Transmutation Products Research Articles

Quantitative analysis of transmutation nuclides in pure tungsten irradiated with high-energy protons and spallation neutrons at 6.4 and 28 dpa

Tungsten is a key material for applications of spallation targets and fusion reactors. Irradiation-induced transmutation products can significantly affect the mechanical and thermal properties of tungsten. However, detailed quantitative analysis of transmutation elements of irradiated tungsten has not been reported and is therefore in high demand, especially in the cases of spallation targets where a large amounts of transmutation elements are produced. In this work, we analyzed the transmutation products in pure tungsten samples irradiated in a target of Swiss Spallation Neutron Source (SINQ) at doses of 6.4 and 28 dpa, the latter being the highest dose ever achieved in spallation targets. Quantitative measurements of 40 nuclides ranging from 144Sm to 188Os were performed using the atom probe tomography (APT) technique. The measured concentrations of transmutation elements are in good agreement with those of neutronic calculations. The APT analysis also revealed clusters of transmutation elements. Due to low irradiation temperature (<500 °C) and low concentration of transmutation elements, the clusters are 1–2 nm in diameter.

Design of a Facility for Simultaneous Irradiation with Two Ion Beams based on the HIPR Accelerator for Simulations Neutron Influence

Ion accelerator facility is a powerful tool to simulate neutron irradiation effects in reactor materials. Defects in the crystal lattice arise and the accumulation of transmutation products (helium and hydrogen) occurs in the structure of the material under the action of neutrons in the structural materials of nuclear installations. At Kurchatov Complex for Theoretical and Experimental Physics the heavy ion accelerator HIPr (heavy ion prototype) is used to simulate radiation damage in steels and alloys using a 5.6 MeV Fe2+ ion beam. The second beam line is designed at the HIPr facility to simultaneously implant helium (or hydrogen) into the region of defects. The second beam line provides a beam of helium ions with energy up to 300 keV. The report presents a description of second beam line design and a status of construction the second beam line.

First-principles study of the interaction of nitrogen with transition metal solutes in tungsten

The choice of tungsten (W) as the plasma-facing material requires seeding impurities into the edge plasma for radiative cooling, and gaseous nitrogen (N) is one of the most likely impurities to be used for this purpose. In this work, first-principles calculations related to the interactions between N and transition metal (TM) solutes were performed. The interactions between the TM solutes and N are predominantly attractive and very localized. Specifically, the 3d solutes exhibit a stronger attraction to N than the 4d and 5d solutes. Consequently, most TM solutes can alter the N distribution, promoting the N aggregation within their neighboring shells, and impeding the N diffusion. Moreover, this effect is more conspicuous in the 3d solutes related to the 4d and 5d solutes. In the Sol-Vac-N complexes, the vacancy assumes a predominant role. Most TM solutes diminish the capability of vacancies to capture N. The exception arises in Ti, V, Zr, Nb, Hf, and Ta, where these solutes enhance the vacancies' ability to capture N. Further investigation revealed that, for Ti, V, Zr, Hf, Ta, and Os, the capacity of Sol-N pairs to adsorb the additional N and solute atoms is significant. As a result, it can be speculated that the Sol-N pairs for these solutes might continue to adsorb additional N and solute atoms, eventually evolving into nitrides. However, for the primary transmutation product Re, the capacity of Sol-N pairs to adsorb additional Re atoms is negligible. Therefore, it is inferred that the formation of Re nitride is rather unlikely during W's service life as plasma-facing materials.

