634 research outputs found
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Risk-based configuration control: Application of PSA in improving technical specifications and operational safety
Risk-based configuration control is the management of component configurations using a risk perspective to control risk and assure safety. A configuration, as used here, is a set of component operability statuses that define the state of a nuclear power plant. If the component configurations that have high risk implications do not occur, then the risk from the operation of nuclear power plants would be minimal. The control of component configurations, i.e., the management of component statuses, to minimize the risk from components being unavailable, becomes difficult, because the status of a standby safety system component is often not apparent unless it is tested. Controlling plant configuration from a risk-perspective can provide more direct risk control and also more operational flexibility by allowing looser controls in areas unimportant to risk. Risk-based configuration control approaches can be used to replace parts of nuclear power plant Technical Specifications. With the advances in probabilistic safety assessment (PSA) technology, such approaches to improve Technical Specifications and operational safety are feasible. In this paper, we present an analysis of configuration risks, and a framework for risk-based configuration control to achieve the desired control of risk-significant configurations during plant operation
Ageing PSA incorporating effectiveness of maintenance and testing
This paper proposes a new approach to Ageing Probabilistic Safety Assessment (APSA) modelling, which is intended to be used to support risk-informed decisions on the effectiveness of maintenance management programs and technical specification requirements of critical equipment of Nuclear Power Plants (NPP) within the framework of the Risk Informed Decision Making according to R.G. 1.174 principles. This approach focuses on the incorporation of not only equipment ageing but also effectiveness of maintenance and efficiency of surveillance testing explicitly into APSA models and data. An example of application is presented, which centres on a critical safety-related equipment of a NPP in order to evaluate the risk impact of considering different approaches to APSA and the combined effect of equipment ageing and maintenance and testing alternatives along NPP design life. The risk impact of the several alternatives is quantified and the results shows that such risk depends largely on the model parameters, such as ageing factor, maintenance effectiveness, test efficiency.Authors are grateful to the Spanish Ministry of Science and Innovation for the financial support of this work (Research Project ENE2013-45540-R) and the Doctoral Fellow (BES-2011-043906).Martón Lluch, I.; Sánchez Galdón, AI.; Martorell Alsina, SS. (2015). Ageing PSA incorporating effectiveness of maintenance and testing. Reliability Engineering and System Safety. 139:131-140. https://doi.org/10.1016/j.ress.2015.03.022S13114013
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Including test errors in evaluating surveillance test intervals
Technical Specifications require surveillance testing to assure that the standby systems important to safety will start and perform their intended functions in the event of plant abnormality. However, as evidenced by operating experience, the surveillance tests may be adversely impact safety because of their undesirable side effects, such as initiation of plant transients during testing or wearing-out of safety systems due to testing. This paper first defines the concerns, i.e., the potential adverse effects of surveillance testing, from a risk perspective. Then, we present a methodology to evaluate the risk impact of those adverse effects, focusing on two important kinds of adverse impacts of surveillance testing: (1) risk impact of test-caused trips and (2) risk impact of test-caused equipment wear. The quantitative risk methodology is demonstrated with several surveillance tests conducted at boiling water reactors, such as the tests of the main steam isolation valves, the turbine overspeed protection system, and the emergency diesel generators. We present the results of the risk-effectiveness evaluation of surveillance test intervals, which compares the adverse risk impact with the beneficial risk impact of testing from potential failure detection, along with insights from sensitivity studies
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Handbook of methods for risk-based analysis of technical specifications
Technical Specifications (TS) requirements for nuclear power plants define the Limiting Conditions for Operations (LCOs) and Surveillance Requirements (SRs) to assure safety during operation. In general, these requirements are based on deterministic analyses and engineering judgments. Improvements in these requirements are facilitated by the availability of plant-specific Probabilistic Risk Assessments (PRAs). The US Nuclear Regulatory Commission (USNRC) Office of Research sponsored research to develop systematic, risk-based methods to improve various aspects of TS requirements. A handbook of methods summarizing such risk-based approaches has been completed in 1994. It is expected that this handbook will provide valuable input to NRC`s present work in developing guidance for using PRA in risk-informed regulation. The handbook addresses reliability and risk-based methods for evaluating allowed outage times (AOTs), action statements requiring shutdown where shutdown risk may be substantial, surveillance test intervals (STIs), managing plant configurations, and scheduling maintenance
