Nuclear Power Plant Control Research Articles

Seismic risk control of nuclear power plants using seismic protection systems in stable continental regions: The UK case

This article analyses three different strategies on the use of seismic protection systems (SPS) for nuclear power plants (NPPs) in the UK. Such strategies are based on the experience reported elsewhere of seismically protected nuclear reactor buildings in other stable continental regions. Analyses are conducted using an example of application based on a 1000MW Pressurised Water Reactor building located in a representative UK nuclear site. The efficiency of the SPS is probabilistically assessed to achieve possible risk reduction for both rock and soil sites in comparison with conventionally constructed NPPs. Further analyses are conducted to study how the reduction of risk changes when all controlling scenarios of the site are included. This is done by introducing a scenario-based incremental dynamic analysis aimed at the generation of surfaces for unacceptable performance of NPPs as a function of earthquake magnitude (Mw) and distance-to-site (Repi). General guidelines are proposed to potentially use SPS in future NPPs in the UK. Such recommendations can be used by the British nuclear industry in the future development of 12 new reactors to be built in the next two decades to generate 16GWe of new nuclear capacity.

Development of the ALFRED reactor full power mode control system

In this paper, the full power mode control scheme for the pool-type Advanced Lead Fast Reactor European Demonstrator (ALFRED) is presented. The design process of a nuclear power plant control system is a multi-step process, whose final result is the implementation of the feedback controllers. In particular, the control system configuration has been finalized after having considered different strategies to govern the variables of interest (e.g., power produced in the core, coolant temperature, pressure, etc.). In a previous work (Ponciroli et al., 2014b), the most relevant issues regarding both the controlled outputs (e.g., the lead temperature in the cold leg) and the control inputs (e.g., the feedwater inlet temperature and the lead mass flow rate) have been allowed for. Based on these preliminary analyses, the control strategy has been further developed, and the full power mode control scheme for the ALFRED reactor has been implemented. As a major outcome, it has been demonstrated how a decentralized control scheme based on a battery of PI controllers allows obtaining satisfactory performance. Indeed, starting from the linearization of the dedicated object-oriented model, the level of decoupling among the control loops has been verified, confirming the validity of the proposed solution based on the outcomes of the Relative Gain Array (RGA) method. This result has been achieved thanks to a proper tuning of the controller parameters, which allows damping the undesired influence due to the other control loops. Finally, as for the design of the actuators, a quantitative approach based on the outcomes of the system linear stability analysis has been proposed, in order to define the maximum safety value for the extraction speed of the control rods.

Neutrinos for Peace

The fundamental knowledge on neutrinos acquired in the recent years open the possibility of applied neutrino physics. Among it the automatic and non intrusive monitoring of nuclear reactor by its antineutrino signal could be very valuable to IAEA in charge of the control of nuclear power plants. Several efforts worldwide have already started.

Human error probability estimation by coupling simulator data and deterministic analysis

Operator error in diagnosis and execution of task have significant impact on Nuclear Power Plant (NPP) safety. These human errors are classified as mistakes (rule base and knowledge based errors), slip (skill based) and lapses (skill based). Depending on the time of occurrence, human errors have been categorized as i) Category ‘A’ (Pre-Initiators): actions during routine maintenance and testing wherein errors can cause equipment malfunction ii) Category ‘B’ (Initiators): actions contributing to initiating events or plant transients iii) Category ‘C’ (Post-Initiators): actions involved in operator response to an accident. There have been accidents in NPPs because of human error in an operator's diagnosis and execution of an event. These underline the need to appropriately estimate HEP in risk analysis. There are several methods that are being practiced in Probabilistic Safety Assessment (PSA) studies for quantification of human error probability. However, there is no consensus on a single method that should be used. In this paper a method for estimating HEP is proposed which is based on simulator data for a particular accident scenario. For accident scenarios, the data from real NPP control room is very sparsely available. In the absence of real data, simulator based data can be used. Simulator data is expected to provide a glimpse of probable human behavior in real accident situation even though simulator data is not a substitute for real data. The proposed methodology considers the variation in crew performance time in simulator exercise and in available time from deterministic analysis, and couples them through their respective probability distributions to obtain HEP. The emphasis is on suitability of the methodology rather than particulars of the cited example.

