Nuclear safety in the unexpected second nuclear era.

Nuclear energy development has entered an unexpected second nuclear era, which is mainly driven by developing countries. Despite major efforts to pursue a safe nuclear energy system in the first nuclear era, severe nuclear accidents occurred. A basic problem is that we do not have an adequate understanding of nuclear safety. From the viewpoints of risk and the close coupling of technical and social factors, this paper reexamines the nature of nuclear safety and reviews how previous experts understood it. We also highlight the new challenges that we are likely to confront in the unexpected second nuclear era and clarify some of the refinements that need to be made to the concept of nuclear safety from a sociotechnical perspective. These include the following: 1) Risk decisions should be made based on integrating social and technical elements (i.e., "social rationality"); 2) risk needs to be controlled based on the "Wuli-Shili-Renli" framework; 3) systems thinking should be substituted for reductionism in risk assessment, and social mechanisms need to be combined to address uncertainties; and 4) public-centered risk communication should be established. This contribution can provide a theoretical foundation for improving our understanding of the nature of nuclear safety and for transforming the concept of nuclear safety in the unexpected second nuclear era.

The design of a direct charge nuclear battery with high energy conversion efficiency.

Direct charging nuclear batteries (DCNB) have the potential of being widely used to meet the special requirements in the area of aerospace and ocean. The current application of direct charging nuclear batteries is restricted by the low energy conversion efficiency, commonly less than 10%. This low efficiency is limited mainly by issues of low source efficiency and shunt factor among others, such as collection and geometry factors. Based on a numerical simulation and empirical calculations we here propose a design of DCNB by utilization of a sub-micrometer thickness radiation source to increase the source efficiency, both-side emission, and collection of decay particles to improve the collection and geometry factors, as well as impedance matching of batteries and load to improve the shunt factor, among other various optimizations. The energy conversion efficiency of DCNB with this design reaches over 20%. The successful deployment of the current design should vastly improve the energy conversion efficiency of DCNBs, and also establish a theoretical foundation for extending the scope of applications of DCNBs in the future.

[Development and Validation of Dynamic Intensity Modulated Accurate Radiotherapy System KylinRay-IMRT].

KylinRay-IMRT is the advanced radiotherapy treatment planning module of accurate radiotherapy system (KylinRay) aiming to provide accurate and efficient plan design platform. In this paper the system design, main functions and key technologies of KylinRay-IMRT were introduced. KylinRay-IMRT supports three dimensional conformal radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT) and many other types of treatment plan design with function modules including patient data management, image registration and fusion, image contouring, image three dimensional reconstruction and visualization, three dimensional conformal radiotherapy planning, intensity modulated radiotherapy planning, plan evaluation and comparison, and report print. KylinRay-IMRT has been tested by the national standard YY/T 0889-2013, the results showed that the performance of KylinRay-IMRT can fully meet the standard requirements.

Halogen bonding versus hydrogen bonding induced 2D self-assembled nanostructures at the liquid-solid interface revealed by STM.

We design a bifunctional molecule (5-bromo-2-hexadecyloxy-benzoic acid, 5-BHBA) with a bromine atom and a carboxyl group and its two-dimensional self-assembly is experimentally and theoretically investigated by using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The supramolecular self-organization of 5-BHBA in two different solvents (1-octanoic acid and n-hexadecane) at the liquid-solid interface at different solution concentrations is obviously different due to the cooperative and competitive intermolecular halogen and hydrogen bonds. Three kinds of nanoarchitectures composed of dimers, trimers and tetramers are formed at the 1-octanoic acid/graphite interface based on -COOHHOOC-, triangular C[double bond, length as m-dash]OBrH-C, -BrO(H), BrBr, and OH interactions. Furthermore, by using n-hexadecane as the solvent, two kinds of self-assembled linear patterns can be observed due to the coadsorption, in which the dimers are formed by intermolecular -COOHHOOC- hydrogen bonds. The molecule-solvent and solvent-solvent van der Waals force and intermolecular hydrogen bonds dominate the formation of coadsorbed patterns. We propose that the cooperative and competitive halogen and hydrogen bonds are related to the polarity of the solvent and the type of molecule-solvent interaction. The intermolecular binding energy of different dimers and their stability are supported by theoretical calculations. The result provides a new and innovative insight to induce the 2D self-assembled nanostructures by halogen and hydrogen bonds at the liquid-solid interface.

