•Typical PT-SCWR fuel uses single-region pins consisting of a homogeneous mixture of ThO2 and PuO2.•Using two regions (central for the ThO2 and peripheral for the PuO2) reduces the fuel ...temperature.•Single-region-pin melting-to-average power ratio is 2.5 at 0.0MWd/kg and 2.3 at 40MWd/kg.•Two-region-pin melting-to-average power ratio is 36 at 0.0MWd/kg and 10.5 at 40MWd/kg.•Two-region-pin performance drops with burnup due to fissile-element buildup in the ThO2 region.
The Pressure-Tube Supercritical-Water-Cooled Reactor (PT-SCWR) is one of the concepts under investigation by the Generation IV International Forum for its promise to deliver higher thermal efficiency than nuclear reactors currently in operation. The high coolant temperature (>625K) and high linear power density employed by the PT-SCWR cause the fuel temperature to be fairly high, leading to a reduced margin to fuel melting, thus increasing the risk of actual melting during accident scenarios. It is therefore desirable to come up with a fuel design that lowers the fuel temperature while preserving the high linear power ratio and high coolant temperature. One possible solution is to separate the fertile (ThO2) and fissile (PuO2) fuel materials into different radial regions in each fuel pin. Previously-reported work found that by locating the fertile material at the centre and the fissile material at the periphery of the fuel pin, the fuel centreline temperature can be reduced by ∼650K for fresh fuel compared to the case of a homogeneous (Th–Pu)O2 mixture for the same coolant temperature and linear power density. This work provides a justification for the observed reduction in fuel centreline temperature and suggests a systematic approach to lower the fuel temperature. It also extends the analysis to the dependence of the radial temperature profile on fuel burnup. The radial temperature profile is determined from the analytical solution of the steady-state heat conduction equation in the fuel pin, ignoring azimuthal dependence and axial heat flow. The temperature dependence of the thermal conductivity is accounted for, as is the radial dependence of the volumetric power density, which is determined from detailed lattice-level transport calculations performed using the lattice code DRAGON. The reduction in the centreline fuel temperature is shown to be caused partly by a reduction in the heat flux in the case of the two-region fuel and partly by the higher thermal conductivity of both pure ThO2 and pure PuO2 compared to that of a ThO2–PuO2 mixture. The centreline temperature of the two-region fuel is shown to be higher for irradiated fuel than for fresh fuel, a fact explained by the depletion of the fissile material in the peripheral region and the buildup of fissile material in the central region.
► Response functions have been calculated for gas-filled and scintillation detectors. ► Simulations have used Monte Carlo calculation for neutron and gamma radiation. ► Different effects have been ...taken into account in the simulation. ► The simulated response functions have been compared with experiments. ► The obtained results are in a good agreement within the experiment uncertainty.
Monte Carlo simulation of a detector response function presents a very challenging problem. The detector response functions have been calculated for different neutron and gamma detectors:
3He gas filled proportional counter, NE213 organic scintillator, BrillanCe 350 or LaCl
3(Tl), and an ionization chamber with mixed gas composition. MCNPX code was used for simulations. The simulations were done with different neutron and gamma energies. The effects of neutron scattering, wall effects, recoil continua and contribution from charged particles have been included. The detector response function for the NE213 organic scintillator was obtained with consideration of light output curves of different products of neutron reactions with materials of the scintillator. The simulated data has been compared with experiments.
Silicon photomultiplier devices (SiPM) were investigated as a possible front-end detector system for the electromagnetic barrel calorimeter of the GlueX Project at Jefferson Laboratory, USA, and ...compared against a traditional 2 in vacuum photomultiplier tube. The SiPM has gain and timing resolution comparable to that of a PMT, requires a simple electronic circuit and is not sensitive to magnetic fields. These attributes allow us to conclude that it is feasible to use the SiPM as a front-end detector for this calorimeter.