Improvement and optimization of master/bypass valve switching process for steam generator level control of nuclear power plant

Improvement and optimization of master/bypass valve switching process for steam generator level control of nuclear power plant

The Method of Control of Nuclear Power Plant with VVER-1000 Reactor in Maneuverable Mode

The Method of Control of Nuclear Power Plant with VVER-1000 Reactor in Maneuverable Mode

Aspects of the Nuclear Power Plant Control Room System Contributing to Safe Operation

The performance of a nuclear power plant's operational steering entity, the control room system, has a major impact on operational safety. The construction and modernization of nuclear power plants create a need to evaluate control room systems to assess if they fulfil their purpose to support safe operation. The aim of this study was to identify a foundation for evaluation measures, i.e. to find aspects of the control room system that contribute to safe operation from a human factors perspective. A number of professionals in roles influencing the operation and/or design of Swedish nuclear power plants were interviewed: reactor operators, shift supervisors, instructors, human reliability analysis specialists, human factors specialists, and personnel from the Swedish Radiation Safety Authority. A number of aspects contributing to safe operation were identified and categorised in six overall themes: situations, functions, tasks, structural elements, and characteristics. Situations describe states of and/or events in the surrounding environment that the control room system must be able to handle. Functions are the abilities the control room system must have, and tasks are what operators or technical systems in the control room system must be able to perform. Structural elements are the entities that constitute the control room system, and the characteristics of the structural elements establish conditions for the design of artefacts as well as the behaviours and abilities of personnel. These aspects are examples of what is required for controlled performance of the control room system, a prerequisite for safe operation. Together the themes serve as a structure for defining evaluation measures. The themes can be considered variables or constants when deciding on control room system evaluation measures, a choice that must be made for each evaluation. User experience aspects contribute to safe operation, but the operators’ well-being has a value in its own right and should be considered as an additional goal when designing and evaluating control rooms.

Establishing a Value Chain for Human Factors in Nuclear Power Plant Control Room Modernization

Commercial nuclear power plants in the United States (U.S.) have operated reliably and efficiently for decades. With a second 20-year life extension of operation beyond the plant's original operating licenses now being considered by many utilities, there are opportunities to achieve even greater efficiencies, while maintaining high operational reliabilities, through strategic, risk- and economically-informed, upgrades to plant systems and infrastructure. The U.S. Department of Energy's Light Water Reactor Sustainability (LWRS) program supports the commercial nuclear industry's modernization efforts through research and development (R&D) activities across many areas to help establish the technical and economic bases for modernization activities. The Advanced Instrumentation, Information, and Control Systems Technologies pathway is one R&D focus area for the LWRS program, and has researchers at Idaho National Laboratory working with select utility partners to use human factors and instrumentation and controls R&D to help modernize the plant's main control room. However, some in the nuclear industry have not been as enthusiastic about using human factors R&D to inform life extension decision-making. Part of the reason for this may stem from uncertainty decision-makers have regarding how human factors fits into the value chain for nuclear power plant control room modernization. This paper reviews past work that has attempted to demonstrate the value of human factors, and then describes the value chain concept, how it applies to control room modernization, and then makes a case for how and why human factors is an essential link in the modernization value chain.

Evaluating Presence for Customer Experience in a Virtual Environment: Using a Nuclear Power Plant as an Example

ABSTRACTIn contrast to experiences offered by traditional media, this study used a three‐dimensional virtual environment to evaluate customer experiences. The aims of this study were twofold: first, to investigate whether virtual interaction can impress customers in a visual or auditory sense and thereby further induce “presence”; and second, to understand how to provide a better sense of presence by using virtual interactions. This study used a nuclear power plant control room to construct virtual customer experience patterns. The results of the questionnaire showed no statistical significance, except for one question: “How responsive was the environment to actions that you initiated (or performed)?” During the experience, interactively receiving information in the active model offered a more significant sense of presence. For the physiological measurement, we used the multiscale entropy of complexity to analyze the heart rate. The complexity index for the active model proved significantly larger than for the passive, indicating better adaptability to the active model.

Steam Generator Water Level Intelligent Control of PWR Nuclear Power Plant Based on Feed Water Regulation

Water level control of the steam generator is an important indicator of the safe operation of nuclear power plant. The traditional PID controller system has the disadvantages of large amount of overshoot, long adjusting time, etc. Steam generator has complex, nonlinear and time-varying characteristics. This article proposes the adopting the BP neural network intelligent control algorithm. The simulation experiments results indicated that: Comparing with traditional PID control it has smaller overshoot and shorter adjustment time, more ideal control effect c.

