Vol.28,

Steam-gas pressurizers are self-pressurizing, and since steam and noncondensable gas are used to sustain their pressure, they experience very complicated thermal-hydraulic phenomena owing to the presence of the latter. A steam-gas pressurizer model was developed using Relap5 code to investigate such a pressurizer’s thermal-hydraulic characteristics. The important thermal-hydraulic processes occurring in the pressurizer model include bulk flashing, rainout, wall condensation with noncondensable gas, and interfacial heat and mass transfer. The pressurizer model was verified using results from insurge experiments performed at the Massachusetts Institute of Technology. It was found that noncondensable gas was one of the important factors governing the pressure response, and the accuracy of the developed model would change with different mass fractions and types of noncondensable gas.

373

Accurate and reliable nuclear data libraries are essential for calculation and design of advanced nuclear systems. A 1200 fine group nuclear data library HENDL/FG (Hybrid Evaluated Nuclear Data Library / Fine Group) with neutrons of up to 150 MeV has been developed to improve the accuracy of neutronics calculations and analysis. Corrections of Doppler, resonance self-shielding and thermal up-scatter effects were done for HENDL/FG. Shielding and critical safety benchmarks were performed to test the accuracy and reliability of the library. The discrepancy between calculated and measured nuclear parameters fell into a reasonable range.

409

The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion techniques to investigate the diffusion behavior of HTO and ⁹⁹TcO₄⁻ on GMZ bentonite of various densities. Diffusion rates were calculated by measuring the diffusion coefficients (D_e, D_a), plotting breakthrough curves, and interpreting experiment data. The apparent and effective diffusion coefficients of HTO ranged from (1.68±0.40)×10⁻¹¹ to (2.80±0.62)×10⁻¹¹ m²/s and from (4.61±1.28)×10⁻¹² to (16.2±2.50)×10⁻¹² m²/s, respectively. The apparent and effective diffusion coefficients of ⁹⁹TcO₄⁻ range from (5.26±0.16)×10⁻¹² to (7.78±0.43)×10⁻¹² m²/s and from (1.49±0.002)×10⁻¹² to (4.16±0.07)×10⁻¹² m²/s, respectively. The distribution coefficients of HTO and ⁹⁹TcO₄⁻ ranged from (0.70±0.12)×10⁻² to (1.36±0.53)×10⁻² mL/g and from (1.12±0.06)×10⁻² to (5.79±2.22)×10⁻²mL/g, respectively. The D_e and K_d values were shown to decrease with an increase in the bulk dry density of compacted bentonite. Our results show that HTO and ⁹⁹Tc could be considered non-sorbent radionuclides. The data obtained in this study provide a valuable reference for the safety assessment of waste repositories.

534

The objective of the present study is to calculate photon shielding parameters for seven polyethylene-based neutron shielding materials. The parameters include the effective atomic number (Z_eff), the effective electron density (N_eff) for photon interaction and photon energy absorption, and gamma-ray kerma coefficient (k_γ). The calculations of Z_eff are presented as a single-valued and are energy-dependent. While Z_eff values were calculated via simplistic power-law method, the energy-dependent Z_eff for photon interaction (Z_PI-eff) and photon energy absorption (Z_PEA-eff) are obtained via the direct method for energy ranges of 1 keV–100 GeV and 1 keV–20 MeV, respectively. The k_γcoefficients are calculated by summing the contributions of the major partial photon interactions for energy range of 1 keV–100 MeV. In most cases, data are presented relative to pure polyethylene to allow direct comparison over a range of energy. The results show that combination of polyethylene with other elements such as lithium and aluminum leads to neutron shielding material with more ability to absorb neutron and γ-rays. Also, the kerma coefficient first increases with Z of the additive element at low photon energies, and then converges with pure polyethylene at energies greater than 100 keV.

