Vol.32,

Based on the Hugenholtz-Van Hove theorem, six basic quantities of the EoS in isospin asymmetric nuclear matter are expressed in terms of the nucleon kinetic energy t(k), the isospin symmetric and asymmetric parts of the single-nucleon potentials U₀(ρ,k) and U_sym,i(ρ,k). The six basic quantities include the quadratic symmetry energy E_sym,2(ρ), the quartic symmetry energy E_sym,4(ρ), their corresponding density slopes L₂(ρ) and L₄(ρ), and the incompressibility coefficients K₂(ρ) and K₄(ρ). By using four types of well-known effective nucleon-nucleon interaction models, namely the BGBD, MDI, Skyrme, and Gogny forces, the density- and isospin-dependent properties of these basic quantities are systematically calculated and their values at the saturation density ρ₀ are explicitly given. The contributions to these quantities from t(k), U₀(ρ,k), and U_sym,i(ρ,k) are also analyzed at the normal nuclear density ρ₀. It is clearly shown that the first-order asymmetric term U_sym,1(ρ,k) (also known as the symmetry potential in the Lane potential) plays a vital role in determining the density dependence of the quadratic symmetry energy E_sym,2(ρ). It is also shown that the contributions from the high-order asymmetric parts of the single-nucleon potentials (U_sym,i(ρ,k) with i>1) cannot be neglected in the calculations of the other five basic quantities. Moreover, by analyzing the properties of asymmetric nuclear matter at the exact saturation density ρ_sat(δ), the corresponding quadratic incompressibility coefficient is found to have a simple empirical relation K_sat,2=K₂(ρ₀)-4.14 L₂(ρ₀).

496

The utilization of neutrons markedly affects the medical isotope yield of a subcritical system driven by an external D-T neutron source. The general methods to improve the utilization of neutrons include moderating, multiplying, and reflecting neutrons, which ignores the use of neutrons that backscatter to the source direction. In this study, a stacked structure was formed by assembling the multiplier and the low-enriched uranium (LEU) solution to enable the full use of neutrons that backscatter to the source direction and further improve the utilization of neutrons. A model based on SuperMC was used to evaluate the neutronics and safety behavior of the subcritical system, such as the neutron effective multiplication factor, neutron energy spectrum, medical isotope yield, and heat deposition. Based on the calculation results, when the intensity of the neutron source was 5×10¹³ n/s, the optimized design with a stacked structure could increase the yield of ⁹⁹Mo to 182 Ci/day, which is approximately 16% higher than that obtained with a single-layer structure. The inlet H₂O coolant velocity of 1.0 m/s and initial temperature of 20 °C were also found to be sufficient to prevent boiling of the fuel solution.

417

A detailed investigations of different decay modes, namely, alpha decay, beta decay, cluster decay, including heavy particle emission (Z_c > 28), and spontaneous fission, was carried out, leading to the identification of new cluster and beta-plus emitters in superheavy nuclei with 104 ≤ Z ≤ 126. For the first time, we identified around 20 beta-plus emitters in superheavy nuclei. Heavy-particle radioactivity was observed in superheavy elements of atomic number in the range 116 ≤ Z ≤ 126. ^292-293Og were identified as ⁸⁶Kr emitters, and ²⁹⁸122 and ³⁰⁰122 were identified as ⁹⁴Zr emitters, whereas heavy-particle radioactivity from ⁹¹Y was also observed in ²⁹⁹123. Furthermore, the nuclei ³⁰⁰124 and ³⁰⁶126 exhibit ⁹⁶Mo radioactivity. The reported regions of beta-plus and heavy-particle radioactivity for superheavy nuclei are stronger than those for alpha decay. The identified decay modes for superheavy nuclei are presented in a chart. This study is intended to serve as a reference for identifying possible decay modes in the superheavy region.

