Thrust load on welded-pad reinforced nozzle in an ellipsoidal pressure vessel head

A thin shell analysis is performed to investigate the stress distribution of welded-pad reinforced nozzles in ellipsoidal pressure vessel heads. A comparison of the structural behavior of such a nozzle to an integrally reinforced nozzle shows that a sixty percent higher stress is present in a typical nozzle-vessel geometry. A parametric study is performed for welded-pad reinforced nozzles in ASME 2:1 pressure vessel heads. Results are presented as stress concentration factors and shear stress concentration factors as functions of nondimensional nozzle-vessel geometries.     

Concept study for a combined reinforced concrete containment

A variety of different types of steel and concrete containments have been designed and constructed in the past. Most of the concrete containments had been pre-stressed, offering the advantage of small displacements and a certain leak-tightness of the concrete itself. However, considerable stresses in concrete as well as in the tendons have to be maintained during the whole lifetime of the plant in order to guarantee the required pre-stressing. The long-time behaviour and the ductility in the case of beyond-design-load cases must be verified. Contrary to a pre-stressed containment a reinforced containment will only be significantly loaded during test conditions or when needed in case of an accident. It offers additional margins which can be used especially for dynamic loads such as impacts or for beyond-design events.The aim of this paper is to show the feasibility of a so-called combined containment which means a containment capable of resisting both severe internal accidents and external hazards, mainly the aircraft crash impact as considered in the design of nuclear power plants in Germany.The concept is based on a lined reinforced containment without pre-stressing. The mechanical resistance function is provided by the reinforced concrete and the leak-tightness function is provided by a so-called composite liner made of non-metallic materials. Some results of tests performed at Siemens laboratories and at the University of Karlsruhe which show the capability of a composite liner to bridge over cracks at the concrete surface will be presented in the paper.The study shows that the combined reinforced concrete containment with a composite liner offers a robust concept with high flexibility with respect to load requirements, beyond-design events and geometrical shaping (arrangement of openings, an integration of adjacent structures). The concept may be further optimized by partial pre-stressing at areas of high concentration of stresses such as at transition zones or at disturbances around large openings.     

Pressure vessel nozzle repair

The dissimilar metal weldment joining Boiling Water Reactor (BWR) nozzles to safe-ends is one of the more complex configurations in the entire recirculation system. Field installation techniques typically specify that a special shop weld deposit (butter) be placed on the end of the nozzle prior to final shop post-weld heat treatment (PWHT) in order to facilitate field welding without PWHT. The shop weld deposit is normally an Inconel or stainless steel and does not require additional field heat treatment after welding. Soon BWR vessels used Inconel 182 manual shielded metal arc electrodes to weld deposit the butter. This manual process produces a deposit which is now known to be susceptible to intergranular stress corrosion cracking (IGSCC), especially under severe conditions such as crevices and/or cold work.Recently two BWRs have experienced, IGSCC of I-182 weld deposits in which axially oriented cracking progressed into the low alloy steel nozzle material. Although IGSCC extension from weld butter into nozzle material has been observed in other BWRs, these cases appeared to be the deepest. At Taiwan Power Company's Chinshan Unit 2 a repair has been completed in which the defect was verified visually, the old butter and defect removed by machining, the butter restored with PWHT and a new safe-end installed. At Carolina Power and Light's Brunswick Unit 1 a large number of deep axial indications have been identified on nine nozzles by ultrasonic examination. Weld overlay repairs using a temperbead procedure have been completed as a temporary measure while preparing for a permanent repair at the next refueling outage.Details of the cracking observations and repair activities are discussed. Concurrent repairs/replacements of safe-ends will also be described.     

Gas leakage rate through reinforced concrete shear walls: Numerical study

Unlined reinforced concrete shear walls are often used as ‘tertiary boundaries’ in the United States Department of Energy (DOE) to house dangerous gases. An unanticipated event, such as an earthquake, may cause gases stored inside the walls to disperse into the environment resulting in excess pollution. To address this concern, in this paper, a methodology to numerically predict the gas leakage rate through these shear walls under lateral loading conditions is proposed. This methodology involves finite element and flow rate analysis. Strain distributions are obtained from the finite element analysis, and then used to simulate the crack characteristics on the concrete specimen. The flow rate through the damaged concrete specimen is then estimated using flow rate formulas available from the literature. Results from an experimental specimen are used to evaluate the methodology, and particularly its robustness in the flow rate estimation.     

