Identification of radiation treatment of wheat （Triticum aestivum. L）and rice （Oryza sativa. L） samples using thermoluminescence of contaminating minerals

Food irradiation is gaining popularity worldwide and this technology is important to improve quality and reduce the post harvest losses of food. Because of the rapid commercialization of irradiated foods throughout the world, compliance of different regulations relating to use of technology in different countries and demand of consumers for clear labelling of irradiated foods, there is need for the development of analytical methods to detect radiation treatment of food. Among several methods studied so far, thermoluminescence （TL） is an important method that can be used to find out the irradiation history of food that contain even a very minute amount of dust particles. In this study, the irradiated and unirradiated wheat and rice samples were analyzed using the TL method. The samples were purchased from the local market of Peshawar and irradiated to radiation doses of 0.5 and 1.0 kGy using Co-60 gamma irradiator at the Nuclear Institute for Food and Agriculture （NIFA）, Peshawar. The mineral contaminants were isolated by jet water, ultrasonic treatment, and density gradient. TL glow curves of the isolated minerals from irradiated and unirradiated samples were recorded between the temperature ranges of 50-500℃ using a TL reader. Generally, the glow curves for irradiated samples showed much higher TL intensities （TL1） than the unirradiated samples. The results were normalized by rerradiation of mineral samples to gamma-ray dose of 1.0 kGy followed by determination of the second glow curves （TL2）. The ratio of the area of first glow curve to that of second glow curve （TL1/TL2） was calculated for selected temperature intervals and compared with the recommended values for unirradiated and irradiated samples. Finally, the shapes of the glow curves for irradiated and unirradiated samples were also analyzed. On the basis of these results （comparison of TL-intensities, TL1/TL2 ratios and shapes of the glow curves）, all the irradiated and unirradiated samples of wheat and rice were unequivocally identified.     

旁路阀调节对高温气冷堆闭式布雷顿循环瞬态特性影响研究

闭式布雷顿循环是第4代高温堆核能系统的关键技术之一,其典型的动态过程是旁路阀调节。为分析这一过程,建立了循环中关键部件的动态模型,其中压气机在径向平衡模型基础上耦合了对附面层发展的预测,兼顾了计算效率与准确性;换热部件模型基于双曲型守恒律方程,对工质的热物性和参数的快速变化有较好的适应性。在此基础上根据回路的质量守恒和压力平衡原则将各部件的模型耦合,建立了系统的动态模型。由于旁路阀调节是氦气透平发电系统主要的功率快速调节手段,瞬态效应较为显著,以模块式高温气冷堆（HTR-10GT）旁路阀开启后的过渡过程作为算例,分析了主要循环参数的响应特性,并通过分析,给出了降低输出功率的机制。计算结果表明：系统的容积惯性对旁路阀调节的响应速度影响较大,而阀门的开度则决定了系统在末态的输出功率;回热器的温度冲击现象可能发生在调节过程中,但可通过两旁路阀联动的方式缓解;反应堆出口温度变化幅度很小,因此反应堆模型的准确程度对结果基本无影响。     

Extraction of Uranium from Sea Water by Method of Dispersion and Deposition

The extraction of uranium from sea water by the adsorption on the mixture of titanic acid and bentonite making the uranium rich deposit on the sea bottom is described. The purpose of this work is the minimization of energy required for contacting the vast volume of sea water with the adsorbent. Unique features of bentonite are applied to the coagulation of adsorbent forming the particles of suitable size in the sea water to make uranium rich deposit on the sea bottom close to the land. The concentration of uranium in the deposit is about 380 times that of sea water, and the loss of titanium is about 2% of the total amount of titanium which is used with the bentonite of ten times as much as it.

The depths of sea necessary to make uranium rich deposit for the various conditions were calculated and the result was obtained that 50 m was sufficient for this method. As a trial of the second stage of concentration of deposited uranium, the continuous RIP method was carried out in counter-current fluidized bed which was operated without reversal of flow.

The results reported in this paper are based on the laboratory scale experiments using the artificial sea water and on the calculations concerned with the rate of adsorption in agitated systems.     

