Application of Fracture Control to Mitigate Failure Consequence Under BDBE

2020 ◽  
Author(s):  
Naoto Kasahara ◽  
Takashi Wakai ◽  
Izumi Nakamura ◽  
Takuya Sato ◽  
Masakazu Ichimiya
Keyword(s):  
Failure Modes ◽  
Natural Frequencies ◽  
Reactor Vessel ◽  
The Other ◽  
Severe Accident ◽  
Seismic Loads ◽  
Strength Evaluation ◽  
Modes Of Failure ◽  
Design Basis ◽  
Fracture Control

Abstract As a lesson learned from the Fukushima nuclear power plant accident, the industry recognized the imporatance of mitigating accident consequences after Beyond Design Basis Events (BDBE). We propose the concept of applying fracture control to mitigate failure consequences of nuclear components under BDBE. Requirements are different between Design Basis Events (DBE) and BDBE. In the case of DBE, it requires preventing occurrence of failures, and thus, its structural approach is strengthening. On the other hand, BDBE requires mitigating failure consequences. The simple strengthening approach with DBE is inappropriate for this BDBE requirement. As the structural strengthening approach for mitigating failure consequences, we propose applying the concept of fracture control. The fundamental idea is to control the sequence of failure locations and modes. Preceding failures release loadings and prevent further catastrophic consequent failures. At the end, locations and modes of failure are limited. Absolute strength evaluation for each failure mode is not easy especially for BDBE. Fracture control, however, requires only relative strength evaluation among different locations and failure modes. Our paper discusses two sample applications of our proposed method. One is a fast reactor vessel under severe accident conditions. Our method controls the upper part of a vessel above the liquid coolant surface weaker than the lower part. This strength control maintains enough coolant even after a high pressure and high temperature condition causes failure of the reactor vessel because structural failure in the upper part releases internal pressure to protect the lower part. The other example is the piping under a large earthquake. Our proposal controls strength of supports weaker than the piping itself. When the supports fail first, natural frequencies of piping systems drop. When the natural frequencies of dominant modes are lower than the peak frequency of seismic loads, seismic loads hardly transfer to the piping and catastrophic failures such as collapse or break are avoided.

Difference of Strength Evaluation Approach Between for DBE and for BDBE

2017 ◽  
Author(s):  
Naoto Kasahara ◽  
Takuya Sato
Keyword(s):  
Failure Modes ◽  
New Technologies ◽  
Lessons Learned ◽  
Failure Behavior ◽  
Design Factor ◽  
Strength Evaluation ◽  
Evaluation Approach ◽  
Design Basis ◽  
Probabilistic Evaluation ◽  
Actual Strength

Preparation for beyond design basis events (BDBE) becomes important as the lessons learned from the Fukushima Daiichi nuclear accident. The objective of strength evaluation for design basis events (DBE) is a confirmation to prevent structural failure for assumed events. For BDBE, main objectives are weak point survey, deterministic and probabilistic risk assessment, and planning of countermeasures including potable equipment and accident management. According to the above objectives, strength evaluation approach have to be different between for DBE and for BDBE. (1) DBE Conservative approach to prevent of failure. Design by analysis concept is basically adopted Assumption of hypothetical failure modes to prevent actual failure modes Stress criteria to bond actual strength Elastic analyses for conservative loading assumption Design factor to bound uncertainties (2) BDBE Best estimation of failure behavior with uncertainties to plan mitigations Identification of realistic failure modes to identify failure consequences Criteria by dominant parameters of failure phenomena Inelastic analyses for realistic loading prediction Probabilistic evaluation to quantify uncertainties. Strength evaluation concept has not yet been established for BDBE. It is necessary to discuss from basic philosophy to make sharable concepts. Adequate criteria is required to meet above concepts. Instead of stress, strain is one of candidate. New evaluation technics are desired to satisfy above criteria. This paper indicates the direction of strength evaluation for BDBE with same examples proposals. Its aims is to promote international discussions and to implement new technologies to actual countermeasures against BDBE.