An Investigation of the Effect of Wide Range Gamma Radiation from Nanoindentation of the SAC305 Solder Alloy

This study utilises nanoindentation testing to investigate the impact of varying gamma radiation doses on the micromechanical properties of Sn-Ag-Cu (SAC) alloy. Specifically, the focus is on evaluating changes in hardness, reduced modulus, and creep behaviour. The stencil-printed method and reflow soldering process were employed to apply the SAC solder paste and create solder joints on the surface of the printed circuit board. The soldered samples underwent exposure to gamma radiation at different doses, specifically 5, 50, 500, 5000, and 50000 Gy. The solder received in its original state was used as the control sample. Subsequently, the samples were subjected to a nanoindentation test in order to ascertain the correlation between load and depth, depth and dwell time, when exposed to radiation. The load-depth curve results indicate that there is a transition in the behaviour of solder joint materials from elastic to plastic deformation as the radiation dose increases. A finding has been made indicating that exposure to gamma radiation has the potential to induce a transition in the behaviour of SAC from an elastic state to a plastic state. The exposure to radiation doses has been found to induce changes in the atomic arrangement and structural properties of materials, leading to an increase in their hardness values. Nevertheless, it was observed that with increasing radiation doses up to 500 Gy, there was a noticeable decrease in the hardness value, which can be attributed to the occurrence of softening behaviour. Exposure to a high dose exceeding 5000 Gy leads to atomic displacement and transmutation products, subsequently resulting in plastic deformation. The stress exponent value signifies the occurrence of the deformation mechanism in solder material when exposed to gamma radiation. The study revealed that there was a shift in the deformation mechanism from grain boundary sliding to dislocation climb as the radiation dose increased from low to high levels.

Quantum field stabilization of the di-neutron enabling low energy deuterium fusion

The free space di-proton (1p1p) and di-neutron (onon) are not bound and are non-existent. However, the latter can and does exist as a 1So entity in the confines of a quantum field of a nearby nucleus. Igor Kadenko et al. have shown that when a single low energy neutron approaches within femtometers of a Tb or Au nucleus, on actually sequesters a neutron from the nuclear skin to form the di-neutron (on↓on↑) residing in the quantum field (QF) of the heavy nucleus. This product can be expressed as [Φn1⊗Φn2]⊗ΦNuc (a three-body problem), leaving the di-neutron free to fuse with the nearby nucleus leading to useful transmutation products. During Fleischmann-Pons heat effect (FPHE) electrolysis experiments, the di-neutron is also formed via deuteron-electron capture; Φe-⊗ΦD+ (for a near relativistic electron) suggests a positive scattering length (electron penetration below the Bohr radius) and di-neutron formation. Since the uncharged onon can freely pass through the Coulomb barrier of the deuteron (2D+), the resulting hydrogen-4 can undergo electro-weak decay to 4He. The di-neutron provides a mechanism for the FPHE observed during the electrolysis of palladium deuteride in D2O, which has now been confirmed and reproduced by M. R. Staker.

Evolution of Irradiation Defects in W and W-Re Systems: A Density Functional Theory and Rate Theory Study

In a fusion environment, tungsten, a plasma-facing material in a reactor, is subject to the irradiation of high-energy neutrons, generating a large amount of displacement damage and transmutation products (such as rhenium, Re). We studied the evolution of defects under irradiation in W and W-Re systems using the density functional theory (DFT) and rate theory (RT) method. The results indicate that the evolution of irradiation defects is mainly affected by the irradiation dose, dose rate, and temperature. During irradiation, loops form first in W, followed by the generation of voids, which are due to the different migration energies of point defects. Higher dose rates result in a higher density and larger size of defects in tungsten. Higher temperatures cause a decrease in void density and an increase in size. The results obtained at 600 °C were in good agreement with the reported TEM data. In W-Re alloys, it is indicated that the formation of loops is delayed because Re suppresses the nucleation of loops. The dynamic introduction of Re in W stabilizes the growth of defects compared to W-Re alloys, suggesting that transmuting elements have less detrimental effects on irradiation than alloying. As defect densities and sizes were quantified under different irradiation conditions, the results provide data for the multi-scale simulation of the radiation damage and thermal/mechanical properties in plasma-facing materials under fusion conditions.