非均匀两相流传热管流致振动中阻尼模拟研究

In the flow-induced vibration analysis of the heat exchanger tube of the stream generator, the damping of each position on the tube is different, since the secondary side of the tube is the two-phase flow (stream-water) and the void-fraction is gradually increased from bottom to top. It is necessary to study the simulation of the tube damping in non-uniform two-phase flow. The study is based on the Pettigrew's damping formula of tube in two-phase flow and the void-fraction distribution along the tube in the typical example. For the two-phase damping component of the tube damping, the disadvantage of damping overestimation of void-fraction processing method in common engineering software are analyzed. The reason is the nonlinearity of the void-fraction influence coefficient. The method of segmentation weighting void-fraction is developed. The effects of different segment lengths are studied, indicating that the section lengths should be minimized. For the subsequent segmentation damping weighting problem, the effects of different weighting factors in engineering methods and standards are compared, and the difference is small. The results of flow-induced vibration analysis with different damping inputs were compared to judge the applicability of Pettigrew's damping formula. From the above four researches, the recommended simulation method of the tube damping in non-uniform two-phase flow is given to more accurately carry out the flow-induced vibration analysis of heat exchanger tube.     

Method of In-Service Calibration of Electromagnetic- Flowmeter for LMFBR Utilizing Average Frequency of Output Voltage Fluctuation

In the LMFBR, electromagnetic-flowmeters (EMFs) have been extensively used. A calibration method for EMF using cross-correlation of its output voltage fluctuations has been proposed. This method, however, requires two pairs of electrodes, and it is desired to develop an alternative method without this requirement.

In the present paper, the process by which the turbulent behavior of a fluid in a pipe is transformed into the output voltage fluctuation is considered; and the average frequency weighted by the square root of the autopower spectral density of the fluctuation is developed as a function of the flow rate. The average frequency is proportional to the product of the flow rate and the square root of the friction coefficient of the pipe. Consequently, the flow rate is determined by measuring the average frequency, once the proportional coefficient is obtained.

The experiment was conducted with a 12 in. diameter saddle coil type EMF in the primary cooling system of “JOYO” reactor. Though the experimental value of the proportional coefficient was somewhat deviated from the calculated one, it is concluded that the performance degradation of the EMF can be calibrated with an accuracy of 1–2% error.     

CEFR 100%额定功率运行汽轮机发电能力分析

中国实验快堆(CEFR)首次100%额定功率发电运行中,实际电功率较设计值相差较多。为判断影响机组实际发电能力的主要原因,以现场采集的运行数据和汽轮机厂商提供的设计资料为基础,进行了相应的计算分析。对汽轮机内效率进行修正,绘制汽轮机近似热力过程曲线,并通过实测的各段抽汽压力,在热力过程曲线上获得抽汽焓值;利用换热器的能量守恒和流量守恒的基本方程进行除氧器和各加热器的热平衡计算,获得各段抽汽的流量;利用汽轮机的功率计算方程,得到汽轮机发电功率的计算值。通过计算值与实际值的比较分析,得出主蒸汽参数不达标是影响CEFR汽轮机发电能力的主要因素。     

Experimental Study on Base-triggered Explosions in Molten-tin/Water Systems

The mechanism of explosions triggered at the bottom of a pool of liquid (i.e., base-triggered explosions) was experimentally investigated by dropping molten tin into water. We studied the effect of the tin temperature, the water temperature, the water depth, and the distance between the walls at the bottom of the pool on the tendency for explosions to occur. The experimental results showed that base-triggered explosions occurred at the bottom surface of the tank when the water temperature was near its saturation temperature. The occurrence of base-triggered explosions was also affected by the water depth. According to the interaction at the base, the observed explosions could be classified into two types: instantaneous and delayed explosions. The difference between the triggering mechanisms was explained by considering the homogeneous nucleation temperature of the water and the instantaneous interfacial temperature. The occurrence of delayed explosions was also affected by the distance between the side walls at the bottom of the pool. As the bottom surface area decreased, the tendency for base-triggered explosion increased.     

