Time-Dependent Neutronics in Structural Materials of Inertial Fusion Reactors and Simulation of Defect Accumulation in Pulsed Fe and SiC (original) (raw)
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Nuclear Instruments and …, 2001
The coupling of a new radiation transport (RT) solver with an existing multimaterial fluid dynamics code (ARWEN) using Adaptive Mesh Refinement named DAFNE, has been completed. In addition, improvements were made to ARWEN in order to work properly with the RT code, and to make it user-friendlier, including new treatment of Equations of State, and graphical tools for visualization. The evaluation of the code has been performed, comparing it with other existing RT codes (including the one used in DAFNE, but in the single-grid version). These comparisons consist in problems with real input parameters (mainly opacities and geometry parameters). Important advances in Atomic Physics, Opacity calculations and NLTE atomic physics calculations, with participation in significant experiments in this area, have been obtained. Early published calculations showed that a DT x fuel with a small tritium initial content (x53%) could work in a catalytic regime in Inertial Fusion Targets, at very high burning temperatures (4100 keV). Otherwise, the cross-section of DT remains much higher than that of DD and no internal breeding of tritium can take place. Improvements in the calculation model allow to properly simulate the effect of inverse Compton scattering which tends to lower T e and to enhance radiation losses, reducing the plasma temperature, T i . The neutron activation of all natural elements in First Structural Wall (FSW) component of an Inertial Fusion Energy (IFE) reactor for waste management, and the analysis of activation of target debris in NIF-type facilities has been completed. Using an original efficient modeling for pulse activation, the FSW behavior in inertial fusion has been studied. A radiological dose library coupled to the ACAB code is being generated for assessing impact of environmental releases, and atmospheric dispersion analysis from HIF reactors indicate the uncertainty in tritium release parameters. The first recognition of recombination barriers in SiC, modify the understanding of the calculation of displacement per atom, dpa, to quantify the collisional damage. An important analysis has been the confirmation, using Molecular Dynamics (MD) with an astonishing agreement, of the experimental evidence of low-temperature amorphization by damage accumulation in SiC, which could modify extensively its viability as a candidate material for IFE (fusion in general) applications. The radiation damage pulse effect has also been assessed using MD and Kinetic Monte Carlo diffusion of defects, showing the dose and driver frequency dependences. #
Modelling of materials under irradiation in inertial fusion reactors: Damage, tritium and activation
Neutron intensities and energy spectra in structural support materials versus time after target emission are presented for two IFE protections (LiPb, Flibe); these data are strongly required for evaluation of pulse effect. A multiscale modelling (MM) study of pulse irradiation in metals (Fe) has been extended up to the microscopic scale; we explain physics effects and remark differences with continuous irradiation. Static and dynamic validation of a new tight-binding molecular dynamics code to accurately determine defects energetic in SiC is presented. The effect of HT is remarked together with that of HTO when studying tritium releases; it is shown that HT contributes 90-98% to the total dose from ingestion of natural agriculture and meat and the rest comes from inhalation by the re-emission to the atmosphere. A Monte Carlo procedure estimates the effect of activation cross section uncertainties in the accuracy of inventory calculations and final materials consequences, which is based on simultaneous random sampling of all the cross sections and it is implemented in the activation code ACAB. The procedure is applied in collaboration with LLNL to the analysis at the National Ignition Facility gunite chamber shielding under a reference pulsing operation. Preliminary results show that the 95 percentile of the distribution of the relative error of the contact dose rate can take values up to 1.2. Model is also promising when applied to the uncertainty analysis of activation in IFE power plants, by using a continuous-pulsed model to represent the IFE real pulsed irradiation.