Structural Analysis Approach for Risk Assessment Under BDBE

2016 ◽  
Author(s):  
Naoto Kasahara ◽  
Izumi Nakamura ◽  
Hideo Machida ◽  
Koji Okamoto ◽  
Takuya Sato
Keyword(s):  
Risk Assessment ◽  
Structural Analysis ◽  
Failure Modes ◽  
The Other ◽  
Analysis Approach ◽  
Inelastic Analysis ◽  
Design Basis ◽  
Other Hand ◽  
Safety Margins ◽  
Defense In Depth

Based on the lessons learned from the Fukushima nuclear power plant accident, it is recognized the importance of the risk assessment and mitigation for failure consequences to avoid catastrophic failure of pressure equipment during severe accidents (SA) and excessive earthquake. The objectives of structural design (from the first layer to the third layer of the defense-in-depth) is strength confirmation under assumed loading conditions. On the other hand, ones of risk assessment and mitigation (the forth layer of the defense-in-depth) is prediction of realistic failure scenarios. Through investigation of failure locations and modes of main components under both severe accident and excessive earthquake, different failure modes from DBE(Design Basis Events) were identified for BDBE(Beyond Design Basis Events). To clarify these modes, the failure mechanisms were studied with some strength experiments. For most of failure modes, their dominant parameters are inelastic strain rather than stress. So that large scale inelastic analysis methods were studied and extended to very high temperature and large strain. By using above results, this paper has proposed the new structural analysis approach for risk assessment under BDBE. This is the extension of “design by analysis” concept. However it is clearly different from design approach from next viewpoints. (1) Additional failure modes to design condition Such additional failure modes induced by excessive loadings are considered for as local failure, creep rupture, creep buckling, ratcheting collapse and so on. (2) Identification of dominant failure modes Design codes require conservative evaluation against all of assumed failure modes. On the other hand, risk assessment needs adequate failure scenarios, where failure locations, modes and their order are important. For that reason, dominant failure modes have to be identified. To identify dominant modes, failure mode map concept was proposed. (3) Best estimation To estimate realistic accident phenomena, the best estimation is required. Therefore, dominant strength parameters and criteria without safety margins should be adopted. Through strength mechanism investigations, plastic and creep strain are recognized as more dominant parameters than stress for many failure modes. So that realistic inelastic analyses are recommended for BDBE.

Mechanical Stress Improvement Process (MSIP) Used to Prevent and Mitigate Primary Water Stress Corrosion Cracking (PWSCC) in Reactor Vessel Piping at V.C. Summer

2003 ◽  
Author(s):  
E. A. Ray ◽  
K. Weir ◽  
C. Rice ◽  
T. Damico
Keyword(s):  
Water Stress ◽  
Stress Corrosion ◽  
Mechanical Stress ◽  
Stress Corrosion Cracking ◽  
Reactor Vessel ◽  
Corrosion Cracking ◽  
The Other ◽  
Water Reactor ◽  
Improvement Process ◽  
Primary Water

During the October 2000 refueling outage at the V.C. Summer Nuclear Station, a leak was discovered in one of the three reactor vessel hot leg nozzle to pipe weld connections. The root cause of this leak was determined to be extensive weld repairs causing high tensile stresses throughout the pipe weld; leading to primary water stress corrosion cracking (PWSCC) of the Alloy 82/182 (Inconel). This nozzle was repaired and V.C. Summer began investigating other mitigative or repair techniques on the other nozzles. During the next refueling outage V.C. Summer took mitigative actions by applying the patented Mechanical Stress Improvement Process (MSIP) to the other hot legs. MSIP contracts the pipe on one side of the weldment, placing the inner region of the weld into compression. This is an effective means to prevent and mitigate PWSCC. Analyses were performed to determine the redistribution of residual stresses, amount of strain in the region of application, reactor coolant piping loads and stresses, and effect on equipment supports. In May 2002, using a newly designed 34-inch clamp, MSIP was successfully applied to the two hot-leg nozzle weldments. The pre- and post-MSIP NDE results were highly favorable. MSIP has been used extensively on piping in boiling water reactor (BWR) plants to successfully prevent and mitigate SCC. This includes Reactor Vessel nozzle piping over 30-inch diameter with 2.3-inch wall thickness similar in both size and materials to piping in pressurized water reactor (PWR) plants such as V.C. Summer. The application of MSIP at V.C. Summer was successfully completed and showed the process to be predictable with no significant changes in the overall operation of the plant. The pre- and post-nondestructive examination of the reactor vessel nozzle weldment showed no detrimental effects on the weldment due to the MSIP.