Unfolding the measured neutron spectra in the irradiation chamber of the UZrH reactor using iterative method

In the procedure of neutron fluence measurement in the whole energy range （10^-4 eV-18 MeV）, in the irradiation chamber of a UZrH reactor, the neutron energy spectra are unfolded using the method of minimizing directed divergence and SAND-II, which are used broadly at home and abroad. These methods belong to the iterative methods. In this article, the procedure of the spectra unfolding using the two methods is described in detail. The neutron spectrum distribution unfolded by the two methods agree well with each other. In the end, the major differences of the two iterative methods are compared with each other, and the main factors affecting the accuracy of the spectra unfolding with the iterative method are discussed.     

Comparative study on breakdown characteristics of trigger gap and overvoltage gap in a gas pressurized closing switch

Gas pressurized closing switches are one of the most important elements in FLTD-based systems. Improving the trigger performance of gas switches is useful for optimizing the output parameters and the reliability of the FLTD. In this paper, the breakdown characteristics of the trigger gap and the overvoltage gap are studied experimentally. The reasons for the different breakdown performance of the two gaps are also investigated. The results show that the breakdown delay of the trigger gap is more influenced by the trigger voltage, while the breakdown delay of the overvoltage gap is more influenced by the working coefficient and always higher than that of the trigger gap. The jitter of the trigger gap is more influenced by the trigger voltage and accounts more than 60% of the total switch jitter, while the jitter of the overvoltage gap is hardly changed with the trigger voltage as well as the working coefficient and maintains less than 1.4 ns. It is proved that the discharging product from the trigger gap can effectively reduce the breakdown delay and jitter of the overvoltage gap. Based on that, the effect and improvement of pre-ionization on the two gaps are also studied. It is concluded that the jitter of the trigger gap reduces obviously when the pre-ionization is added, while the pre-ionization almost has no effect on the jitter of the overvoltage gap. The jitter of the overvoltage gap is about two times higher than the trigger gap in the pre-ionizing switch.     

一种因参考光源强度变化导致的热释光剂量测量结果偏差的修正方法

在热释光剂量测量中，参考光源强度是影响测量结果的重要因素之一。对参考光源强度的调整往往通过调整测量仪器的高压来实现，但调高高压参数会导致测量仪器暗电流增加，进而导致测量值偏差增大。频繁的调整高压参数，也可能会使仪器的稳定性变差。针对参考光源强度变化导致的测量偏差，提出利用测量时的参考光源强度值与校准测量时参考光源强度值的变化求出相应的修正系数，进行测量结果修正。该方法经标准值样片测量检验，其测量值更准确、误差更小，与标准辐照值的偏差小于5%，表明该方法可行，可在实际工作中应用。     

大流量气溶胶滤膜标准γ体源制备技术

为制备大流量气溶胶滤膜标准γ体源，采用参数优化的专用滴源装置，将放射性标准溶液⁶⁰Co定量滴注在气溶胶取样滤膜上，晾干后对角折叠，并采用专用压样装置压制成与测量样品几何形状一致、密实的圆盘形固态物，密封保存。采用差重法对制备的滤膜标准γ源进行活度定值，制备的气溶胶滤膜标准γ体源活度值为4.4×10⁴ Bq，相对扩展不确定度U（k=2）为3.6%。采用分割压制法对气溶胶滤膜标准γ体源进行均匀性测量，相对标准偏差低于5%。制备的滤膜标准γ源可为测量大流量气溶胶样品的γ谱仪效率刻度服务。     

Gamma-ray attenuation technique for measuring void fraction in horizontal gas-liquid two-phase flow

The measurement of void fraction is of importance to the oil industry and chemical industry. In this article, the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by using a single-energy γ-ray system is described. The γ-ray source is the radioactive isotope of 241Am with γ-ray energy of 59.5 keV. The time-averaged value of the void fraction in a 50.0-mm i.d. transparent horizontal pipeline is measured under various combinations of the liquid flow and gas flow. It is found that increasing the gas flow rate at a fixed liquid flow rate would increase the void fraction. Test data are compared with the predictions of the correlations and a good agreement is found. The result shows that the designed γ-ray system can be used for measuring the void fraction in a horizontal gas-liquid two-phase flow with high accuracy.     

