Nuclear microscopy in Alzheimer’s disease

The elemental composition of the two types of brain lesions which characterise Alzheimer’s disease (AD) has been the subject of intense scrutiny over the last decade, ever since it was proposed that inorganic trace elements, particularly aluminium, might be implicated in the pathogenesis of the disease. The major evidence for this involvement was the detection of aluminium in the characteristic lesions of the AD brain; neuritic plaques and neurofibrillary tangles (NFTs). Using the powerful combination of Particle-Induced X-ray Emission (PIXE), Rutherford Backscattering Spectrometry (RBS) and Scanning Transmission Ion Microscopy (STIM), it is possible to image and analyse structures in brain sections without recourse to chemical staining. Previous results on elemental composition of senile plaques indicated the absence of aluminium at the 15 parts per million level. We have more recently focused on the analysis of neurofibrillary tangles (NFTs), destructive structural defects within neurons. Imaging and analysis of neurons in brain tissue presented a greater challenge due to the small dimensional size compared with the plaques. We describe the methodology and the results of imaging and analysing neurons in brain tissue sections using Nuclear Microscopy. Our results show that aluminium is not present in either neurons or surrounding tissue in unstained sections at the 20 ppm level, but can be observed in stained sections. We also report elemental concentrations showing significant elevations of phosphorus, sulphur, chlorine, iron and zinc.     

The effect of pre-stressing and annealing on the young's modulus of some nuclear graphites

Studies have been made on the decrease in the dynamic Young's modulus of some nuclear graphites caused by pre-stressing or cyclic loading in compressive mode and its recovery due to annealing up to 2000 °C. It is found that the decrease in the modulus is well represented by the formulae, $\text{E}\text{E}{}_0\text{= ? Aσ}{}^2\text{+B}$ for ex-truded graphites and $\text{(E ? E}{}_{\mathrm{c}}\text{)}\text{(E}{}_0\text{?E}{}_{\mathrm{c}}\text{) = B}\text{exp}\text{( ? Aσ}{}^2\text{)}$ for moulded ones, where E, E_c and E₀ are the modulus at a pre-stress σ, that at pre-stress equal to fracture stress and that with no pre-stressing, respectively. A and B are constants. Annealing experiments show that the moduli of extruded graphites recover almost completely below 1000 °C, while in the case of moulded graphites complete recovery is not attained even at 2000 °C. The activation energy obtained for the recovery of an extruded graphite below 1000 °C is about 0.6 eV.     

A flow rule based on Huddleston’s multiaxial rupture criterion as a yield function

An elastic–plastic constitutive equation is proposed to develop a continuum damage model for multiple flawed medium. The constitutive model takes into account the effect of hydrostatic stress to describe the decrease of rigidity and flow stress in tension and has an extended form of Huddleston’s equi-rupture function. The decrease of those properties due to an evolution of damage is described by a proper selection of parameters in the yield function in accordance with a state of damage. Some case studies are shown. The model can be extended to include the kinematic and combined hardening rules or incorporated in constitutive equations for finite element calculations such as unified models.     

C. Rubbia’s hybrid plant concept: a preliminary technical and economic analysis

The long term development of nuclear energy depends, inter alia, on the ability to use the abundant fertile materials (238U and/or thorium) and on an accepted management of the long-lived radioactive wastes. In order to meet both these objectives, C. Rubbia has presented a new version of an old concept: the hybrid reactor where a subcritical reactor is fed with neutrons produced by spallation. In his concept, the reactor is a molten lead cooled fast reactor, which can use either the uranium or the thorium cycle, and burn the minor actinides and some fission products. The present work is a preliminary and partial technical and economic analysis of the reactor part of C. Rubbia’s proposal as they were set forth in a French Parliamentary audition in November 1996. The technical conclusions are that many of the design options proposed are not optimum and the uncertainties important, which is not particularly surprising at this stage of the concept. The economic ‘guesstimate’ yields a cost per kWh anywhere between one and two times that of a modern light water reactor, which is in contradiction with C. Rubbia’s claims (half the cost!), but in a range which warrants more conceptual work before drawing any conclusions. Alternative design concepts are suggested.     

Structural shock tests of prototype FBR “MONJU” scale models

This paper presents some results of experiments which simulate the structural dynamic response of a LMFBR primary coolant boundary to a hypothetical core disruptive accident (HCDA) based on scale models and high explosives. It was noted that high explosives are no longer a good simulant of the HCDA. However, the main purpose of the program, which included this experiment, is not to experimentally predict the dynamic response of the reactor structure at the HCDA, but to validate computer codes, which describe the pressure wave propagation and damage process in the reactor structures, using data obtained from these model experiments. The experiments were undertaken using many 1/15 scale simple models of the reactor vessels and internal structures, as well as 1/15 and 1/7.5 scale complex models of the interim design of prototype LMFBR ‘MONJU’. Simple model experiments involved a series of shock tests using pentolite to investigate the configuration effects of the vessel restraining section, the dipped-plate effect and the core barrel effect, respectively.     

