401 Search Results

The value of the recovered uranium (RU) from high assay low-enriched uranium (HALEU) used nuclear fuels was evaluated. Three utilizations of the recovered uranium were considered in this study, which include the cases that RU is used as a fissile material of nuclear fuel, RU is reused in the original advanced reactor after reenrichment, and RU is reused in conventional light water reactors after down-blending. In this study, the RU values were identified by comparing the cost of making a unit mass of fuel with RU versus the fuel cost with the equivalent fresh enriched uranium (EU). A series of bounding analyses for calculating the fuel costs were conducted using several selected reactor types, which include microreactors, advanced thermal reactors, and fast reactors having a burnup of 2 – 165 GWd/t (with residual U-235 content in discharged fuels of 0.8 - 19.6%). This study concludes that RU having a residual U-235 content higher than ~7% would cost less than the fresh EU. The affordability increases as the residual U-235 content in RU increases. For instance, the fuel cost with RU having the residual U-235 content of 19.6% is about 85% cheaper than the fuel cost with the equivalent fresh EU. This study observed that reusing RU after reenrichment in the original microreactor is impractical because the U-235 content in the re-enriched RU fuel would need to be higher than the limit for low-enriched uranium (<20%) to provide the same burnup performance due to parasitic absorption from U-236. It is noted that this study focused on the recovery of uranium only, and the value of other fissile materials (such as Pu) in the used nuclear fuel was not considered even though those are bred significantly in fast reactors. In addition, the impacts of uncertainties in the cost data and the value of RU of TRISO fuels were not evaluated in this study due to the limited information on the cost data uncertainties and the separation cost from TRISO fuels.

The Systems Analysis and Integration campaign assessed the pros and cons of high-assay low-enriched uranium (HALEU) utilization in advanced reactors and associated fuel cycles. The assessment was done for three example fuel cycles at equilibrium states: once-through, limited recycle, and continuous recycle (CR) starting with HALEU. Front- and back-end fuel cycle parameters and the Levelized Cost of Fuel (LCF), which is the Levelized Cost of Electricity excluding reactor cost, of the three example fuel cycles were calculated using a single Analysis Example Reactor. The pros and cons of HALEU utilization were assessed by normalizing the fuel cycle parameters and LCF to a unit of electricity generation (GWe-year) and comparing them with a Basis of Comparison. In this study, a sodium-cooled reactor with sodium-bonded metallic fuel having a burnup of ~100 GWd/t was used as the Analysis Example Reactor because its technology readiness level is high, and the burnup and fuel enrichment are in the middle of those ranges of advanced reactor concepts that are under development. The current once-through Light Water Reactors (OT-LWRs) with <5% low-enriched uranium and 50 GWd/t burnup were used as the Basis of Comparison. In addition, a series of sensitivity analyses was conducted by varying burnup, enrichment, fuel forms, and reactor types to capture the design variations in two once-through Advanced Reactor Demonstration Program (ARDP) reactors, Natrium with sodium-free metallic fuel having a burnup of ~150 GW/t and Xe-100 with Tristructural-Isotropic (TRISO) pebble fuel having a burnup of ~168 GWd/t.

Here, we report the measurement of K^*0 meson at midrapidity (|y|< 1.0) in Au+Au collisions at $$\sqrt{s_{NN}}$$ = 7.7, 11.5, 14.5, 19.6, 27 and 39 GeV collected by the STAR experiment during the RHIC beam energy scan (BES) program. The transverse momentum spectra, yield, and average transverse momentum of K^*0 are presented as functions of collision centrality and beam energy. The K^*0/K yield ratios are presented for different collision centrality intervals and beam energies. The K^*0/K ratio in heavy-ion collisions are observed to be smaller than that in small system collisions (e+e and p+p). The K^*0/K ratio follows a similar centrality dependence to that observed in previous RHIC and LHC measurements. The data favor the scenario of the dominance of hadronic re-scattering over regeneration for K^*0 production in the hadronic phase of the medium.

Azimuthal anisotropy of produced particles is one of the most important observables used to access the collective properties of the expanding medium created in relativistic heavy-ion collisions. Here, in this paper, we present second (v₂) and third (v₃) order azimuthal anisotropies of $$K_{S}^{0}$$, Φ, Λ, Ξ, and Ω at midrapidity (|y| < 1) in Au+Au collisions at $$\sqrt{s_{NN}}$$= 54.4 GeV measured by the STAR detector. The v₂ and v₃ are measured as a function of transverse momentum and centrality. Their energy dependence is also studied. v₃ is found to be more sensitive to the change in the center-of-mass energy than v₂. Scaling by constituent quark number is found to hold for v₂ within 10%. This observation could be evidence for the development of partonic collectivity in 54.4 GeV Au+Au collisions. Differences in v₂ and v₃ between baryons and antibaryons are presented, and ratios of v₃/v$$^{3/2}_{2}$$ are studied and motivated by hydrodynamical calculations. The ratio of v₂ of Φ mesons to that of antiprotons [v₂(Φ)/v₂($$\overline{p}$$)] shows centrality dependence at low transverse momentum, presumably resulting from the larger effects from hadronic interactions on antiproton v₂.