493

Radiation-induced atomic displacement damage is a pressing issue for materials. The present work investigates the number of atomic displacements using the Primary Knock-on Atom (PKA) energy E_PKA and threshold displacement energy E_d as two major parameters via low-energy SRIM Binary Collision Approximation (BCA) full cascade simulations. It is found that the number of atomic displacements cannot be uniquely determined by E_PKA/E_d or E_D/E_d (E_D refers to the damage energy) when the energy is comparable with E_d. The effective energy E_D,eff proposed in the present work allows to describing the number of atomic displacements for most presently studied monatomic materials by the unique variable E_D,eff/E_d. Nevertheless, it is noteworthy that the BCA simulation damage energy depends on E_d, whereas the currently used analytical method is independent of E_d. A more accurate analytical damage energy function should be determined by including the dependence on E_d.

473

A global variance reduction (GVR) method based on the SPN method is proposed. First, global multi-group cross-sections are obtained by Monte Carlo (MC) global homogenization. Then, the SP3 equation is solved to obtain the global flux distribution. Finally, the global weight windows are approximated by the global flux distribution, and the GVR simulation is performed. This GVR method is implemented as an automatic process in the RMC code. The SP3-coupled GVR method was tested on a modified version of the C5G7 benchmark with a thickened water shield. The results show that the SP3-coupled GVR method can improve the efficiency of the MC criticality calculation.

357

To benefit from recent advances in modeling and computational algorithms, as well as the availability of new covariance data, sensitivity and uncertainty analyses are needed to quantify the impact of uncertain sources on the design parameters of small prismatic high-temperature gas-cooled reactors (HTGRs). In particular, the contribution of nuclear data to the k_eff uncertainty is an important part of the uncertainty analysis of small-sized HTGR physical calculations. In this study, a small-sized HTGR designed by China Nuclear Power Engineering Co., Ltd. was selected for k_eff uncertainty analysis during full lifetime burnup calculations. Models of the cold zero power (CZP) condition and full lifetime burnup process were constructed using the Reactor Monte Carlo Code RMC for neutron transport calculation, depletion calculation, and sensitivity and uncertainty analysis. For the sensitivity analysis, the Contribution-Linked eigenvalue sensitivity/Uncertainty estimation via Track length importance Characterization (CLUTH) method was applied to obtain sensitive information, and the "sandwich" method was used to quantify the k_eff uncertainty. We also compared the k_eff uncertainties to other typical reactors. Our results show that ²³⁵U is the largest contributor to k_eff uncertainty for both the CZP and depletion conditions, while the contribution of ²³⁹Pu is not very significant because of the design of low discharge burnup. It is worth noting that the radioactive capture reaction of ²⁸Si significantly contributes to the k_eff uncertainty owing to its specific fuel design. However, the k_eff uncertainty during the full lifetime depletion process was relatively stable, only increasing by 1.12% owing to the low discharge burnup design of small-sized HTGRs. These numerical results are beneficial for neutronics design and core parameters optimization in further uncertainty propagation and quantification study for small-sized HTGR.

332

A gas-cooled nuclear reactor combined with a Brayton cycle shows promise as a technology for high-power space nuclear power systems. Generally, a helium–xenon gas mixture with a molecular weight of 14.5–40.0 g/mol is adopted as the working fluid to reduce the mass and volume of the turbomachinery. The Prandtl number for helium–xenon mixtures with this recommended mixing ratio may be as low as 0.2. As the convective heat transfer is closely related to the Prandtl number, different heat transfer correlations are often needed for fluids with various Prandtl numbers. Previous studies have established heat transfer correlations for fluids with medium-high Prandtl numbers (such as air and water) and extremely low-Prandtl fluids (such as liquid metals); however, these correlations cannot be directly recommended for such helium–xenon mixtures without verification. This study initially assessed the applicability of existing Nusselt number correlations, finding that the selected correlations are unsuitable for helium–xenon mixtures. To establish a more general heat transfer correlation, a theoretical derivation was conducted using the turbulent boundary layer theory. Numerical simulations of turbulent heat transfer for helium–xenon mixtures were carried out using Ansys Fluent. Based on simulated results, the parameters in the derived heat transfer correlation are determined. It is found that calculations using the new correlation were in good agreement with the experimental data, verifying its applicability to the turbulent heat transfer for helium–xenon mixtures. The effect of variable gas properties on turbulent heat transfer was also analyzed, and a modified heat transfer correlation with the temperature ratio was established. Based on the working conditions adopted in this study, the numerical error of the property-variable heat transfer correlation was almost within 10%.

