Commentary on the basic philosophy and recent development of safety margins

1976 ◽  
Vol 3 (3) ◽  
pp. 409-416 ◽  
Author(s):  
Franz Knoll
Keyword(s):  
Safety Margin ◽  
Building Code ◽  
Structural Failure ◽  
Design Rules ◽  
Human Errors ◽  
Safety Margins ◽  
Low Levels ◽  
Basic Philosophy

The principal effects influencing safety margins are recapitulated. Human errors are found to be the major source of structural failure. A revised format for safety margins is proposed, using partial factors, one of which should represent the effects of human errors. It should be used as a basic safety margin, reflecting the fact of the importance of human errors.Recent changes in design rules as set forth in the National Building Code of Canada 1975, are discussed and criticized for having reduced effective safety margins to unacceptably low levels. Examples are given to illustrate possible consequences of the use of such low safety margins.

scholarly journals Bootstrap and Order Statistics for Quantifying Thermal-Hydraulic Code Uncertainties in the Estimation of Safety Margins

2008 ◽  
Vol 2008 ◽  
pp. 1-9 ◽  
Author(s):  
Enrico Zio ◽  
Francesco Di Maio
Keyword(s):  
Confidence Interval ◽  
Order Statistics ◽  
Nuclear Reactor ◽  
Safety Margin ◽  
Fuel Cladding ◽  
Complete Group ◽  
Bootstrap Technique ◽  
Safety Margins ◽  
Group Distribution

In the present work, the uncertainties affecting the safety margins estimated from thermal-hydraulic code calculations are captured quantitatively by resorting to the order statistics and the bootstrap technique. The proposed framework of analysis is applied to the estimation of the safety margin, with its confidence interval, of the maximum fuel cladding temperature reached during a complete group distribution blockage scenario in a RBMK-1500 nuclear reactor.

scholarly journals Assessment of Hand Function Through the Coordination of Contact Forces in Manipulation Tasks

2013 ◽  
Vol 36 (1) ◽  
pp. 5-160 ◽  
Author(s):  
Slobodan Jaric ◽  
Mehmet Uygur
Keyword(s):  
Hand Function ◽  
Safety Margin ◽  
Tangential Component ◽  
Contact Forces ◽  
Load Force ◽  
Dominant Hand ◽  
Factors Affecting ◽  
Relative Safety ◽  
Safety Margins ◽  
Mechanical Factors

Exploration of force coordination has been one of the most often used approaches in studies of hand function. When holding and manipulating a hand-held object healthy individuals are typically able to highly coordinate the perpendicular (grip force; GF) with the tangential component of the contact force (load force; LF). The purpose of this review is to present the findings of our recent studies of GF-LF coordination. Regarding the mechanical factors affecting GF-LF coordination, our data suggest that both different hand segments and their particular skin areas could have markedly different friction properties. It also appears that the absolute, rather than relative safety margin (i.e., how much the actual GF exceeds the minimum value that prevents slipping) should be a variable of choice when assessing the applied magnitude of GF. The safety margin could also be lower in static than in free holding tasks. Regarding the involved neural factors, the data suggest that the increased frequency, rather than an increased range of a cyclic LF could have a prominent detrimental effect on the GF-LF coordination. Finally, it appears that the given instructions (e.g., 'to hold' vs. 'to pull') can prominently alter GF-LF coordination in otherwise identical manipulation tasks. Conversely, the effects of handedness could be relatively week showing only slight lagging of GF in the non-dominant, but not in the dominant hand. The presented findings reveal important aspects of hand function as seen through GF-LF coordination. Specifically, the use of specific hand areas for grasping, calculation of particular safety margins, the role of LF frequency (but not of LF range) and the effects of given instructions should be all taken into account when conducting future studies of manipulation tasks, standardizing their procedures and designing routine clinical tests of hand function.

The hydraulic architecture of Eucalyptus trees growing across a gradient of depth-to-groundwater

2015 ◽  
Vol 42 (9) ◽  
pp. 888 ◽  
Author(s):  
Sepideh Zolfaghar ◽  
Randol Villalobos-Vega ◽  
Melanie Zeppel ◽  
Derek Eamus
Keyword(s):  
Hydraulic Conductivity ◽  
Leaf Area ◽  
Water Availability ◽  
Safety Margin ◽  
Hydraulic Architecture ◽  
Sapwood Area ◽  
Huber Value ◽  
Xylem Vulnerability ◽  
Safety Margins ◽  
Hydraulic Safety

