The topology based multi-fluid flow model of Silverman (Silverman, Nuclear Engineering and Design, 2021, Vol. 383, pp. 111421) presents a unified model that is able to correctly describe the interactions between the fluids in the flow field for any flow topology (i.e. dispersed or separated flows). This model can simulate the flow starting from single-fluid conditions, moving to dispersed flows and up to separated fluids flow. To apply this model to general multi-fluid simulations, a revised version of the HLLC flow solver is developed here. A few benchmarks present the ability of the new model and solver to simulate compressible multi-fluid flows. Some of the results presented here indicate that the topology of a multi-fluid mixture has an effect on its stability and structure.

The paper presents a novel pressure-corrected formulation of the immersed boundary method (IBM) for the simulation of fully compressible non-Boussinesq natural convection flows. The formulation incorporated into the pressure-based fractional step approach facilitates simulation of the flows in the presence of an immersed body characterized by a complex geometry. Here, we first present extensive grid independence and verification studies addressing incompressible pressure-driven flow in an extended channel and non-Boussinesq natural convection flow in a differentially heated cavity. Next, the steady-state non-Boussinesq natural convection flow developing in the presence of hot cylinders of various diameters placed within a cold square cavity is thoroughly investigated. The obtained results are presented and analyzed in terms of the spatial distribution of path lines and temperature fields and of heat flux values typical of the hot cylinder and the cold cavity surfaces. Flow characteristics of multiple steady-state solutions discovered for several configurations are presented and discussed in detail.

Computing the working conditions and transient processes of nuclear reactors is important for both the safety and design of these reactors. The operation of nuclear reactors depends on various phenomena resulting from different flow regimes in the core. To accurately describe the system's operation, multiphase, multi-scale models should be integrated for dispersed and separate flow topologies. This work presents a new multiphase flow model which accounts for the actual flow topology (dispersed or separate) and provides a unified model for all flow regimens. The basis of the new model is a physical insight that guides the averaging process of the multiphase conservation equations. The study defines a topology function for each fluid which expresses its connectivity on the scale of the computation grid. The new topological function is used to divide the mixture's averaged conservation equations into phasic equations in a way which correctly accounts for stress and heat transfers in the mixture. From this perspective, we show a unified model which is able to correctly describe the interactions between the phases in the flow field. This model can provide the flow starting from dispersed conditions and moving to separate flows.

A compact Liquid Lithium Target (LiLiT) has been operating at SARAF for several years with beam power of several kW (1.9-2.5 MeV, up to 2 mA). When bombarding the lithium with low energy protons neutrons are generated. The neutron source, mainly used for nuclear astrophysics research, was decommissioned in 2016 towards an upgraded model - with possible applications to Boron Neutron Capture Therapy (BNCT) and material-science studies. The improved version has been designed to sustain 50 kW proton beam power (2.5 MeV, ~20 mA) to provide sufficient neutron flux required for clinical BNCT application. The new model has a 50 mm wide lithium jet to enable dissipation of the higher beam power and an improved heat exchanger to remove the power to a secondary cooling loop. A new Annular Linear INduction electro-magnetic pump (ALIN) has been designed and built to provide the required lithium flow rate. Other mechanical improvements facilitate the maintenance of the system and the robustness of operation. Radiological risks due to the 7Be produced in the reaction are reduced by using an integrated lead shielding of the lithium reservoir. An integrated neutron moderator is being designed to adjust the neutron energy to the spectrum best suited to BNCT. A low power (6 kW) model of the new design with a narrower nozzle (18 mm wide) and a rotating-magnet electro-magnetic pump is operating at SARAF to support the ongoing astrophysics and nuclear research program [1], [2]. To fulfill clinical BNCT, the upgraded LiLiT model will require an accelerator of appropriate energy and intensity. The design features of the new system are presented in this paper.

