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 %.
Neutronic benchmark experiments are carried out at JET aiming to assess the neutronic codes and data used in ITER analysis. Among other activities, experiments are performed in order to validate ...neutron streaming simulations along long penetrations in the JET shielding configuration. In this work, neutron streaming calculations along the JET personnel entrance maze are presented. Simulations were performed using the MCNP code for Deuterium-Deuterium and Deuterium- Tritium plasma sources. The results of the simulations were compared against experimental data obtained using thermoluminescence detectors and activation foils.
The neutron and gamma radiations in large fusion reactors are responsible for damage to charged couple device (CCD) cameras deployed for applied diagnostics. Based on the ASTM guide E722-09, the ...'equivalent 1 MeV neutron fluence in silicon' was calculated for a set of CCD cameras at the Joint European Torus. Such evaluations would be useful to good practice in the operation of the video systems.
Fast neutron induced water activation will result in significant additional nuclear heating loads to cryogenic components in the ITER fusion reactor during operation, which are considered as an ...important issue in the ITER design. A water activation experiment has been proposed at the Joint European Torus (JET) which would enable measurements of radiation dose rates and 16N concentrations in water, activated in the most representative fusion ermronment achievable, and extrapolability to ITER conditions. This paper presents a study aimed at establishing the experiment feasibility, in terms of the identification and selection of an experimental location at JET, and the definition of an experimental setup enabling accurate measurements of the quantities of interest. A suitable experimental location in JET was identified in the basement of the JET Torus Hall. The expected 16O(n,p)16N activation rates in the cooling water in the JET tokamak were determined through Monte Carlo particle transport calculations and the induced 16N activity in the water was propagated to the experimental location. Subsequent calculations were performed to determine the expected detector response to 16N γ rays for three different JET pulse scenarios. Two scintillator γ detectors were calibrated with standard γ calibration sources and tested with a 244Cm/13C neutron source, also emitting 6.13 MeV γ rays, corresponding to the 16N γ ray energy. The presented work demonstrates the feasibility of a water activation experiment at JET and provides valuable information for the experiment design.
•Calculation of neutron spectra in irradiation positions to be used during the upcoming DD, DT and TT campaigns at JET.•Evaluation of the hybrid Monte Carlo by use of ADVANTG for improvement of ...results.•Determination of the acceleration ratio in case of thermal neutron flux calculations.
The neutron fluxes and spectra were characterized for four locations close to the plasma and related to activation experiments, as the preparation for the upcoming experimental campaigns in JET. The focus was on the study of a variance reduction technique in order to obtain statistically significant results in the parts of the neutron energy spectra, important for irradiation experiments. The DD, DT and TT plasmas were studied with the Monte Carlo hybrid method and the use of the ADVANTG program for generation of weight windows as variance reduction method to accelerate Monte Carlo simulations. The calculations were optimized to obtain low statistical uncertainties for all energy bins in the 640 energy group structure and for all three plasma sources. This included the acceleration of calculations for reaction rates of capture reactions, i.e. in the thermal flux region in irradiation positions on the first wall. Speed-ups due to use of the hybrid method in excess of two orders of magnitude were found with respect to analog calculations despite the vicinity of the plasma source.
•The heating load due to water activation and the decay of N-16 produced in the water-based cooling systems has been identified as an important challenge for the ITER design.•A water activation ...experiment has been proposed at the Joint European Torus (JET), to measure radiation dose and N-16 concentrations in a fusion environment.•We present the preparatory computational and experimental work required for the preparation of the water activation experiment at JET.
Fast neutron induced water activation will result in significant additional nuclear heating loads to cryogenic components in the ITER fusion reactor during operation, which are considered as an important issue in the ITER design. A water activation experiment has been proposed at the Joint European Torus (JET) which would enable measurements of radiation dose rates and 16N concentrations in water, activated in the most representative fusion environment achievable, and extrapolability to ITER conditions. This paper presents a study aimed at establishing the experiment feasibility, in terms of the identification and selection of an experimental location at JET, and the definition of an experimental setup enabling accurate measurements of the quantities of interest. A suitable experimental location in JET was identified in the basement of the JET Torus Hall. The expected 16O(n,p)16N activation rates in the cooling water in the JET tokamak were determined through Monte Carlo particle transport calculations and the induced 16N activity in the water was propagated to the experimental location. Subsequent calculations were performed to determine the expected detector response to 16N γ rays for three different JET pulse scenarios. Two scintillator γ detectors were calibrated with standard γ calibration sources and tested with a 244Cm/13C neutron source, also emitting 6.13 MeV γ rays, corresponding to the 16N γ ray energy. The presented work demonstrates the feasibility of a water activation experiment at JET and provides valuable information for the experiment design.