放射性气体~(220)Rn的准确测量研究

220Rn的准确测量是天然辐射照射剂量评价体系中的重要研究内容之一。基于常用的几种测氡仪,我们开发了它们的220Rn测量功能,并比较了它们的220Rn测量结果。结果表明,AB5抓取式测量方法其原理简单,测量结果稳定,可以作为220Rn测量的参考方法,但其探测下限较高;RAD7的220Rn测量结果受干燥剂状态的影响,需要适时刻度;AlphaGuard流气式测量虽然具有探测下限低的优点,但结果易受采样流速和前端采样管路状况的影响,只能作一般性参考。     

Comparative study of ADS for minor actinides transmutation

The methodology of the efficiency comparison of the different ADS-burners is discussed. ADS with lead–bismuth coolant (fast neutron spectrum), molten salt ADS (intermediate spectrum) and heavy water ADS (thermal spectrum) are chosen as representatives for the comparison. The first results of the suggested approach are discussed.     

Multi-dimensional modelling of multiphase flow physics: high-speed nozzle and jet flows — a case study

Multi-dimensional modelling of multiphase flows has become more prevalent as computer capabilities have significantly expanded. Such analyses are necessary if the flow physics demonstrates behavior that is fundamentally different from the estimates of one-dimensional analyses. Multiphase multi-dimensional behavior may involve physical mechanisms that interact with the flow field transverse to the main fluid direction and feedback into downstream processes. Consider the physics of high-speed internal nozzle flow, downstream external jet flow and the dynamics of jet breakup. This is a prime example of a coupled problem where multi-dimensional aspects may need to be considered. This paper examines multiphase physics as an illustration of the conditions under which multi-dimensional modelling would be required. Internal nozzle flow can involve cavitation phenomena, and as the geometry becomes more abrupt or asymmetric, multi-dimensional modelling is required. High-speed simulations using our internal flow model, CAVALRY, indicate that cavitation behavior can become oscillatory as the nozzle shape is altered. This exiting internal flow emerges as a multi-dimensional external jet flow, whose downstream breakup can be noticeably influenced by the inlet conditions as well as the jet breakup mechanisms. Jet breakup models first developed for the TEXASV model are utilized in the multi-dimensional KIVA code simulations for gas–liquid flows. The simulation results suggest that similar jet breakup mechanisms are operative for a multi-fluid system. Our comparisons to particular sets of data for high-speed nozzle flow and jet breakup in a gas suggest that the approach can be extended to multiphase systems using similar concepts; i.e. TEXAS-3d.     

Comparative study on Charpy specimen reconstitution techniques

Reconstitution techniques are often used to allow material from previously fractured Charpy-V specimens to be reused for additional experiments. This paper presents a comparative experimental study of various reconstitution techniques and evaluates the feasibility of these methods for future use in shielded cells. The following techniques were investigated: arc stud welding, 6.0 kW CO₂ continuous wave laser welding, 4.5 kW YAG continuous wave laser welding and friction welding. Subsize Charpy specimens were reconstituted using a 400 W YAG pulsed wave laser. The best result was obtained with arc stud welding; the resilience of the reconstituted specimens and the load-displacement curves agreed well with the reference specimens, and the temperature elevation caused by the welding process was limited to the vicinity of the weld. Good results were also obtained with friction welding; this process led to the best quality welds. Laser welding seems to have affected the central part of the specimens, thus leading to different resilience values and load-displacement curves.     

Design feasibility study of a divertor component reinforced with fibrous metal matrix composite laminate

Fibrous metal matrix composites possess advanced mechanical properties compared to conventional alloys. It is expected that the application of these composites to a divertor component will enhance the structural reliability. A possible design concept would be a system consisting of tungsten armour, copper composite interlayer and copper heat sink where the composite interlayer is locally inserted into the highly stressed domain near the bond interface. For assessment of the design feasibility of the composite divertor concept, a non-linear multi-scale finite element analysis was performed. To this end, a micro-mechanics algorithm was implemented into a finite element code. A reactor-relevant heat flux load was assumed. Focus was placed on the evolution of stress state, plastic deformation and ductile damage on both macro- and microscopic scales. The structural response of the component and the micro-scale stress evolution of the composite laminate were investigated.     

消脂素的间接碘标记法与直接碘标记法的对比研究

间接碘标记法是先以氯胺T（ch-T）法标记对羟基苯丙酸琥珀酰亚胺脂（Bolton-hunter试剂,BH试剂）,制备125I-BH,然后于冰浴中与LEP联结,得到125I-LEP;直接碘标记法是以ch-T法按常规对LEP直接进行标记。结果显示,间接碘标记法标记的125I-LEP放射性比活度为1．43MBq／μg,125I的总标记率为37．8％,所建立的RIA的灵敏度为0．25μg/L,在45天内标准曲线（0．5-30μg／L）稳定,B：Bo位于92．7％-17．5％到94．6％-22．8％之间。直接法制备的125I-LEP,放射性比活度为1．79MBq／μg,125I的总标记率为41．4％,方法灵敏度为0．37μg/L。在44天内标准曲线（0．5～30μg／L）亦较稳定,B：B0位于87．7％～23．7％到91．4％-35．2％之间。表明两方法的标准曲线稳定性在45天内差异不大,均能满足临床工作的需求。     

