高温气冷堆反应堆厂房外墙及蒸发器舱室抗飞机撞击数值分析

反应堆抗大飞机撞击是需要考虑的外部事件,对反应堆的安全评价非常重要。本文在耦合冲击动力学有限元模型的基础上,提出了双层平行墙体承受飞机撞击的等效模拟方法,研究了高温气冷堆（HTGR）较薄的方形蒸发器舱室抗商用飞机撞击能力。建立了反应堆厂房外墙受商用飞机撞击穿透评价标准,并进行了商用飞机撞击反应堆厂房外墙仿真计算,得到了飞机剩余动能曲线。飞机撞击蒸发器舱室的计算中,保守假设飞机穿过外墙后无质量损失,形态完好,以剩余速度撞击方形蒸发器舱室。评估表明,蒸发器舱室结构在撞击条件下的整体损伤微小,可为保护内部关键设备提供重要的屏障功能。      

Darlington GS vacuum building - Internal structures and foundation

This paper describes the evolution of the internal structure from initial concept to final design. Fundamental changes to the original configuration were precipitated by the action of large seismic forces acting on a top-heavy configuration. Prestressing was eliminated in deference to high humidity. Aspects of the elevated water tank's peripheral support beam are discussed vis-à-vis an adjacent slipforming operation, and practical construction limitations on steel placement. Also reviewed are the shortening of peripheral columns due to shrinkage and creep, and considerations of crack control for purposes of water-tightness. The authors justify the choice of stainless steel for fabrication of the siphon system's riser pipes. The foundation slab must resist the combined effects of vacuum pressure, hydrostatic uplift, and the seismic reactions of the internal structure and perimeter wall. The dependency of a key foundation component, the gallery roof slab, on the dome tendon layout is high-lighted; and aspects of its constructability are reviewed in light of congestion of vertical tendon anchorages, and of reinforcement. The design of the air-tight slab liner is reviewed, attention focusing on weld design under vacuum and accident temperature loads; on corrosion protection; and on the related construction access bulkhead - its ASME requirements and fabrication tolerances.     

Dynamic behaviour of tunnels under impact loads

Safety related structures of a nuclear power plant are often required to withstand the effects of an aircraft impact load. Underground tunnels, carrying cables and pipes between buildings, also belong to this class of structures. For the design of components located inside the tunnels one must know the response of the structure of the connection points of the components. Acceleration response spectra and relative displacements are of major interest. Using finite element techniques in order to idealize the tunnel and the surrounding soil the effects of the various parameters on the dynamic response of the tunnels are investigated.It is found that some of the main parameters which influence the dynamic response of a tunnel are: soil stiffness and layering, depth of embedment and the thickness of the concrete, protective slab. Vertical accelerations are also affected by the stiffness of the tunnel.     

An overview of major aspects of the aircraft impact problem

This paper identifies the major aspects of the aircraft impact problem and spotlights the most relevant topics for future investigations. The emphasis is on three main topics: modeling techniques, influence of non-linear behavior, and importance of damping in the dynamic structural response analyses for aircraft impact loading. Results are presented from brief studies involving response of linear and nonlinear simple systems to short-duration impulsive loadings of the aircraft impact type. For linear elastic cases, the transient and free vibration components are studied separately for systems with different natural periods. The influence of damping on floor response spectra is also studied both in the form of peak values as well as the corresponding frequency shifts. For nonlinear systems, ranges of required ductility ratios for a typical aircraft impact loading are compared against available ductility ratios for typical wall and slab panels. An extensive literature survey is carried out on several major topics pertinent to the aircraft impact problem, encompassing various disciplines of engineering. Results and discussions on the basis of this literature survey are presented for major topics.     