Cooperation and competition between halogen bonding and van der Waals forces in supramolecular engineering at the aliphatic hydrocarbon/graphite interface: position and number of bromine group effects.

Herein, the photophysical properties of two π-conjugated thienophenanthrene derivatives (6,9- and 5,10-DBTD) are reported. Their self-assembled monolayers in aliphatic hydrocarbon solvents under different concentrations were investigated by scanning tunneling microscopy on a graphite surface. The STM results revealed that the self-assembled structures of the two geometrical isomers exhibited absolutely different behaviors. At the aliphatic solvent/graphite interface, 6,9-DBTD produced almost a single stable coassembled linear structure, except for that with n-tridecane as the solvent. However, the self-assembly of 5,10-DBTD showed structural diversity, and it presented a gradient variety through increasing the chain length of the aliphatic solvents as well as the solution concentration. All ordered self-assembled adlayers critically depend on not only the interchain van der Waals (vdW) interactions, but also on multiple intermolecular interactions, including BrO[double bond, length as m-dash]C and BrS hetero-halogen bonds, homo-BrBr interactions, and HBr and HO hydrogen bonds. We proposed that the cooperation and competition of the intermolecular interactions involving a Br atom and interchain vdW forces induce this structural variety. Density functional theory calculations support to unravel the different elementary structural units based on halogen bonds and hydrogen bonds and were useful tools to dissect and explain the formation mechanism.

Controllable Orientation of Ester-Group-Induced Intermolecular Halogen Bonding in a 2D Self-Assembly.

Halogen bonding with high specificity and directionality in the geometry has proven to be an important type of noncovalent interaction to fabricate and control 2D molecular architectures on surfaces. Herein, we first report how the orientation of the ester substituent for thienophenanthrene derivatives (5,10-DBTD and 5,10-DITD) affects positive charge distribution of halogens by density functional theory, thus determining the formation of an intermolecular halogen bond and different self-assembled patterns by scanning tunneling microscopy. The system presented here mainly includes heterohalogen X···O═C and X···S halogen bonds, H···Br and H···O hydrogen bonds, and I···I interaction, where the directionality and strength of such weak bonds determine the molecular arrangement by varying the halogen substituent. This study provides a detailed understanding of the role of ester orientation, concentration, and solvent effects on the formation of halogen bonds and proves relevant for identification of multiple halogen bonding in supramolecular chemistry.

Effects of the position and number of bromine substituents on the concentration-mediated 2D self-assembly of phenanthrene derivatives.

The effects of the position and number of bromine substituents on the self-assembled patterns of phenanthrene derivatives by changing multiple weak intermolecular interactions were investigated at the 1-octanoic acid/graphite interface at different concentrations by scanning tunneling microscopy. Two Br substituted DBHP molecules (2,7-DBHP, 3,6-DBHP) and BHP without a Br group formed a linear lamellar pattern by the van der Waals interactions between the alkoxyl chains in each lamella at high concentrations, which forces the phenanthrene derivatives to self-organize in a π-π stacked edge-on conformation. On decreasing the solution concentration, owing to the molecule-molecule van der Waals force and BrBr halogen bonds or the molecule-solvent cooperative BrO (C[double bond, length as m-dash]O) hydrogen and BrHO-hydrogen bonds, 2,7-DBHP molecules were found to form two kinds of network structures, whereas 3,6-DBHP molecules formed only a zigzag pattern due to the intermolecular BrBr van der Waals type interactions. One bromine substituted phenanthrene derivative (3-DBHP) formed a dislocated linear pattern by two C-HBr hydrogen bonds in each dimer. These observations revealed that an important modification of the position and number of halogen substituents might dramatically change the self-assembly behaviors by different intermolecular interactions including BrBr and BrO halogen bonding, BrBr van der Waals type interactions, and HBr hydrogen bonding. DFT calculations were explored to unravel how slightly tuning the molecular structure defines the geometry of a 2D self-assembled nanoarchitecture through the different elementary structural units having BrBr and BrH interactions.

Dynamic evaluation of environmental impact due to tritium accidental release from the fusion reactor.

As one of the key safety issues of fusion reactors, tritium environmental impact of fusion accidents has attracted great attention. In this work, the dynamic tritium concentrations in the air and human body were evaluated on the time scale based on accidental release scenarios under the extreme environmental conditions. The radiation dose through various exposure pathways was assessed to find out the potential relationships among them. Based on this work, the limits of HT and HTO release amount for arbitrary accidents were proposed for the fusion reactor according to dose limit of ITER. The dynamic results aim to give practical guidance for establishment of fusion emergency standard and design of fusion tritium system.

