Redundant Safety Systems Research Articles

Performance evaluation of nuclear fuel in a reactor based on the CAREM 25

Nuclear energy has been proven as a viable option for strengthening a power grid, and the expansion of the Brazilian nuclear programme is becoming a reality in light of new reactor projects currently in the licensing and/or construction stage in the country. The object of study in this paper is a small modular reactor (SMR) based on the CAREM 25 Reactor designed in Argentina that represents an innovation in nuclear reactor research in Latin America and belongs to the category of advanced reactors. It is a reduced-size Pressurized Water Reactor (PWR) with integrated primary and secondary circuits, passive and redundant safety systems, light water cooling, and a power output of 25 MW. In this study, the behaviour of certain safety parameters related to a nuclear fuel rod operating at high burnup is evaluated, considering different types of coatings commonly used in the country. The aspects addressed are related to plant operational safety and fuel integrity, such as fuel centreline temperature, cladding surface temperature, oxide layer thickness on the rod surface, and hydrogen concentration in the cladding. The results obtained show that the tool used for simulating the performance of fuel rods in conventional PWR reactors, such as the FRAPCON line, can be applied to smaller modular reactors as well, along with the feasibility of using well-established coatings in the country.

(Invited) The Design, Fabrication, and Operation of a MW-Scale Low-Temperature Electrolyzer System to Support Industry and the U.S. Dept. of Energy

Over the last 15 years the National Renewable Energy Laboratory (NREL) has supported industry and the U.S. Department of Energy by providing independent evaluation and performance validation of next generation electrolyzer stacks. Designated a U.S. Department of Energy user facility, the Energy Systems Integration Facility (ESIF) houses a comprehensive balance-of-plant infrastructure designed to support a wide range of drop-in electrolyzer stacks with capacities of up to 1 MW direct current (DC) electrical power. This NREL designed and fabricated infrastructure includes four individual power supplies (250V, 4000A Total), high-quality and high-flow deionized water (DIW) supply (up to 300 GPM), water polishing and particulate filters to achieve better than 10MΩ-cm resistive water, heat rejection via a plate heat exchanger and facility chilled water, gas/liquid phase separation of hydrogen and oxygen from water, and a hydrogen dryer bed to reduce water vapor content to less than 5 parts per million by volume to enable compression, storage and use in a wide variety of applications including light- and heavy-duty fueling, onsite fuel cell research and development (R&D), and biological and thermochemical processes requiring hydrogen. Safety, monitoring, data archiving, and control of the electrolyzer and balance of system are achieved using custom controls programmed specifically to achieve a safe and flexible architecture.Robust and redundant safety systems ensure safe and reliable long-duration, unattended operation of the electrolyzer with downstream compression equipment and systems consuming the product gas directly from the stack. Working with a small business, NREL is working to develop a low-cost individual cell voltage (iCVM) monitoring system capable of monitoring 100’s of cell voltages in the 2 – 3V range at a rate of 1 sample per second. The presentation will highlight critical safety considerations including reliable hydrogen-in-oxygen monitoring, lessons learned, and performance date taken over last 15 years of designing, building, and operating lab- and megawatt-scale low-temperature water electrolyzer systems.

Prospects for the development of small nuclear power plants in Russia

This article reviews the main properties of the modular design of small nuclear power plants (SNPPs), shows the possibility of reducing the cost and construction time of this class of plants through factory production, the effect of serialization, and the reduction of redundant safety systems. The prospects for significant expansion of the field of application of nuclear technologies due to their modularity and the possibility to ensure high safety performance are presented. Possible areas of SNPP use for power supply of remote territories including the Arctic area, production of high-potential heat and hydrogen for industrial consumers, and other applications are analyzed. It shows the need to develop and implement a new nuclear energy technology platform based on SNPPs to solve the problems of global decarbonization of the world economy by significantly expanding the scope of nuclear energy technologies in addition to the currently developed technological platform of a closed nuclear fuel cycle with fast neutron reactors and the technological platform of controlled thermonuclear fusion. The authors propose to create a pilot site for testing technologies for captive production of hydrogen (heat) for an industrial consumer, as well as other technologies for the utilitarian use of SNPPs based on a pilot demonstration of a nuclear power plant with a high-temperature (about 1100C) fast neutron reactor with a gas coolant.