Energy absorbers used against impact loading

In the WWER-440 reactor the primary piping consists of six horizontal loops going rapidally from the pressure vessel, each loop having a horizontal steam generator. In this reactor type the relatively long primary piping with many curved sections requires special attention in order to successfully eliminate the consequences of the design basis accident. Emergency supports are located in appropriate places to restrict the movements of the pipe. Under normal conditions there is a gap of some centimeters between the pipe and a support so that in the pipe can be deformed freely under changing loads. This paper deals with those energy-absorbing structures used at the Loviisa Nuclear Power Plant for protection against impact loading. Places and circumstances where energy-absorbing structures are employed are specified. Development and design of impact absorber elements are discussed and impact tests are described.     

Verification of the local structural response of building structures in the anchorage areas of heavy components

In both nuclear and non-nuclear areas of power plants, sections of structures, parts of systems and components are attached to walls and floors by means of anchor plates with bolts, anchor sleeves and bolts and through bolts arranged either in groups or individually.In order to simplify the determination of the transfered vibrations induced by external events (e.g. earthquake, aircraft crash), it is normally assumed that the nodal point between component and concrete possesses rigid body characteristics and the building structure (walls, floors) is also inflexible in the anchorage area.In the course of the parametric studies performed, the nonlinear effects on the anchorage area of a component (in this case an anchor plate and concrete slab) were calculated and the effect of these on the actual vibration behavior and the local structural responses of the building structure at the place of installation of heavy components were investigated.The investigations performed reveal that by taking into account the local behaviour in the anchoring point, it is possible to reduce the dynamic response considerably. More detailed examination of the influence of additional parameters (especially of the geometry of the anchor plates and anchor bolts and their material characteristics) will require further investigations aimed at establishing the characteristics of typical anchor plates.     

Some aspects of the reliability-based design of reactor containment structures

A rational procedure for the design of reactor containment structures is carried out within a probabilistic framework. Various risk concepts such as the return period, non-encounter probability and the reliability function are discussed. Internal load conditions caused by system failure such as LOCA pressure loads, and external load conditions caused, for instance, by impact due to aircraft crashes, external pressure waves and natural hazards such as earthquakes and severe storms, are described by extreme value distributions of the largest values of the Fisher-Tippett types. Statistical and physical arguments are given to support their application. The occurrence of these rare events with respect to time is modeled by a Poisson process. The ultimate strength of a PWR containment structure for the steel (liner) shell is also modeled by an extreme value distribution (of the smallest values). As a good approximation the load action of the shell structure is determined by linear elastic analysis. The failure criterion considered here is that of reaching the ultimate tensile strength at one point of the structure. A numerical example of the reliability analysis of a steel shell structure under internal overpressure is carried out.     

Penetration resistance of reinforced concrete containment structures

Containment structures not only provide a leak tight barrier, but also play a role in ensuring that the structures can withstand the impact load from projectile impacts or internal plant accidents. In assessing the containment structures of nuclear power plants, predicting the characteristics of impact resistance in relation to design and safety considerations is relevant. This investigation proposes a simple but effective method of performing numerical analysis on perforation resistance of reinforced concrete containment structures. In this work, normal and oblique impacting is considered to examine the residual velocity and impact phenomena of an ogive-nose steel projectile with various impact velocities against a reinforced concrete slab. Additionally, a phase diagram is devised to describe the ballistic terminal phenomena of projectile and target. This model could assess the resistance to penetration to results in the optimum design of the containment structures in nuclear power plants.     

Numerical and Experimental Investigation on the Attenuation of Electromagnetic Waves in Unmagnetized Plasmas Using Inductively Coupled Plasma Actuator

The attenuation of electromagnetic(EM) waves in unmagnetized plasma generated by an inductively coupled plasma(ICP) actuator has been investigated both theoretically and experimentally. A numerical study is conducted to investigate the propagation of EM waves in multilayer plasma structures which cover a square flat plate. Experimentally, an ICP actuator with dimensions of 20 cm×20 cm×4 cm is designed to produce a steady plasma slab. The attenuation of EM waves in the plasma generated by the ICP actuator is measured by a reflectivity arch test method at incident waves of 2.3 GHz and 10.1 GHz, respectively. A contrastive analysis of calculated and measured results of these incident wave frequencies is presented, which suggests that the experiment accords well with our theory. As expected, the plasma slab generated by the ICP actuator can effectively attenuate the EM waves, which may have great potential application prospects in aircraft stealth.     