Here, we report a measurement of cumulants and correlation functions of event-by-event proton multiplicity distributions from fixed-target Au+Au collisions at $$\sqrt{s_\text{NN}}$$ = 3 GeV measured by the STAR experiment. Protons are identified within the rapidity (y) and transverse momentum ($$p_T$$) region –0:9 < $$\textit{y}$$ < 0 and 0:4 < pT < 2:0 GeV/c in the center-of-mass frame. A systematic analysis of the proton cumulants and correlation functions up to sixth-order as well as the corresponding ratios as a function of the collision centrality, $$p_T$$, and $$\textit{y}$$ are presented. The effect of pileup and initial volume fluctuations on these observables and the respective corrections are discussed in detail. The results are compared to calculations from the hadronic transport UrQMD model as well as a hydrodynamic model. In the most central 5% collisions, the value of proton cumulant ratio $$C_4 = C_2$$ is negative, drastically different from the values observed in Au+Au collisions at higher energies. Compared to model calculations including Lattice QCD, a hadronic transport model, and a hydrodynamic model, the strong suppression in the ratio of $$C_4/C_2$$ at 3 GeV Au+Au collisions indicates an energy regime dominated by hadronic interactions.

We present the first measurements of transverse momentum spectra of $$π^±, K^±, p(\overline{p})$$ at midrapidity ($|y|$ < 0.1) in $$\cup + \cup$$ collisions at $$\sqrt{s_{NN}} = 193$$ GeV with the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The centrality dependence of particle yields, average transverse momenta, particle ratios and kinetic freezeout parameters are discussed. The results are compared with the published results from Au+Au collisions at $$\sqrt{s_{NN}} = 200$$ GeV in STAR. The results are also compared to those from A Multi Phase Transport (AMPT) model.

Despite decades of progress since Yukawa first developed a description of the force between nucleons in terms of meson exchange, a full understanding of the strong interaction remains a major challenge in modern science. One remaining difficulty arises from the non-perturbative nature of the strong force, which leads to the phenomenon of quark confinement at distances on the order of the size of the proton. Here we show that in relativistic heavy-ion collisions, where quarks and gluons are set free over an extended volume, two species of produced vector (spin-1) mesons, namely φ and K^*0 , emerge with a surprising pattern of global spin alignment. In particular, the global spin alignment for φ is unexpectedly large, while that for K^*0 is consistent with zero. The observed spin-alignment pattern and magnitude for the φ cannot be explained by conventional mechanisms, while a model with a connection to strong force fields, i.e. an effective proxy description within the Standard Model and Quantum Chromodynamics, accommodates the current data. This connection, if fully established, will open a potential new avenue for studying the behaviour of strong force fields.

AbstractPartons traversing the strongly interacting medium produced in heavy-ion collisions are expected to lose energy depending on their color charge and mass. We measure the nuclear modification factors for charm- and bottom-decay electrons, defined as the ratio of yields, divided by the number of binary nucleon–nucleon collisions, in $$$$\sqrt{s_{\textrm{NN}}}=200$$$$ s NN = 200 GeV Au+Au collisions to p+p collisions ($$$$R_{\textrm{AA}}$$$$ R AA ), or in central to peripheral Au+Au collisions ($$$$R_{\textrm{CP}}$$$$ R CP ). We find the bottom-decay electron $$$$R_{\textrm{AA}}$$$$ R AA and $$$$R_{\textrm{CP}}$$$$ R CP to be significantly higher than those of charm-decay electrons. Model calculations including mass-dependent parton energy loss in a strongly coupled medium are consistent with the measured data. These observations provide evidence of mass ordering of charm and bottom quark energy loss when traversing through the strongly coupled medium created in heavy-ion collisions.

Here, elliptic flow measurements from two-, four- and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at $$\sqrt{s_{NN}}$$ = 193 GeV, Cu+Au at $$\sqrt{s_{NN}}$$ = 200 GeV and Au+Au spanning the range $$\sqrt{s_{NN}}$$ = 11.5 - 200 GeV. The measurements show a strong dependence of the flow fluctuations on collision centrality, a modest dependence on system size, and very little if any, dependence on particle species and beam energy. The results, when compared to similar LHC measurements, viscous hydrodynamic calculations, and Glauber model eccentricities, indicate that initial-state-driven fluctuations predominate the flow fluctuations generated in the collisions studied.

The STAR Collaboration reports measurements of the transverse single-spin asymmetries, A_N, for inclusive jets and identified ‘hadrons within jets’ production at midrapidity from transversely polarized pp collisions at $$\sqrt{s}$$ = 200 GeV, based on data recorded in 2012 and 2015. The inclusive jet asymmetry measurements include A_N for inclusive jets and A_N for jets containing a charged pion carrying a momentum fraction z > 0.3 of the jet momentum. The identified hadron within jet asymmetry measurements include the Collins effect for charged pions, kaons and protons, and the Collins-like effect for charged pions. The measured asymmetries are determined for several distinct kinematic regions, characterized by the jet transverse momentum p_T and pseudorapidity η, as well as the hadron momentum fraction z and momentum transverse to the jet axis j_T. These results probe higher momentum scales (Q² up to ~ 900 GeV²) than current, semi-inclusive deep-inelastic scattering measurements, and they provide new constraints on quark transversity in the proton and enable tests of evolution, universality and factorization breaking in the transverse-momentum-dependent formalism.