Identifying the key development areas for small nuclear power plants

The paper considers the key characteristics of the small nuclear power plant (SNPP) modular design, demonstrates the possibility for reducing the construction cost and time for this class of plants due to factory fabrication, the effect of series manufacturing, and less redundant safety systems. It has been shown that it is possible to extend considerably the fields of application for nuclear technologies thanks to modularity and the possibility of ensuring high safety indicators. Potential applications for SNPPs have been analyzed, including power supply to remote (Arctic) territories, switchover from (renovation of) coal-based electricity generation, high-potential heat and hydrogen production for commercial consumers, and other applications. Rationale has been provided for most typical consumer requirements that define the greatest efficiency of the SNPP application in the given field. The need has been shown for developing and introducing a new technology platform for the SNPP-based nuclear power to decarbonize globally the world economy thanks to expanding greatly the application of nuclear power technologies in addition to the technology platform currently developed for the CNFC with fast reactors (addressing the objective of fuel supply and waste recycling) and the controlled nuclear fusion technology platform (addressing the objective of long-term global energy supply). The new platform needs to be based on an extensive international cooperation involving the formation of international consortiums. It has been proposed that a test site be set up to elaborate hydrogen (heat) production technologies for an individual commercial consumer (captive production) and other technologies for the practical use of SNPPs based on a pilot demonstration nuclear power plant.

Multi-state Risk-Based Maintenance Analysis of Redundant Safety Systems Using the Markov Model and Fault Tree Method

The risk-based maintenance strategy has received special attention in the safe operation of nuclear power plants. Simultaneous quantification of the positive and negative effects of maintenance activities and components degradation effect makes it possible to accurately evaluate the risk criterion for safety systems of nuclear power plants. However, it is difficult to integrate the effects of maintenance and components degradation into the standard reliability approaches. A straightforward approach for considering components degradation and different maintenance policies is to make use of Markov maintenance models. In this article, the effectiveness of maintenance activities (including changes in the surveillance test intervals and alteration in the different maintenance policies) on the components unavailability with considering aging effects is quantified using Markov maintenance models and then by coupling these models and the fault tree method, the risk measure is upgraded from the component level to the system level. The proposed models are applied to evaluate the unavailability of two safety systems of VVER-1000/V446 nuclear power plants as case studies. The results show that the Markov method due to its multi-state nature is effective in the conservative evaluation of risk measures so that the unavailability computed by the coupling process is higher than the original unavailability (calculated by system fault tree using PSA data of nuclear power plants) for all maintenance policies. In addition, this study illustrates that the developed Markov maintenance models could be applied to the large-scale whole plant level and provides a proper transition from the classical PSA methods to new techniques. This approach integrates the effects of maintenance strategies and components degradation. Also, it provides a practical and a more accurate tool to determine the technical specification of a real nuclear power plant from the risk point of view.

Reliability modelling of redundant safety systems without automatic diagnostics incorporating common cause failures and process demand

Redundant safety systems are commonly used in the process industry to respond to hazardous events. In redundant systems composed of identical units, Common Cause Failures (CCFs) can significantly influence system performance with regards to reliability and safety. However, their impact has been overlooked due to the inherent complexity of modelling common cause induced failures. This article develops a reliability model for a redundant safety system using Markov analysis approach. The proposed model incorporates process demands in conjunction with CCF for the first time and evaluates their impacts on the reliability quantification of safety systems without automatic diagnostics. The reliability of the Markov model is quantified by considering the Probability of Failure on Demand (PFD) as a measure for low demand systems. The safety performance of the model is analysed using Hazardous Event Frequency (HEF) to evaluate the frequency of entering a hazardous state that will lead to an accident if the situation is not controlled. The utilisation of Markov model for a simple case study of a pressure protection system is demonstrated and it is shown that the proposed approach gives a sufficiently accurate result for all demand rates, durations, component failure rates and corresponding repair rates for low demand mode of operation. The Markov model proposed in this paper assumes the absence of automatic diagnostics, along with multiple stage repair strategy for CCFs and restoration of the system from hazardous state to the “as good as new” state.

