Missile Impacts Research Articles

Safety Assessment of Airtight Protective Doors of Nuclear Power Plants Subjected to Wind-Borne Missile Impact

This paper aims to study the dynamic response and damage of airtight protective doors of nuclear power plants subjected to tornado and wind-borne missile impact. Firstly, a safety performance evaluation method is proposed, considering the structural characteristics of the airtight protective door and relying on support rotation and airtightness. Then, the commercial finite element (FE) program LS-DYNA is utilized to perform the numerical simulations of airtight protective doors in nuclear power plants exposed to tornadoes and wind-borne missile impacts. Subsequently, the parameter analysis method is employed to investigate the impact of keel quantity, size and arrangement, door panel thickness, door core material, and boundary conditions on the dynamic response, airtightness, and failure mode of the airtight protective door. The results show that tornado wind pressure has little effect on the resistance of airtight protective doors and that the impact load of wind-borne missiles plays a leading role. The number and thickness of the keel have significant effects on the force transfer mode and failure mode of airtight protective doors. The thickness of the door panel has a great influence on the damage mode and airtightness of airtight protective doors. The door core improves the local resistance of the airtight protective door to a certain extent, and foam aluminum material has a better energy absorption effect. The change in boundary conditions has little influence on the resistance of airtight protective doors.

Study on the relationship of design parameters and damage modes for RC slabs subjected to large-scale hard missile impacts base on task-driven approach

This study proposes a novel hybrid ensemble learning (EL) model that integrates CatBoost and SMOTE-NC algorithms to evaluate the damage modes of reinforced concrete (RC) slabs under large-scale hard missile impacts, overcoming the limitations of conventional approaches. To develop the optimization model, a database was constructed using publicly published experimental data from 304 large-scale missile impact tests conducted on RC plates. Furthermore, the SMOTE-NC oversampling algorithm is employed to optimize the database and address the issue of class imbalance. Subsequently, four ensemble machine learning models and empirical formulas are assessed. The findings indicate that the hybrid ensemble learning model combining CatBoost and SMOTE-NC exhibits superior performance, showcasing robustness and efficacy. Furthermore, through the application of SHAP analysis, it was revealed that velocity, thickness, concrete compressive strength, missile mass, reinforcement ratio, and missile diameter are the most influential variables, and they interact with each other in significant ways. Notably, the analysis indicated that once the concrete compressive strength reaches a certain value, further improvements may have a detrimental effect on penetration resistance. Additionally, the impact of yield strength on slab performance becomes more pronounced as the slab thickness decreases. Drawing upon these findings, a proposed approach for damage assessment and protection design utilizing an interpretable hybrid EL model was introduced. However, it is crucial to acknowledge that the applicability of this model is confined to RC targets with finite thickness, specifically engineered to withstand large-scale hard missile impacts.

Modeling the behavior of reinforced concrete slabs subjected to impact

In recent years, safety of nuclear power plants against external missile impacts such as those due to tornadoes has gained significant attention. In many cases, advanced simulation tools based on finite element method (FEM) or smooth particle hydrodynamics (SPH) are being employed to simulate missile impact behavior and to evaluate vulnerability of nuclear facilities. Due to the complex nature of impact behavior, it requires appropriate calibration of parameters in the advanced simulation models that are used to represent them. In this manuscript, we propose a novel approach for modeling the behavior of reinforced concrete slabs subjected to missile impact. First, we use data from one experimental study to develop and calibrate various models needed to conduct the finite element analysis. Then, the calibrated models are used to conduct a predictive analysis for a different experimental setup. A comparison of the experiment and the analytical results for the new test provides confidence in the predictive capability of the simulation approach with calibrated parameters.

