Vol.30,

This study investigated the level of natural radioactivity and radiological risks of 40 different ceramic tiles through gamma-ray spectroscopy using a high-purity germanium detector. The calculated activity concentrations were evaluated to determine their potential radiological risks to human health. Furthermore, the activity concentrations were subjected to the RESRAD-BUILD computer code to assess the effect of ventilation rate, dweller position, and room size and direction on the total effective dose (TED). The simulated TED received by a receptor when changing the ventilation rate in a room ranged from 0.26 ± 0.01 to 0.61 ± 0.01 mSv/y; however, the percentage variations in the TED due to dweller position and room size from all directions are 34%, 31%, and 35%, and 33%, 27%, and 40% for the x, y, and z-directions, respectively. The overall TED received by the dweller based on room size and direction is 0.75 mSv/y. The calculated radiological risk parameters were all below the recommended maximum limit. However, the TED received by the dweller is significantly affected by the directions of the measurement, position, room size, and ventilation. Therefore, estimating the TED from one direction would underestimate the total dose received by the dweller.

478

The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper, a discrete element method-computational fluid dynamics (DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly-designed fluoride- salt-cooled pebble-bed reactors.

493

The critical size of a finite homogenous slab is investigated for one-speed neutrons using the alternative phase function (AG, Anlı-Güngör) in place of the scattering function of the transport equation. First, the neutron angular flux expanded in terms of the Chebyshev polynomials of second kind (U_N approximation) together with the AG phase function is applied to the transport equation to obtain a criticality condition for the system. Then, using various values of the scattering parameters, the numerical results for the critical half-thickness of the slab are calculated and they are tabulated in the tables together with the ones obtained from the conventional spherical harmonics (P_N) method for comparison. They can be said to be in good accordance with each other.

391

Delayed neutron loss is an important parameter in the safety analysis of molten salt reactors. In this study, to obtain the effective delayed neutron fraction under flow condition, a delayed neutron precursor transport was implemented in the Monte Carlo code MCNP. The Molten Salt Reactor Experiment (MSRE) model was used to analyze the reliability of this method. The obtained flow losses of reactivity for ²³⁵U and ²³³U fuels in the MSRE are 223 pcm and 100.8 pcm, respectively, which are in good agreement with the experimental values (212 pcm and 100.5 pcm, respectively). Then, six groups of effective delayed neutron fractions in a small molten salt reactor were calculated under different mass flow rates. The flow loss of reactivity at full power operation is approximately 105.6 pcm, which is significantly lower than that of the MSRE due to the longer residence time inside the active core. The sensitivity of the reactivity loss to other factors, such as the residence time inside or outside the core and flow distribution, were evaluated as well. As a conclusion, the sensitivity of the reactivity loss to the residence time inside the core is greater than to other parameters.

371

A liquid metal reactor (LMR) loaded with a fuel compound of uranium and beryllium (U–Be alloy fuel), which was cooled by a lead–bismuth eutectic alloy (PbBi), has been applied in Russian Alfa-class nuclear submarines. Because of the large amount of beryllium in the core, the reaction between the beryllium atoms and neutrons could result in the accumulation of ³He and ⁶Li, which are called the "poisoned elements" owing to their large thermal neutron capture cross section. The accumulation of neutron absorber can affect the performance of a reactor. In this study, the Super Monte Carle Simulation (SuperMC) code, which was developed by Institute of Nuclear Energy Safety Technology of the Chinese Academy of Sciences (INEST, CAS), was adopted to illustrate the influence of beryllium on an LMR.

425

A novel amidoxime-based fibrous adsorbent, denoted as PE/PP-g-(PAAc-co-PAO), was prepared by pre-irradiation grafting of acrylic acid and acrylonitrile onto polyethylene-coated polypropylene skin-core (PE/PP) fibers using ⁶⁰Co γ-ray irradiation, followed by amidoximation. The original and modified PE/PP fibers were characterized by a series of characterization methods to demonstrate the attachment of amidoxime (AO) groups onto the PE/PP fibers. Breaking strength tests confirmed that the fibrous adsorbent could maintain good mechanical properties. The adsorption capacity of the PE/PP-g-(PAAc-co-PAO) fibers was investigated in simulated seawater with an initial uranium concentration of 330 μg/L. The uranium adsorption capacity was 2.27 mg/g-adsorbent after 24 h in simulated seawater, and the equilibrium data were well-described by the Freundlich isotherm model. The PE/PP-g-(PAAc-co-PAO) adsorbent exhibited good regeneration and recyclability during five adsorption-desorption cycles. The adsorption test was also performed in simulated radioactive effluents with uranium concentrations of 10 and 100 μg/L. The effect of the pH value on the adsorption capacity was also studied. At a very low initial concentration 10 μg/L solution, the PE/PP-g-(PAAc-co-PAO) fiber could remove as much as 93.0% of the uranium, and up to 71.2% of the uranium in the simulated radioactive effluent. These results indicated that the PE/PP-g-(PAAc-co-PAO) adsorbent could be used in radioactive effluents over a wide range of pH values. Therefore, the PE/PP-g-(PAAc-co-PAO) fibers, with their high uranium selectivity, good regeneration and recyclability, good mechanical properties, and low cost, are promising adsorbents for extracting uranium from aqueous solutions.