Optimum shape design of pressure vessel and nozzle junction

Thick spherical pressure vessels are frequently used in nuclear structural applications. The design of the junction of pipe nozzles and vessels needs careful consideration. In this paper the optimum shape design of the junction is considered. Minimization of the stress concentration factor is considered as the objective function. The junction is completely defined by a set of four curves which in turn depend upon four design variables. The stresses in the junction due to internal pressure are evaluated by finite element analysis using ring-shaped isoparametric elements. Stresses are sampled at a number of selected points along the boundary of the junction. The optimization of the nonlinear programming problem is carried out by an improved move limit method of sequential linear programming. Optimum shapes for internal pressure loading are presented for different transition lengths. The effect of axial load on the nozzle of optimum shapes is studied for a few cases. Detailed discussion of the results is presented.     

Failure assessment of RPV nozzle under loss of coolant accident

In case of a postulated loss of coolant accident (LOCA) of a reactor pressure vessel (RPV), the nozzle region experiences higher stresses and lower temperatures than the remaining part of the RPV. Thus, the nozzle is to be considered in the RPV safety assessment. For a LOCA event, three-dimensional elastic–plastic finite element calculations of stresses and strains in the intact RPV were performed. Using the substructure technique, fracture mechanics analyses were then carried out for several postulated cracks in the nozzle corner and in the circumferential weld below the nozzle. For different crack geometries and locations, the J-integral and the stress intensity factor were calculated as functions of the crack tip temperature. Based on the K_IC-reference curve and the J_R curve, both brittle and ductile instability of the postulated cracks were excluded. In order to reduce the expenses of three-dimensional finite element analyses for various crack geometries, an analytical procedure for calculating stress intensity factors of subclad cracks in cylindrical components was extended for cracks in the nozzle corner.     

Comparative study of two schemes for obtaining153Gd samples

Translated from Atomnaya Énergiya, Vol. 64, No. 4, pp. 302–304, April, 1988.     

两种钚同位素丰度无损分析技术方法的实验比较研究

经过多年的研究和发展,美国洛斯·阿拉莫斯和劳伦斯·利弗莫尔国家实验室各自发展了钚材料的无损分析技术方法。该方法应用高分辨率γ探测器探测钚材料放射的γ射线,分析研究γ射线谱,从中解出所蕴涵的钚的丰度信息,以满足核保障机制中衡算测量的要求。介绍了这两种分析技术方法的对比测试实验,通过比较,研究、分析这两种分析技术方法的特点。     

Comparative study of a boron dilution scenario in VVER reactors

Subsequent studies have identified many scenarios, which can lead to reactivity excursions due to boron dilution. The comparative study, presented in this paper, deals with the so-called “restart of the first reactor coolant pump’’ scenario and its reactor-dynamic consequences for both Russian designed VVER reactor types, VVER-440 and VVER-1000. The transient simulations were performed using the three-dimensional core dynamics code DYN3D. The DYN3D modeling features, including recent developments, as well as the cross-section methodology involved in these calculations, are described. The analyzed accident scenario is outlined together with the assumptions made. The results of core response in this boron dilution accident for both VVER reactors are compared within the ranges, determined by the two reactivity values of interest: the criticality limit and the reactivity initiated accident (RIA) limit.     

Stresses in ellipsoidal pressure vessel heads with noncentral nozzle

The objective of this paper is further investigation of the shell intersection problem. The shell theory and finite element method are used for stress analysis of nozzle connections in ellipsoidal heads of the pressure vessels. Ellipsoidal heads having attached nozzles considerably displaced from the head axis are mainly considered. The features of the numerical procedure, structural modeling of nozzle-head shell intersections and SAIS special-purpose computer program are discussed. The results of stress analysis and parametric study of an ellipsoidal vessel head with a noncentral nozzle under internal pressure loading are presented.     

Development of stress indices for nonradial branch connections

This paper presents a brief summary of the technical basis for the recommended stress indices for 45 degree lateral connections under internal pressure and in-plane moment loadings.Starting with the historical background of the Pressure Vessel Research Committee's (PVRC) long range program on lateral connections, this paper highlights the various aspects intrinsic to this program such as model selection, analysis technique, finite element discretization, loading conditions, material properties and boundary conditions.A discussion of the stress index method and its application to the pressure vessel and piping design is offered as a prelude to the recommended code indices. Proposed changes to Par. NB-3338.2(C) (1) of Subsection NB of the ASME Code pertaining to lateral nozzles in cylindrical vessels and Par. NB-3650 relative to branch connections in piping systems are presented and discussed in detail.Besides, this paper discusses the need to develop additional data in the range of geometric parameters, 0.5 ≤ d/D ≤ 1.0 and 10 ≤ D/T ≤ 50, and under other remaining loading conditions to broaden the application of the stress index method.