is required for fusion blanket design. An experiment using an imaging plate and activation materials (Dy, In, and Au) was performed to measure spatial distribution of neutron flux. Neutrons were generated by a discharge-type compact fusion neutron source whose neutron production rate was more than 107 n/s. A linearity between the total number of active nuclides made by neutron and photo-stimulated luminescence per area on the activation material was confirmed for three orders of magnitude. The relationships between the total number of decay of activation in the materials and the flux of the neutron in a simplified breeder assembly was measured and compared with the computation by MCNP.

Improvement of the Neutron Production Rate of IEC Fusion Device by the Fusion Reaction on the Inner Surface of the IEC Chamber

Neutrons are generated in the inertial electrostatic confinement (IEC) device through different types of fusion reactions of the fuel gas such as deuterium (D) and tritium (T). Fusion in the IEC device takes place via various kinds of collisions like beam-beam collision, beam–background gas collision, and beam-target collision on the electrode surfaces. Two identical anodes for the IEC chamber made from titanium (Ti) and SUS-316L stainless steel (SS) are used to study the effect of the anode material on the neutron production rate (NPR). The NPRs from the chambers are measured at different applied powers. The achieved NPRs, so far, for Ti and SS are 8.9 × 107 n/s at 5.25 kW (75 kV, 70 mA) and 2.8 × 107 n/s at 10.5 kW (70 kV, 150 mA), respectively. The normalized NPR (NPR rated to the cathode current) from the Ti chamber is three to four times higher than that from the SS chamber. We observed a better NPR for the Ti chamber compared with the SS chamber. This is explained by the fusion reaction occurring between the neutrals and D atoms adsorbed/embedded on the inner surface of the anode. Moreover, the Ti chamber shows an improvement of the NPR as a function of the operating time ranging from 1.5 to 1.75 after 25 h from the first discharge.

Discharge current enhancement in inertial electrostatic confinement fusion by impulse high magnetic field

Effect of strong pulsed magnetic field on the discharge behavior of a cylindrical inertial electrostatic (IEC) device has been investigated both theoretically and experimentally. By applying strong pulsed magnetic field in a new fabricated miniature cylindrical IEC device equipped with Inductively Coupled Plasma (ICP), discharge current amplifications were observed at ordinary pressures as well as low pressure ICP-assisted operational regime with deuterium gas. The obtained results indicate the evidence for significant amplification of discharge current up to more than one hundred times. Since the neutron production rate has been previously proven to be linearly dependent on the discharge current, then this study might open new investigations for probable increment of fusion reaction rates in IEC devices with additional strong magnetic field.

Preparation for a neutronics experiment using a discharge fusion device and an imaging plate neutron detector

Tritium breeding ratio (TBR) is one of the most important parameters determining the tritium self-sufficiency of a deuterium-tritium fusion reactor. A neutronics experiment is planned to measure the spectral neutron fluences two-dimensionally (2D) using a discharge-type compact fusion neutron source and a neutron imaging plate (NIP), respectively. We report a calibration method for the NIP and optimization of the discharge condition to enhance the neutron production rate. A linear relationship between the neutron fluence in the NIP and photostimulated luminescence (PSL) per area was obtained in the range of the neutron fluence from 103 to 107 n/cm2. A neutron production rate higher than 107 n/s was successfully achieved by the optimized discharge condition. It is shown that a quantitative 2D measurement by the NIP is feasible using the linear relationship and a correlation coefficient on the energy spectrum.

Radionuclide neutron source trajectories in the closed nuclear fuel cycle

Abstract The highest efficiency in the usage of nuclear energy resources can be implemented in fast breeder reactors of generation IV. It is achieved thanks to the ability of consuming minor actinides (MAs) in energy production. One of the options to use this benefit is full recycling of MAs to close the nuclear fuel cycle. Monte Carlo burn up (MCB), an integrated burn-up calculation code, deals with the complexity of the burn-up process which is applied to the European Lead-cooled Fast Reactor (ELFR). MCB uses continuous energy representation of cross section and spatial effects of full core reactor model; however, it automatically calculates nuclide production in all possible reactions or decay channels. Multi-recycling of MAs can cause an intensified build-up of curium, berkelium and californium. Some of their isotopes are strong neutron emitters from spontaneous fission, which hinders fuel recycling. The implementation of a novel methodology for trajectory period folding allows us to trace the life cycle of crucial MAs from the beginning of the reactor life towards the state of adiabatic equilibrium. The result of the analysis performed is presented, showing the sources of strong contribution to the neutron production rate. The parametric sensitivity analysis method for selected nuclide reactions is applied, revealing sensitivity of transmutation chains for the production of neutron emitter isotopes.

TRITIUM BREEDING CALCULATION IN A STELLARATOR BLANKET

In current blanket projects, tritium breeding ratio (TBR), the ratio of tritium production rate to the neutron production rate, is low (1.1…1.2). The MCNPX Monte-Carlo code has been used to model the neutron kinetics and to look for a principal possibility of increase TBR within a stellarator blanket limited space.

Modulations of the cosmic muon signal in ten years of Borexino data

We have measured the flux of cosmic muons in the Laboratori Nazionali del Gran Sasso at 3800 m w.e. to be (3.432 ± 0.003)⋅ 10−4 m−2s−1 based on ten years of Borexino data acquired between May 2007 and May 2017. A seasonal modulation with a period of (366.3 ± 0.6) d and a relative amplitude of (1.36 ±0.04)% is observed. The phase is measured to be (181.7 ± 0.4) d, corresponding to a maximum at the 1st of July. Using data inferred from global atmospheric models, we show the muon flux to be positively correlated with the atmospheric temperature and measure the effective temperature coefficient αT = 0.90 ± 0.02. The origin of cosmic muons from pion and kaon decays in the atmosphere allows to interpret the effective temperature coefficient as an indirect measurement of the atmospheric kaon-to-pion production ratio rK/π = 0.11+0.11−0.07 for primary energies above 18 TeV. We find evidence for a long-term modulation of the muon flux with a period of ∼ 3000 d and a maximum in June 2012 that is not present in the atmospheric temperature data. A possible correlation between this modulation and the solar activity is investigated. The cosmogenic neutron production rate is found to show a seasonal modulation in phase with the cosmic muon flux but with an increased amplitude of (2.6 ± 0.4)%.