A study on the resistance of SC walls subjected to missile impact using large-scale impact tests

Nuclear power plants (NPP) should resist local impact loads such as aircraft engine impact as well as internal and external missile impacts based on the international regulations for NPP structures. Although a wide variety of studies on the local responses of conventional reinforced concrete (RC) walls under impact loading have been performed and the design methods for preventing local failure are previously established, no appropriate design methodology is available for steel-plate concrete (SC) walls except for that recently cited in AISC N690 specifications.In this paper, the local resistance and behavior of SC walls subjected to missile impact were investigated experimentally. A total of ten large-scale impact tests for SC and RC walls were performed. The SC wall specimens were designed using various parameters including wall thickness and steel-plate thickness (reinforcement ratio). A set of RC wall specimens were designed for comparison. Initial and residual velocities of projectile, strain and acceleration of the rear plate, local failure mode and deformation, etc. were measured utilizing high speed cameras and various instrumentation devices. From this study, the actual local impact behaviors of SC walls were investigated and the quantitative impact resistance was evaluated. Overall, the current AISC N690 design method was somewhat conservative and needs to be improved for beyond-design-basis events such as aircraft engine impact.

A Simplified Approach to Analysis of Reinforced Concrete Slabs Subjected to Hard Missile Impacts

This paper presents a nonlinear finite element analysis (NLFEA) procedure employing a smeared rotating crack macro-modeling approach for analysis of reinforced concrete structures under hard missile impacts. It represents a middle ground between simplified methods based on single degree of freedom (SDOF) systems and complex meso-or micro-element hydrocodes. Three hard missile impact tests were modeled and the results were compared with experimental results in terms of residual velocity, damage shape, and impact depth. Good correlations were obtained.

Local Effects of Impact into Concrete Structure

Impact of missiles into reinforced concrete structures can have various effects. Soft impacts (deformation of missile is more significant than deformation of target structure) might cause global failure, while hard impacts of quasi-rigid missiles only affect the impact zone and cause local failure such as cracks, penetration, perforation, etc. In our paper, local effects caused by hard missiles are examined. Missile parameters are close to possible primary and secondary missiles induced by tornados and aircraft impacts. Potential modelling and calculation methods are summarized and a calibrated FE model is presented. Based on FE model calculations, new semi-empirical formulae are deduced that can be applied for medium size hard missile impacts.

IMPACT ANALYSES AND TESTS OF CONCRETE OVERPACKS OF SPENT NUCLEAR FUEL STORAGE CASKS

A concrete cask is an option for spent nuclear fuel interim storage. A concrete cask usually consists of a metallic canister which confines the spent nuclear fuel assemblies and a concrete overpack. When the overpack undergoes a missile impact, which might be caused by a tornado or an aircraft crash, it should sustain an acceptable level of structural integrity so that its radiation shielding capability and the retrievability of the canister are maintained. A missile impact against a concrete overpack produces two damage modes, local damage and global damage. In conventional approaches [1], those two damage modes are decoupled and evaluated separately. The local damage of concrete is usually evaluated by empirical formulas, while the global damage is evaluated by finite element analysis. However, this decoupled approach may lead to a very conservative estimation of both damages. In this research, finite element analysis with material failure models and element erosion is applied to the evaluation of local and global damage of concrete overpacks under high speed missile impacts. Two types of concrete overpacks with different configurations are considered. The numerical simulation results are compared with test results, and it is shown that the finite element analysis predicts both local and global damage qualitatively well, but the quantitative accuracy of the results are highly dependent on the fine-tuning of material and failure parameters.