The mechanical properties of thin foils (similar to 25 mu m), to be used as a target's window in a high intensity accelerator, require non-standard characterization techniques. In the current research, the innovative small punch test technique (SPT) had been used to map and determine the mechanical properties of SS 316L foil irradiated by high intensity of proton beams. The SPT results and the energy to fracture are presented and the fracture modes were determined by scanning electron microscopy (SEM) observations and electron backscatter diffraction (EBSD) analysis. The irradiated samples were exposed to 3.6 MeV proton bombardment at 250 mu A and 290 mu A, for 42 and 5 h, respectively. The major damage, as was reflected by significant ductility and energy to fracture losses, was associated with the irradiated zones which experienced the highest temperature and protons flux. Based on the observed evidence of deformation twins and dense dislocation bands, as well as the EBSD analysis, it was revealed that the limited deformation in the irradiated samples is related mainly to radiation damage and probably a minor effect of hydrogen embrittlement phenomenon. The limited ductility was explained by the accumulation of radiation damage that most probably hinder dislocations mobility through crystallographic glide. Nevertheless, these alternative deformation mechanisms involve nucleation and propagation of dislocation slip bands (DSBs) and intra-grain fragmentation. The DSBs intersections were proposed as the source for stress localization, which initiates crack formation which was followed by crack propagation through slip bands. This cracking mechanism was exhibited by a unique "saw tooth" fracture mode. (C) 2020 Elsevier B.V. All rights reserved.

This paper demonstrates that that nuclear track detectors made of CR39 plates are suitable for detecting low energy protons and alpha-particles. The authors present evidence for a background line that arises from the interaction of neutrons with ${}^{17}$O inside the CR39 plate. This can be used for self-calibration of the CR39 detector

Knowledge of the neutron capture of copper and cobalt isotopes is important for the understanding of abundances of the heavier elements produced via the weak $s$ process. There are considerable discrepancies for the $^{63}\mathrm{Cu}(n,\ensuremath{\gamma})^{64}\mathrm{Cu}$ and $^{65}\mathrm{Cu}(n,\ensuremath{\gamma})^{66}\mathrm{Cu}$ cross-section values in the literature. New measurements of these cross sections were performed at the SARAF phase I facility using a high-power quasi-Maxwellian neutron source produced by irradiation of the liquid-lithium target (LiLiT) with an intense continuous-wave proton beam. The cross sections were measured by counting the activity of the irradiated targets. The measurement allowed us to evaluate the $^{63}\mathrm{Cu}(n,\ensuremath{\gamma})^{64}\mathrm{Cu}$, $^{65}\mathrm{Cu}(n,\ensuremath{\gamma})^{66}\mathrm{Cu}$, and $^{59}\mathrm{Co}(n,\ensuremath{\gamma})^{60}\mathrm{Co}$ Maxwellian averaged cross sections at 30 keV, obtaining values of $70.4\ifmmode\pm\else\textpm\fi{}1.{8}_{\mathrm{exp}}\ifmmode\pm\else\textpm\fi{}2.{4}_{\mathrm{syst}}$, $26.8\ifmmode\pm\else\textpm\fi{}1.{5}_{\mathrm{exp}}\ifmmode\pm\else\textpm\fi{}1.{0}_{\mathrm{syst}}$, and $38.1\ifmmode\pm\else\textpm\fi{}0.{9}_{\mathrm{exp}}\ifmmode\pm\else\textpm\fi{}0.{9}_{\mathrm{syst}}\phantom{\rule{0.16em}{0ex}}\mathrm{mb}$, respectively. The results are compared with previous measurements in the literature.

Neutrons play a dominant role in the stellar nucleosynthesis of heavy elements and the quest for accurate experimental determinations of neutron-induced reaction cross sections becomes more stringent with the refinement of nuclear and astrophysical models. We review here an experimental nuclear-astrophysics program using a high-intensity neutron source based on the 7Li(p, n)7Be reaction with a Liquid-Lithium Target (LiLiT) at the Soreq Applied Research Accelerator Facility (SARAF) Phase I. The quasi-Maxwellian neutron spectrum with effective thermal energy $ kT \approx 30$ keV, characteristic of the thick-target 7Li(p, n) yield at proton energy $ E_p \approx 1.92$ MeV close to its neutron threshold, is well suited for laboratory measurements of neutron capture reactions along the astrophysical s -process path. The high-intensity proton beam (in the mA range) of SARAF and the high power (few kW) dissipation of LiLiT result in the most intense source of neutrons available today at stellar-like energies. The principle, design and properties of the LiLiT device and recent measurements of Maxwellian Averaged Cross Sections (MACS) based on activation of targets of astrophysical interest are described. Decay counting or atom counting methods (accelerator mass spectrometry, atom-trap trace analysis) are used for the detection of short-lived or long-lived activation products, respectively. In a different realm of applications, the 7Li(p, n) reaction is a leading candidate as an accelerator-based neutron source for Boron Neutron Capture Therapy (BNCT). The high neutron yield achievable from a liquid-lithium target, its sustainability of operation under kW-power incident beams and the recent availability of small-size high-intensity accelerators are compatible with a hospital-based clinical facility. An effort towards the characterization and realization of a liquid-lithium target for BNCT is reviewed. Perspectives of pending and future developments towards SARAF Phase II, based on a 40MeV, 5mA CW proton/deuteron superconducting linear accelerator, are summarized.