Effect of Delamination on Natural Frequencies of E-glass and S-glass Epoxy Composite Plates

2021 ◽  
Author(s):  
P. K. Karsh ◽  
Bindi Thakkar ◽  
R. R. Kumar ◽  
Abhijeet Kumar ◽  
Sudip Dey
Keyword(s):  
Natural Frequencies ◽  
Epoxy Composite ◽  
Orientation Angle ◽  
Laminated Composite ◽  
Composite Plates ◽  
Mode Shapes ◽  
Transverse Shear Deformation ◽  
The Finite Element Method ◽  
Modes Of Failure ◽  
Ply Orientation

The delamination is one of the major modes of failure occurring in the laminated composite due to insufficient bonding between the layers. In this paper, the natural frequencies of delaminated S-glass and E-glass epoxy cantilever composite plates are presented by employing the finite element method (FEM) approach. The rotary inertia and transverse shear deformation are considered in the present study. The effect of parameters such as the location of delamination along the length, across the thickness, the percentage of delamination, and ply-orientation angle on first three natural frequencies of the cantilever plates are presented for S-glass and E-glass epoxy composites. The standard eigenvalue problem is solved to obtain the natural frequencies and corresponding mode shapes. First three mode shape of S-Glass and E-Glass epoxy laminated composites are portrayed corresponding to different ply angle of lamina.

A Review on Role of Aluminum Matrix Materials, Failure Causes and Optimization Techniques

2021 ◽  
Vol 6 (3) ◽  
pp. 1-11
Author(s):  
Tilahun Y ◽  
◽  
Mesfin G ◽  
Keyword(s):  
Failure Modes ◽  
Matrix Material ◽  
Aluminum Matrix ◽  
Ductile Failure ◽  
Failure Surface ◽  
Optimization Techniques ◽  
Alloy Matrix ◽  
Modes Of Failure ◽  
Causes Of Failure

Aluminum is a metal matrix material which is widely used in different industrial as well as engineering applications.it has a great advantage due to its remarkable properties like less density, formability, and light in weight, recyclability and other properties. but, failure of aluminum matrix materials are the main problems in aluminum industries now a days.in this review role of aluminum and its alloys as matrix materials, their failure modes, causes of failure and optimization techniques to minimize this failure modes and causes of failure are discussed. Sources are reviewed which are from 2005 to recent one. Consequently, most modes of failure, causes of failure and most optimization techniques of aluminum and its alloy matrix materials are found. most modes of failure are mechanical related like fatigue failure, surface cracking, ductile failure, porosity formation, and stress related like stress corrosion cracking, surface weakness due to repeated stresses and other factors are summarized.in causes of failure mostly like corrosion formation, wear formation and poor mechanical properties are discussed.

Uncertainty Analysis in Quantitative Risk Assessment

1996 ◽  
Vol 118 (1) ◽  
pp. 121-124 ◽  
Author(s):  
S. Quin ◽  
G. E. O. Widera
Keyword(s):  
Risk Assessment ◽  
Uncertainty Analysis ◽  
Set Theory ◽  
Fuzzy Set ◽  
Fuzzy Set Theory ◽  
Failure Modes ◽  
The Other ◽  
Quantitative Risk Assessment ◽  
Engineering Practice ◽  
Criticality Analysis

Of the quantitative approaches applied to inservice inspection, failure modes, effects,criticality analysis (FMECA) methodology is recommended. FMECA can provide a straightforward illustration of how risk can be used to prioritize components for inspection (ASME, 1991). But, at present, it has two limitations. One is that it cannot be used in the situation where components have multiple failure modes. The other is that it cannot be used in the situation where the uncertainties in the data of components have nonuniform distributions. In engineering practice, these two situations exist in many cases. In this paper, two methods based on fuzzy set theory are presented to treat these problems. The methods proposed here can be considered as a supplement to FMECA, thus extending its range of applicability.

Failure Modes of Tapered Suction Caissons Under Vertical Pull-Out Loads

2007 ◽  
Author(s):  
Mahmood Nabipour ◽  
Mostafa Zeinoddini ◽  
Mahmood R. Abdi
Keyword(s):  
Failure Modes ◽  
Numerical Approach ◽  
Local Failure ◽  
Superior Performance ◽  
Soil Plug ◽  
Pull Out ◽  
Modes Of Failure ◽  
Numerical Studies ◽  
Second Mode ◽  
Suction Caissons

The pull-out performance of conventional upright suction caissons has been investigated by different researchers. However, no attention has been formerly paid to tapered suction caissons. Some numerical studies already conducted by the authors demonstrated that tapered caissons exhibit pull-out capacities well above than that from their corresponding upright caissons. This paper deals with different failure mechanisms of tapered suction caissons and discusses some reason for their superior performance. A numerical approach has been used and different combinations of caisson types/ soil categories have been examined. With tapered suction caissons two different modes of failure have been discerned. The first mode has been noticed to develop in weak clays and sands under drained conditions. This mode corresponds to a shear sliding failure in the soil plug along the caisson’s interior wall. Concurrently a soil wedge is formed in the soil body adjacent to the caisson. The second mode of failure has been observed in higher strength drained clays and undrained clays and sands. With this failure mode a local failure at the bottom of the soil plug has been noticed to happen. At the same time the failure is extended to the lower surfaces of a soil wedge outside of the caisson. The detached soil plug accompanies the caisson in its movement upward following the local failure.