518

The preparation of nuclear-grade zirconium and hafnium is very important for nuclear power. The separation of hafnium from zirconium in a hydrochloric acid solution by solvent extraction was investigated with di(2-ethylhexyl)phosphoric acid (D2EHPA). The effects of hydrochloric acid concentration, extractant concentration, diluents, and temperature on the distribution coefficient of hafnium and zirconium were studied. The species extracted were ZrOA₂·2HA and HfOA₂·2HA. In this process, the separation factors varied with different diluents and followed the order octane > hexane > toluene > chloroform. A high separation factor value of 4.16 was obtained under the conditions of a solution containing 0.05 mol/L HCl and 0.01 mol/L D2EHPA for the separation of hafnium from zirconium. The extraction reaction was endothermic.

522

Removal of X-ray induced carbon contamination on beamline optics was studied using radio-frequency plasma with an argon/hydrogen (Ar/H₂) mixture. Experiments demonstrated that the carbon removal rate with Ar/H₂ plasma was higher than that with pure hydrogen or argon. The possible mechanism for this enhanced removal was discussed. The key working parameters for Ar/H₂ plasma removal were determined, including the optimal vacuum pressure, gas mixing ratio, and source power. The optimal process was performed on a carbon-coated multilayer, and the reflectivity was recovered.

505

Sr-substituted ABO₃ perovskite oxides such as La_0.6Sr_0.4MnO_3−δ (LSM) and La_0.6Sr_0.4FeO_3−δ (LSF) are widely used as oxygen electrode materials in solid oxide cells. The substituted Sr is not adequately stable under the operating conditions, because of the surface segregation of Sr. Herein, we focused on investigating the relationship between the local geometric structure due to Sr substitution and stability of LSM and LSF. We characterized the local geometric structure of Sr atoms via X-ray absorption spectroscopy. A greater Debye-Waller factor and a longer bond length of both the second and third Sr–O shells were observed in LSF, which demonstrates that LSF has a higher local structural disorder and that Sr in LSF requires less energy to segregate. After 20 h of heat treatment in the presence of a Fe-Cr alloy interconnect, the Sr/La molar ratio on LSF was observed to be much larger than that on LSM. This result unequivocally suggests that Sr in LSF is not as stable as in LSM, and the reaction between Sr and Cr accelerates the Sr surface segregation in LSF.

453

Fourier transform infrared (FTIR) spectroscopy has emerged as a viable alternative to biochemical and molecular biology techniques for bacterial typing with advantages such as short analysis time, low cost, and laboratorial simplicity. In this study, synchrotron radiation-based FTIR (SR-FTIR) spectroscopy with higher spectral quality was successfully applied to 16 types foodborne pathogenic bacteria. Combined with principal component analysis (PCA) and hierarchical cluster analysis (HCA), we found that the specific spectral region is 1300-1000 cm^-1, which reflects the information of phosphate compounds and polysaccharides, and can be used as the signature region to cluster the strains into a similar groups with this genetic taxonomic method. These findings demonstrated that FTIR spectra combined with HCA have a great potential in quickly typing bacteria depending on their biochemical signatures.

382

The 13-MeV proton linac of the Compact Pulsed Hadron Source (CPHS) at Tsinghua University, China, is composed of a 50-keV electron cyclotron resonance proton source, a 3-MeV four-vane-type radio-frequency quadrupole (RFQ) accelerator, and a drift tube linac (DTL). Precise measurement of the beam energies at the exit of the RFQ and the DTL are critical for DTL commissioning. Two button-type beam position monitors (BPMs) installed downstream of the RFQ are used to perform the measurement using a time-of-flight method. The effects of several factors on phase measurement accuracy are analyzed. The phase measurement accuracy of the BPMs at CPHS is better than ±1.03° at 325 MHz after corrections, corresponding to an energy measurement error of ±0.07%. The beam energy measured at the exit of the RFQ is 2.994 ± 0.0022 MeV, which is consistent with the design value.