Due to high neutron and gamma-ray yields and large size plasmas many future fusion reactor plasma parameters such as fusion power, fusion power density, ion temperature, fuel mixture, fast ion energy ...and spatial distributions can be well measured by various fusion product diagnostics. Neutron diagnostics provide information on fusion reaction rate, which indicates how close is the plasma to the ultimate goal of nuclear fusion and fusion power distribution in the plasma core, which is crucial for optimization of plasma breakeven and burn. Depending on the plasma conditions neutron and gamma-ray diagnostics can provide important information, namely about dynamics of fast ion energy and spatial distributions during neutral beam injection, ion cyclotron heating and generated by fast ions MHD instabilities. The influence of the fast particle population on the 2-D neutron source profile was clearly demonstrated in JET experiments. 2-D neutron and gamma-ray source measurements could be important for driven plasma heating profile optimization in fusion reactors. To meat the measurement requirements in ITER the planned set of neutron and gamma ray diagnostics includes radial and vertical neutron and gamma cameras, neutron flux monitors, neutron activation systems and neutron spectrometers. The necessity of using massive radiation shielding strongly influences the diagnostic designs in fusion reactor, determines angular fields of view of neutron and gamma-ray cameras and spectrometers and gives rise to unavoidable difficulties in the absolute calibration. The development, testing in existing tokomaks and a possible engineering integration of neuron and gamma-ray diagnostic systems into ITER are presented.
The fusion power output of fusion plasmas is measured using the neutron yield detectors due to its linear relation to the fusion yield. Absolutely calibrated neutron yield detectors are thus a ...crucial part of the plasma diagnostics system and the absolute accuracy of their calibration must be ensured.
The transition of the Joint European Torus's (JET's) first wall material from carbon (C) wall to ITER-like (Be/W/C) first wall was a significant change in the structure of the machine and recalibration of the main neutron yield detectors was needed to maintain the required measurement uncertainty of less than ±10%. The neutron yield detectors were thus recalibrated through two in situ calibrations to deuterium-deuterium neutrons in 2013 and deuterium-tritium neutrons in 2017 using
252
Cf spontaneous fission source and a compact neutron generator, respectively.
We describe the extensive neutronics calculations performed in support of these latest calibration experiments. These analyses were performed using Monte Carlo simulations to better understand the calibration procedure, optimize the experiments, ensure personnel safety, and quantify the effects of the uncharacteristic circumstances during calibration experiments. This paper focuses on assessments of the effects of the uncharacteristic circumstances, e.g., the presence of the remote handling system in the machine due to its use in neutron source delivery, difference in the neutron emission spectrum, and differences in the neutron source shape. Lessons learned, findings, and relevance for calibrations of future large tokamaks are discussed.
► We developed a simple but quick-running computational model of the JET tokamak. ► 5–10% of the neutrons hitting the fission chambers penetrate the tokamak wall, other come via ports. ► The highest ...contribution to a certain fission chambers is via the closest port and the second highest contribution is via the port closest to the neutron source. ► The torus hall wall significantly affects the external fission chambers response due to back scattering of neutrons.
Neutron yield measurements are the basis for the determination of the absolute fusion reaction rate and the operational monitoring with respect to the neutron budget during any campaign for JET, the Joint European Torus. After the 2010 changes of the JET plasma-facing materials (Carbon wall to ITER-Like Wall transition), confirmation of the neutron yield calibration will be ensured by direct measurements using a calibrated 252Cf neutron source deployed inside the JET vacuum vessel. In order to thoroughly understand the transport of neutrons from the vacuum vessel to the fission chamber detectors mounted outside the vessel on the transformer limbs and thus to computationally support the JET neutron calibrations project, we developed a simple but quick-running computational model of the JET tokamak for performing Monte Carlo neutron transport calculations.
From the modelling we find that a minority of the neutrons hitting the fission chambers penetrate the tokamak wall, whilst most come via the ports. The highest contribution to a fission chamber response comes via the port nearest to a point neutron source and the second highest contribution comes via the next nearest ports. If the port is blocked by a massive object, the fission chamber response is decreased by up to the contribution of that port. It was observed that the torus hall wall significantly affects the response of each external fission chamber due to back scattering of neutrons.
The whole process of understanding and improving the knowledge of the neutron yield calibration for JET is of great interest for ITER, where the methods and procedures for calibrating the neutron yield monitors are still being developed, but the requirement is for 10% accuracy in the fusion yield determination, as it is in JET.
► We model JET remote handling system in MCNP. ► We examine the effect of JET remote handling system on neutron monitor response. ► The integral effect of JET RH system on neutron monitors is less ...than 5%.
After the coated CFC wall to ITER-Like Wall (Beryllium/Tungsten/Carbon) transition in 2010–2011, confirmation of the neutron yield calibration will be ensured by direct measurements using a calibrated 252Cf neutron source deployed by the in-vessel remote handling boom and Mascot manipulator inside the JET vacuum vessel. Neutronic calculations are required to calculate the effects of the JET remote handling (RH) system on the neutron monitors. We developed a simplified geometrical computational model of the JET remote handling system in MCNP. In parallel we developed a script that translates the RH movement data to transformations of individual geometrical parts of the RH model in MCNP. After that a benchmarking of the model was performed to verify and validate the accordance of the target positions of source and RH system with the ones from our model. In the last phase we placed the JET RH system in the simplified MCNP model of the JET tokamak and studied its effect on neutron monitor response for some example source positions and boom configurations.
As the correction factors due to presence of the JET RH system can potentially be significant in cases when the boom is blocking a port close to the detector under investigation, we have chosen boom configurations so that this is avoided in the vast majority of the source locations. Examples are given.
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