Effect of repeated electrical breakdowns on mineral and natural ester insulating oils

Transformer insulating oils are exposed to repeated electrical discharge or breakdowns inside power transformers. Durability tests are conducted to analyze the ability of oil to resist decomposition due to such high electrical stresses. With the increasing demand for alternative insulating oils for oilimmersed transformers, it is worthy to compare the performance of different types of insulating oils (conventional mineral-based insulating oil and natural ester-based insulating oil) under repeated electrical breakdown. In this paper, the AC breakdown voltage of different mineral-based and natural ester-based insulating oils is reported. Durability tests were conducted based on the AC breakdown voltage behavior of insulating oils after 50 electrical breakdown shots. The AC breakdown voltage of each insulating oil sample was assessed according to the ASTM D1816 standard test method. Based on the results, it can be concluded that the dissimilarity in chemical composition of the insulating oils has a significant effect on the AC breakdown voltage behavior of these oils under repeated electrical breakdowns

Emerging Avenues for Utilization of Exotic Germplasm

Breeders have been successful in increasing crop performance by exploiting genetic diversity over time. However, the reported annual yield increases are not sufficient in view of rapid human population growth and global environmental changes. Exotic germplasm possesses high levels of genetic diversity for valuable traits. However, only a small fraction of naturally occurring genetic diversity is utilized. Moreover, the yield gap between elite and exotic germplasm widens, which increases the effort needed to use exotic germplasm and to identify beneficial alleles and for their introgression. The advent of high-throughput genotyping and phenotyping technologies together with emerging biotechnologies provide new opportunities to explore exotic genetic variation. This review will summarize potential challenges for utilization of exotic germplasm and provide solutions

The physics, dosimetry and microdosimetry of boron neutron capture theraphy

A validated experimental and numerical procedure is described detailing macroscopic and microscopic dose calculations forming the basis of a protocol for the pre-clinical biological characterisation of the University of Birmingham’s BNCT facility. Fundamental reference dosimetric measurements have been carried out at the University of Birmingham’s accelerator based NCT facility and the Massachusetts Institute of Technology (MIT) research reactor to characterise macroscopic and microscopic doses and derive correction factors for the irradiation of V79 cells incubated in boric acid and irradiated as monolayers. On and off-axis thermal neutron, fast neutron and photon doses have been measured and calculated with standard macroscopic dosimetry techniques (foils and ion chambers) from which normalised MCNPX calculations are used to derive perturbation factors and off-axis corrections for cell flask irradiations. Microdosimetric correction factors are calculated for the boron dose component using Monte Carlo methods to simulate lithium ion and alpha particle tracks in semi-stochastic geometries representative of cell monolayer irradiations, incubated in a medium with 50ppm boric acid. Further simulations of recoil protons from nitrogen capture reactions allow for the calculation of correction factors for the non-uniform distribution of the nitrogen dose at the cellular level

DEVELOPMENT AND EXPERIMENTAL VALIDATION OF RESPONSE MODELLING FOR TIME-OF-FLIGHT NEUTRON DETECTION AND IMAGING SYSTEMS

The application and feasibility of a time-of-flight neutron detection system is explored for sources with time correlated gamma-ray and neutron emissions, such as the spontaneous fission emitter, Cf-252. For the emission of multiple gamma rays and neutrons from a single spontaneous fission event, a near instantaneous gamma-ray detection followed by a later neutron detection on a multi-detector array allows for an associated time-of-flight to be determined for a neutron arising from that event. Using a suite of purpose developed analysis tools, Monte-Carlo simulation and experimental data are compared for the Cf-252 water tank source facility at Lancaster University. Applying a bespoke time-of-flight imaging algorithm, vector-based optimisation (VBO), the true source location is determined within 21 cm by this approach

DEVELOPMENT AND EXPERIMENTAL VALIDATION OF RESPONSE MODELLING FOR TIME-OF-FLIGHT NEUTRON DETECTION AND IMAGING SYSTEMS

The application and feasibility of a time-of-flight neutron detection system is explored for sources with time correlated gamma-ray and neutron emissions, such as the spontaneous fission emitter, Cf-252. For the emission of multiple gamma rays and neutrons from a single spontaneous fission event, a near instantaneous gamma-ray detection followed by a later neutron detection on a multi-detector array allows for an associated time-of-flight to be determined for a neutron arising from that event. Using a suite of purpose developed analysis tools, Monte-Carlo simulation and experimental data are compared for the Cf-252 water tank source facility at Lancaster University. Applying a bespoke time-of-flight imaging algorithm, vector-based optimisation (VBO), the true source location is determined within 21 cm by this approach

A Preliminary Inter-centre Comparison Study for Photon, Thermal Neutron and Epithermal Neutron Responses of Two Pairs of Ionisation Chambers Used for BNCT