Pressure Balanced Type Membrane Covered Polarographic Oxygen Detector for Use in High Temperature-High Pressure Water

Component analysis of gamma-ray doses in criticality accident situations is indispensable for further understanding on emission behavior of gamma-rays and accurate evaluation of external exposure to human bodies. Such dose components were evaluated, categorizing gamma-rays into four components: prompt, delayed, pseudo components in the period of criticality, and a residual component in the period after the termination of criticality. This evaluation was performed by the combination of dosimetry experiments at the TRACY facility using a thermoluminescent dosimeter (TLD) made of lithium tetra borate and computational analyses using a Monte Carlo code. The evaluation confirmed that the dose proportions of the above components varied with the distance from the TRACY core tank. This variation was due to the difference in attenuation of the individual components with the distance from the core tank. The evaluated dose proportions quantitatively clarified the contribution of the pseudo and the residual components to be excluded for accurate evaluation of gamma-ray exposure. Such the contribution sum increased with increase in the distance from the core tank and was estimated to be in the range of 16 to 40% of the total gamma-ray dose measured by the TLD at TRACY.     

Ion beam analyses of particulate matter in exhaust gas of a ship diesel engine

There is an urgent need to reduce emission of the particulate matter (PM) in the exhaust gas from ship diesel engines causing various health hazards and serious environmental pollution. Usually the heavy fuel oil (HFO) for ships is of low quality, and contains various kinds of impurities. Therefore, the emission of PM along with exhaust gas from ship diesel engines is one of the most serious environmental issues. However, the PM fundamental properties are not well known. Therefore, it is important to perform elemental analysis of the PM. The HFO contains sulfur with a relatively high concentration of a few percent. It is important to make quantitative measurements of sulfur in the PM, because this element is poisonous for the human body. In the present work, PM samples were collected from exhaust gas of a test engine, and RBS and PIXE analyses were applied successfully to quantitative analysis of the PM samples. The RBS analysis enabled quantitative analysis of sulfur and carbon in the collected PM, while heavier elements such as vanadium and iron were analyzed quantitatively with the PIXE analysis. It has been found that the concentration ratio of sulfur to carbon was between 0.007 and 0.012, and did not strongly depend on the output power of the engine. The S/C ratio is approximately equal to the original composition of the HFO used in the present work, 0.01. From the known conversion ratio 0.015 of sulfur in the HFO to sulfates, the conversion ratio of carbon in the HFO to the PM is found to be 0.01-0.02 by the RBS measurements. On the other hand, the PIXE analysis revealed a vanadium enrichment of one order of magnitude in the PM.     

Study on Incipient Cracks at Inner Surface of Cladding Liner after High Power Irradiation Test

10x10 BWR segmented rods with a burnup of about 30 MWd/kgU were subjected to high power irradiation tests in the R2 reactor. Metallography on the cladding showed small incipient cracks with a depth of 10mm at the inner surface of the cladding liner after the irradiation tests. In order to investigate the incipient cracks, several post irradiation examinations were performed. Local micro-hardness of the liner was measured with an indentation force of 1 g. The results showed that the hardness was significantly increased at the inner surface facing the fuel. Electron probe micro-analysis (EPMA) of the liner gave an elemental profile showing an increased amount of fission products at the inner surface and the profile agreed with the micro-hardness profile. Scanning electron microscopy showed propagation of the incipient cracks along grain boundaries. Elemental mapping with EPMA showed concentrated cadmium at the incipient cracks. Considering these observed facts, the cause of the crack formation could be stress corrosion cracking (SCC). Applied hoop stress history to the liner during the irradiation test was calculated with a fuel performance analysis code. Based on the results of the observation and calculation, the process of the crack formation and propagation was discussed.     

Behaviour of package for transport of spent fuel assemblies exposed to beyond regulation fires