High-spin states and level structure in stable nucleus strontium-84.

High-spin states of (84)Sr are populated through the reaction (70)Zn ((18)O, 4n) (84)Sr at the beam energy of 75 MeV. The measurements of excitation functions, γ-γ coincidences, directional correlations of oriented states (DCO) ratios and γ-transition intensities are performed using eight anticompton HPGe detectors and one planar HPGe detector. Based on the experimental results, we establish a new level scheme of (84)Sr, in which 12 new states and nearly 30 new γ-transitions are identified in the present work. The positive-parity yrast band is extended to spin I(π) = 24(+), while one negative-parity band is extended to spin I(π) = 19(-) and it is found that the even-spin and odd-spin members in high-spin states show the nature of signature staggering. The deformation of (84)Sr is studied by calculating the total-Routhian-surfaces (TRS) of positive-parity yrast states in the cranked shell model formalism.

Comparison of serum from gastric cancer patients and from healthy persons using FTIR spectroscopy.

Since serum can reflect human beings' physiological and pathological conditions, FTIR spectroscopy was used to compare gastric cancer patients' serum with healthy persons' serum in this study. The H2959/H2931, H1646/H1550, H1314/H1243, H1453/H1400 and H1080/H1550 ratios were calculated, among these ratios, the H2959/H2931 ratio might be a standard for distinguishing gastric cancer patients from healthy persons. Then curve fitting was processed using Gaussian curves in the 1140-1000 cm(-1) region, and the result showed that the RNA/DNA ratios of gastric cancer patients' serum were obviously lower than those of healthy persons' serum. The results suggest that FTIR spectroscopy may be a potentially useful tool for diagnosis of gastric cancer.

SU-E-T-504: Incident Fluence Reconstruction Based on Monte Carlo Finite-Size Pencil Beam Model for Dose Guided Radiation Therapy.

PURPOSE: In dose guided radiation therapy, incident fluence is one of the important parameters for both influence verification and dose reconstruction. The objective of this investigation was to develop a method to obtain the incident fluence for dose reconstruction in dose guided radiation therapy (DGRT). METHODS: An incident fluence reconstruction model based on Monte Carlo Finite-size pencil beam (MCFSPB) model and "Matthew Effect" Conjugate-gradient (CG) algorithm was developed, where the MCFSPB model was developed by FDS Team (www.fds.org.cn) and the "Matthew Effect" was proposed to advance the accuracy of CG lgorithm. Then, by measuring dose with amorphous silicon flat panel (a-Si flat panel), the incident fluence was unfolded. An artifical head phantom was used to test sample. By using the incident fluence to dose calculation with MCFSPB, the 2D and 3D dose was also reconstructed and compared with the measurement dose and the planing dose respectively. The Passing Rate of Dose Difference (PRDD) in 3% was used to learn the accuracy. RESULTS: Two representative cases (6MV and 10MV) with both five beams were used for beam-by-beam verification, and the corresponding incident fluence was obtained. By comparing the measurement dose with the calculation dose on measurement plane, the results showed that the PRDD (3%) in field was 100%. And by comparing 3D plannning dose with 3D reconstructed dose, the results indicated that the PRDD (3%) in field was 95%∼98%. CONCLUSIONS: The incident fluence reconstruction model based on MCFSPB model and "Matthew Effect" Conjugate-gradient algorithm was developed. The tested results indicated its accuracy. This study is expected to be applied to 3D dose reconstruction and 3D dosimetric verification in DGRT. Supported by the National Natural Science Foundation under grant No.30900386 and the National Science Foundation of Anhui Province (Nos.090413095 and 111040606Q55).

SU-E-T-204: A Prototype of Dose-Guided Radiation Therapy.