428

Owing to the inherent instability of the natural circulation system, flow instability can easily occur during the operation of a natural circulation lead-cooled fast reactor, especially during the startup phase. A comprehensive startup scheme for SNCLFR-100, including primary and secondary circuits, is proposed in this paper. It references existing more mature startup schemes in various reactor types. It additionally considers the restriction conditions on the power increase in other schemes and the characteristics of lead-based coolant. On this basis, the multi-scale coupling code ATHLET-OpenFOAM was used to study the flow instability in the startup phase under different power-step amplitudes and power duration times. The results showed that obvious flow instability phenomena were found in the different startup schemes, such as the short-term backflow phenomenon of the core at the initial time of the startup. Moreover, an obvious increase in the flow rate and temperature to the peak value at the later stage of a continuous power rise was observed, as well as continuous oscillations before reaching a steady state. It was determined that the scheme with smaller power-step amplitude and a longer power duration time requires more time to start the reactor. Nevertheless, it will be more conducive to the safe and stable startup of the reactor.

371

The photoelectric device of a scintillation dosimeter converts photons produced by radiation into an electrical signal. Its features directly determine the overall performance of the dosimeter. For a plastic scintillation fiber dosimeter (PSFD) with a current readout mode, systematic studies of the stability and light-dose response were performed for the photomultiplier tube (PMT), silicon photomultiplier (SiPM), avalanche photodiode (APD), and photodiode (PD). The temperature stability, long-term stability, repeatability, signal-to-noise ratio (SNR), and current dose response of the PSFD with the abovementioned photoelectric devices were studied using a pulsed LED light source and the Small Animal Radiation Therapy platform. An exponential relationship between the dark/net current and temperature was obtained for all the devices. It is shown that the APD is the most sensitive device to temperature, with a current dependence on temperature reaching 6.5%℃^-1 at room temperature, whereas for the other devices this dependence is always <0.6%℃^-1. In terms of long-term stability, the net current of PD can change by up to 4% when working continuously for 8 h and 2% when working intermittently for 32 h, whereas for the other devices, the changes are all <1%. For the dose response, the PMT and SiPM exhibit excellent linear responses and SNRs within the range of 0.1–60 Gy/min. For the PSFD with a current readout mode, the performance of the PMT and SiPM is concluded to be better than that of the other devices in the study. In particular, the SiPM, which has a compact size, low bias voltage, and antimagnetic interference, has great advantages for further applications.

470

Currently, the liquid scintillation method is widely used to measure the activity of tritiated water in the primary circuit of nuclear power plants, which leads to the continuous production of radioactive waste during measurement. In addition, the real-time activity information of tritiated water cannot be obtained. To solve this problem, herein we present an online tritiated water measurement method based on plastic scintillators, that used the optical transport process in the Geant 4 software toolkit to build a model of plastic scintillation detection for tritiated water. Through simulation, the basic geometric dimensions of the detector were determined. In this dimension, using one detector to measure for 3 h, when the tritiated water activity was 100 Bq/L, its resolution was 16% (16 Bq/L). In addition, calculations were performed for the presence of other background signals to obtain the minimum detectable concentration.

335

A software package to be used in high-speed oscilloscope-based three-dimensional bunch-by-bunch charge and position measurement is presented. The software package takes the pick-up electrode signal waveform recorded by the high-speed oscilloscope as input, and it calculates and outputs the bunch-by-bunch charge and position. In addition to enabling a three-dimensional observation of the motion of each passing bunch on all beam position monitor pick-up electrodes, it offers many additional features such as injection analysis, bunch response function reconstruction, and turn-by-turn beam analysis. The software package has an easy-to-understand graphical user interface and convenient interactive operation, which has been verified on the Windows 10 system.

