Nuclear Science and Techniques

Two in-vacuum undulators have been developed for the first time in China at Shanghai Synchrotron Radiation Facility (SSRF), which has been opened to users since May, 2009. The precision of mechanical system is important to ensure performances of magnetic field. Efforts were made to manufacture in-vacuum undulator with high mechanical properties. The taper mechanism is adopted for the first time in the design of an in-vacuum undulator. A finite element analysis was performed to find out the deformation of out-vacuum girder and minimize the effect of linear rolling guide on it. In this article, the design and analysis results for the in-vacuum undulator are described.

The variable-included angle plane-grating monochromator is a homemade key equipment of the scanning transmission X-ray microscopy (STXM) beamline at Shanghai Synchrotron Radiation Facility (SSRF). Monochromatic light of various wavelengths is achieved by an effective control system that handles the rotation of the plane mirror and plane grating mounted in a high vacuum chamber. M511.DDB made by PI Corp. is used as motion stage which has a DC servo motor controlled by a C862 controller based on RS232 protocol. The software platform of STXM is EPICS, so the local control functions are implemented by LabVIEW program to satisfy physics control. For the remote control functions, the program is integrated into EPICS with ShareMemoryIOC. Experimental tests show that the repeat precision of motion control is less than 0.2 μm, which meets the control demand.

Basic properties of a silica-based octyl(phenyl)-N,N-diisobutylcarbamoyl-methylphosphine oxide (CMPO) extraction resin (CMPO/SiO₂-P) was investigated. Adsorption behavior for some rare earth elements (RE) which are constituents of high level liquid waste (HLLW) and the long-term stability of the extraction resin in nitric acid solution were examined. The CMPO extraction resin was significantly stable in 3 mol·L⁻¹ HNO₃ solution at 50ºC. Furthermore, the RE(III) were efficiently separated from non-adsorptive fission product (FP) elements such as Sr(II) in a column experiment using a highly nitric acid solution. The separation behaviors of the elements are considered to result from the difference in their adsorption and elution selectivity based on the complex formation with CMPO. There was no strong dependency of RE(III) separation efficiency on feed solution flow rate. Only from the perspectives of the acid-resistant behavior of CMPO extraction resin and the elution kinetics for the metal ions with the extraction resin, the CMPO extraction resin can be used in the modified MAREC process for HLLW partitioning.

Acrylic acid (AAc) and styrene (St) were grafted onto poly(vinylidene fluoride) (PVDF) powder or membrane samples by pre-irradiation graft copolymerization. The grafted chains were proved by FT-IR spectroscopy analysis. The degree of grafting (DG) of the grafted PVDF was determined by fluorine elemental analysis (FEA) method, and was compared with the DGs determined by weighing method, acid-base back titration method and quantitative FT-IR method. The results show that the FEA method is accurate, convenient and universal, especially for the grafted polymer powders.

Supramolecular structures formed by H₄TPPS₄^2– have been widely used for different applications. In this paper, the stability of H₄TPPS₄²⁻ nanorods on mica substrate is investigated by atom force microscopy (AFM) observation. An irreversible transformation of H₄TPPS₄^2– from nanorods (3.8±0.4 nm in height) to a lower film structure (1.9±0.4 nm in height) was found with the samples incubated at various relative humidities (RH). The transformation rate depends strongly on the RH and environment temperature.

To investigate the influence of radiolysis on kinetics and factors of dimethyl phthalate(DMP), the aqueous DMP solution is degraded by 1.8 MeV E-beam, following pseudo-first-order kinetics. The rate constant of DMP degradation decreased exponentially with increasing initial DMP concentration. The DMP is favorably degraded by radical scavengers under its low concentration and alkaline condition. At high doses, the DMP is attacked by e_aq^– and ·OH, producing monomethyl phthalate, phthalate acid, and a series of aliphatic carboxylic acids, which are completely mineralized into H₂O and CO₂.

Experiments were performed on a high-speed online random neutron analyzing system (HORNA system) with a ²⁵²Cf neutron source (up to 1 GHz sampling rate and 3 input data channel), to obtain time- and frequency- dependent signatures which are sensitive to changes in the composition, fissile mass and configuration of the fissile assembly. The data were acquired by three high-speed synchronized acquisition cards at different detector angles, source-detector distances and block sizes. According to the relationship between ²⁵²Cf source and the ratio of power spectral density, R_psd, all the signatures were calculated and analyzed using correlation and periodogram methods. Based on the results, the simulated autocorrelation functions were utilized for identifying different fissile mass with Elman neural network. The experimental results show that the R_psd almost remains at constant amplitude in frequency range of 0–100 MHz, and is only related to the angle and source-detector distance. The trained Elman neural network is able to distinguish the characteristics of autocorrelation function and identify different fissile mass. The average identification rate reached 90% with high robustness.

Pu-Pu, Pu-U and U-U interatomic potentials must be known in molecular dynamics (MD) calculation of the effects of U recoil nucleus produced by self irradiation on physical properties and phase stability in δ-Pu. Because of the lack of experimental data for fitting Pu-U and U-U potentials, electronic states and potential data of PuU and U₂ molecules are obtained by ab initio calculations with B3LYP hybrid exchange-correlation functional. The valence electrons of Pu and U atoms are treated with contraction basis sets, and the cores are approximated with relativistic effective core potential. The results show that electronic states for the ground states are X¹¹Σ_u⁺ and X⁹Σ_g⁺. The pair potential data are fitted with the Murrell-Sorbie analytical potential function. The LDA+U calculations on the Pu-U intermetallic compound are performed with Perdew and Wang exchange-correlation functional at the spin-polarized level. The material parameters, such as the cohesive energies, elastic constants, and bulk modulus, are used to fit the 0-K universal Rose EOS, so the Pu-U EAM potential model is obtained.

In this paper, an improved decision model is developed for its use as a tool to respond to emergencies at nuclear power plants. Given the complexity of multi-attribute emergency decision-making on nuclear accident, the improved TOPSIS method is used to build a decision-making model that integrates subjective weight and objective weight of each evaluation index. A comparison between the results of this new model and two traditional methods of fuzzy hierarchy analysis method and weighted analysis method demonstrates that the improved TOPSIS model has a better evaluation effect.

In this paper, the reactor core cooling and its melt progression terminating is evaluated, and the initiation criterion for reactor cavity flooding during water injection is determined. The core cooling in pressurized-water reactor of severe accident is simulated with the thermal hydraulic and severe accident code of SCDAP/RELAP5. The results show that the core melt progression is terminated by water injection, before the core debris has formed at bottom of core, and the initiation of reactor cavity flooding is indicated by the core exit temperature.