Identification of Failure Modes Under Design Extension Conditions

2015 ◽  
Author(s):  
Naoto Kasahara ◽  
Izumi Nakamura ◽  
Hideo Machida ◽  
Hitoshi Nakamura ◽  
Koji Okamoto
Keyword(s):  
High Temperature ◽  
Nuclear Power ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
External Pressure ◽  
Lessons Learned ◽  
Local Failure ◽  
Severe Accident ◽  
Mitigation Measures ◽  
Loading Mode

As the important lessons learned from the Fukushima-nuclear power plant accident, mitigation of failure consequences and prevention of catastrophic failure became essential against severe accident and excessive earthquake conditions. To improve mitigation measures and accident management, clarification of failure behaviors with locations is premise under design extension conditions such as severe accidents and earthquakes. Design extension conditions induce some different failure modes from design conditions. Furthermore, best estimation for these failure modes are required for preparing countermeasures and management. Therefore, this study focused on identification of failure modes under design extension conditions. To observe ultimate failure behaviors of structures under extreme loadings, new experimental techniques were adopted with simulation materials such as lead and lead-antimony alloy, which has very small yield stress. Postulated failure modes of main components under design extension conditions were investigated according three categories of loading modes. The first loading mode is high temperature and internal pressure. Under this mode, ductile fracture and local failure were investigated. At the structural discontinuities, local failure may become dominant. The second is high temperature and external pressure loading mode. Buckling and fracture were investigated. Buckling occurs however hardly break without additional loads or constraints. The last loading is excessive earthquake. Ratchet deformation, collapse, and fatigue were investigated. Among them, low-cycle fatigue is dominant.

scholarly journals THE MODELING OF SPILLS RESULTING FROM THE CATASTROPHIC FAILURE OF ABOVE GROUND STORAGE TANKS AND THE DEVELOPMENT OF MITIGATION

2008 ◽  
Vol 2008 (1) ◽  
pp. 949-956
Author(s):  
W. Atherton ◽  
J. W. Ash ◽  
R. M. Alkhaddar
Keyword(s):  
Large Scale ◽  
Structural Integrity ◽  
Oil Spills ◽  
Health And Safety ◽  
The Other ◽  
Catastrophic Failure ◽  
Storage Tanks ◽  
Modes Of Failure ◽  
Mode Of Failure ◽  
Mitigation Technique

ABSTRACT The risk of accidents involving the catastrophic failure of storage tanks is estimated to be low, in the region of 5 × l0−6 per tank year. However, recent accidents involving major oil spills at storage facilities located in Belgium (2004) along with USA and England (2005) have shown that tank failures do nevertheless occur. Causalities of such events vary; the consequences however are ordinarily the same, incurring environmental, financial and infrastructure losses. The normal mitigation technique employed to prevent such losses is secondary containment, usually in the form of a bund wall or earthen dyke. Researchers have investigated the reliability of such methods, examining the effects of tank failure, both theoretically and experimentally in terms of loss of containment. A United Kingdom Health and Safety Executive (HSE) review conducted in 1997 concluded that the then available data was limited and focussed attention on the work of Greenspan and Johansson (1981) and the later work of Trobojevic and Slater (1989). This led to the HSE commissioning Liverpool John Moores University (LIMU) in 2003 to undertake a large-scale spill-modelling program with the aim of quantifying the level of overtopping and the magnitudes of the dynamic pressures on the bunds. The study examined the effect of axisymmetric releases on a total of 96 tank and bund arrangements. Such losses have proven to be significant and in some cases the nature of the dynamic pressures has brought in to question the structural integrity of the bunds themselves. Research has since concentrated on modelling alternative modes of failure, such as directional releases, which could be considered to be the more common mode of failure likely to be encountered. The conclusions to this work have generated additional research to investigate possible methods of mitigation that could be incorporated into the design of facilities with the ultimate aim of further reducing losses in the event of tank failure. Two promising methods have been identified, one involving modification to the primary containment (tank) with the other being a change to the design of the profile of the secondary containment (bund wall).

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