Impact load for tornado-generated missiles

Nuclear power plant structures are designed to resist impact loads from tornado-generated missiles. The paper gives a method to determine the contact pressure at the interface of the missile and the target, and the velocity and deceleration time-histories of the missile. It also gives a method to obtain the design load due to impact by tornado-generated missiles. The calculated design load compares very well with the total support reaction from a full-scale dynamic test. The comparison between the predicted deceleration and the deceleration recorded in a test is excellent. The method of determining the deceleration has also been used with very good results for earth-penetrating missiles.     

Penetration depth in concrete for nondeformable missiles

The ability of the NDRC equations to estimate the penetration depth in concrete structures has been reevaluated using the presently available test results. This study confirms the industry notion that the NDRC equations overpredict the penetration depth. The NDRC equations, when used with a safety factor, can give a penetration depth about two standard deviations away from the mean value. In a probabilistic formulation the use of this penetration depth is over-conservative and unrealistic. The NDRC equation is updated here statistically using the presently available test results. This statistical NDRC equation significantly improves the predicted penetration depth. However, the form of the NDRC equation may not be ideal. A new relationship is proposed here to estimate the penetration depth by introducing a dimensionless impact factor. It has been shown here that the proposed relationship is better than the NDRC or even the statistical NDRC equations.     

Probability and containment of turbine missiles

With the trend toward ever larger nuclear power generating plants with large high-speed turbines, an important plant design consideration is the potential for and consequences of mechanical failure of turbine rotors. Such rotor failure could result in high-velocity disc fragments (turbine missiles) perforating the turbine casing and jeopardizing vital plant systems. The designer must first estimate the probability of any turbine missile damaging any safety-related plant component for his turbine and his plant arrangement. If the probability is not low enough to be acceptable to the regulatory agency, he must design a shield to contain the postulated turbine missiles. Alternatively, the shield could be designed to retard (to reduce the velocity of) the missiles such that they would not damage any vital plant system. In this paper, some of the presently available references that can be used to evaluate the probability, containment and retardation of turbine missiles are reviewed; various alternative methods are compared; and subjects for future research are recommended.     

Elastic-plastic creep response of structures under composite time history of loading

High temperature nuclear reactor components are subject to a complex history of thermal and mechanical loading cycles. To evaluate the adequacy of such components, detailed information on the accumulated inelastic strains and strain cycling is required. This paper presents the theory, describes efficient numerical techniques accounting for plasticity, creep and overall equilibrium, describes the overall structure of the resulting computer program, and demonstrates the capability of the analysis method on a real three-dimensional structure. Starting with the principle of virtual work, exact equilibrium equations are derived for a stepwise Lagrangian formulation. The resulting equilibrium equations are then specialized to the incremental Piola-Kirchhoff stress computation and to small incremental strain formulation. Classical plasticity theory is used to develop a novel method based on the concept of ‘plastic stress’ for consideration of inelastic behavior. It is shown that the material's stress-strain curves can be followed to any desired degree of accuracy both for isotropic and kinematic hardening. It is further shown that for kinematic hardening it is necessary to base the incremental change on the state corresponding to the mean of the initial and the final states to satisfy the yield condition at the final state. The equation of state and strain hardening is used to describe the creep behavior. A novel numerical technique to describe a complex load history is developed by using time as a parameter, history breakpoint determination by scanning of various load vectors, and by linear interpolation between any two breakpoints in the load history. Efficient criteria for load incrementation in the form of a fraction of the total ‘plastic stress’ for any sequence of two load history break points are developed and made an internal function of the program. This saves the user significant hardship when faced with guessing the load increment for an unknown state of the solution at any of the load history breakpoints. The ‘plastic stress’ load vector concept is utilized with interation and extrapolation to converge to the equilibrium states with simultaneous satisfaction of the stress-strain relations for each of the iterated states. The essential features of the computer program DYPLAS-FSH, based on the theory and techniques described above, and a postprocessor program POR-FSH, based on RDT F9-5T for ratcheting and fatigue evaluation, are identified and discussed. In summary, the new results of this work are the efficient handling of an arbitrary load history, introduction of the ‘plastic stress’ concept for inelastic computation, novel implementation of classical plasticity with recognition of incrementation conditions for the kinematic hardening, use of the load incrementation algorithm based on the ‘plastic stress’ concept, and development of a computer code capable of solving practical three-dimensional problems.     

Nonlinear 3-D dynamic time history analysis in the reracking modifications for a nuclear power plant

An independent seismic response evaluation of spent fuel storage racks was performed on the reracking modifications for a typical operating pressurized water reactor type nuclear power plant using nonlinear dynamic time history analysis methods per the U. S. Nuclear Regulatory Commission (USNRC) criteria. The submerged free standing rack system and surrounding water are coupled due to fluid-structure-interaction effects using potential theory. Three dimensional (3-D) single rack and whole pool multiple rack finite element models were developed with features that allow the consideration of geometrically and materially nonlinearities including 1) the impact of a fuel bundle to a rack cell, a rack to adjacent racks or pool walls, and rack support legs to a pool floor; 2) the hydrodynamic coupling of a fuel assembly with a rack and of a rack with adhacent racks or pool walls; and 3) the tilting and frictional sliding of the rack supports. The methodologies and typical results using a 3-D single rack model as well as a 3-D whole pool multiple rack model developed herein are presented.     