The dual ionisation chamber technique is the recommended method for mixed field dosimetry of epithermal neutron beams. Its importance has been long recognised and it has featured highly in the dosimetry exchange programme of the MIT BNCT group. This paper presents initial data from an ongoing inter-comparison study involving two identical pairs of ionisation chambers used at the BNCT facilities of Petten, NL and of the University of Birmingham, UK. The goal of this study is to evaluate the photon, thermal neutron and epithermal neutron responses of both pairs of TE(TE) (Exradin T2 type) and Mg(Ar) (Exradin M2 type) ionisation chambers in similar experimental conditions. At this stage, the work has been completed for the M2 type chambers and is intended to be completed for the T2 type chambers in the near future. Photon calibration: The photon responses of the ionisation chambers were obtained in 6 and 10 MV clinical photon beams at the University Hospital Birmingham. Photon calibration factor ratios, in terms of dose to water (Petten/Birmingham) of 1.077 ± 0.006 and 1.029 ± 0.005 were found for the M2 and T2 type chambers, respectively. Thermal neutron response: The thermal neutron sensitivities of the M2 type ionisation chambers were determined using the thermal neutron beam available at the Low Flux Reactor, Petten. Ratios of the integrated charge measured for each chamber indicate a ratio (Petten/Birmingham) of 0.980 ± 0.007 for the M2 chambers. BNCT epithermal neutron beam: Measurements in a reference PMMA cubic phantom were performed using the M2 type ionisation chambers in the epithermal neutron beam of the High Flux Reactor, Petten. At a depth of 2.5 cm, a ratio of the integrated charge for the chambers yields a sensitivity ratio (Petten/Birmingham) of 0.985 ± 0.008.JRC.F.4-Safety of future nuclear reactor

A Preliminary Inter-centre Comparison Study for Photon, Thermal Neutron and Epithermal Neutron Responses of Two Pairs of Ionisation Chambers Used for BNCT

The dual ionisation chamber technique is the recommended method for mixed field dosimetry of epithermal neutron beams. This paper presents initial data from an ongoing inter-comparison study involving two identical pairs of ionisation chambers used at the BNCT facilities of Petten, NL and of the University of Birmingham, UK. The goal of this study is to evaluate the photon, thermal neutron and epithermal neutron responses of both pairs of TE(TE) (Exradin T2 type) and Mg(Ar) (Exradin M2 type) ionisation chambers in similar experimental conditions. At this stage, the work has been completed for the M2 type chambers and is intended to be completed for the T2 type chambers in the near future.JRC.F.4-Safety of future nuclear reactor

Estimating the neutron yield in a deuterium plasma with the JET neutron camera

The JET neutron camera is a well-established detector system at JET, which has 19 sightlines each equipped with a liquid scintillator. The system measures a 2D profile of the neutron emission from the plasma. A first principle physics method is used to estimate the DD neutron yield that is based on JET neutron camera measurements and is independent of other neutron measurements. This paper details the data reduction techniques, models of the neutron camera, simulations of neutron transport, and detector responses used to this end. The estimate uses a simple parameterized model of the neutron emission profile. The method makes use of the JET neutron camera’s upgraded data acquisition system. It also accounts for neutron scattering near the detectors and transmission through the collimator. These components together contribute to 9% of the detected neutron rate above a 0.5 MeVee energy threshold. Despite the simplicity of the neutron emission profile model, the DD neutron yield estimate falls on average within 10% agreement with a corresponding estimate from the JET fission chambers. The method can be improved by considering more advanced neutron emission profiles. It can also be expanded to estimate the DT neutron yield with the same methodology

Detailed reproduction of the neutron emission from the compact DT neutron generator used as an in-situ 14 MeV calibration neutron source at JET

A compact DT neutron generator (NG) based on the mixed-beam operation was used as a calibration neutron source in the latest in-situ calibration of neutron detectors at the Joint European Torus (JET). In order to meet the requirement for the total uncertainty of the neutron detector calibration below ±10 %, the neutron emission properties had to be experimentally characterized and reproduced through detailed modelling of the neutron source characteristics and geometry of the neutron generator. The detailed neutronics simulations were an essential part of both NG characterization and JET neutron detector calibration. The complex neutron emission properties of the NG were reproduced through a combination of simulations and highresolution neutron spectroscopy measurements. This meant that six different DT neutron source components resulting from NG's mixed beam operation were explicitly simulated and their relative intensities scaled based on experimentally obtained neutron spectrum measurements. Furthermore, the detailed model of the NG's geometry was produced based on information from the supplier of the NG and images from a computer tomography (CT) scan. Finally, the positioning of the neutron source inside the JET tokamak during in-situ calibration was reproduced based on the information from the remote handling system (RHS) at JET, the system responsible for the positioning of the source during the calibration experiment. The extensive effort presented in the paper significantly contributed to the total uncertainties of the calibration factors well within the target value of ±10 %