562

Linear alkylbenzene (LAB) will be used as solvent for the liquid scintillator in the central detector of Jiangmen Underground Neutrino Observatory (JUNO). The sheer size of the detector imposes significant challenges and the necessity to further improve the optical transparency of high-quality LAB. In order to study high optical transparencies, we continuously improve our measurement setup and use monochromatic light to measure the attenuation lengths of LAB samples. Moreover, the effects of organic impurities on LAB samples are studied to understand their interaction mechanisms and further improve the optical transparency of LAB.

416

The water equivalent ratio (WER) was calculated for polypropylene (PP), paraffin (PA), polyethylene (PE), polystyrene (PS), polymethyl methacrylate (PMMA), and polycarbonate (PC) materials with potential applications in dosimetry and medical physics. This was performed using the Monte Carlo simulation code, MCNPX, at different proton energies. The calculated WER values were compared with National Institute of Standards and Technology (NIST) data, available experimental and analytical results, as well as the FLUKA, SRIM, and SEICS codes. PP and PMMA were associated with the minimum and maximum WER values, respectively. Good agreement was observed between the MCNPX and NIST data. The biggest difference was 0.71% for PS at 150 MeV proton energy. In addition, a relatively large positive correlation between the WER values and the electron density of the dosimetric materials was observed. Finally, it was noted that PE presented the most analogous depth dose characteristics to liquid water.

393

The objective of this work was to use the Geant4 toolkit to perform simulation studies on the personal dose response of fluorescent nuclear track detectors (FNTDs). The entire structure of the FNTD response can be designed, and the detector’s energy and dose responses can be optimized in a broad energy range (0.01 eV–20 MeV). In general, the detectors used ⁶LiF and CH₂ converters that have high energy and high dose response at neutron energies lower than 10 eV and greater than 1 MeV, respectively. The method of least squares was used to optimize the dose response of H^*(10) and the energy response corresponding to R_total. The values of the optimized response of H^*(10) lie between 0.8 and 1.4, corresponding to the energy ranges 0.01 eV–70 keV and 4–14MeV, respectively. This occupies nearly eight out of the nine orders of the total energy range. Even though the optimized response of R_total is constrained between 0.89 and 1.1 in the energy range of 0.01 eV–20 MeV, it is suitable for obtaining the broad neutron spectrum of fluence with good accuracy.

462

To control the steady state operation of Tokamak plasma, it is crucial to accurately obtain its shape and position. This paper presents a method for use in rapidly detecting plasma configuration during discharge of the Experimental Advanced Superconducting Tokamak (EAST) device. First, a visible/infrared integrated endoscopy diagnostic system with a large field of view is introduced, and the PCO.edge5.5 camera in this system is used to acquire a plasma discharge image. Based on analysis of various traditional edge detection algorithms, an improved wavelet edge detection algorithm is then introduced to identify the edge of the plasma. In this method, the local maximum of the modulus of wavelet transform is searched along four gradient directions, and the adaptive threshold is adopted. Finally, the detected boundary is fitted using the least square iterative method to accurately obtain the position of the plasma. Experimental results obtained using the EAST device show that the method presented in this paper can realize expected goals and produce ideal effects; this method thus has significant potential for application in further feedback control of plasma.

430

With the aim of simulating the harsh temperature condition of space, a thallium-activated cesium iodide crystal (CsI:Tl) detector readout with a PIN photodiode (CsI:Tl(PD))and with a silicon photomultiplier (CsI:Tl(SiPM)) are investigated over a temperature range from -40° to 40°C. With the increase in temperature, the output signal increases by ∼24% with CsI:Tl(PD) and decreases by ∼69% with CsI:Tl(SiPM). To reduce the effect of temperature in outer space, a method of bias voltage compensation is adopted for CsI:Tl(SiPM). Our study demonstrates that after correcting the temperature the variation in the analog-to-digital converter’s amplitude is <3%.

644

As technology scales down, clock distribution networks (CDNs) in integrated circuits (ICs) are becoming increasingly sensitive to single-event transients (SETs). The SET occurring in the CDN can even lead to failure of the entire circuit system. Understanding the factors that influence the SET sensitivity of the CDN is crucial to achieving radiation hardening of the CDN and realizing the design of highly reliable ICs. In this paper, the influences of different sequential elements (D-flip-flops and D-latches, the two most commonly used sequential elements in modern synchronous digital systems) on the SET susceptibility of the CDN were quantitatively studied. Electrical simulation and heavy ion experiment results reveal that the CDN-SET-induced incorrect latching is much more likely to occur in DFF and DFF-based designs. This can supply guidelines for the design of IC with high reliability.

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