A review of procedures for the analysis and design of concrete structures to resist missile impact effects

Concrete containment walls and internal concrete barrier walls are often required to withstand the effects of missile impact. Potential missiles include external tornado generated missiles (steel rods, steel pipes, wooden poles, and automobiles), aircraft crash, and internal accident generated missiles (turbine blade, and steel pipe missiles resulting from pipe break). Impacting missiles can be classified as either ‘hard’ or ‘soft’ depending upon whether the missile deformability is small or large relative to the target deformability. This paper only deals with the effects of ‘hard’ missile impact. Missile velocities between 100 and 1500 ft/sec are emphasized. ‘Hard’ missile impact results in both local wall damage and in overall dynamic response of the target wall. Local damage consists of spalling of concrete from the front (impacted) face and scabbing of concrete from the rear face of the target together with missile penetration into the target. If damage is sufficient the missile may perforate or pass through the target. This paper reviews the various empirical procedures commonly used for determining penetration depth, perforation thickness, and scabbing thickness for concrete targets subjected to ‘hard’ missile impact. Results obtained from these procedures are compared with test data results for low velocity impacts (200–1500 ft/sec). Design recommendations to prevent detrimental local wall damage are presented. Overall dynamic response of the target wall consists of flexural deformations and a potential flexural or shear failure if the strain energy capacity of the wall does not exceed the kinetic energy input to the wall by the striking ‘hard’ missile. Simplified procedures are defined for determining the dynamic response of the target wall and for preventing overall failure of the wall. Included are procedures for defining the effective target mass to be used in determining the fraction of the total missile kinetic energy which is transferred or ‘input’ into the target wall. Also included are procedures for defining the total strain energy capacity of the target wall as determined from the moment and rotational capacities of flexural yield hinges and the yield line deformation pattern of the wall. Lastly, criteria for preventing a premature shear failure are presented.     

Structural analysis of aircraft impact on a nuclear powered ship

As part of a general safety analysis, the reliability against structural damage due to an aircraft crash on a nuclear powered ship is evaluated. This structural analysis is an aid in safety design. It is assumed that a Phantom military jet-fighter hits a nuclear powered ship. The total reaction force due to such an aircraft impact on a rigid barrier is specified in the guidelines of the Reaktor-Sicherheitskommission (German Safety Advisory Committee) for pressurized water reactors.This paper investigates the aircraft impact on the collision barrier at the side of the ship. The aircraft impact on top of the reactor hatchway is investigated by another analysis. It appears that the most unfavorable angle of impact is always normal to the surface of the collision barrier. Consequently, only normal impact will be considered here. For the specific case of an aircraft striking a nuclear powered ship, the following two effects are considered: Local penetration and dynamic response of the structure.The local penetration occurs at points where the engines or other rigid objects hit the structure. It is assumed that the aircraft engine is a rigid body projectile and the side wall of the ship is the target. The applied steel penetration formulae for projectiles were empirically derived for military applications, where both the projectile and the target are unlike those of an impact of an aircraft engine. For this reason it is expedient to calculate the upper and the lower limit values of the penetration depths. The results show that the highest penetration depth is less than the sum of all wall thicknesses of the collision barrier.The solution of the dynamic analysis is obtained by using the finite element method. The results are the eigenmodes, the eigenfrequencies, the displacements of the nodes, and the stresses in the applied plane stress elements. It is shown that the maximum stress which only appears in one element is on the same level as the yield stress of the St. 42 steel. The structural analysis shows that the collision barrier is a sufficient safeguard against the perforation of the engine and against the cracking of the structure as a result of the dynamic response to an aircraft impact.     