Investigations of microstructure and tensile properties of neutron irradiated 6061 aluminum alloys

Effects of neutron irradiation on the microstructure and mechanical properties of CMRR (China Mianyang Research Reactor) structural material pure aluminum and 6061 alloy were studied by scanning/transmission electron microscopy (S/TEM) and tensile tests. The fast neutron (E > 0.1 MeV) fluences of 1.09–2.89 × 1022 n•cm−2 produced damage doses of 1.6–4.2 displacements per atom (dpa). Voids and faulted 1/3<111> dislocation loops were observed in both pure aluminum and 6061 alloy. In particular, voids tended to preferentially aggregate on coarse Cu-rich and fine Mg2Si precipitates which contributes to the higher irradiation tolerance in terms of void formation for 6061 alloy, suggesting that the uniformly distributed precipitates can act as trapping sites for defect clusters during irradiation and thus promote recombination. The size and density of Mg2Si precipitates showed a slight increase and Cu-rich precipitates emerged in 6061 alloy after neutron irradiation. Moreover, radiation-induced segregation was also detected along the grain boundaries. After tensile testing, the pure aluminum showed a lower yield strength and larger uniform elongation than 6061 alloy, where a moderate uniform elongation was still reserved after irradiation to 4.2dpa. The severely reduced ductility in 6061 alloy is supposed to be caused by the transmutation product silicon which contributes to the increase of dispersed multiple precipitates after irradiation. Our results indicate that precipitates especially Mg2Si play a decisive role in void suppression, but are not suitable in diminishing the radiation hardening.

Clustering fusion algorithm for selection of historical beam steady-state transmission data in CAFe facility

Accelerator-driven systems (ADS) are promising technologies for nuclear waste transmutation and energy production. The China ADS Front-end Superconducting Demo Linac (CAFe) is a prototype of the China Initiative Accelerator Driven System (CiADS), which aims to verify the feasibility of key technologies of CiADS. In this article, a novel method for historical data screening of the beam transport in the medium energy beam transport (MEBT) section of CAFe is presented. A clustering fusion algorithm based on unsupervised learning and beam transmission characteristics is designed to extract a large number of samples with the beam in steady-state transmission from historical beam data. A deep neural network model was constructed to fit the beam transport characteristics and verify the reliability of the screened data samples. The method can improve the efficiency and accuracy of data analysis and provide valuable insights for the optimization and control of beam transport in CAFe.

Consequences of Neutron Energy Spectrum on Radiation Damage, Gas Production, and Transmutations in Fusion Materials

The inclusion of test modules in the U.S. Fusion Prototypic Neutron Source (FPNS) offers the opportunity to test a wide variety of materials in a representative radiation environment of the fusion Pilot Plant, DEMO, and power plant. The testing may include various generations of structural materials for conventional and advanced blanket and divertor concepts. Since all structural materials derived from the fission industry are inadequate for fusion applications (due to the more damaging effects of the 14-MeV fusion neutrons), radiation-resistant reduced-activation structural materials (reduced-activation ferritic-martensitic steel, vanadium alloy, W alloy, and SiC/SiC composites) were specifically developed for fusion and could be tested in the FPNS to qualify for the highly irradiated fusion components surrounding the plasma. The large atomic displacement and the helium and hydrogen generations by fusion neutrons are unique to fusion materials. The most important attribute for the FPNS would be the typical fusion-relevant He/displacements per atom (dpa) ratio of ~10 for steel in particular. By comparison, irradiation in the fission spectrum of the High Flux Irradiation Facility (HFIR) would underestimate the dpa and provide a very low He/dpa ratio of ~0.3 for steel, which is irrelevant to fusion. This paper reviews the neutron irradiation impacts and presents a few examples of dpa and transmutation products for steel, W, and SiC based on modeling in several fusion design studies. The operating conditions of advanced U.S. fusion power plants were considered along with the credible lifetime goal of 200 dpa and 20 MW·yr/m2 fluence that could be achieved with directed research and development programs coupled with the construction of the FPNS 14-MeV neutron facility.