PURPOSE: With the advancement in dosimetric devices and the development of dose reconstruction algorithm, the implementation of dose-guided radiation therapy (DGRT) is feasible. In order for DGRT to be performed clinically, a prototype of DGRT was developed in this study. METHODS: The prototype adopted a strategy for DGRT that adjusted the treatment plan for future fractions to compensate for dosimetric errors from past fractions, which included four main functional modules: management of patient plan information, dose reconstruction, dose evaluation, plan adjustment. we developed our dose reconstruction procedure, including the dosimetric calibration of the portal image acquired using electronic portal image device (EPID) during treatment and three-dimensional (3D) patient dose reconstruction based on Monte Carlo Finite-size pencil beam (MCFSPB) model and Conjugate-gradient (CG) algorithm developed by FDS Team (www.fds.org.cn). The dose evaluation tools including 3D Gamma analysis and dose-volume-histogram (DVH) analysis were also available which were used to compare the reconstruction dose with the planning dose. Finally we re-optimizing the treatment plan according to the information provided by dose evaluation. RESULTS: In order to validate the availability of the workstation prototype, lots of experiments were carried out based on head phantom. The result showed that disagreement between the reconstructed dose and the planning dose (calculated by the Accurate Radiotherapy System (ARTS) developed by FDS Team) was observed by the DGRT prototype when there existed position error for head phantom or the accelerator delivery was not accurate. CONCLUSIONS: An effective prototype for DGRT has been developed. With these techniques, the clinical implementation of DGRT is possible in the near future. Supported by the National Natural Science Foundation under grant No.30900386 and the National Science Foundation of Anhui Province (Nos.090413095 and 111040606Q55).

Repeated positioning in accurate radiotherapy based on virtual net technique and contrary reconstruction scheme.

This paper presents a new repeated positioning system for external radiotherapy. A new scheme is proposed to rebuild patient's body surface 3-D image based on simple stereo vision model and virtual net technique, which improves the reconstruction precision of the template. For the calculation of the positioning error, the contrary reconstruction scheme is adopted and the positioning speed is greatly improved. The 3-D reconstructed video image of the right position in the first positioning is used as the reference template for the next positioning, and the positioning error is evaluated by projecting the template image into the patient's real-time video images and calculating the correlation ratio in the areas limited by the triangle of the reference image.

'A finite size pencil beam for IMRT dose optimization'--a simpler analytical function for the finite size pencil beam kernel.

A simple and finite-termed analytical function for the finite size pencil beam kernel was constructed. The dose cross-profile of a semi-infinite field with field edge at x = 0 can be well fitted by the Boltzmann function. The pencil beam cross-profile of width 2x(0) can be obtained as the difference between two semi-infinite fields shifted by 2x(0). If the profile is centred about x = 0, it can derive from P(x + x(0)) - P(x - x(0)). The penumbra influence can be taken by the penumbra tuning factor f. The parameters A(1), A(2), A(3), A(4), f can be obtained by fitting depth-dose curves and cross-profiles for a set of square fields. The two-dimensional dose distribution F(x, y, x(0), y(0), A(1), A(2), A(3), A(4), f(1), f(2)) of a pencil beam of width (2x(0), 2y(0)) is defined by multiplication of two independent one-dimensional profiles.

An integrative radiation protection control system based on a CAN bus for the HT-7U tokamak fusion device.

A radiation protection control system has been designed, based on distributed computers and consideration of the features of the radiation source of the HT-7U fusion experimental device, for protecting the workers and the public against neutron and photon radiation, and especially for ensuring that workers cannot unexpectedly enter an area of high radiation level in any case. A multisubsystem (irradiation monitoring subsystem, access control subsystem, safety interlock subsystem and other related facilities) integration concept is proposed for the design. This system has been implemented on the basis of the up-to-date industrial field bus CAN, featuring simplicity and flexibility of installation and maintenance, capability for real-time long distance communication and multi-master protocol.

Diffusion of Eu(III) in compacted bentonite-effect of pH, solution concentration and humic acid.

The effect of pH, Eu(III) solution concentration and humic acid on the diffusion of Eu(III) in compacted bentonite (rho(b) = 1000 +/- 30 kg/m(3)) was studied with "in-diffusion" method at an ionic strength of 0.1M NaClO(4). The results (K(d) values from the first slice and theoretical calculation, apparent and effective diffusion coefficients) derived from the new capillary method are in good agreement with the literature data under similar conditions, and fit the Fick's second law very well. The results suggest that the diffusion of Eu(III) is dependent on pH values and independent on solution concentration in our experimental conditions. Humic acid forms precipitation/complexation with Eu(III) at the surface of compacted bentonite and thus deduces the diffusion/transport of Eu(III) in compacted bentonite. The K(d) values in compacted bentonite are in most cases lower than those in powdered bentonite obtained from batch experiments. The difference between the K(d) values from powdered and compacted bentonite is a strong function of the bulk density of the bentonite. The results suggest that the content of interlaminary space plays a very important role to the diffusion, sorption and migration of Eu(III) in compacted bentonite.