Simulation of Impact Tests With Hard, Soft and Liquid Filled Missiles on Reinforced Concrete Structures

Vital parts of nuclear facilities are commonly protected by reinforced concrete (rc-) structures. In order to assess the barrier effectiveness of these structures, different internal and external loads have to be considered. Among others, external missile impacts, for instance due to an airplane crash, are assumed to be relevant loading cases. In this context, impacts of nondeformable (“hard”), deformable (“soft”) as well as liquid filled (“wet”) missiles are considered. Major rc-target failure mechanisms are global bending, punching and perforation. This paper presents simulations with the computer program AUTODYN (ANSYS INC., 2010, ANSYS AUTODYN, Version 13.0 & Theory Manual) on intermediate- and large-scale impact experiments dealing with the aforementioned failure mechanisms. Missile velocities are in the range of 110 to 250 m/s. In particular, two different intermediate scale test series are considered. One test deals with predominant punching failure and perforation of a rc-slab (target) hit by a hard missile. Further, bending vibration of slabs impacted by soft missiles is analyzed, whereupon the influence of liquid infill on loading and target response is pointed out. Finally, a large scaled test with combined bending and punching failure of a rc-slab due to soft missile impact is considered. Results of numerical simulation and tests are compared. It is found, that the used concret material model developed by Riedel, Hiermaier, and Thoma (RHT) (Riedel, 2004, “Beton Unter Dynamischen Lasten: Meso-Und Makromechanische Modelle Und Ihre Parameter, Fraunhofer–Ernst-Mach-Institut, Freiburg/Br., ISBN 3-8167-6340-5) is suitable to reproduce the responses of rc-structures subjected to various kinds of impact conditions. Sensitivities of simulation results on modeling parameters are discussed.

Analysis of hurricane pressure cycling following missile impact for residential structures

The research reported herein describes the approach used in the first ever direct simulation of the pressure cycles expected to be experienced by windows after being impacted by wind-borne debris in a hurricane. The approach uses wind tunnel measured time histories of pressures obtained from the Boundary Layer Wind Tunnel at the University of Western Ontario, coupled with a wind-borne debris impact model and simulated hurricanes. The modeling approach inherently takes into account the effects of changes in wind direction and wind speed as a hurricane passes by a site. The effect of storm duration is included through the use of very long time series of wind tunnel pressures coupled with the modeled hurricane wind speeds and directions. With information on the debris impact time within a given storm, we couple the simulated hurricane wind speeds with the wind tunnel measured time histories of wind induced pressures to derive the characteristics of the pressures experienced by a window after impact. Using these time series of pressures referenced to the design pressure as defined in ASCE-7-98, we performed an up-crossing analyses and pressure range analyses in order to develop the information needed for possible impact and pressure cycling test protocols. The results of the pressure cycle counting following impact clearly indicate that the requirements of the 1994 edition of the South Florida Building Code (SFBC) are extremely conservative with respect to the negative pressure cycle requirements, irrespective of the target design reliability and impact momentum required for glass breakage. The results also show that the number of pressure cycles expected to be experienced by a structure located in Miami, following the impact of debris with a momentum equal to that of the 9 lb two-by-four impacting at 50 fps is significantly less than required in the SFBC. The results indicate that the impact and pressure cycle requirements for windows and doors: (i) should vary with location and the desired level of reliability. (ii) should require impacting a window with a much lower momentum than currently specified in the SFBC, followed with the appropriate pressure cycling test, and finally impacting the window with a larger missile, with no pressure cycle tests after this final impact. A test protocol taking into account these two features would be much more realistic than the current SFBC requirements. The test would require the first impact to be consistent with the more common smaller debris generated in a hurricane, but would still provide for a system that provides protection from the relatively infrequent large missile impacts.

Estimates of radiological risk from depleted uranium weapons in war scenarios.