368

TiBCN films were deposited on Si(100) and cemented carbide substrates by using multi-cathodic arc ion plating in C₂H₂ and N₂ atmosphere. Their structure and mechanical properties were studied systematically under different N₂ flow rates. The results showed that the TiBCN films were adhered well to the substrates. Rutherford backscattering spectroscopy was employed to determine the relative concentration of Ti, B, C and N in the films. The chemical bonding states of the films were explored by X-ray photoelectron spectroscopy, revealing the presence of bonds of TiN, Ti(C,N), BN, pure B, sp² C-C and sp³ C-C, which changed with the N₂ flow rate. TiBCN films contain nanocrystals of TiN/TiCN and TiB₂/Ti(B,C) embedded in an amorphous matrix consisting of amorphous BN and carbon at N₂ flow rate of up to 250 sccm.

468

Extraction behavior of thorium(IV) and uranium(VI) from nitric acid (HNO₃) was studied using N,N,N’,N’-Tetraoctyldiglycolamide (TODGA) as extractant in different ionic liquids, and isooctane as comparison. Slope analyses with varying HNO₃ concentrations and diluents revealed the extraction mechanism. With increasing length of alkyl chain and HNO₃ concentration, the extraction mechanism of TODGA/IL system changed from cation exchange to neutral complex or/and anion exchange, and the molar ratio between TODGA and metal ions varied gradually from 2:1 to 1:1 for Th(IV) and 3:1 to 1:1 for U(VI). The kinetics and thermodynamic studies of Th(IV) and U(VI) by the best TODGA/[C₂mim][NTf₂] system showed that the exaction reached equilibrium within 2 h and extraction reactions were endothermic. Compared to TODGA/isooctane system, TODGA/[C₂mim][NTf₂] system presented higher radiation stability under γ-irradiation. Therefore, it would have a promising application in spent fuel reprocessing.

411

Image-guided radiotherapy (IGRT) provides precise positioning for the tumor target, but it may bring extra irradiation dose in the target positioning with a cone beam CT (CBCT) which has been increasingly used in IGRT. In this work, we focused on biological effects of the low-dose irradiation in IGRT, which have not been considered so far. Primary human fibroblasts cells from the lung and MRC-5 were irradiated by a CBCT. DNA double-strand breaks (γ-H2AX foci) and micronucleus frequency of the irradiated samples were analyzed. Compared to the control, the γ-H2AX foci yields of the samples irradiated to 16 mGy increased significantly, and the micronuclei rate of the samples irradiated for three days increased notably. The dose by imaging guidance device can be genotoxic to normal tissue cells, suggesting a potential risk of a secondary cancer. The effects, if confirmed by clinical studies, should be considered prudentially in designing IGRT treatment plans for the radiosensitive population, especially for children.

466

XRF(X-ray fluorescence) scan methodology is important for elemental mapping of samples at a synchrotron radiation facility. To save the experiment time and improve the experiment efficiency, one should develop an efficient XRF scan method. In this paper, a new scan mode is presented. It can map arbitrary-shaped areas without stopping the motors. The control and data acquisition system integrates motor controlling, detector triggering, and data acquisition and storage. The system realizes the arbitrary-shaped 2D-mapping and fluorescence data acquisition synchronously. SR-XRF mapping has been performed with a standard gold mask to verify the validity of this method at beamline BL15U1 of the Shanghai Synchrotron Radiation Facility. The results show that this method reduces the total scan time and improves the experiment efficiency.

492

A moderator of paraffin wax assembly has been demonstrated where its thickness can be optimized to thermalize fast neutrons. The assembly is used for measuring fast neutron flux of a neutron probe at different neutron energies, using BF₃ (Φ1″and 2″) and ³He(Φ0.5″) neutron detectors. The paraffin wax thickness was optimized at 6 cm for the neutron probe which contains an Am-Be neutron source. The experimental data are compared with Monte Carlo simulation results using MCNP5 version 1.4. Neutron flux comparison and neutron activation techniques are used for measuring neutron flux of the neutron probe to validate the optimum paraffin moderator thickness in the assembly. The neutron fluxes are measured at (1.17 ± 0.09)×10⁵ n/s and (1.19 ± 0.1)×10⁵ n/s, being in agreement with the simulated values. The moderator assembly can easily be utilized for essential requirements of neutron flux measurements.