Radioactivity of neutron-irradiated cat’s-eye chrysoberyls

The recent report of marketing of radioactive chrysoberyl cat’s-eyes in South-East Asian markets has led us to use an indirect method to estimate the threat to health these color-enhanced gemstones may pose if worn close to skin. We determined the impurity content of several cat’s-eye chrysoberyls from Indian States of Orissa and Kerala using PIXE, and calculated the radioactivity that would be generated from these impurities and the constitutional elements if a chrysoberyl was irradiated by neutrons in a nuclear reactor for color enhancement. Of all the radioactive nuclides that could be created by neutron irradiation, only four (⁴⁶Sc, ⁵¹Cr, ⁵⁴Mn and ⁵⁹Fe) would not have cooled down within a month after irradiation to the internationally accepted level of specific residual radioactivity of 2 nCi/g. The radioactivity of ⁴⁶Sc, ⁵¹Cr and ⁵⁹Fe would only fall to this safe limit after 15 months and that of ⁵⁴Mn could remain above this limit for several years.     

The spectral Green’s function linear-nodal method for one-speed X, Y-geometry discrete ordinates deep penetration problems

A new spectral nodal method is developed for the solution of one-speed discrete ordinates (S_N) problems with isotropic scattering in X, Y geometry. In this method, the spectral Green’s function (SGF) scheme, originally developed for solving S_N problems in slab-geometry with no spatial truncation error, is generalized to solve the one-dimensional transverse-integrated S_N linear-nodal equations with linear polynomial approximation for the transverse leakage terms. The resulting SGF-linear-nodal (SGF-LN) equations are solved with the full-node inversion (FNI) iterative scheme, which uses the best available estimates for the node-entering quantities to evaluate the node angular quantities in all the exiting directions as the equations are swept across the system. We give numerical results that illustrate the accuracy of the SGF-LN method for coarse-mesh calculations.     

Recovery of neutron-induced damage of SiC by thermal annealing up to 1400 °C

Recovery of the specimen length of neutron-irradiated SiC was observed using a precision dilatometer. The specimens were heated isothermally and isochronally. The accuracy of length measurement at high temperature using the dilatometer was compared with that of length measurement at room temperature using a micrometer. It was clarified that the dilatometer method showed high accuracy and stability. The dilatometer method was applied to observe length recovery by isothermal annealing at 1200 °C of the neutron-irradiated SiC, and at least two recovery rates were clarified.     

High power millimeter wave experiment of torus diamond window prototype for ITER EC H&CD system

The design of the torus diamond window for the ITER electron cyclotron heating and current drive (EC H&CD) system has advanced considering a reliable and manufacturable structure. The diamond window prototype was fabricated based on the design and the high power experiment was carried out to verify the millimeter wave transmission capability. Transmission of 740 kW-100 s was demonstrated and no significant temperature increase of the window structure and no damage on the diamond disk were obtained. The temperature saturation of the cooling water for the window was observed and loss tangent of 7.8 × 10^?6, which was the lowest value that we had ever obtained at JAEA, was evaluated. This result indicates that the diamond window design is feasible and promising the high power more than 1 MW transmission.     

R&D activities on manufacturing plasma-facing unit for prototype of ITER divertor outer target in JADA

Japan Domestic Agency (JADA) carried out R&Ds activities to improve joining CFC monoblocks onto a CuCrZr cooling tube in PFUs to boost the success rate of joint and to confirm load carrying capability of the monoblock attachments to Steel Support Structure (SSS) against tensile force simulating electromagnetic load to pull PFUs from SSS. In joining the CFC monoblocks to the cooling tube, JADA has adopted brazing by using noble-metal-free filler with the following improvements; (1) metalizing joint surface of CFC using Ti-coating with accurate thickness controlling, (2) Changing buffer layer material from soft pure copper to Cu–W alloy. By using the present improved joint, JADA has manufactured three mock-ups with 5 CFC monoblocks and tested against repetitive high heat loads more than 20 MW/m². All of CFC monoblocks of each mockup can survive the high heat loads throughout 1000 cycles with no degradation of heat removal capability. Regarding the load carrying capability of monoblock attachments to SSS, tensile experiments were carried out using the same geometries of CFC and tungsten monoblocks in PFUs and the results show that both geometries and joints meet the ITER requirements, that is, 3 kN and 8 kN, respectively.     

Optical and structural properties of ZnO thin films; effects of high energy electron irradiation and annealing

High energy electron irradiation (HEEI) effects on the as-grown and annealed ZnO thin films grown by electrochemical deposition were investigated. Both samples were exposed to the sequential electron irradiations of 6, 12 and 15 MeV energies at a fluence of 1 × 10¹² e⁻/cm². The results of X-ray diffraction suggest that a highly strong crystallographic structure can be produced by annealing process. Photoluminescence (PL) studies show that the EI produces violet emission which results from the zinc interstitial. Recombination lifetime (RL) values of the both films reveal that the high quality crystals are obtained. The decreasing trends of RL values with increasing electron energy have been explained by the formation of crystal defects due to the HEEI.     