Several weapons used during the recent conflict in Yugoslavia contain depleted uranium, including missiles and armor-piercing incendiary rounds. Health concern is related to the use of these weapons, because of the heavy-metal toxicity and radioactivity of uranium. Although chemical toxicity is considered the more important source of health risk related to uranium, radiation exposure has been allegedly related to cancers among veterans of the Balkan conflict, and uranium munitions are a possible source of contamination in the environment. Actual measurements of radioactive contamination are needed to assess the risk. In this paper, a computer simulation is proposed to estimate radiological risk related to different exposure scenarios. Dose caused by inhalation of radioactive aerosols and ground contamination induced by Tomahawk missile impact are simulated using a Gaussian plume model (HOTSPOT code). Environmental contamination and committed dose to the population resident in contaminated areas are predicted by a food-web model (RESRAD code). Small values of committed effective dose equivalent appear to be associated with missile impacts (50-y CEDE < 5 mSv), or population exposure by water-independent pathways (50-y CEDE < 80 mSv). The greatest hazard is related to the water contamination in conditions of effective leaching of uranium in the groundwater (50-y CEDE < 400 mSv). Even in this worst case scenario, the chemical toxicity largely predominates over radiological risk. These computer simulations suggest that little radiological risk is associated to the use of depleted uranium weapons.

Local Damage Assessment of Metal Barriers under Turbine Missile Impacts

Turbine missiles resulting from the failure of rotary machines in nuclear-power plants could cause severe damages and endanger public safety. This paper presents the current state of the art on models and methodologies for predicting the magnitude of damages and the possibility of the missile leaving the casing structure. Eight empirical methods for the perforation of steel by rigid missiles were collected and analyzed using over 30 test data from experimental works of the past two decades. Based upon the analyses, several modifications of the empirical and semiempirical formulas are proposed to evaluate the problem of containment and to better reflect the amount of damage resulting from turbine missile impact. The modified formulas are shown to be accurate for over 90% of the test results. It was also found that use of an equivalent missile diameter was helpful in accounting for the piercing impacts in the experimental works. It further reduced the nonconservative nature of the predictions.

Post-breakage behavior of architectural glazing in Windstorms

The selection of architectural glazing products for use in tall buildings has evolved into a complex process in a relatively short period of time. Many new factors have to be considered in the design procedure, and the array of new available products has created unlimited design choices. Among the new design considerations are missile impacts and the behavior of glass after breakage in a windstorm. Post-breakage behavior is described, principally, in terms of resistance to small missile impact, glass particle fallout and the propensity of glass panels to remain in the frame. These behavioral characteristics are directly related to hazards to people and a desire to protect the building and its interior furnishings and equipment from the effects of windstorms.

Missile Impacts as Sources of Seismic Energy on the Moon

Seismic signals recorded from impacts of missiles at the White Sands Missile Range are radically different from the signal recorded from the Apollo 12 lunar module impact. This implies that lunar structure to depths of at least 10 to 20 kilometers is quite different from the typical structure of the earth's crust. Results obtained from this study can be used to predict seismic wave amplitudes from future man-made lunar impacts. Seismic energy and crater dimensions from impacts are compared with measurements from chemical explosions.

Behavior Of Composite And Multiple BarriersUnder Turbine Missile Impacts

The impact of turbine missiles on barriers in nuclear power plants could cause severe damages and endanger public safety. This paper evaluates the available models and empirical methods that predict the extent of damages of turbine missile impact on composite and multiple barriers. A method of analysis is used in which the missile' s residual velocity after perforating each layer becomes the impact velocity for the next layer. Recommendations are made as to the most accurate models for barriers made of concrete and steel layers. INTRODUCTION Turbine missiles are irregularly shaped fragments that result from the failure or fracture of steam generator turbines [1] . The impact of missiles on surrounding facilities in nuclear power plants could cause severe damages and endanger public safety [2] . Various methods of damage analysis for composite and multiple barriers are reviewed. To evaluate the performance of available empirical methods , test results for 45 full-scale and small scale experiments were assembled from the literature for a variety of testing situations, missile types and orientations, targets and materials [3] . Missile impacts are often categorized as either hard or soft. Hard impacts such as that of a steel missile on concrete barriers essentially generate no significant deformation in the projectile [4] . On the other hand, in soft impacts [5] such as that of a steel missile on metal targets relative hardness plays an Transactions on the Built Environment vol 8, © 1994 WIT Press, www.witpress.com, ISSN 1743-3509