Local damage assessment of turbine missile impact on composite and multiple barriers

Fracture of rotary machines could result in turbine missiles, which are the irregularly shaped projectiles travelling at high velocities. The impact of such missiles on barriers in nuclear power plants has the potential to cause severe damages to the facilities, and endanger public safety. This paper applies the available damage assessment models for composite and multiple barriers to test data from experimental works of the past 2 decades. 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. The study indicates that composite action of dissimilar materials acting as a single unit improves the efficiency of the barrier. Recommendations are made as to the most accurate models and most appropriate parameters for barriers made of concrete and steel layers.     

核电厂机械设备可靠度计算方法探索

目前核电厂可靠性数据多是针对设备类的统计数据,针对特定设备的可靠性数据较少。使用设计数据计算特定设备的可靠度,可丰富可靠性数据库。本文在机械产品可靠度计算步骤的基础上,研究了机械产品可靠度计算常用的强度-应力干涉模型,推导出不同分布函数对应的可靠度计算公式,计算了某核电厂的钩爪零件在断裂失效模式下的可靠度。研究结果表明：使用机械设备可靠度分析计算的一般步骤对核电厂机械设备进行可靠性分析计算是适合的;使用强度 应力干涉模型计算设备的可靠度是有效的。     

Characterising polyurethane foam as impact absorber in transport packages

Abstract

Transport and storage packages used for the safe transport of radioactive materials are required to satisfy IAEA regulations. One key design requirement for a radioactive material transport package is that under a 9 m regulatory drop test, containment functions are maintained. For certain payload types, such as fuel assemblies, impact loads on the payloads may need to be controlled in order to maintain spacing and confinement. To achieve all of this, detailed and accurate characterisation of the impact absorbing material is important in order to design an effective shock absorber. Polyurethane foam is an excellent energy absorbing material because it has a relatively high specific strength, a large compressive deformation, much of this at constant force, and a predictable compressive strength characteristic. Traditionally various types of wood have been used for this purpose, however foams are a more cost effective alternative, which are readily available, and can be formed and shaped easily. Some grades may have the added advantage of providing an almost isotropic crush response, combined with significant thermal protection. The general compressive strength properties of foams and their temperature dependencies are well documented by manufacturers; however, strain rate sensitivity and stiffness variation with orientation are not readily available. Hence impact compression tests for polyurethane foams for a range of densities from 56 to 320 kg m^–3 were specified by Rolls-Royce and performed by the Health and Safety Laboratory. These tests included dynamic conditions for a range of strain rates and temperatures and a selection of orientations of the foam. Following collation of the test results, property curves were derived for the range of temperatures at which the package was expected to operate in service between –10 and +75°C. The properties for a given specification of foam will vary within a defined tolerance range, mainly due to the variables inherent during manufacture. Hence nominal static curves were derived for each foam and a number of factors were taken into account to derive the full range of foam properties: density, compressive strength, temperature and manufacturer supplied tolerance. The net result of this work was a series of force displacement plots, depicting upper and lower bounds to account for the cumulative effects of many variables. Accounting for these upper and lower performance bounds is an essential approach in justification of any modern package design. This paper describes the characterisation and mathematical modelling of polyurethane foam for use as the main impact energy absorber in a new design of package for transporting fresh fuel. The non-linear finite element (FE) code LS-DYNA was used to carry out simulation of the tests. The HONEYCOMB material model available in LS-DYNA was used to accurately predict the test measurements of the foam material. The properties derived for the foam were then used as input to the full FE model used for the licensing of the new package design. Full scale drop testing of the package demonstrated good correlation of deformations between test and FE model analysis, providing good validation evidence of the foam characterisation in the transport package.     

Critical impact energy for the perforation of metallic plates

This paper investigates the empirical formulae used in engineering practice to predict the critical perforation energy of metallic plates struck by rigid projectiles in the sub-ordnance regime. Main factors affecting the critical perforation energy are identified and valid conditions for each empirical formula are compared. Dimensional analysis is conducted to show the dependence of the non-dimensional critical impact energy on other influential non-dimensional numbers. Available empirical formulae are re-expressed in non-dimensional forms. A modified Jowett/AEA equation is proposed to predict the critical perforation energy of a flat-ended short projectile. The present work increases the confidence of using these empirical formulae and can be regarded as a quick guide for ballistic protection design of metallic shields and steel armour plates.     