Physics of Plasmas, 2011
Ignition requires precisely controlled, high convergence implosions to assemble a dense shell of deuterium-tritium (DT) fuel with qR>$1 g=cm 2 surrounding a 10 keV hot spot with qR $ 0.3 g=cm 2 . A working definition of ignition has been a yield of 1MJ.Atthisyieldthea−particleenergydepositedinthefuelwouldhavebeen1 MJ. At this yield the a-particle energy deposited in the fuel would have been 1MJ.Atthisyieldthea−particleenergydepositedinthefuelwouldhavebeen200 kJ, which is already 10A^morethanthekineticenergyofatypicalimplosion.TheNationalIgnitionCampaignincludeslowyieldimplosionswithduddedfuellayerstostudyandoptimizethehydrodynamicassemblyofthefuelinadiagnosticsrichenvironment.Thefuelisamixtureoftritium−hydrogen−deuterium(THD)withadensityequivalenttoDT.ThefractionofDcanbeadjustedtocontroltheneutronyield.Yieldsof10 Â more than the kinetic energy of a typical implosion. The National Ignition Campaign includes low yield implosions with dudded fuel layers to study and optimize the hydrodynamic assembly of the fuel in a diagnostics rich environment. The fuel is a mixture of tritium-hydrogen-deuterium (THD) with a density equivalent to DT. The fraction of D can be adjusted to control the neutron yield. Yields of 10A^morethanthekineticenergyofatypicalimplosion.TheNationalIgnitionCampaignincludeslowyieldimplosionswithduddedfuellayerstostudyandoptimizethehydrodynamicassemblyofthefuelinadiagnosticsrichenvironment.Thefuelisamixtureoftritium−hydrogen−deuterium(THD)withadensityequivalenttoDT.ThefractionofDcanbeadjustedtocontroltheneutronyield.Yieldsof10 14À15 14 MeV (primary) neutrons are adequate to diagnose the hot spot as well as the dense fuel properties via down scattering of the primary neutrons. X-ray imaging diagnostics can function in this low yield environment providing additional information about the assembled fuel either by imaging the photons emitted by the hot central plasma, or by active probing of the dense shell by a separate high energy short pulse flash. The planned use of these targets and diagnostics to assess and optimize the assembly of the fuel and how this relates to the predicted performance of DT targets is described. It is found that a good predictor of DT target performance is the THD measurable parameter, Experimental Ignition Threshold Factor, ITFX $ Y Â dsf 2.3 , where Y is the measured neutron yield between 13 and 15 MeV, and dsf is the down scattered neutron fraction defined as the ratio of neutrons between 10 and 12 MeV and those between 13 and 15 MeV.
Nuclear Fusion, 2013
The neutron spectrum from a cryogenically layered deuterium-tritium (dt) implosion at the National Ignition Facility (NIF) provides essential information about the implosion performance. From the measured primary-neutron spectrum (13-15 MeV), yield (Y n) and hot-spot ion temperature (T i) are determined. From the scattered neutron yield (10-12 MeV) relative to Y n , the down-scatter ratio, and the fuel areal density (ρR) are determined. These implosion parameters have been diagnosed to an unprecedented accuracy with a suite of neutron-time-of-flight spectrometers and a magnetic recoil spectrometer implemented in various locations around the NIF target chamber. This provides good implosion coverage and excellent measurement complementarity required for reliable measurements of Y n , T i and ρR, in addition to ρR asymmetries. The data indicate that the implosion performance, characterized by the experimental ignition threshold factor, has improved almost two orders of magnitude since the first shot taken in September 2010. ρR values greater than 1 g cm −2 are readily achieved. Three-dimensional semi-analytical modelling and numerical simulations of the neutron-spectrometry data, as well as other data for the hot spot and main fuel, indicate that a maximum hot-spot pressure of ∼150 Gbar has been obtained, which is almost a factor of two from the conditions required for ignition according to simulations. Observed Y n are also 3-10 times lower than predicted. The conjecture is that the observed pressure and Y n deficits are partly explained by substantial lowmode ρR asymmetries, which may cause inefficient conversion of shell kinetic energy to hot-spot thermal energy at stagnation.
Laser and Particle Beams, 2005
In the field of computational modelling for S&E analysis our main contribution refers to the computational system ACAB [1] that is able to compute the inventory evolution as well as a number of related inventory response functions useful for safety and waste management assessments. The ACAB system has been used by Lawrence Livermore National Laboratory (LLNL) for the activation calculation of the National Ignition Facility (NIF) design [2] as well as for most of the activation calculations, S&E studies of the HYLIFE-II and Sombrero IFE power plants . Pulsed activation regimes can be modeled (key in inertial confinement fusion devices test/experimental facilities and power plants), and uncertainties are computed on activation calculations due to cross section uncertainties. In establishing an updated methodology for IFE safety analysis, we have also introduced time heat transfer and thermalhydraulics calculations to obtain better estimates of radionuclide release fractions. Off-site doses and health effects are dealt with by using MACSS2 and developing an appropriate methodology to generate dose conversion factor (DCF) for a number of significant radionuclides unable to be dealt with the current MACSS2 system. We performed LOCA and LOFA analyses for the HYLIFE-II design. It was demonstrated the inherent radiological safety of HYLIFE-II design relative to the use of Flibe. Assuming typical weather conditions, total off-site doses would result below the 10-mSv limit. The dominant dose comes from the tritium in HTO form. In the Sombrero design, a severe accident consisting of a total LOFA with simultaneous LOVA was analyzed. Key safety issues are the tritium retention in the C/C composite, and the oxidation of graphite with air that should be prevented. The activation products from the Xe gas in the chamber are the most contributing source to the final dose leading to 47 mSv. We also analyzed the radiological consequences and the chemical toxicity effects of accidental releases associated to the use of Hg, Pb, and
Implosion Physics, Alternative Targets Design and Neutron Effects on Inertial Fusion Systems
A new radiation transport code has been coupled with an existing multimaterial fluidynamics code using Adaptive Mesh Refinement (AMR) and its testing is presented, solving ray effect and shadow problems in S N classical methods. Important advances in atomic physics, opacity calculations and NLTE calculations, participating in significant experiments (LULI/France), have been obtained. Our new 1D target simulation model allows considering the effect of inverse Compton scattering in DT x targets (x<3%) working in a catalytic regime, showing the effectiveness of such tritium-less targets. Neutron activation of all natural elements in IFE reactors for waste management and that of target debris in NIF-type facilities have been completed. Pulse activation in structural walls is presented with a new modeling. Tritium atmospheric dispersion results indicate large uncertainties in environmental responses and needs to treat the two chemical forms. We recognise recombination barriers (metastable defects) and compute first systematic high-energy displacement cascade analysis in SiC, and radiation damage pulses by atomistic models in metals. Using Molecular Dynamics we explain the experimental evidence of low-temperature amorphization by damage accumulation in SiC.