Heterogeneity in water availability acts as an important driver of variation in plant structure and function. Changes in hydraulic architecture represent a key mechanism by which adaptation to changes in water availability can be expressed in plants. The aim of this study was to investigate whether differences in depth-to-groundwater influence the hydraulic architecture of Eucalyptus trees in remnant woodlands within mesic environments. Hydraulic architecture of trees was examined in winter and summer by measuring the following traits: Huber value (HV: the ratio between sapwood area and leaf area), branch hydraulic conductivity (leaf and sapwood area specific), sapwood density, xylem vulnerability (P50 and Pe) and hydraulic safety margins across four sites where depth-to-groundwater ranged from 2.4 to 37.5 m. Huber value increased significantly as depth-to-groundwater increased. Neither sapwood density nor branch hydraulic conductivity (sapwood and leaf area specific) varied significantly across sites. Xylem vulnerability to embolism (represented by P50 and Pe) in both seasons was significantly and negatively correlated with depth-to-groundwater. Hydraulic safety margins increased with increasing depth-to-groundwater and therefore trees growing at sites with deeper water tables were less sensitive to drought induced embolism. These results showed plasticity in some, but not all, hydraulic traits (as reflected in HV, P50, Pe and hydraulic safety margin) in response to increase in depth-to-groundwater in a mesic environment.

Best Estimate Plus Uncertainty Analysis of LBLOCA for a Pickering B CANDU Reactor

2010 ◽  
Author(s):  
Larry Blake ◽  
George Gavrus ◽  
Jack Vecchiarelli ◽  
J. Stoklosa
Keyword(s):  
Power Plants ◽  
Safety Margin ◽  
Reactor Power ◽  
Natural Uranium ◽  
Nuclear Industry ◽  
Initial Increase ◽  
Power Pulse ◽  
Pulse Phase ◽  
Best Estimate ◽  
Safety Margins

The Pickering B Nuclear Generating Station consists of four CANDU reactors. These reactors are horizontal pressure tube, heavy water cooled and moderated reactors fuelled with natural uranium. Under a postulated large break loss of coolant accident (LOCA), positive reactivity results from coolant void formation. The transient is terminated by the operation of the safety systems within approximately 2 seconds of the start of the transient. The initial increase in reactor power, terminated by the action of the safety system, is termed the power pulse phase of the accident. In many instances the severity of an LBLOCA can be characterized by the adiabatic energy deposited to the fuel during this phase of the accident. Historically, Limit of Operating Envelope (LOE) calculations have been used to characterize the severity of the accident. LOE analyses are conservative analyses in which the key operational and safety related parameters are set to conservative or limiting values. Limit based analyses of this type result in calculated transient responses that will differ significantly from the actual expected response of the station. As well, while the results of limit calculations are conservative, safety margins and the degree of conservatism is generally not known. As a result of these factors, the use of Best Estimate Plus Uncertainty (BEPU) analyses in safety analyses for nuclear power plants has been increasing. In Canada, the nuclear industry has been pursuing best estimate analysis through the BEAU (Best Estimate Analysis and Uncertainty) methodology in order to obtain better characterization of the safety margins. This approach is generally consistent with those used internationally. Recently, a BEAU analysis of the Pickering B NGS was completed for the power pulse phase of a postulated Large Break LOCA. The analysis comprised identification of relevant phenomena through a Phenomena Identification and Ranking (PIRT) process, assessment of the code input uncertainties, sensitivity studies to quantify the significance of the input parameters, generation of a functional response surface and its validation, and determination of the safety margin. The results of the analysis clearly demonstrate that the Limit of Operating Envelope (LOE) results are significantly conservative relative to realistic analysis even when uncertainties are considered. In addition, the extensive sensitivity analysis performed to supplement the primary result provides insight into the primary contributors to the results.

scholarly journals TRANSIENT ANALYSIS OF SIMULTANEOUS LOFA AND RIA IN RSG-GAS REACTOR AFTER 32 YEARS OPERATION

2020 ◽  
Vol 22 (3) ◽  
pp. 111
Author(s):  
Muhammad Darwis Isnaini ◽  
Iman Kuntoro ◽  
Muhammad Subekti
Keyword(s):  
Research Reactor ◽  
Safety Margin ◽  
Low Flow ◽  
Maximum Temperature ◽  
Design Parameters ◽  
Transient Condition ◽  
Trip Time ◽  
Safety Margins ◽  
Fuel Meat ◽  
The Impact