飞机撞击下高温气冷堆乏燃料厂房损伤研究

本文针对典型高温气冷堆乏燃料厂房在双发商用飞机撞击载荷下的响应及结构完整性开展研究，并探讨结构特性对撞击损伤的影响。对乏燃料厂房及飞机分别建立有限元模型，通过弹体-目标相互作用分析模拟了飞机撞击过程，综合IAEA与NRC的评价准则对乏燃料厂房在飞机撞击下的损伤程度进行评估。数值结果表明：厂房上对应于机身及发动机的撞击位置发生可接受的局部损伤；乏燃料贮存井墙体对于提高构筑物抗飞机撞击能力有重要作用。此外，构筑物外形对损伤有很大影响，圆柱形壳体的抗飞机撞击能力显著强于方形厂房，是核电厂厂房设计的优化方向之一。     

Impact of probability risk assessment on containment

The structural reliability analysis of containments as contributing factors to risk analyses of nuclear power plants is presented. In this context probabilistic models for the occurrence and effects of potential internal loading conditions (i.e. LOCA) as well as external loads (i.e. earthquake and aircraft impact) have been developed and utilized within a reliability concept. The analysis is exemplified by application to a spherical containment structure located in an area of low seismicity.     

An approach to evaluate the design load time history for normal engine impact taking into account the crash-velocity distribution

Examination of crash records for military aircraft indicates that in the definition of the excitation due to aircraft impact against nuclear structures, the engines should be considered as independent projectiles and, if necessary, its effects superimposed on those due to the aircraft and/or parts thereof. For the development of reliability based design criteria, it is also necessary to associate different excitation levels to (conditional) probabilities of occurrence. The paper presents a detailed discussion of the characteristics of the reaction-time curve for a Phantom GE J79-8 turbojet engine, together with a procedure to correlate any reaction-time curve to its (conditional) probability of occurrence.     

Analysis of Internal and External Bypass Circuit Design for ITER Poloidal Field Converter System

This paper describes the bypass circuit design applied to International Thermonuclear Experimental Reactor (ITER) poloidal field converter system. In the baseline design, an internal bypass scheme was designed for purposes of quench protection and reactive power reduction by bypass operation. However, due to the potential risks that exist in case of fault protection, internal bypass scheme is abandoned finally and external bypass scheme is proposed to replace the internal bypass design. In this paper, the weakness of internal bypass design has been reviewed and the reliability of external bypass design at different sites is analyzed. Simulations based on SIMULINK are performed to confirm the reasonability and availability of external bypass proposals.     

Theoretical study of aircraft impact on reactor containment structures

In containment design there is a requirement to protect the reactor system from the effects of external hazards and hence it is necessary to provide suitable wall thicknesses. Experimental work undertaken by the UKAEA is being carried out as a general study and this paper describes some theoretical studies for the particular case of an aircraft impact. The theoretical study utilizes a finite difference dynamic code based upon dynamic relaxation initially developed for static problems The code models concrete, reinforcement and prestressing throughout the short term non-linear range. Concrete is assumed to have a limited tensile stress capacity, coupled with a shear carrying capacity which is dependent upon the aggregate and crack size. In addition a yield condition can be specified to allow for triaxial stress states both initial and subsequent to failure. The paper briefly describes the theory and makes comparisons for different concrete thicknesses.     

Optimized reinforcement of nuclear power plant structures for aircraft impact forces