基于Geant4的肺部计数器效率校准及其受核素分布影响研究

效率校准是人体内照射活体监测中的一个关键环节,是影响内污染活体测量准确性的一个重要因素。利用人体躯干物理模型的CT扫描图片和实验确定的探测器晶体尺寸,分别建立了三维人体数字模型和高纯锗探测器的计算模型,进而通过调用Geant4工具包,编写了模拟肺部计数器的蒙特卡罗程序,用以校准计数器效率。在此基础上,结合ICRP生物动力学模型,模拟计算全身其他器官滞留核素对肺部计数器计数的贡献,研究核素在其他器官的分布对计数器效率的影响。结果表明:肺部计数器效率的蒙特卡罗校准结果与实验测量结果相对偏差为2.47%(对59.5 ke V)和-8.58%(对17.5 ke V);在摄入核素241Am的最初2天内和50天后,人体的实际探测效率要高于只考虑肺部滞留的探测效率,在其他器官分布的核素在肺部计数器的计数占总计数的60%以上,而在摄入中期(第3—50天),二者结果较为一致,AMAD为1μm时,其他器官内核素的计数小于20%,AMAD为5μm时,其他器官内核素的计数在30%以内。     

Current status and technical description of Chinese 2 × 250 MWth HTR-PM demonstration plant

After the nuclear accidents of Three Mile Island and Chernobyl the world nuclear community made great efforts to increase research on nuclear reactors and to develop advanced nuclear power plants with much improved safety features. Following the successful construction and a most gratifying operation of the 10 MW_th high-temperature gas-cooled test reactor (HTR-10), the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University has developed and designed an HTR demonstration plant, called the HTR-PM (high-temperature-reactor pebble-bed module). The design, having jointly been carried out with industry partners from China and in collaboration of experts worldwide, closely follows the design principles of the HTR-10.Due to intensive engineering and R&D efforts since 2001, the basic design of the HTR-PM has been finished while all main technical features have been fixed. A Preliminary Safety Analysis Report (PSAR) has been compiled.The HTR-PM plant will consist of two nuclear steam supply system (NSSS), so called modules, each one comprising of a single zone 250 MW_th pebble-bed modular reactor and a steam generator. The two NSSS modules feed one steam turbine and generate an electric power of 210 MW.A pilot fuel production line will be built to fabricate 300,000 pebble fuel elements per year. This line is closely based on the technology of the HTR-10 fuel production line.The main goals of the project are two-fold. Firstly, the economic competitiveness of commercial HTR-PM plants shall be demonstrated. Secondly, it shall be shown that HTR-PM plants do not need accident management procedures and will not require any need for offsite emergency measures.According to the current schedule of the project the completion date of the demonstration plant will be around 2013. The reactor site has been evaluated and approved; the procurement of long-lead components has already been started.After the successful operation of the demonstration plant, commercial HTR-PM plants are expected to be built at the same site. These plants will comprise many NSSS modules and, correspondingly, a larger turbine.     

Uncertainty and sensitivity analysis of MCPs’ trip events at Ignalina NPP

Eight main circulation pumps (MCPs) are employed for the cooling water forced circulation through the RBMK-1500 reactor at the Ignalina nuclear power plant (NPP). There have been a few events when one or more MCPs were inadvertently tripped.This paper presents investigation of a one MCP trip event and all MCPs’ trip events at Ignalina NPP. Thermal-hydraulic analysis was conducted using the best estimate system code RELAP5/MOD3.3. Uncertainty and sensitivity analysis of flow energy loss in different parts of the main circulation circuit (MCC), initial conditions and code-selected models was performed. Such analysis allows to estimate the influence of separate parameters on the calculation results and find those modelling parameters that have the largest impact on the investigated events. Uncertainty analysis indicates that natural circulation provides adequate cooling in the case of all MCPs tripped, and that the reactor is reliably cooled by forced circulation in the case of a single tripped MCP. On the basis of this analysis, recommendations for the further improvement of model are developed.     

Development of ‘Pad Element’ for detailed core deformation analyses and its verification

It is important to understand the deformation behaviors of FBR core in the aspects of safety and economy, and to attain more precise analyses of the core mechanics for sophistication of the core structure design. However, the interaction among subassemblies, which occurs as the result of contact between pad surfaces of adjacent subassemblies, makes the core mechanics complicated. Therefore, it is important to consider the characteristics of pads in the analysis in order to realize detailed analysis. The aim of this study is to develop special ‘Pad Element’, which owes the role to treat the interaction between subassemblies at their pads precisely. In this paper, the detailed formulation of ‘Pad Element’ and the analysis results of an example problem for verification are described.     

Underground siting of nuclear power plants with emphasis on the ‘cut-and-cover’ technique

This paper provides a survey of activities in the field of underground siting in Europe. Emphasis is placed on the ‘cut-and-cover’ technique because of the geological and topographical conditions prevailing in Germany. Basic considerations show the potential of an additional level of containment, of better protection against external effects, and of better conditions for decommissioning. Design concepts for HTR systems and especially for LWR systems which do not require extensive changes in the above-ground design are defined, and a preliminary assessment is given.