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.     

Optimization of the protection of a potentially dangerous object from missiles

A probabilistic model for initiation of an accident involving a potentially dangerous object by a missile attack is developed. A formulation of the problem of optimization of protection with constraints on the mass of the protection, taking account of differences in the probabilities of effects and the vulnerability of an object with respect to the directions of fire, is given. Examples of solutions of the problem by the linear-programming method are presented for means of transportation and for transport containers. 1 figure, 2 tables, 5 references. Petr Velikii Military Academy, Strategic Rocket Forces. Translated from Atomnaya énergiya, Vol. 87, No. 5, pp. 376–383, November, 1999.     

An energy approach study of the penetration of concrete by rigid missiles

This paper presents an energy approach for investigating the penetration of concrete by rigid missiles and the associated phenomena. However, the principal assumptions made here must be validated experimentally before giving the proposed subject further considerations. In the following, a new measure for concrete resistance to penetration by hard missiles is presented. The suggested term for this measure is “the Volumetric Crushing Energy Density” of concrete which can be described as the energy required for converting a unit volume of concrete to separate particles under compressive loading so that the particles of the crushed volume meet certain gradation criteria. Using this quantity, an explanation of the scale effect is postulated. Moreover, a dimensionless semi-analytical formula for the penetration depth of a rigid missile in a concrete target is proposed which includes a large number of the variables of the problem. The formula assumes that the penetration incident may include several successive phases where the set of variables that governs the impact is different during each phase, and the variables that characterize the impact during each phase correlate in a different manner as well. Furthermore, many of the penetration depth formulae available in the literature are rewritten according to the formula proposed here where the concrete penetration resistance of any incident is estimated by modifying the resistance of “reference impact incidents.” The rewritten formulae show the wide variation of the values of concrete resistance which are implicitly included in the original formulae. Finally, the proposed formula is applied using data of penetration experiments presented by Forrestal et al. [Forrestal, M.J., Altman, B.S., Cargile, J.D., Hanchak, S.J., 1994. An empirical equation for penetration depth of ogive-nose projectiles into concrete targets. Int. J. Impact Eng. 15(4), 395-405; Forrestal, M.J., Frew, D.J., Hickerson, J.P., Rohwer, T.A., 2003. Penetration of concrete targets with deceleration-time measurements. Int. J. Impact Eng. 28, 479-497] to estimate the values of penetration resistance of the concrete targets.     

Deformation and perforation of clamped work-hardening plates struck transversely by blunt missiles

A simple theory is given in this paper for the behaviour of clamped circular work-hardening plates struck transversely by flat-ended projectiles which travel at low velocities. By closely following the previous studies, force-displacement relationships are obtained and used to predict the deformation and perforation of the plates. It is shown that the theoretical predictions agree well with the experimental results on fully clamped steel plates when strain rate effects are taken into account.     

Development of Deuterium-Tritium Loading Vessel for Laser Fusion Target

Tritium permeation at 350°C through stainless steel wall of a vessel filled with deuterium-tritium gas of 6.1 × 10⁶ Pa pressure was practically suppressed by Au plating of 20μm thick applied to the outside surface. The apparent diffusivity of hydrogen through plated Au layer, derived from the experimental data, was 2 x 10^?11 cm²/s for 470°C, which is 10^?5–10^?6 times smaller than what would be expected from values reported for wrought Au, and the apparent solubility was very significantly higher than similarly expected level. Gas analysis of the Au layer indicated that the effective suppression of tritium permeation is attributable to trapping of hydrogen by C contained in the Au as impurity. Adequate tightness against tritium leakage has been achieved by Au plating on a vessel used for loading glass microspheres with deuterium-tritium gas, intended for laser fusion targets.     