Abstract

Institut de Radioprotection et de Sûreté Nucléaire (IRSN) performed a study relative to the thermal behaviour of a new TN International package design for transport of spent fuel assemblies called TN®112. The aim of this study is to evaluate the behaviour of the package exposed to fires, with durations and temperatures different from those required in the IAEA regulation TS-R-1 (respectively 30 min and 800°C). Its main objective is to provide quantitative data available for safety assessment in emergency situations involving fires. Moreover it can also be used for a cross comparison with the analysis of the thermal behaviour of the package during the IAEA regulatory fire test presented by the applicant in the package design safety analysis report. This study is based on numerical calculations performed with the code THERMX-PROTEE. The three-dimensional model used represents a quarter of the upper half of the package, where the closure system is located. The thermal behaviour of the neutron-shielding resin located in the cavity plug, the trunnions and the packaging body was modelled to allow simulation of endothermic reactions of vaporisation. During the heating phase of the fire test, the water vapour produced in the heated resin components is transferred and condensed in the nearby colder elements; the associated thermal transfers can rapidly increase the temperature of the colder elements. The part of the vapour which cannot be condensed when most of the nearby resin elements reach a temperature above 100°C is evacuated through the holes that are distributed throughout the external envelope of the packaging and closed by fusible plugs under normal conditions. A specific calculation module has been developed to take into account the corresponding energy transfers. This module was qualified by comparison with the results of experimental fire tests. The calculations performed in the framework of this study cover fire temperatures between 400 and 1000°C. One of the results of those calculations is the time necessary to reach the maximum allowable temperature of the elastomer gaskets.     

辐射波HEMP模拟器关键参数数值分析

根据国际电工委员会(IEC)制定的最新高空核电磁脉冲(HEMP)标准,对辐射波模拟器关键结构的指标参数进行分解.分析了不同模拟器激励源和双锥结构对辐射电场波形关键参数的影响,基于分析曲线提出脉冲源的指标,最后给出辐射波HEMP模拟器自由空间辐射电场的计算波形.论文结果对此类模拟器的设计具有重要参考价值.     

Current status of radiation therapy for prostate cancer

Radiotherapy for the treatment of prostate cancer has been extensively explored in the past. Along with the comprehensive understanding of the biology of prostate cancer and rapid advances in terms of technology, the out- come of treatment for the patients with prostate cancer has improved. The authors review radiotherapy as the primary treatment for the disease, with particular emphasis on the technological advances from both the radiobiological and radiophysics aspects. Nonconventional fractionated irradiation like hyper- or hypo-fractionation has been imple- mented in the clinic, the final results still need to be confirmed in the future. Technological advances like IMRT, IGRT, in the last two decades have significantly improved the delivery of external radiotherapy to the prostate. This has re- sulted in an overall increase in the total dose that can be safely delivered to the prostate, which has led to modest im- provements in the biochemical outcome. However, establishing the standard therapy for prostate cancer remains con- troversial. It is hoped that the next decades will bring continued advances in the development of biologicals that will further improve current clinical outcomes.     

Coating Microspheres with Zirconium Carbide-Carbon Alloy by Iodide Process

Simultaneous deposition of carbon and zirconium from vapor produced by the reaction between methyl iodide vapor and zirconium sponge was studied with the application of a spouted bed constituted by a funnel carrying a charge of alumina microspheres, which were blown upward and held in dynamic suspension by a jet of the vapor and gases spouting from the funnel. The purpose of the experiment was to determine the conditions favorable for obtaining a coat of zirconium carbide-carbon alloy on the microspheres. Deposition of the vapor on the microspheres, leading to the formation of the carbon alloy coating, was found to take place at temperatures exceeding 1,100°C. The C/Zr ratio of the deposited coat was found to increase with deposition temperature. The hydrogen concentration in the spouting gas affected both the deposition yield and the chemical composition of the deposit. Repeated use of the sponge was found to impair its performance due to deactivation by premature deposition of carbon.     

Gamma radiation levels in the ambient environment of the QNPP Base

Monitoring results of gamma dose rate level in 1992～2004 in the ambient environment of the Qinshan Nuclear Power Plants(QNPP)Base,the northeast of Zhejiang Province,are reported in this paper.It is shown that the gamma dose rate of five monitoring sites of 2.5 km to QNPP Base is 84～113 nGy/h,with an average of 96 nGy/h in the 13 years.The average value is close to the background level of 93 nGy/h prior to operation of the QNPP Base,and is lower than the monitoring result of 101 nGy/h at the reference site in Hangzhou City.Within 50 km from the QNPP Base,the cumulative dose rate of the thermoluminescent dosimeter(TLD)is 90 nGy/h,which is lower than the back- ground level of 111 nGy/h.