News - Paris Air Show: SureFly takes helicopters to another level

Helicopters have an image problem: they are seen as complicated, difficult to fly and not generally as safe as winged aircraft. Ohio-based electric truck manufacturer Workhorse is set to change all that with its SureFly personal helicopter that's as easy to fly as a drone and is stacked with redundant safety systems.

Current issues in patient safety in surgery: a review.

Current surgical safety guidelines and checklists are generic and are not specifically tailored to address patient issues and risk factors in surgical subspecialties. Patient safety in surgical subspecialties should be templated on general patient safety guidelines from other areas of medicine and mental health but include and develop specific processes dedicated for the care of the surgical patients. Safety redundant systems must be in place to decrease errors in surgery. Therefore, different surgical subspecialties should develop a specific curriculum in patient safety addressing training in academic centers and application of these guidelines in all practices. Clearly, redundant safety systems must be in place to decrease errors in surgery, in analogy to safety measures in other high-risk industries. Specific surgical subspecialties are encouraged to develop a specific patient safety curriculum that address training in academic centers and applicability to daily practice, with the goal of keeping our surgical patients safe in all disciplines. The present review article is designed to outline patient safety practices that should be adapted and followed to fit particular specialties.

Optimal staggered testing strategies for heterogeneously redundant safety systems

Staggered testings are effective in improving the availability of redundant safety instrumented systems, and the optimal staggered time of testings for a system of two homogeneous components with the same testing interval has been proved as half of the testing interval. In this study, the impact of staggered time on the effectiveness of staggered testings for heterogeneous systems is examined, and the optimal staggered time is found still as half of the testing interval for systems with components different in failure rates but same in testing interval. In terms of systems with two components different in testing intervals, the optimal testing time is revealed as half of the shorter interval. Case studies of safety instrument systems present the same results. And then, Monte Carlo simulation based on Petri net models for these systems also confirms the conclusions obtained by numerical formulas. Such findings are helpful to effectively apply staggered testing strategies in more redundant systems.

Hemodialysis: Core Curriculum 2014

From the Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, TN. Received May 1, 2013. Accepted in revised form July 1, 2013. Originally published online November 21, 2013. Address correspondence to Thomas A. Golper, MD, S3303 Medical Center North, Vanderbilt University Medical Center, 21st Ave S, Nashville, TN 37232. E-mail: thomas.golper@vanderbilt. edu 2013 by the National Kidney Foundation, Inc. 0272-6386/$36.00 http://dx.doi.org/10.1053/j.ajkd.2013.07.028 PRINCIPLES OF DIALYSIS AND HOW MODALITIES DIFFER

Physiology and Redundancy

This year's Walter B. Cannon lecture is titled “Is Physiology Redundant?” I chose this title to reflect two divergent definitions of the word redundant. In the first definition, redundant can mean extra, nonessential, or no longer needed. In the 1980s and 1990s, the view that physiology as a

Hybrid reliability model for nuclear reactor safety system

The dependability of critical safety systems needs to be quantitatively determined in order to verify their effectiveness, e.g. with regard to regulatory requirements. Since modular redundant safety systems are not required for normal operation, their reliability is strongly dependent on periodic inspection. Several modeling methods for the quantitative assessment of dependability are described in the literature, with a broad variation in complexity and modeling power. Static modeling techniques such as fault tree analysis (FTA) or reliability block diagrams (RBD) are not capable of capturing redundancy and repair or test activities. Dynamic state space based models such as continuous time Markov chains (CTMC) are more powerful but often result in very large, intractable models. Moreover, exponentially distributed state residence times are not a correct representation of actual residence times associated with repair activities or periodic inspection. In this study, a hybrid model combines a system level RBD with a CTMC to describe the dynamics. The effects of periodic testing are modeled by redistributing state probabilities at deterministic test times. Applying the method to the primary safety shutdown system of the BR2(Belgian Reactor 2)—nuclear research reactor, resulted in a quantitative as well as a qualitative assessment of its reliability.