Scoping Studies for a Lead-Lithium-Cooled, Minor-Actinide-Burning, Fission-Fusion Hybrid Reactor Design

A feasibility study of a subcritical fission-fusion hybrid reactor using lead-lithium eutectic as a coolant and minor actinides (MAs) as fuel is presented. Such a reactor could support the fission community by transmuting MAs and the fusion community by breeding tritium. The feasibility of such a reactor for the burnup of MAs is assessed in terms of burnup performance, tritium breeding, and safety characteristics. Tandem mirrors are a promising neutron source technology, and a deuterium-tritium tandem mirror is considered here for the neutron source with power Psource = 1.13 MW assumed for scoping purposes. Subcritical reactivities from keff = 0.9800 to keff = 0.9950 were considered, representing the initial reference for subcritical reactivity and the assessed upper limit, respectively. Stability analyses indicated the reactivity would be stable under perturbations of fuel, coolant, and inlet temperatures, with a positive reactivity insertion expected during reactor shutdown. This range corresponded to nuclear heating values of 150 to 650 MW and mass burn rates of 53 to 216 kg/year. The upper mass burn rate limit would require 1110 reactor years with a capacity factor of 0.9 to fission the global supply of MAs and could offset the annual U.S. MA production with eight reactors. Tritium breeding was assessed for keff = 0.9800 and 3.795% 6Li enrichment in the coolant, and a tritium breeding ratio of 1.602 0.017 was tallied, suggesting the reactor could, without elevated 6Li enrichment, produce tritium to both sustain operation and supply tritium for other fusion devices. Time-series modeling of fuel burnup was conducted for a four-batch loading scheme and three different fuel residence times at keff = 0.9800, which showed system performance would drop with burnup, and that the rate of this drop was lower for longer fuel residence times, motivating a means of reactivity control. Last, changes in fuel composition with burnup were assessed for relative concentrations of MAs, transmutation products, and fission products. The breeding of plutonium in the blanket was calculated and found to be of minimal proliferation concern.

Ab-initio investigation of mechanical and fracture-related properties of W-Re σ and χ precipitates

Tungsten (W) is a leading candidate for plasma-facing materials in fusion reactors. Recently, experiments have shown that during neutron irradiation, W and its transmutation products, mainly rhenium (Re), will form precipitates of the σ and χ types. This study identifies close-packed planes of the σ- and χ-phases in the W-Re system and uses ab-initio methods to identify mechanical properties such as elastic constants, generalized stacking fault energies (GSFE), and fracture toughness associated with brittle and ductile mechanisms. By utilizing a sublattice model we demonstrate how these properties depend on the Re content. For Re concentrations in the range where the σ- and χ-phases are stable, we find a weak dependency on the Re content, meaning that the elemental composition has little influence on the mechanical and fracture-related properties.

Simulation study on uniaxial tensile mechanical and thermal properties of rhenium tungsten alloys

As an important potential first wall material in fusion reactor, tungsten will be irradiated by 14.1 MeV fusion neutron and then transmutated to rhenium, osmium, and tantalum during service. Due to rhenium is the main of transmutation products, which will affect the mechanical and thermal properties of the tungsten matrix. Based on this, in this work, the Young's Modulus and thermal properties of W-Re alloys with different rhenium contents were calculated by using the first principle calculations. Then, the uniaxial tensile processes in [100], [110], [111] and [211] directions were simulated by molecular dynamic simulation method. The results show that the tensile strength of W-Re alloy decreases gradually with the increase of rhenium content. With the increase of the rhenium content, the heat capacity of the material will decrease, and the thermal expansion coefficient increases.

Solubility of Bi in Li–Pb Eutectic Alloy Between 508 and 623 K

Liquid lithium–lead (Li–Pb) eutectic alloy is one of the candidate liquid tritium breeding materials of fusion blanket and it contains bismuth (Bi) as an initial impurity or transmutation product from lead. The saturated solubility of Bi, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> (wt.ppm), in Li–Pb was measured in the temperature range from 508 to 623 K. The measured results were plotted on the graph with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> (wt.ppm) versus 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> . From these plots, a positive temperature dependence, where the solubility decreases as the temperature is lowered, is confirmed. The equation of the solubility of Bi in Li–Pb was obtained, too. In addition, the dissolution enthalpy of Bi in Li–Pb, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta H_{\mathrm {sol}}$ </tex-math></inline-formula> , was quantified from this equation. The precipitation morphology of Bi in Li–Pb was also investigated. X-ray diffraction was used to analyze the precipitates collected from the surface of the liquid phase. As a result, the peak pattern of Li3Bi was found from the precipitate. Moreover, the amount of polonium produced when the cold trap is introduced to a Li–Pb loop of a fusion reactor was predicted from the solubility obtained in this study.