316

In the present study, samples of a titanium carbide nanoparticle-reinforced nickel alloy (Ni–TiC_NP composite) were irradiated with 1 MeV He ions at 700 °C. The evolution of He bubbles and nanohardness was characterized using transmission electron microscopy (TEM) and nanoindentation, respectively. TEM images showed that the size and number density of He bubbles in the grains were affected by the He ion fluence. The number density first increased significantly and then decreased with increasing ion dose, while the size exhibited an inverse trend. Moreover, the swelling induced by He bubbles continuously increased with increasing ion dose. He bubbles also formed in the grain boundaries, interior of the TiC nanoparticles, and interfaces between the TiC nanoparticles and Ni matrix. Nanoindentation measurements indicated a decrease in nanohardness after irradiation, which is attributed to the disappearance of intrinsic dislocation lines caused by He ion irradiation.

431

We irradiated pea seeds with neutrons from a ²⁵²Cf source and studied the radiation dose effects on various morphological development parameters during the growth of M₁ generation peas. We found that in the dose range of 0.51–9.27 Gy, with the increase in neutron absorbed dose, the morphological development parameters of M₁ generation peas at the initial seedling stage showed an obvious trend with three fluctuations. With the development of pea, this trend gradually weakened. Further analysis and verification showed that the main trend in the M₁ generation of pea seeds was an inhibitory effect induced by neutron irradiation, and there was a good linear correlation between the inhibitory effect and neutron absorption dose. We successfully demonstrated the background removal of mutant plants and defined morphological development parameters for peas that match the overall development of plants. Our results will positively impact neutron mutation breeding and automatic agriculture.

350

Grain boundaries (GBs) have critical influences on the stability and properties of various materials. In this study, first-principles calculations were performed to determine the effects of four metallic impurities (Ni, Al, Bi, and Pb) and three nonmetallic impurities (H, O, and N) on the GBs of silicon carbide (SiC), using the Σ5(210) GBs as models. The GB energy and segregation energy (SE) were calculated to identify the effects of impurities on the GB stability. Electronic interactions considerably influenced the bonding effects of SiC. The formation of weak bonds resulted in the corrosion and embrittlement of GBs. The co-segregation of Bi, Pb, and O was also investigated in detail.

335

The beam windows of high-energy beam lines are important, and it is sometimes difficult to design because it is necessary to ensure particle propagation with minimum disturbance and fulfill mechanical requirements at the same time. The upstream decay pipe window of the Long Baseline Neutrino Facility at Fermilab has an extremely large diameter (1.8 m), with a thickness of only 1.5 mm to separate the helium atmosphere in the decay pipe and the nitrogen atmosphere on the other side. Furthermore, the center of this dish-shaped window is expected to be a 200-mm-diameter beryllium (Be) dish welded to the outside aluminum alloy A6061, and this welded combination must withstand extreme conditions of a 2.4-MW, high-energy proton beam without leakage. These severe conditions make the design of this window an unprecedented challenge. This paper describes the static thermal-structural analyses based on which the structure has been optimized, as well as dynamic analyses for understanding the shockwave effects originating in the beam. After optimization, the maximum von Mises stresses in the window decreased significantly in both normal operation and accident cases, making our design very reasonable.

329

The third harmonic superconducting cryomodule is being designed for the Shanghai High repetition rate XFEL and Extreme light facility (SHINE) project, which is under construction. In contrast to the European X-ray Free Electron Laser (E-XFEL) project, the 3.9 GHz cryomodules in the SHINE project will operate in the continuous wave regime with higher radio frequency average power for both cavities and couplers. We propose a 3.9 GHz fundamental power coupler with an adjustable antenna length, for satisfying the SHINE project requirements. Here, we describe the 3.9 GHz fundamental power coupler’s design considerations and power requirements for various operating modes of the SHINE Linac. We also present the results of the radio frequency simulation and optimization, including the studies on multipacting and thermal analysis of the proposed 3.9 GHz coupler.

400