In the field of computational modelling for S&E analysis our main contribution refers to the computational system ACAB [1] that is able to compute the inventory evolution as well as a number of related inventory response functions useful for safety and waste management assessments. The ACAB system has been used by Lawrence Livermore National Laboratory (LLNL) for the activation calculation of the National Ignition Facility (NIF) design [2] as well as for most of the activation calculations, S&E studies of the HYLIFE-II and Sombrero IFE power plants . Pulsed activation regimes can be modeled (key in inertial confinement fusion devices test/experimental facilities and power plants), and uncertainties are computed on activation calculations due to cross section uncertainties. In establishing an updated methodology for IFE safety analysis, we have also introduced time heat transfer and thermalhydraulics calculations to obtain better estimates of radionuclide release fractions. Off-site doses and health effects are dealt with by using MACSS2 and developing an appropriate methodology to generate dose conversion factor (DCF) for a number of significant radionuclides unable to be dealt with the current MACSS2 system. We performed LOCA and LOFA analyses for the HYLIFE-II design. It was demonstrated the inherent radiological safety of HYLIFE-II design relative to the use of Flibe. Assuming typical weather conditions, total off-site doses would result below the 10-mSv limit. The dominant dose comes from the tritium in HTO form. In the Sombrero design, a severe accident consisting of a total LOFA with simultaneous LOVA was analyzed. Key safety issues are the tritium retention in the C/C composite, and the oxidation of graphite with air that should be prevented. The activation products from the Xe gas in the chamber are the most contributing source to the final dose leading to 47 mSv. We also analyzed the radiological consequences and the chemical toxicity effects of accidental releases associated to the use of Hg, Pb, and
The ACAB system [1] to compute the inventory evolution as well as a number of related inventory response functions useful for safety and waste management has been used by Lawrence Livermore National Laboratory (LLNL) for the activation calculation of the National Ignition Facility (NIF) design as well as for most of the activation calculations, S&E studies of the HYLIFE-II and Sombrero IFE power plants with a severe experimental testing at RTNS-II of University Berkeley. Pulsed activation regimes can be modelled (key in inertial confinement fusion devices test/experimental facilities and power plants), and uncertainties are computed on activation calculations due to cross section uncertainties. In establishing an updated methodology for IFE safety analysis, we have also introduced time heat transfer and thermal-hydraulics calculations to obtain better estimates of radionuclide release fractions.
IFMIF, a fusion relevant neutron source for material irradiation current status
Journal of Nuclear Materials, 2014
The d-Li based International Fusion Materials Irradiation Facility (IFMIF) will provide a high neutron intensity neutron source with a suitable neutron spectrum to fulfil the requirements for testing and qualifying fusion materials under fusion reactor relevant irradiation conditions. The IFMIF project, presently in its Engineering Validation and Engineering Design Activities (EVEDA) phase under the Broader Approach (BA) Agreement between Japan Government and EURATOM, aims at the construction and testing of the most challenging facility subsystems , such as the first accelerator stage, the Li target and loop, and irradiation test modules, as well as the design of the entire facility, thus to be ready for the IFMIF construction with a clear understanding of schedule and cost at the termination of the BA mid-2017. The paper reviews the IFMIF facility and its principles, and reports on the status of the EVEDA activities and achievements.