Knowledge of the neutron capture of copper and cobalt isotopes is important for the understanding of abundances of the heavier elements produced via the weak s process. There are considerable discrepancies for the Cu-63(n, gamma)Cu-64 and Cu-65(n, gamma)Cu-66 cross-section values in the literature. New measurements of these cross sections were performed at the SARAF phase I facility using a high-power quasi-Maxwellian neutron source produced by irradiation of the liquid-lithium target (LiLiT) with an intense continuous-wave proton beam. The cross sections were measured by counting the activity of the irradiated targets. The measurement allowed us to evaluate the Cu-63(n, gamma)Cu-64, Cu-65(n, gamma)Cu-66, and Co-59(n, gamma)Co-60 Maxwellian averaged cross sections at 30 keV, obtaining values of 70.4 +/- 1.8(exp) +/- 2.4(syst), 26.8 +/- 1.5(exp) +/- 1.0(syst), and 38.1 +/- 0.9(exp) +/- 0.9(syst) mb, respectively. The results are compared with previous measurements in the literature.

Soreq Nuclear Research Center (SNRC) and CEA collaborate for the upgrade of the existing Soreq Applied Research Accelerator Facility (SARAF) accelerator up to 5mA Continuous Wave (CW) 40 MeV deuteron and proton beams (Phase 2). SNRC is upgrading the injector: the ion source, the low energy beam transport line and the 4-rods Radio Frequency Quadrupole (RFQ). CEA is in charge of the development and commissioning of the medium energy beam transport line and the superconducting linac. This paper presents the status of the SARAF linac development by CEA and the installation and testing of a new set of rods electrodes in the SARAF RFQ.

The mechanical properties and the fracture morphology of the inner surface of blisters formed in polycrystalline and single crystal tungsten under MeV proton irradiation, were studied. The tungsten samples were irradiated at Soreq Applied Research Accelerator Facility (SARAF) by 2.2 MeV protons, at various samples temperatures and proton doses. The morphology of the irradiated samples was observed by examining cross sections of blisters obtained by focused ion beam (FIB). The thickness of the blister cap was found to be in good agreement with the irradiating protons stopping range, regardless of sample structure, temperature or total dose. Increased curvature of the surfaces was observed with increased temperature for polycrystalline and single crystal blisters and was interpreted as increased ductility of the blister growth process. The ductility is more substantial in single crystal blisters, pointing to the role of grain boundaries in blisters growth mechanism. The cap of one blister was removed, exposing the inner fracture surface of a blister and supporting the validity of the cross sectional observations. The mechanical properties in the vicinity of a blister formed in a single crystal sample were characterized by nano-indentation. The hardness near the irradiated surface was found to increase both in the vicinity of the blister and beyond. This observation suggests that the elevation of the blister cap does not cause significant strain hardening. For the blister cap, the hardness was found to increase with increasing depth from the irradiated surface, correlating with increased irradiation damage. (C) 2019 Elsevier B.V. All rights reserved.

Single and polycrystalline tungsten samples were irradiated with 2.2 MeV protons at Soreq Applied Research Accelerator Facility (SARAF). Hydrogen blisters were obtained for both single crystal and polycrystalline samples, elucidating the role of grain boundaries in blister formation. The effect of temperature and flux on the critical formation dose for blisters and on their dimensions was studied. It was found that for single crystals, the critical formation dose is one order of magnitude higher than for polycrystalline tungsten at high temperature irradiation conditions. Upon reducing the irradiation temperature to ambient, the critical dose for formation of blisters in single crystals was reduced by a factor of three while in polycrystalline tungsten there was no significant change with temperature, thus indicating the role of grain boundaries in blister formation. Larger blisters were obtained in single crystals than in polycrystalline tungsten at ambient temperature conditions, identifying the grain boundaries as a preferential additional hydrogen trap. The height to area ratio of the blisters is found to be strongly temperature dependent and only weakly dependent on irradiation flux for both single and polycrystalline samples. (C) 2018 Elsevier B.V. All rights reserved.