Reactor buildings of nuclear power plants and, to some extent, also other buildings of the plant, according to the present safety requirements, have to be able to withstand aircraft impact forces. The building has to withstand this loading only once since afterwards it will be out of use. Accordingly, other criteria for design and the necessary safety measures are valid than in the case of service loads. Large deformations and the development of large cracks due to such loadings are insignificant from a construction point of view for reinforced concrete structures, i.e. the stresses can build up to the ultimate load carrying capacity. From the nuclear safety point of view, however, some restrictions are possible in this regard, e.g. to obstruct the penetration of fuel through the cracks. Basically all mild steels, with large ductility and without brittle fracture under sudden load increases, are suitable for this purpose. High stresses in the structure would, however, require uneconomical concentrations of mild steel. It is for this reason that the use of high strength steels, e.g. St 110/135, has been introduced in Germany for this kind of loading.Since the permissible deformations of reinforced concrete structures due to aircraft impact are large, a new kind of reinforcement is at hand. Through the use of wire strands or cables of high strength steel it is possible to reach a condition of cracks and large deformations due to ultimate loads in zones of point loading. The reinforcement takes on a distinctly curved shape and is able to carry the normal loads and shears through a suspension-structure action. The deformability of the structure for the analysed limit load state can be further increased through a bond-free net. This measure allows a more uniform stretching of the cables or strands over a larger zone.By making use of the higher allowable deformability of the structure and this type of reinforcement, savings in longitudinal reinforcement are possible. Reinforcement for shear is not relevant with this model and serves only a structural purpose. The structural thickness can be decreased as it depends only on the protection from penetration and is independent of the requirements for bending and shear.     

大型商用飞机撞击钢板混凝土结构安全壳的有限元分析

为研究不同场地条件对大型商用飞机撞击核电厂结构的冲击响应影响，采用规范推荐的集总参数场地动力模型考虑不同的均质场地条件。基于荷载时程分析法进行了某大型商用飞机撞击钢板混凝土结构安全壳的冲击响应对比分析。分析结果表明，随场地剪切波速的增大，安全壳的冲击响应减小，当考虑为固定端时，其响应最小；当场地的剪切波速较大，即场地较硬时，假设为固定端的边界条件是合理的，当场地较软时，应考虑场地的弹性作用；场地阻尼效应对于冲击响应的影响很小，可忽略不计。针对某特定场地，大型商用飞机对钢板混凝土结构安全壳的冲击响应较小，不会引起结构的整体破坏，是可接受的。     

A critical reappraisal of nuclear power plant safety against accidental aircraft impact

The overall problem of nuclear power plant safety against an accidental aircraft impact is discussed in relation with its structural analysis and design. Associated risks, such as fire, which is a potential source of damage for buildings and other structures, are not considered.The paper is divided in two parts. In part I different approaches used for determining the reaction-time curve are discussed. The influence on the results of target motions is examined next. It is shown that for the evaluation of structural response an aircraft-structure interaction analysis is usually an unnecessary refinement, “mean” reaction-time and impact area-time curves being sufficient to define the excitation. Preliminary results for oblique impact are also given. Since the conditional probability of a normal impact is very small, the consideration of oblique impact may become acceptable in future design criteria.In part II, available solutions for the resulting structural dynamic problem are reviewed. The feasibility of resorting to a static analysis is also discussed. Present practices to evaluate floor response spectra are reviewed next. The short-comings of the “deterministic” approach are pointed out. It is proposed to define the excitation as a mean plus a fluctuating force. The latter is treated as a nonstationary random process and the problem solved by numerical integration in the time domain. Although such solutions get prohibitively expensive when the number of degrees of freedom becomes large, results obtained for simple models may help to clarify which are the important variables of the problem.     

A complex study on the reliability assessment of the containment of a PWR Parts I–III

The intention of this paper is to contribute to the development of methods to be used for the quantification of the risk of nuclear power plants. For this purpose a reliability analysis of a structural component, i.e. a reactor containment structure is carried out. Detailed information in various fields had to be developed and compiled. The project consists of three parts: Part I concentrates mainly on the analysis of the load condition of the steel hull following a Loss of Coolant Accident (LOCA). Part II deals with the material aspects of the design properties of containment steels and furthermore the behaviour of concrete under impact load conditions are discussed. Part III of the paper is concerned on the one hand with external load conditions, and on the other hand with assembling the information of the previous parts to a reliability analysis.The methodology is exemplified by applying the general and theoretical results to the containment of the PWR-plant “Biblis B”.