Local effects of impactors on concrete structures

Available formulae for predicting the penetration depth, scabbing thickness, and perforation thickness of concrete structures impacted by solid missiles are summarized, reviewed, and compared. Based on quadratic and cubic regression analysis of existing data, two new formulae have been proposed for predicting the penetration depth of concrete due to the impact by solid missiles. The new penetration equations are compared statistically with NDRC penetration formula and two other recent penetration formulae. Also, new simple formulae have been proposed for predicting the scabbing thickness and perforation thickness of concrete walls.     

Beneficial influence of the weldment rupture of cask impact limiter case on the impact absorbing behavior

In the cask impact limiter design, the functions of steel case should be evaluated for the protection of the filler materials and the impact energy absorption by the buckling deformation in both the fire and impact accidents. The objective of this paper is to evaluate the beneficial influence of the intermittent weldment of the cask impact limiter case on the cask impact behavior. This paper describes the test results for the joint strength evaluation of intermittent weldment and the cask impact analysis considering the weldment rupture of the impact limiter case. The weldment rupture of the impact limiter case causes to lose their constraining effect for the wood blocks, which are filled into the metal incasement between the case and the gussets. The weldment rupture of the impact limiter case reduces the impact force which acts on the impact target significantly in vertical and horizontal drop impacts. Therefore the beneficial effect of weldment rupture should be considered in the impact limiter design and the cask impact analysis.     

Nonlinear analysis techniques of block masonry walls in nuclear power plants

Concrete masonry walls have been used extensively in nuclear power plants as non-load bearing partitions serving as pipe supports, fire walls, radiation shielding barriers, and similar heavy construction separations. When subjected to earthquake loads, these walls should maintain their structural integrity. However, some of the walls do not meet design requirements based on working stress allowables. Consequently, utilities have used non-linear analysis techniques, such as the arching theory and the energy balance technique, to qualify such walls. This paper presents a critical review of the applicability of non-linear analysis techniques for both unreinforced and reinforced block masonry walls under seismic loading. These techniques are critically assessed in light of the performance of walls from limited available test data. It is concluded that additional test data are needed to justify the use of nonlinear analysis techniques to qualify block walls in nuclear power plants.     

A simple sizing optimization technique for an impact limiter based on dynamic material properties

According to IAEA regulations, a transportation package for radioactive material should perform its intended function of containing the radioactive contents after a drop test, which is one of the hypothetical accident conditions. Impact limiters attached to a transport cask absorb most of the impact energy. So, it is important to determine the shape, size and material of impact limiters properly. The material data needed in this determination is a dynamic one. In this study, several materials considered as those of impact limiters were tested by drop weight equipment to acquire the dynamic material characteristics data. The impact absorbing volume of the impact limiter was derived mathematically for each drop condition. A size optimization of the impact limiter was conducted. The derived impact absorbing volumes were applied as constraints. These volumes should be less than the critical volumes generated based on the dynamic material characteristics. The derived procedure to decide the shape of the impact limiter can be useful at the preliminary design stage when the transportation package's outline is roughly determined and applied as an input value.     

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.     

Development of packaging to transport new standardised range of disposal canisters to geological disposal facility in UK

Radioactive Waste Management Limited (RWM) of the Nuclear Decommissioning Authority (NDA) is developing concepts to demonstrate the viability of using a standardised range of disposal canister (DC) designs for geological disposal of high level waste and spent fuel in the UK. The standardised DC are designed for disposal in a geological disposal facility with integrity requirements in the range 10?000 to 100?000 years. International Nuclear Services (INS) is also a subsidiary of the NDA and working with RWM to develop a design of packaging for transporting these DC, which is called the disposal canister transport container (DCTC). Initial studies undertaken by INS focused on optimising payload and geometry for the canister designs. Subsequent studies focused on achieving criticality safety requirements for transport, which established the use of multiple water barriers, were required for higher enriched spent fuels. The results of this initial work were presented at the International Nuclear Engineering society conference at London in 2012. Subsequently, RWM commissioned INS to develop the design of DCTC to a level where it would be viable for licensing as a transport package with appropriate level of technical understanding. A specific requirement of RWM was that the loaded DCTC should be capable of transportation on an existing design of four axle rail wagon, within a gross mass of 90 t, this giving considerable logistic and overall cost benefits. Recent development work has focused on detailed impact, thermal and shielding analysis and how these influence the DCTC transport mass and the position of that mass in relation to the four axle rail wagon, both of which influence its capability for the required transport. In terms of meeting mass limits, achieving the specified radiation shielding performance (neutron and gamma) for the spent fuel was found to be a major challenge. However, of equal challenge was to accommodate the high forces generated under impact accident conditions due to the high mass ratio of contents to container. In order to mitigate these forces, the shock absorber designs needed to be carefully judged because their dimensions were restricted by the rail wagon design. This paper describes the DCTC development work, how the design challenges were addressed and the conclusions reached.     