The ^{36}Ar(n,γ)^{37}Ar (t_{1/2}=35  d) and ^{38}Ar(n,γ)^{39}Ar (269 yr) reactions were studied for the first time with a quasi-Maxwellian (kT∼47  keV) neutron flux for Maxwellian average cross section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ^{37}Ar/^{36}Ar and ^{39}Ar/^{38}Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ^{37}Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ^{36}Ar and ^{38}Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron-capture cross sections of ^{36,38}Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak s process. The new production cross sections have implications also for the use of ^{37}Ar and ^{39}Ar as environmental tracers in the atmosphere and hydrosphere.

SARAF (Soreq Applied Research Accelerator Facility) is based on a 5 mA, 40 MeV, proton/deuteron accelerator. Phase-I, operational since 2010, provides proton and deuteron beams up to 4 and 5 MeV, respectively, for basic and applied research activities. The high power Liquid-Lithium jet Target (LiLiT), with 1.912 MeV proton beam, provides high flux quasi-Maxwellian neutrons at kT similar to 30 keV (about 2 x 10(10) n/s/cm(2)/mA on the irradiated sample, about 1 cm from the target), enabling studies of s-process reactions relevant to nucleo-synthesis of the heavy elements in giant AGB stars. With higher energy proton beams and with deuterons, LiLiT can provide higher fluxes of high energy neutrons up to 20 MeV. The experimental program with SARAF phase-I will be enhanced shortly with a new target room complex which is under construction. Finally, SARAF phase-II, planned to start operation at similar to 2023, will enable full capabilities with proton/ deuteron beams at 5 mA and 40 MeV. Liquid lithium targets will then be used to produce neutron sources with intensities of 10(15) n/s, which after thermalization will provide thermal neutron (25 meV) fluxes of about 10(12) n/s/cm(2) at the entrance to neutron beam lines to diffraction and radiography stations.

The original SARAF 3.8 m long 4-rod Radio Frequency Quadrupole (RFQ) has been successful in acceleration of 4 mA ContinuousWave (CW) proton beam and pulsed deuteron beam to 1.5 MeV/u. However, conditions for running CW deuteron beam have not been achieved in the original design. A new 4-rod structure has been designed and implemented, with the goal of reducing the RF power required for CW deuteron operation while slightly compromising the RFQ exit energy to 1.27 MeV/u. The new 4-rod structure was manufactured, and installed in place of the old rod electrodes. Superior field homogeneity was achieved. The RFQ was successfully conditioned to the RF power 200 kW required for CW deuteron operation, with sufficient power margin. The commissioning with proton and deuteron beams showed that most of beam parameters are close to the designed specifications. The first operation with CW RF power of 5 mA deuteron beam was demonstrated. In addition, a 1.1 mA CW deuteron beam was transported through the superconducting module. The future scope of RFQ improvements is discussed.

The Soreq Applied Research Accelerator Facility (SARAF) is under construction in the Soreq Nuclear Research Center at Yavne, Israel. When completed at the beginning of the next decade, SARAF will be a user facility for basic and applied nuclear physics, based on a 40 MeV, 5 mA CW proton/deuteron superconducting linear accelerator. Phase I of SARAF (SARAF-I, 4 MeV, 2 mA CW protons, 5 MeV 1 mA CW deuterons) is already in operation, generating scientific results in several fields of interest. The main ongoing program at SARAF-I is the production of 30 keV neutrons and measurement of Maxwellian Averaged Cross Sections (MACS), important for the astrophysical s-process. The world leading Maxwellian epithermal neutron yield at SARAF-I (\(5 \times 10^{10}\) epithermal neutrons/s), generated by a novel Liquid-Lithium Target (LiLiT), enables improved precision of known MACSs, and new measurements of low-abundance and radioactive isotopes. Research plans for SARAF-II span several disciplines: precision studies of beyond-Standard-Model effects by trapping light exotic radioisotopes, such as 6He, 8Li and 18, 19, 23Ne, in unprecedented amounts (including meaningful studies already at SARAF-I); extended nuclear astrophysics research with higher energy neutrons, including generation and studies of exotic neutron-rich isotopes relevant to the rapid (r-) process; nuclear structure of exotic isotopes; high energy neutron cross sections for basic nuclear physics and material science research, including neutron induced radiation damage; neutron based imaging and therapy; and novel radiopharmaceuticals development and production. In this paper we present a technical overview of SARAF-I and II, including a description of the accelerator and its irradiation targets; a survey of existing research programs at SARAF-I; and the research potential at the completed facility (SARAF-II).