The Necessary and Sufficient Conditions for Representing Lipschitz Bivariate Functions as a Difference of Two Convex Functions
In the article the necessary and sufficient conditions for a representation
of Lipschitz function of two variables as a difference of two convex functions
are formulated. An algorithm of this representation is given. The outcome of
this algorithm is a sequence of pairs of convex functions that converge
uniformly to a pair of convex functions if the conditions of the formulated
theorems are satisfied. A geometric interpretation is also given
Skyrme-Rpa Description of Dipole Giant Resonance in Heavy and Superheavy Nuclei
The E1(T=1) isovector dipole giant resonance (GDR) in heavy and super-heavy
deformed nuclei is analyzed over a sample of 18 rare-earth nuclei, 4 actinides
and three chains of super-heavy elements (Z=102, 114 and 120). Basis of the
description is self-consistent separable RPA (SRPA) using the Skyrme force
SLy6. The self-consistent model well reproduces the experimental data (energies
and widths) in the rare-earth and actinide region. The trend of the resonance
peak energies follows the estimates from collective models, showing a bias to
the volume mode for the rare-earths isotopes and a mix of volume and surface
modes for actinides and super-heavy elements. The widths of the GDR are mainly
determined by the Landau fragmentation which in turn is found to be strongly
influenced by deformation. A deformation splitting of the GDR can contribute
about one third to the width and about 1 MeV further broadening can be
associated to mechanism beyond the mean-field description (escape, coupling
with complex configurations).Comment: 9 pages, 12 figures, 2 table
Mutations and SNPs of human cardiac sodium channel alpha subunit gene (SCN5A) in Japanese patients with Brugada syndrome
Background: Brugada syndrome is an inherited arrhythmogenic disease characterized by right bundle branch block pattern and ST segment elevation, leading to the change of V1 to V3 on electrocardiogram, and an increased risk of sudden cardiac death resulting from ventricular fibrillation. The sodium channel alpha 5 subunit (SCN5A) gene encodes a cardiac voltage-dependent sodium channel, and SCN5A mutations have been reported in Brugada syndrome. However, single nucleotide polymorphisms (SNPs) and gene mutations have not been well investigated in Japanese patients with Brugada syndrome.
Methods and Results: The SCN5A gene was examined in 58 patients by using PCR and the ABI 3130xl sequencer, revealing 17 SNP patterns and 13 mutations. Of the 13 mutations, 8 were missense mutations (with amino acid change), 4 were silent mutations (without amino acid change), and one case was a mutation within the splicing junction. Six of the eight missense mutations were novel mutations. Interestingly, we detected an R1664H mutation, which was identified originally in long QT syndrome.
Conclusion: We found 13 mutations of the SCN5A gene in 58 patients with Brugada syndrome. The disease may be attributable to some of the mutations and SNPs
Management of axitinib (AG-013736)-induced fatigue and thyroid dysfunction, and predictive biomarkers of axitinib exposure: results from phase I studies in Japanese patients
Background Axitinib is an oral, potent and selective inhibitor of vascular endothelial growth factor receptors (VEGFRs) 1, 2 and 3. We report on data obtained from 18 Japanese patients with advanced solid tumors in two phase I trials that evaluated the safety, pharmacokinetics and antitumor activity of axitinib and also examined potential biomarkers. Methods Six patients received a single 5-mg dose of axitinib followed by 5 mg twice daily (BID), and an additional six patients received axitinib 5 mg BID only. Another six patients received axitinib at 5-mg, 7-mg and 10-mg single doses followed by 5 mg BID. Results Plasma pharmacokinetics following single doses of axitinib was generally linear. Common treatment-related adverse events were fatigue (83%), anorexia (72%), diarrhea (67%), hand–foot syndrome (67%) and hypertension (61%). Sixteen patients (89%) experienced thyroid-stimulating hormone (TSH) elevation. Grade 3/4 toxicities included hypertension (33%) and fatigue (28%). No grade 3/4 fatigue occurred in patients who started thyroid hormone replacement therapy when TSH was elevated. Thyroglobulin elevation was observed in all patients who continued treatment with axitinib for ≥3 months. Abnormal TSH correlated with exposure to axitinib (r = 0.72). Decrease in soluble (s) VEGFR-2 levels significantly correlated with exposure to axitinib (r = –0.94). Axitinib showed antitumor activity across multiple tumor types. Conclusions Axitinib-related thyroid dysfunction could be due to a direct effect on the thyroid gland. Grade 3/4 fatigue and hypothyroidism appear to be controllable with use of thyroid hormone replacement therapy. sVEGFR-2 and TSH may act as biomarkers of axitinib plasma exposure
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