Critical impact energies for scabbing and perforation of concrete target

In this paper, the influences of the relative target thickness (H/d) on those critical impact energies, at which local damage of various forms in concrete targets are initiated, are explored. The empirical formulae developed in the R3 Impact Assessment Procedure [BNFL, 2003. Reinforced Concrete Slab Local Damage Assessment, R3 Impact Assessment Procedure, vol. 3, Appendix H. Magnox Electric plc & Nuclear Electric Limited] are rationalized by different methods. A dimensional analysis was conducted to identify influential non-dimensional numbers, which were subsequently employed in the analyses of the experimental results relevant to scabbing and perforation by flat nosed missiles.The relationships between the non-dimensional impact energy at failure and the non-dimensional target thickness H/d are presented for all of the relevant experimental data in the “World Impact Data” collection [Bainbridge, P., 1988. World Impact Data—S.R.D. Impact Database Version Pre 3i, CCSD/CIWP(88)107(P)]. This collated hundreds of experimental data on local damage in concrete targets due to missile impact from various sources of nuclear industries, as well as experimental data from the UK electrical power industry used to develop empirical formulae in the R3 Impact Assessment Procedure [BNFL, 2003. Reinforced concrete slab local damage assessment, R3 Impact Assessment Procedure, vol. 3, Appendix H. Magnox Electric plc & Nuclear Electric Limited]. The experimental data in Bainbridge [Bainbridge, P., 1988. World Impact Data—S.R.D. Impact Database Version Pre 3i, CCSD/CIWP(88)107(P)] are compared with empirical and semi-empirical formulae for scabbing and perforation in order to examine the effects of H/d on the critical non-dimensional impact energy for these two local failures. An analytical formula based on a penetration-plugging model is employed to give the relationship between the critical impact energy and target thickness for perforation by a flat-ended projectile. Comparisons between these formulae and experimental data are presented.     

Nonlinear dynamic analysis of high energy line pipe whip

This paper describes a nonlinear dynamic analysis of TVA high energy line pipe whip tests using the ABAQUS-EPGEN code. The analysis considers the effects of large deformation and strain rate on resisting moment and energy absorption capability. The numerical results of impact forces, impact velocities, pipe strains, and reaction forces at pipe supports are compared to the TVA test data. The calculated pipe whip impact time and forces are also compared with those predicted using current industry practice.The calculated pipe support reaction forces are found to be in good agreement with the TVA test data except for some peak values at the very beginning of the pipe break. These peaks are believed to be due to stress wave propagation which cannot be addressed by the ABAQUS code. Both elbow crushing and strain rate have been approximately simulated. The effects are found to be important for pipe whip impact evaluation.     

Single event upset mitigation techniques for FPGAs utilized in nuclear power plant digital instrumentation and control

Field programmable gate arrays (FPGAs) are integrated circuits being increasingly used for digital instrumentation and control (I&C) in nuclear power plants (NPPs) because of low cost, re-configurability and low design turn-around time. However, to ensure reliability, proper design techniques must be employed since the memory and logic in FPGAs are susceptible to single event upsets (SEUs). Triple modular redundancy (TMR) has become a common SEU mitigation design technique because of its straightforward implementation and reliable results. Partitioned TMR approaches are introduced in this paper, and formulae derived indicate that the maximum probability of two simultaneous errors [P_E]_max is inversely proportional to the number of logic partitions in a TMR design, when each redundant logic block in every logic partition has the same number of sensitive nodes. However, the maximum logic partitioning design cannot completely eliminate the possibility of two simultaneous upsets. For the example test circuit it is found that [P_E]_max is reduced dramatically from 66.67% for minimum logic partitioning to 4.44% for maximum logic partitioning. Because TMR introduces significant overhead due to its full hardware redundancy, a dual modular redundancy approach is also examined for application to less demanding situations. By comparative analysis this study reaches the conclusion that the maximum logic partitioning TMR implementation is the best solution for digital I&C applications in NPPs where obtaining robustness is of the highest importance, despite its higher area overhead.     