Triple ion beam irradiation of glass-ceramic materials for nuclear fusion technology

The analysis of the radiation damage associated with energetic neutrons is a key factor for the application of glass-ceramics as joining materials in nuclear fusion plants. Triple ion beam irradiation is, currently, the only way to emulate the displacement damage and the effects of transmutation products induced by high energy neutrons at elevated doses by producing a high level of displacements per atom (dpa) and implanting high concentrations of low solubility gases on the glass-ceramic microstructure. In this paper, we investigate calcia-alumina glass-ceramics in which the damage expected in the working conditions of a nuclear fusion plant were reproduced by simultaneous irradiation with Si, He and H ions at different temperatures. TEM analysis of irradiated calcia-alumina samples shows amorphization (due to the Si beam) and partial recrystallization of the irradiated portion and the formation of He bubbles/cavities. The irradiation temperature plays a prominent role in determining the induced damage in terms of recrystallization, phase mixing and bubble size, density and aggregation.

Helium interaction with solutes and impurities in neutron-irradiated nanostructured ferritic alloys: A first principles study

Density functional theory (DFT) calculations are performed to explore the binding between He and alloying solutes, impurities, and transmutation products expected in neutron irradiated nanostructured ferritic alloys (NFAs), here 14YWT is taken as an example. Elements that exhibit significant binding (attraction) with an interstitial He are: Y (binding energy = 0.46 eV), Mg (0.32), O (0.33), Ti (0.16), and C (0.15). Those that provide significant binding to a substitutional He are: O (1.44), Y (1.24), N (0.73), H (0.56), Mg (0.52), Ti (0.34), Si (0.34), C (0.33), Al (0.32), Ni (0.26), Ta (0.23), and Mn (0.16). The presence of these elements in Fe matrix could reduce the transport of He towards oxide particles, dislocations, and internal boundaries, and could promote He bubble nucleation in the matrix. For convenience, we compile existing binding energy data of He with Hen and HenV (He-vacancy) clusters. Dissociation pathway analysis reveals that, in general, the most likely dissociation of a HenV cluster is by a sequential emission of individual He atoms. Furthermore, larger bubbles are more prone to dissociation than smaller ones. In addition, we estimate the binding energy (segregation energy) of He in bulk Y2Ti2O7 (YTO) single crystal, YTO/Fe interface, and YTO particle embedded in Fe, with respect to interstitial He in Fe, from existing formation energies of He in these structures. We also compile available data of He binding with Fe self-interstitial atom (SIA), SIA clusters, and edge and screw dislocations. Note that given the absence of DFT data, the binding with SIA clusters and dislocations are gathered from simulations with empirical potentials. The data presented in this paper is important to inform multiscale simulations of He bubble accumulation.

Interaction of transmutation products with precipitates, dislocations and grain boundaries in neutron irradiated W