Environmental Health Insights into the 2011 Tōhoku Japan Earth quake Disaster.

Environmental Health Insights into the 2011 Tōhoku Japan Earth quake Disaster.

Configuration determination for k-out-of- n partially redundant systems

The k-out-of- n configuration is a widely adopted structure for partially redundant safety systems. This configuration ensures a high level of reliability and safety with limited financial and space resources. It also facilitates on-line Test and Maintenance (T&M) without having to shut the system down. One question a decision maker needs to answer when adopting k-out-of- n systems is: what is the best configuration for the application, i.e. how many channels in total need to be utilized and among these channels, how many channels need to function simultaneously in order for the system to function. There are various factors to consider in order to make this decision. This paper looks at this problem from a reliability engineers point of view. A quantitative analysis is performed for both unavailability and probability of spurious operation due to independent failure. In particular, the relative gain and/or loss of these quantities that occurs due to changing from one configuration to another are compared through rigorous mathematical analysis. The results provide important information that can be used when choosing system configurations to meet regulatory requirements and financial constraints. The two different configurations for shutdown systems in Nuclear Power Plants, the 2-out-of-3 system and the 2-out-of-4 system, are utilized as an example to illustrate the theoretical results.

Modelling and quantification of dependent repeatable human errors in system analysis and risk assessment

Abstract General equations and numerical tables are developed for quantification of the probabilities of sequentially dependent repeatable human errors. Such errors are typically associated with testing, maintenance or calibration (called “pre-accident” or “pre-initiator” tasks) of redundant safety systems. Guidance is presented for incorporating dependent events in large system fault tree analysis using implicit or explicit methods. Exact relationships between these methods as well as numerical tables and simple approximate methods for system analysis are described. Analytical results are presented for a general human error model while the numerical tables are valid for a specific Handbook (THERP) model. Relationships are pointed out with earlier methods and guides proposed for error probability quantification.

Extending Fire PSA of NPP TVO I/II to Instrumentation Systems

Probabilistic fire safety assessment (Fire PSA) of the Finnish nuclear power plant TVO I/II has been extended to include the detailed investigation about the fire risks induced by the unwanted function of the reactor protection system (RPS). This paper describes the main features of RPS as well as the assumptions and the simplifications made during the study. The most important qualitative and quantitative results are told and a number of examples about the fire safety improvements already implemented are given. In the plant with four redundant safety systems and the 2-out-of-4 voting logic in RPS spurious activations of safety related components seem to dominate the risk increasing effect.

Expert systems for emergency alarms analysis during accident situations in nuclear reactors

Abstract Expert system development is an important application of artificial intelligence. During the last few years, many successful expert systems have been developed in various fields like medical diagnosis, geological exploration, office management, etc. Expert systems is a computer software which solves reasonably complex problems where normally one needs an expert in that field to solve them. Recently efforts are being made in developing expert systems to support the operating staff in nuclear reactors. Nuclear power plant is one of the most complex engineering systems and safe and reliable operation is of primary importance. In spite of many automatic and redundant safety systems there are some occasions when the operating staff have to analyse the alarms and take further safety actions. Few of the severe accidents like Three Mile Island in USA and Chernobyl in USSR are attributed to the errors made by the operating staff and/or management. Nuclear engineers or systems analysts who may be expert in analysing an accident situation and advise corrective safety actions may not be readily available during the accident situations in the nuclear power plants. It is possible to model such expert knowledge in expert systems and this can be applied in diagnosing an accident situation like the loss of coolant accident (LOCA) and act as an additional confirmatory aid to the operating staff. Two small expert systems examples have been developed and are explained in this paper. One identifies a spurious LOCA alarm in a heavy water research reactor. The second example identifies the type of medium/small leakage (LOCA) in a coolant circuit of a PWR and suggests the subsequent safety actions. Both the examples have been developed using the expert systems shell VP-expert. They are off-line usable and user interactive. We do not propose expert system application for very fast response safety actions like reactor scram. These two small expert system examples are essentially to support the feasibility study in their applications during accident situations in nuclear power plants.