A commercialized thermal neutron analysis (TNA) sensor has been developed to confirm the presence of buried bulk explosives as part of a multi-sensor anti-tank landmine detection system. Continuing ...improvements to the TNA system have included the use of an electronic pulsed neutron generator that offers the possibility of applying fast neutron analysis (FNA) methods to improve the system's detection capability. This paper describes an investigation into the use of FNA as a complementary component in such a TNA system. The results of a modeling study using simple geometries and a full model of the TNA sensor head are presented, as well as preliminary results from an experimental associated particle imaging (API) system that supports the modeling study results. The investigation has concluded that the pulsed beam FNA approach would not improve the detection performance of a TNA system for landmine or buried IED detection in a confirmation role, and could not be made into a practical stand-alone detection system for buried anti-tank landmines. Detection of buried landmines and IEDs by FNA remains a possibility, however, through the use of the API technique.
The Improved Landmine Detector System, a militarily fielded, teleoperated vehicle-mounted multi-sensor landmine detector, uses a thermal neutron analysis (TNA) detector to confirm the presence of a ...mine by detecting the bulk nitrogen in its explosives. To improve the nitrogen sensitivity or measurement times of the TNA detector, higher gamma ray rates will be required. The chief bottleneck to achieving the maximum possible performance from the present TNA or future versions is the relatively slow fluorescent decay time of the NaI(Tl) scintillators which are currently used. An experimental investigation was undertaken to compare a number of modern, fast inorganic scintillators to NaI(Tl) with respect to parameters relevant to TNA landmine detection, including efficiency, energy resolution, linearity, available size and cost. This paper presents results in the context of the high-rate, high-gamma-energy environments expected in such a TNA application. Large (7.62 cm times 7.62 cm) LaBr 3 :Ce scintillators, and to a lesser degree LaCl 3 :Ce, were found to stand-out as as the principal candidates for the detector upgrade to the TNA confirmation system. Their properties also make them ideal candidates for fast neutron analysis and associated particle imaging bulk explosives detectors.
A neutron Albedo system with time rejection for landmine and IED detection Kovaltchouk, V.D.; Andrews, H.R.; Clifford, E.T.H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2011, Letnik:
652, Številka:
1
Journal Article
Recenzirano
A neutron Albedo system has been developed for imaging of buried landmines and improvised explosive devices (IEDs). It involves irradiating the ground with fast neutrons and subsequently detecting ...the thermalized neutrons that return. A scintillating
6Li loaded ZnS(Ag) screen with a sensitive area of 40
cm×40
cm is used as a thermal neutron detector. Scintillation light is captured by orthogonal arrays of wavelength-shifting fibers placed on either side of the scintillator surface and then transferred to
X and
Y multi-pixel PMTs. A timing circuit, used with pulsed neutron sources, records the time when a neutron detection takes place relative to an external synchronization pulse from the pulsed source. Experimental tests of the Albedo system performance have been done in a sand box with a
252Cf neutron source (no time gating) and with pulsed D–D (2.6
MeV) neutrons from the Defense R&D Ottawa Van de Graaff accelerator (with time gating). Information contained in the time evolution of the thermal neutron field provided improved detection capability and image reconstruction. The detector design is described and experimental results are discussed.
Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave ...function. In this Letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive ω electroproduction off the proton, ep→e′pω, at central Q2 values of 1.60, 2.45 GeV2, at W=2.21 GeV. The results of our pioneering −u≈−umin study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full L/T/LT/TT separations in this never explored kinematic territory. At Q2=2.45 GeV2, the observed dominance of σT over σL, is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes: universal nonperturbative objects only accessible through backward-angle kinematics.
Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave ...function. In this Letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive ω electroproduction off the proton, ep → e'pω , at central Q2 values of 1.60, 2.45 GeV2 , at W=2.21 GeV . The results of our pioneering -u≈-umin study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full L / T / LT / TT separations in this never explored kinematic territory. At Q2=2.45 GeV2 , the observed dominance of σT over σL , is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes: universal nonperturbative objects only accessible through backward-angle kinematics.
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