During the operation of the research reactor RSG-GAS, there are many design parameters should be verified based on postulated accidents. Several design basis accidents (DBA) such as loss of flow accident (LOFA) and reactivity-initiated accident (RIA) also have been conducted separately. This paper discusses about possibility of simultaneous accidents of LOFA and RIA. The accident analyses carry out calculation for transient condition during RIA, LOFA, and postulated accident of simultaneous LOFA-RIA. This study aims to conduct a safety analysis on simultaneous LOFA and RIA, and investigate the impact on safety margins. The calculations are conducted by using the PARET code. The maximum temperature of the center fuel meat at nominal power of 30 MW and steady state conditions is 126.10°C and MDNBR of 2.94. At transients condition, the maximum center fuel meat temperature for LOFA, RIA and simultaneous LOFA-RIA are consecutively 132.99°C, 135.67°C and 138.21°C, and the time of reactor trip are 3.2593s, 3.6494s and 2.7118s, respectively. While the MDNBR for LOFA, RIA and simultaneous LOFA-RIA are respectively at transient condition are 2.88, 2.58 and 2.63, respectively. It is shown that, simultaneous LOFA-RIA has the fastest trip time. In this case, the low flow trip occurs first in advance to over power trip.  From these results, it can be concluded that the RSG-GAS has adequate safety margin against transient of simultaneous LOFA-RIA.Keywords: RSG-GAS, Simultaneous, LOFA, RIA, PARET

scholarly journals En-Route Battery Management and a Mixed Network Equilibrium Problem Based on Electric Vehicle Drivers’ En-Route Recharging Behaviors

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4061
Author(s):  
Kai Liu ◽  
Sijia Luo ◽  
Jing Zhou
Keyword(s):  
Electric Vehicle ◽  
Equilibrium Model ◽  
Transportation Network ◽  
Management Strategies ◽  
Safety Margin ◽  
User Equilibrium ◽  
Network Equilibrium ◽  
Battery Management ◽  
Battery Safety ◽  
Safety Margins

With the rapidly increasing number of electric vehicle users, in many urbans transport networks, there are mixed traffic flows (i.e., electric vehicles and gasoline vehicles). However, limited by driving ranges and long battery recharging, the battery electric vehicle (BEV) drivers’ route choice behaviors are inevitably affected. This paper assumes that in a transportation network, when BEV drivers are traveling between their original location and destinations, they tend to select the path with the minimal driving times and recharging time, and ensure that the remaining charge is not less than their battery safety margin. In contrast, gasoline vehicle drivers tend to select the path with the minimal driving time. Thus, by considering BEV drivers’ battery management strategies, e.g., battery safety margins and en-route recharging behaviors, this paper developed a mixed user equilibrium model to describe the resulting network equilibrium flow distributions. Finally, a numerical example is presented to demonstrate the mixed user equilibrium model. The results show that BEV drivers’ en-route recharging choice behaviors are significantly influenced by their battery safety margins, and under the equilibrium, the travel routes selected by some BEV drivers may not be optimal, but the total travel time may be more optimal.

scholarly journals Safety Evaluation of Silicon Carbide and Zircaloy-4 Cladding during a Large-Break Loss-of-Coolant Accident

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3324 ◽  
Author(s):  
Kwangwon Ahn ◽  
Kyohun Joo ◽  
Sung-Pil Park
Keyword(s):  
Silicon Carbide ◽  
Ultimate Strength ◽  
Safety Margin ◽  
Safety Evaluation ◽  
Loss Of Coolant Accident ◽  
Safety Margins ◽  
Loss Of Coolant

In this study, we aim to conduct structural analyses of cladding materials, such as silicon carbide and zircaloy-4, during a Large-Break Loss-of-Coolant Accident. The safety margin is the key consideration regarding the performance of the cladding materials. Our study shows that, in terms of primary stresses, SiC has a greater safety margin than zircaloy-4 due to SiC having a higher yield and ultimate strength; the cladding outer pressure is not affected by the cladding materials and, thus, the primary stresses of all cladding materials are the same. However, for secondary stresses, zircaloy-4 has the smallest fluctuation and irradiated SiC recorded the largest; secondary stresses and temperature histories are material-dependent. Ultimately, both cladding materials were found to have sufficient safety margins with respect to primary and secondary stresses.