Tungsten is the primary candidate materials for the high neutron flux, high temperature components of a future demonstration fusion reactor. Despite this, there is a lack of data on W under fusion relevant neutron doses and irradiation temperatures. In this study, single crystal and polycrystalline W samples irradiated at the High Flux Reactor (HFR) at 900 ∘C were characterised using Atom Probe Tomography (APT) and Scanning Transmission Electron Microscopy (STEM). Bulk chemical and isotopic concentration predictions were validated by analysing the mass spectrum from APT experiments. A post irradiation composition of W-1.26 ± 0.15 at.%Re - 0.08 ± 0.02 at.%Os - 0.01 ± 0.01 at.%Ta was measured in the single crystal sample, whereas W-1.09 ± 0.07 at.%Re - 0.08 ± 0.02 at.%Os - 0.01 ± 0.01 at.%Ta was measured for the polycrystalline. APT and STEM showed that a high number density of Re and Os rich precipitates had formed under neutron irradiation. These typically consisted of a core rich in Re and Os, surrounded by a less dense Re rich cloud. Multiple analysis methods were applied to investigate the composition of these clusters. APT showed that the centres of some of the precipitates had a rod shaped core which were rich in both Re and Os. Line profile analysis suggests that in the centre of the precipitates, the threshold composition for σ phase formation may have been reached, as has been observed in higher transmutation rate experiments. In addition, dislocations, sub grain boundaries and dislocation loops were all shown to be decorated with both Re and Os, in agreement with predictions from DFT simulations.

Neutron activation and radiation damage assessment for W-Ni-Fe tungsten heavy alloys with variable Ni content

A challenging issue for the magnetic fusion concept of generating nuclear power is the performance of plasma-facing components, particularly in the divertor within the fusion power plant. Tungsten alloys, such as W-TiC, W-La2O3, etc., are the prime candidate structural materials for advanced He-cooled divertors in next-step devices beyond ITER. In recent years, W-Ni-Fe heavy alloys (WHAs) have emerged as more promising alternatives than the above-mentioned alloys. WHAs exhibit superior fracture toughness and better fabricability. However, Ni raises concerns because it may generate an unsafe level of radioactive waste (radwaste). Given the significant promise of WHAs, neutron activation assessment is critically needed, particularly to determine the limit of Ni that can be employed. This is the main purpose of this study. The assessment is provided for disposal option and for recycling alternative of divertors made of WHAs. Additional calculations are performed to obtain the neutron flux and spectrum, transmutation products, and He/H gas production data for a typical divertor design. These additional data are generated to inform future multiscale simulations of microstructure evolution and radiation damage accumulation in WHAs. Furthermore, estimation of atomic displacement damage dose is presented. In the future, the estimated dose should be compared with the more accurate data from the multiscale simulations and revised accordingly.

Development of a solute and defect concentration dependant Ising model for the study of transmutation induced segregation in neutron irradiated W–(Re, Os) systems

In this study, radiation-induced precipitation of transmutation products is addressed via the development of a new solute and vacancy concentration dependant Ising model for the W–Re–Os system. This new model includes interactions between both Os and Re atoms with vacancies, thus facilitating more representative simulations of transmutation in fusion reactor components. Local solute concentration dependencies are introduced for the W–Re, W–Os and Re–Os pair interactions. The model correctly accounts for the repulsion between small clusters of vacancies and the attraction between larger clusters/voids, via the introduction of local vacancy concentration dependant interaction coefficients between pairs of atoms and vacancies. To parameterise the pair interactions between atoms and/or vacancies, the enthalpy of mixing, ΔH mix, for various configurations and solute/defect concentrations, was calculated using density functional theory, within 6 binary systems: W–Re, W–Os, Re–Os, W–vacancy, Re–vacancy and Os–vacancy. The new energy model was implemented into the SPPARKS Monte Carlo code, and successfully used to predict the formation of voids decorated with Re and Os solute atoms. Analysis suggests that there is a strong thermodynamic tendency for Os to bind to these voids with a comparatively weaker binding from Re atoms. The binding energies of various solute/vacancy clusters were calculated and showed that Re and Os solute atoms tend to stabilise small clusters of vacancies, increasing the attractive binding energy between the constituents.

Performance indices optimization of l ong‐lived fission products transmutation in fast reactors

Performance indices optimization of l <scp>ong‐lived</scp> fission products transmutation in fast reactors

Yield of long-lived fission product transmutation using proton-, deuteron-, and alpha particle-induced spallation

Yield of long-lived fission product transmutation using proton-, deuteron-, and alpha particle-induced spallation