The mechanical properties characterization of thin foils to be used as target in high intensity accelerator requires non standards techniques. Previous studies, focused on foils after annealed, cold rolled and heat treatment after rolled, in addition to foils at different thickness, have been carried out to estimate the sensitivity of the small punch test (SPT) technique in foils. In this research we studied the degradation of the mechanical properties of foils due to irradiation damage by high intensity proton beams. For this new study, two samples of SS316L foils have 25 μm thickness were exposed to proton bombardment at 3.6 MeV, and approximately 300 μA of current for a period of 3 hours and 40 hours, separately. The SPT technique revealed that the un-irradiated specimens exhibited the largest load and deformation before failure, rather than the irradiated foils. The electron microscopy observations (SEM) revealed high cross slips and pseudo-cleavage density combined with multiple deformation twinning after irradiation to high energy. The mechanical behavior can be explained by the microstructure. The crack propagation path is in a zigzag fracture mode when multiple deformation twinning occurs close to the stretched zone of the foil and failure. Changes of the SPT measurements were found and the degradation from ductile to brittle crack mode is attributed to radiation damage effects.

The ^{36}Ar(n,γ)^{37}Ar (t_{1/2}=35 d) and ^{38}Ar(n,γ)^{39}Ar (269 yr) reactions were studied for the first time with a quasi-Maxwellian (kT∼47 keV) neutron flux for Maxwellian average cross section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ^{37}Ar/^{36}Ar and ^{39}Ar/^{38}Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ^{37}Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ^{36}Ar and ^{38}Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron-capture cross sections of ^{36,38}Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak s process. The new production cross sections have implications also for the use of ^{37}Ar and ^{39}Ar as environmental tracers in the atmosphere and hydrosphere.

The Soreq Applied Research Accelerator Facility (SARAF) is under construction at the Soreq Nuclear Research Center, Yavne, Israel. When completed at the beginning of the next decade, SARAF will be a user facility based on a 40 MeV, 5 mA CW proton/deuteron superconducting linear accelerator. Phase I of SARAF (4 MeV, 2 mA CW protons, 5 MeV 1 mA pulsed deuterons) is already in operation. By use of a novel liquid lithium jet target (LiLiT), we generated up to 5×10^10 epithermal neutrons/sec, mainly for nuclear astrophysics research of slow neutron capture processes (s-process). We present a survey of research programs and plans at the completed SARAF, which span several disciplines: Precision studies of beyond-Standard-Model effects by trapping light exotic isotopes, such as 6He, 8Li and Ne isotopes, in unprecedented amounts (including meaningful studies already at Phase I); extended nuclear astrophysics research with higher energy neutrons, including generation and studies of exotic neutron-rich isotopes relevant to the rapid (r-) process; high energy neutrons cross section measurements for basic nuclear physics and material science research, including neutron induced radiation damage; neutron based imaging and therapy; and novel radio-pharmaceuticals development and production.

Bismuth capture of neutrons is the termination point of the s-process cycle of nucleosynthesis in stellar environments. A new measurement is reported here for neutron activation of bismuth with an intense quasi-Maxwellian neutron source at kT similar to 30 keV. The measurement was performed at the SARAF phase I accelerator facility by bombarding a 1.5-mA proton beam on the liquid-lithium larget. The cross section of the Bi-209(n,gamma) capture reaction leading to the Bi-210 ground state was determined by combining beta measurements from the Bi-210g decay and a and. from the subsequent Po-210 decay, along with detailed Monte Carlo simulations of the Li-7(p,n) reaction kinematics and the activation experimental setup. Deduced Maxwellian averaged cross sections (MACS) for Bi-209(n,gamma)(210g) Bi at kT = 30 keV using the ENDF, JEFF, and JENDL databases for the corrections and extrapolations yielded a value of 1.84 +/- 0.09 mb. A comparison is made with previous measurements, including time-of-flight (TOF) measurements of the total bismuth capture cross section. Plans for obtaining the MACS for capture to the bismuth-210 metastable state in the reaction Bi-209(n,gamma)Bi-210m are discussed, along with estimates based on our results in comparison with TOF measurements. The bismuth neutron activation cross section is also of importance for design of GenIV reactor coolant and subcritical accelerator driven systems, especially in light of the 3 million year half-life of the Bi-210m isomer.