Collapse of a viewing platform

2000 ◽  
Vol 27 (3) ◽  
pp. 421-432
Author(s):  
John C Wilson
Keyword(s):  
Project Management ◽  
Building Code ◽  
Structural Failure ◽  
Code Construction ◽  
Timber Construction ◽  
Load Limit ◽  
Management Procedures ◽  
Legal Position ◽  
Management Issues

In April 1995 a group of young adults were on a school trip to Department of Conservation (DOC) lands on New Zealand's South Island. Moments after 18 of the group had stepped onto a 3 m × 3 m viewing platform it collapsed and fell 30 m. Fourteen people died and the other four were seriously injured. This paper reviews circumstances that contributed to this tragedy. Features of the construction of the timber platform are presented, along with building code requirements that should have been followed but were not. The principal technical reason for the collapse was simple and straightforward; the cantilevered platform was not properly connected to its foundation. More complex however, was the role of non-technical factors that contributed to the collapse. These included failures in project management, provision of qualified engineering input, construction management, compliance with the building code, construction inspection, and posting of load limit signs. The evolution of DOC and project management issues that allowed these failures to occur are examined. Recommendations of the commission of inquiry are presented and resultant changes in DOC's engineering and management procedures are addressed. The issue of accountability and the legal position of DOC present additional interesting twists to this story. The paper concludes with comments by the author that reflect on factors associated with the platform collapse.Key words: platform, collapse, structural failure, building code, timber construction, nailed connections, project management, commission of inquiry, New Zealand.

Mite not make it home: tracheal mites reduce the safety margin for oxygen delivery of flying honeybees

2001 ◽  
Vol 204 (4) ◽  
pp. 805-814 ◽  
Author(s):  
J.F. Harrison ◽  
S. Camazine ◽  
J.H. Marden ◽  
S.D. Kirkton ◽  
A. Rozo ◽  
...  
Keyword(s):  
Metabolic Rate ◽  
Oxygen Delivery ◽  
Safety Margin ◽  
Exchange Capacity ◽  
Late Winter ◽  
Excess Capacity ◽  
Negative Effects ◽  
Acarapis Woodi ◽  
Safety Margins ◽  
Tracheal Mites

Many physiological systems appear to have safety margins, with excess capacity relative to normal functional needs, but the significance of such excess capacity remains controversial. In this study, we investigate the effects of parasitic tracheal mites (Acarapis woodi) on the safety margin for oxygen delivery and flight performance of honeybees. Tracheal mites did not affect the flight metabolic rate of honeybees in normoxic (21% oxygen) or hyperoxic (40% oxygen) air, but did reduce their metabolic rate relative to uninfected bees when flying in hypoxic air (5 or 10% oxygen), demonstrating that mites reduced the safety margin for tracheal oxygen delivery. The negative effects of mites on flight metabolic rate in hypoxic atmospheres were graded with the number of mites per trachea. For example, in 10% oxygen atmospheres, flight metabolic rate was reduced by 20% by moderate mite infection and by 40% by severe mite infection. Thus, the safety margin for oxygen delivery in honeybees allows them to retain normal flight metabolic rate and behavior despite tracheal mite infection under most conditions. However, the reduction in tracheal gas-exchange capacity may constrain activities requiring the highest metabolic rates, such as flying in cool weather. In support of this hypothesis, bees that were unable to return to the hive during late-winter flights showed significantly higher levels of mite infection than bees that returned safely.

Experimental Study on Ultimate Strength of a Ellipsoidal Dished Head Plate Under Pressure on Convex Surface

2016 ◽  
Author(s):  
Hiroki Yada ◽  
Masanori Ando ◽  
Kazuyuki Tsukimori ◽  
Masakazu Ichimiya ◽  
Yoshinari Anoda
Keyword(s):  
Evaluation Method ◽  
Convex Surface ◽  
Safety Margin ◽  
Fem Analysis ◽  
External Pressure ◽  
Containment Vessel ◽  
Side Pressure ◽  
Safety Margins ◽  
Intermediate Heat Exchanger ◽  
Radioactive Release

Containment vessel is an important structure to prevent a significant and sudden radioactive release, however, the safety margin of the containment vessel against the internal or external pressure are not numerically clarified. Namely, the safety margins due to the relationship of the ultimate toughness of containment vessel structures and maximum design pressure is not clear. Indeed, to clarify the progress of events under the beyond design basis events (BDBE) and to design the BDBE countermeasure equipment, it is necessary to evaluate the pressure toughness of containment vessel adequately. The containment vessel of fast reactor is composed of the various structures. The head plate that forms the boundary between primary and secondary coolant in intermediate heat exchanger has an important role when the progress of the BDBE is considered. In this study, in order to develop the evaluation method of the pressure toughness of the head plate under the BDBE, the ultimate pressure test of the head plate test specimen subjected to convex side pressure was performed, and also FEM analysis was performed for discussion.

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