基于全自动振动装管装置的核燃料棒芯块装管工艺及改进

确定了全自动振动装管的振动频率等参数。由于全自动振动装管工艺易造成包壳管定位差、包壳管管口磨痕等缺陷,影响燃料棒的外观质量,通过对全自动振动装管装置及辅助工装的改进,特别是针对包壳管管口磨痕等缺陷进行了一系列的工艺优化及改进,解决了装管过程中的燃料棒表面磨痕问题,提高了全自动振动装管装置的稳定性和可靠性。     

压水堆堆芯可燃毒物装载的优化计算

成功地将遗传算法和禁忌搜索算法应用于核反应堆堆芯可燃毒物装载优化研究。以大亚湾核电厂堆芯第10循环为例,利用遗传算法对硼玻璃、Gd2O3和IFBA三种常用的可燃毒物进行了优化计算。结果表明,遗传算法对反应堆堆芯可燃毒物装载优化问题是有效的．IFBA可燃毒物的优化结果最好。最后应用由遗传算法和禁忌搜索算法混合而成的杂交优化策略进行了优化计算．该方法可大大提高优化速度。     

Application of the Robust Design Concept for Fuel Loading Pattern

Application of the robust design concept for fuel loading pattern design is proposed as a new approach to improve the prediction accuracy of core characteristics. The robust design is a design concept that establishes a resistant (robust) system for perturbations or noises, by properly setting design variables. In order to apply the concept of robust design to fuel loading pattern design, we focus on a theoretical approach based on the higher order perturbation method. This approach indicates that the eigenvalue separation is one of the effective indices to measure the robustness of a designed fuel loading pattern. In order to verify the effectiveness of the eigenvalue separation as an index of robustness, numerical analysis is carried out for typical 3-loop PWR cores, and we evaluated the correlation between the eigenvalue separation and the variation of relative assembly power due to the perturbation of the cross section. The numerical results show that the variation of relative power decreases as the eigenvalue separation increases; thus, it is confirmed that the eigenvalue separation is an effective index of robustness. Based on the eigenvalue separation of a fuel loading pattern, we discuss design guidelines of a fuel loading pattern to improve the robustness. For example, if each fuel assembly has independent uncertainty on its cross section, the robustness of the core can be enhanced by increasing the relative power at the center of the core. The proposed guidelines will be useful to design a loading pattern that has robustness for uncertainties due to cross section, calculation method, and so on.     

秦山核电厂首次换料方案的确定

简要介绍了秦山核电厂首次换料方案的选择过程，利用优化技术寻找燃料组件的最佳布置，目标函数为组件平均卸料比燃耗最大。所选的换料方案具有较好的经济性与安全性，现已在秦山核电厂首次换料中成功应用。     

核电站放射性废物超压机压饼装载优化研究

从放射性废物最小化角度出发, 将某核电站放射性废物压饼的装载过程简化成装箱问题进行研究, 结合降序最佳适应算法提出了压饼装载优化方案, 并进行模拟运算。结果证明优化方案能明显提高再包装桶的装载率, 同时从压饼存放、转运以及装载效率等方面进行了对比分析, 证明了该优化方案具有可行性。     

特征统计算法(CSA)在堆芯装料方案优化中的应用

针对压水堆堆芯装料优化问题的特殊性,采用了一种更适合于全局优化算法--特征统计算法来求解.本文阐述了该算法的搜索原理以及如何将其应用于堆芯装料优化问题;编制了装料优化程序SCYCLE,应用该程序在2个不同类型的实际堆芯模型上进行了计算,并与其它算法的计算结果进行了比较.结果表明,SCYCLE程序在求解装料优化问题方面具有很高的搜索效率和很好的全局性.     

某压水堆首次装料次临界监督结果分析

某压水堆使用已活化的二次中子源（ASNS）完成首次装料。在首次装料期间,堆内临时中子探测器（TND）发生响应试验结果远高于仿真结果问题和计数率大幅度下降问题。为了查明上述问题的原因,监督工作组对二次中子源特性和由ASNS建立的辐射场进行了分析,对核燃料次临界增殖中子对TND计数率的影响进行了分析和验证,对使用ASNS进行反应堆首次装料的次临界监督数据进行了分析。结果表明：TND周围的辐射场为γ射线和中子形成的混合辐射场;在中子源组件与TND之间安装核燃料组件后,核燃料次临界增殖中子对TND计数率的影响是使其升高;ASNS衰变产生了大量γ射线,TND输出的γ脉冲在主放大器内发生峰堆积导致脉冲幅度畸变,TND响应试验结果远高于仿真结果的原因是脉冲幅度甄别器无法有效甄别畸变后的γ脉冲和中子脉冲;TND计数率大幅度下降的原因为核燃料中的铀屏蔽掉了由ASNS射向TND的大部分γ射线。源量程通道和TND的运行状态满足首次装料程序对次临界监督设备的要求。     

A simple model for predicting energy dissipation of thin plates being perforated by “hard” missiles

For the case of low velocity impact a simple model is derived for the determination of energy dissipation of thin plates being perforated by “hard” missiles. The predicted residual energy of the missile having passed through the target is compared with test results. The tests were carried out with plates made of wood-chips (a rather homogeneous and cheap material). For a projectile with large diameter relative to the thickness of the target it is shown that the energy absorption of the plate is essentially influenced by the fracture type.     

Preliminary Calculation for Loading Scheme of the First Criticality of CFR600

正After the completion of the construction of CFR600power plant,it has to be considered about the first loading scheme of fuels in the reactor core.Reactor physics designers should provide theoretical calculation in advance to