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.

Characterization of SiC Ceramic Tube Prepared by the Combined CVI and CVD Process

2014 ◽  
Vol 94 ◽  
pp. 38-42 ◽  
Author(s):  
Ji Yeon Park ◽  
Dae Jong Kim ◽  
Weon Ju Kim
Keyword(s):  
High Temperature ◽  
Composite Layer ◽  
Ductile Failure ◽  
Fission Products ◽  
Chemical Vapor ◽  
High Strength ◽  
Fuel Cladding ◽  
Loss Of Coolant Accident ◽  
Safety Margins ◽  
Structural Applications

SiCf/SiC composites are one of the candidates for high temperature structural applications because of their high strength and corrosion resistance under severe conditions and stability under neutron irradiation [1~3]. A silicon carbide fuel cladding for the light water cooled reactors (LWRs) may allow a number of advances, including: the increased safety margins under transients and accident scenarios, such as loss of coolant accident; the improved resource utilization via a higher burn-up beyond the present limit of 62 GWd/MTU; and improved waste management [3~5]. Some components of SiCf/SiC composite will be applied as tubular geometry for the high-temperature core parts. The proposed design of an advanced LWR fuel cladding, referred to as Triplex, consists of three layers: an inner SiC monolith, a central SiCf/SiC composite, and an outer dense SiC evrionmental barrier coating. The inner SiC layer provides the strength and hermeticity to contain fission products. The SiCf/SiC composite layer fabricated by the CVI process provides a pseudo-ductile failure mode. The outer SiC thin coating layer protects against corrosion [5]. The chemical vapor deposition (CVD) technique is an effective approach for the fabrication of SiCf/SiC composite and coated SiC monolith [6]. To increase the homogeneity of the microstructure and the deposition rate of a SiC tube, the process parameters should be optimized and modified.

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 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.

Development of Diffusion Barrier Coatings for Mitigation of Fuel-Cladding Chemical Interactions

2012 ◽  
Vol 507 ◽  
pp. 3-7 ◽  
Author(s):  
Vahid Firouzdor ◽  
Lucas Wilson ◽  
Kumar Sridharan ◽  
Brandon Semerau ◽  
Benjamin Hauch ◽  
...  
Keyword(s):  
Diffusion Couple ◽  
Diffusion Barrier ◽  
Nuclear Reactor ◽  
Fuel Cladding ◽  
Oxide Coatings ◽  
Chemical Interactions ◽  
Barrier Coatings ◽  
Deposition Parameters ◽  
Diffusion Characteristics ◽  
Melting Point Eutectic

Fuel Cladding Chemical Interactions (FCCI) in a nuclear reactor occur due to thermal and radiation enhanced inter-diffusion between the cladding and fuel materials, and can have the detrimental effects of reducing the effective cladding wall thickness and the formation of low melting point eutectic compounds. Deposition of diffusion barrier coatings of a thin oxide on the inner surface of the cladding can potentially reduce or delay the onset of FCCI. This study examines the feasibility of using nanofluid-based electrophoretic deposition (EPD) process to deposit coatings of titanium oxide, yttria-stabilized zirconia (YSZ) and vanadium oxide. The deposition parameters, including the nanofluid composition, current, and voltage were optimized for each coating material using test flat substrates of T91 ferritic-martensitic steel. Diffusion characteristics of the coatings were investigated by diffusion couple experiments using the fuel surrogate cerium. These diffusion couple studies performed in the temperature range of 560°C and 585°C showed that the oxide coatings significantly reduce the solid state inter-diffusion between cerium to steel.

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

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