Availability of redundant safety systems with common-mode and undetected failures

The engineered safety features of nuclear power plants contain redundant standby safety systems that are tested periodically to ensure their operability should an emergency occur. Analytical equations are developed in this paper for the unavailability of common m-out-of- n systems, taking into account common-cause failures and failures that are not detectable by regular periodic tests. Consecutive, random and staggered testing schemes are considered. The unavailability model for individual components includes separate downtime contributions due to testing, repair, hardware failures, human testing and repair errors as well as failures caused by true demands. Computer codes have been developed to incorporate these failure modes in the unavailability analysis. The parameters of the model are estimated from documented field data, and typical systems are analyzed to illustrate the methods and the significance of common-mode failures.

Application of Reliability Engineering To Offshore Production Equipment

A reliability study was performed on a subsea completion system using an event-consequence approach. The application of reliability-study information to the economics of offshore equipment design represents a new and useful tool for the oil industry. Introduction Although many papers have been written concerning the different types of reliability studies, few have given concrete examples. This paper shows where the eventconsequence approach fits in the range of possible types of reliability studies. Specific examples are used to give the steps that are required in completing an eventconsequence study and the types of results that can be obtained. Based on experience with the subsea completion-system study, a method for choosing the optimum reliability-study approach is presented. Definitions of Reliability-Study Approaches One can conveniently differentiate among three levels of reliability analyses: hazard analysis, traditional reliability analysis, and event-consequence analysis. Hazard Analysis Hazard analysis is defined as a qualitative evaluation of hazards to the environment of the equipment (system) under consideration. This definition seems to have become generally accepted as far as the oil industry and its regulatory governmental agencies are concerned. The steps taken in performing such an analysis are as follows:Define the system (equipment) to be considered.Define the hazards, such as oil and gas pollution, to life safety.Determine qualitatively what has to fail for a particular hazard to occur. particular hazard to occur.Categorize the hazards as major, minor, or insignificant, depending on type and/or quantity of hazard, and how many levels of redundant safety systems must fail for the hazard to occur. This type of analysis is a "top-down" approach in that hazards such as personal injury, fire, and pollution are listed before asking, "What failures can cause these hazards?" The basis of such an analysis is the hope that the analyst will find all components that will cause the hazards. This top-down approach normally uses a "matrix" that lists failures vs effects, but it turns out to be only a qualitative tool. Thus, without an organized method of examining all components, and without a consistent standard for specific types of equipment, the matrix approach will cause inconsistent and vague results. Hazard Analysis - API Recommended Practice. The American Petroleum Institute has found a very effective means for system-hazards analysis in the development of API "Recommended Practice 14C." It is effective in that it assumes all components in hazardous service need to be reviewed. Thus, this is a "bottom-up" analysis. "Recommended Practice 14C" also achieves consistent results in that it recommends specific types of safety devices for nine major components that make up most of the hazardous process flows on platforms. This standard states specifically that equipment will have two levels of protection independent of the normal control devices. protection independent of the normal control devices. Thus, quality is built into the design. The technique of setting specific requirements for specific equipment will assure a safe design and reduce safety design time from that required by the matrix approach. JPT P. 339

Design Considerations for Meeting Nuclear Safety Systems Separations Criteria

The need for separation of redundant safety systems is well established; however, what constitutes an adequate separation is not. Adequate separation depends upon the nature of the hazards involved, and the vunerability of the protected equipment. This paper categorizes the most prevalent hazards and explores separations techniques, with respect to equipment vunerability, to adequately ensure safety functions.