499

Stripper gas and terminal potential play a key role for the charge state distribution in a tandem pelletron accelerator. The knowledge of this distribution is important for experiments performed on tandem accelerators. The charge state distribution of B, C, Si, Ni, Cu and Au beams are measured by using Ar as stripper gas, and terminal potential is varied from 0.3 – 3.0 MV on 5UDH-2 tandem pelletron accelerator installed at the National Centre for Physics, Islamabad. The individual charge state is measured after the switching magnet at 15° in high-energy portion. It is observed that the higher charge states are stable in the range of lower and middle atomic masses of periodic table, whereas higher atomic mass (Au) shows beam current instability in higher charged states. For carbon, the charge distribution at 1.7 MV terminal potential by varying stripper gas pressure is also studied, which resulted in decreased overall transmission with good current value for higher charge states.

406

In this study, effective atomic numbers (Z_eff) of materials determined at different experimental conditions by measuring the elastic-to-inelastic γ-ray scattering ratios are compared to ZXCOM predictions. It also presents the experimental data obtained via the transmission technique. The agreement and disagreement between ZXCOM and experimental values are investigated. The theoretical basics of determining Z_eff by scattering mode are outlined. The study shows that choosing appropriate experimental conditions can provide a good compatibility between the experimental results and theoretical ZXCOM calculations.

355

The requirement of the fast three-dimensional radiation field calculation is raised during the decommissioning of large-scale nuclear installations. The most often used methods, such as the Monte Carlo and the discrete ordinates methods, have shortcomings in their simulations of such problems. The coupled Monte Carlo-Point Kernel computational scheme is developed to meet the requirement. The facility is separated into the source region and the bulk shielding region, with a common interface. The transport within the source region is simulated using the Monte Carlo method, which is by nature good at treating complex geometries. The radiation field in the bulk shielding region is treated by the point kernel approach to avoid the extremely expensive computation for deep penetration problems. The flow rate through the interface, which is given by the Monte Carlo simulation, is considered as the equivalent surface source for the point kernel calculation. Test calculations from simplified typical waste storage facilities have been performed to validate the coupled scheme by comparing them with the results conducted by the Monte Carlo method directly. The good agreement of the results, as well as the significant saving in computing time, indicates that the coupled method is suitable for the fast three-dimensional radiation field calculation.

374

An algorithm for Monte Carlo simulation of bremsstrahlung emission by electrons based on the framework of SuperMC is presented in this paper. With efficient and accurate methods to sample the angular distribution and energy of bremsstrahlung photons. The photon energy is sampled according to scaled energy-loss differential cross sections tabulated by Seltzer and Berger. A novel hybrid model for photon angular distribution by low and high energy incident electrons are developed. The model uses Tsai’s full form of angular distribution function with atomic form factors for high energy incident electrons. For electrons of <500 keV, a simple efficient and accurate analytical distribution function is developed, using adjustable parameters determined from the fitting of numerical values of the shape functions tabulated by Kissel et al. The efficiency of sampling photon energy is 80%. Our angular sampling algorithm for high energy electron bremsstrahlung based on Tsai distribution function is very efficient (sampling efficiency~70%) in the useful photon energy range.

396

A tracking system composed of three multi-wires proportional chambers (MWPCs) for the external target facility of the Cooler Storage Ring (CSR) is reported in this paper. The active areas of the MWPCs are 518×400●thin;mm, 582×450●thin;mm, and 710×500●thin;mm. Each MWPC consists of a series of alternately placed cathode and anode wire planes and can measure position along the directions of -30°, 0°, and 30° relative to horizontal. The construction and operation of the detectors are described and a method for track reconstruction is introduced. A track-finding efficiency of about 62% and a spatial resolution of 1.21 mm have been achieved. The pion and proton can be identified clearly with the tracking system combined with a time-of-flight system.

510

Surveying ionizing radiations of the surrounding with a smartphone provides a low-cost and convenient utility for the general public. We developed a smartphone application (App) that uses the built-in camera with a CMOS sensor and a radiation signal extraction algorithm. After a calibration through a series of radiation exposures, the App could display radiation dose rate and cumulative dose in real-time without requiring covering the camera lens. A smartphone with this App can be used as a fast survey tool for ionizing radiations.

459