Development of design guidance for low velocity impacts on concrete floors

It has been recognised in the UK, that where designers or safety assessors have to consider the effects of dropped loads on various targets, there is uncertainty associated with the fact that these are low velocity impacts. This uncertainty arises for a variety of load/target combinations, but in this paper we concern ourselves with loads which are massive and with reinforced concrete floor targets.The major uncertainty for dropped load assessments, lies in the fact that the designer does not have access, in general, to relevant data. Instead, it is usual, for design purposes, to make use of empirical formulae which are intended for high velocity missiles. The design process involves using the empirical formulae not only for the local damage which they are intended to address, but also to define a load-time history or impulse for the purposes of determining slab response.This paper indicates the range of events that need to be considered, the manner in which the designer approaches the task of making his assessment of the target and the limits of applicability of the available empirical methods. The programme now in progress in the UK is outlined and some of the results emerging are presented.     

The effect of random temperature fluctuations on creep and creep rupture of cylindrical tubes

The design of LMFBR plants requires extensive creep analysis, since many in-core structures and primary system components operate at elevated temperatures. In the design process, exact information on the temperature field is often lacking and this, together with the temperature sensitivity of creep phenomena, leads to uncertainties in derived quantities such as strain and total deformation. This study considers the qualitative and quantitative implications of random temperature data by deriving expressions for the expectation value and variance of quantities such as displacement and stress in creep of thin, pressurized tubes. Also, a nondeterministic analog of an existing theory of creep rupture is employed to study the impact of random temperature fluctuations on time to brittle and ductile rupture. Data for stainless steel are applied in various numerical examples and these, together with analytical considerations, are used to formulate qualitative generalizations of importance to the design process.     

14.5MeV（n,2n）反应同质异能态截面比的系统学

在实验数据的基础上，使用Ｈａｕｓｅｒ－Ｆｅｓｈｂａｃｈ理论，在一定的假定和近似下进行了１４．５ＭｅＶ（ｎ，２ｎ）反应同质异能态截面比的系统学研究。在３５≤Ａ≤２０９、０≤Ｊｍ≤１６、０≤Ｊｇ≤８范围内，通过获得的系统学参数，可以很好地预言无实验数据核素的１４．５ＭｅＶ（ｎ，２ｎ）反应同质异能态截面比。     

Quantitative prediction of natural circulation in an LMFR with a similarity law and a water test

This paper is devoted to logical derivation of a similarity law for single-phase natural circulation expected in a liquid metal fast reactor (LMFR). Though the way of the derivation is principally conventional, this paper shows that explicit definition of a representative velocity and a representative temperature difference, as used in previous studies, is generally inappropriate in formulating a similitude law. The paper also presents formulae which allow to directly convert water test results into actual plant values. Using the conversion formulae, it is demonstrated that data acquired in a small scale water experiment can be converted and the results are comparable with results of actual LMFR computation. The accuracy of the experimental prediction is discussed.     

Static and shock-tension loaded headed studs in reinforced concrete

By means of experimental investigations and theoretical approaches, methods were developed which take hold of the process of static and shock-tension loaded headed studs embedded in reinforced concrete. For the analysis of the failure mechanism, the test results available from the literature as well as own experiments were used. In particular, shock loads where tension builds up within milliseconds were considered. For both the static stress and the dynamic load-bearing capacity, design formulae could be developed by applying dimensional analysis. These design rules permit the determination of the most relevant variables which describe the failure mechanism.     

Conservative availability analyses including dependent failures in redundant I&C-systems with recurrent tests

In this paper analytic formulae are derived to estimate conservatively the unavailability of a two out of four digital safety Instrumentation and Control (I&C) system with recurrent tests. The analytic formulae disclose the influence of the different parameters on the system’s unavailability. In particular, the choice of a proper test interval is essential to guarantee the required low unavailability. The extraordinary self-checking capabilities of digital systems are taken into account by use of an appropriate failure model together with the treatment of dependent failures of the integrated software–hardware system. The underlying methodology is approved by licensing experts of nuclear facilities in Germany.     

Evaluation of aseismic integrity in the HTTR core-bottom structure IV. Structural integrity of connecting elements between graphite components

Former investigation on the aseismic test for core-bottom structure in the high temperature engineering test reactor (HTTR) clarified the response of acceleration, strain, impact load etc. Following this investigation the component test of connecting elements between graphite components was carried out to evaluate their fracture load and fracture mode. The stress analysis was also performed to estimate the stress profile by the analytical approach. The seismic design load is also estimated by considering the load concentration factor. In this paper the experimental and analytical results are compared and the structural integrity of these connecting elements is discussed under the severest earthquake condition postulated in the HTTR structural design.