Early-Stage Design and Evaluation for Nuclear Power Plant Control Room Upgrades

As control rooms are modernized with new digital systems at nuclear power plants, it is necessary to evaluate operator performance with these systems as part of a verification and validation process. While there is regulatory and industry guidance for some modernization activities, there are no well defined standard processes or predefined metrics available for assessing what is satisfactory operator interaction with new systems, especially during the early design stages. This paper proposes a framework defining the design process and metrics for evaluating human system interfaces as part of control room modernization. The process and metrics are generalizable to other applications and serve as a guiding template for utilities undertaking their own control room modernization activities.

Comparison between conventional and digital nuclear power plant main control rooms: A task complexity perspective, part I: Overall results and analysis

Digitalization is a trend in safety-critical complex systems. It changes the way human interacts with systems. We have less empirical knowledge about its potential negative effects on human. In our study, we compared conventional and digital main control rooms (MCRs) in nuclear power plants (NPPs) from a task complexity perspective. Complexity factors in MCRs were quantified in terms of three aspects, frequency of occurrence, complexity induced by their being, and impact caused by them. A total of 69 licensed operators participated in the study. The study consists of two parts. In Part I, overall results and analysis were reported. Generally, operators in digital MCRs perceived higher frequency and higher impact of complexity factors than those in conventional MCRs, no matter in abnormal/emergency or normal situations. Operators in digital MCRs perceived higher complexity than those in conventional MCRs in abnormal/emergency situations. These findings suggest that operators in digital MCRs experience higher complexity and workload which may reduce their reliability. These findings imply that we should caution the side-effects of ubiquitous digitalization in complex industrial systems. Relevance to industryDigital technologies are widely deployed in the nuclear industry. They change the working environments in which operators interact with NPP systems. There is insufficient research on operator experience on the changes brought by technological developments in NPP control rooms. Our findings imply that we should take care of the potential negative effect of digitalization on operator working environments.

원전 디지털 계측제어시스템 사이버보안 기술 체계 수립 방법 연구

ABSTRACT Nuclear Power Plant Instrumentation and Control System(NPP I&C) which is used to operate safely is changing from analog technology to digital technology. Ever since NPP Centrifuge of Iran Bushehr was shut down by Stuxnet attack in 2010, the possibility of cyber attacks against the NPP has been increasin g. However, the domestic and international regulatory guideline s that was published to strengthen the cyber security of the NPP I&C describes security requirements and method s to establish policies and procedures. These guidelines are not appropriate for the development of real applicable cyber security technology . Therefore, specialized cyber security technologies for the NPP I&C need to be developed to enhance the security of nuclear power plants. This paper proposes a cyber security technology d evelopment system which is exclusively for the development of nuclear technology. Furthermore, this method has been applied t o the ESF-CCS developed by The KINCS R&D project.Keywords: CyberSecurity, Digital Instrumentation & Control System, Logic al, Logical Architecture, Threat접수일(2013년 11월 19일), 수정일(2014년 4월 3일), 게재확정일(2014년 4월 16일)* 본 연구는 2013년도 산업통상자원부의 재원으로 한국에너지기술평가원(KETEP)의 지원을 받아 수행한 연구과제입니다. (No. 20121510100030)

Trait, state or artefact? Assessing experts’ regulatory focus in nuclear power plant control

We apply the theory of regulatory focus in the field of nuclear power plant (NPP) control. The first pilot study was conducted at the German simulator centre for NPPs. Here, we tested the influence of accident training lessons on the experts' regulatory focus. In a second study, we tested and validated two chronically regulatory focus questionnaires to decide which measurement would be more suitable for future research. The Work Regulatory Focus scale was translated into German, and the Regulatory Concerns Questionnaire was adapted to a work environment. The combined evidence of both studies shows that the regulatory focus of the experts does not change during the training lessons. Study 2 shows that both questionnaires were able to adequately measure the regulatory focus, but that they produce artificially contradictory outcomes that could be misleading. Recommendations and considerations for using the questionnaires are provided. Theoretical and practical implications on the influence of experts' regulatory focus on working and decision-making behaviour using standard procedures in NPP control are given.

Schutzzielorientiertes Design der Sicherheitsleittechnik

Safety instrumentation and control in nuclear power plants has to be systematically designed and revisable in order to meet the highest safety requirements. A safety objective oriented design process is presented in combination with the defence in depth philosophy. The approach is applicable for the construction of new plants like the European Pressurized Reactor (EPR) and for the comprehensive refurbishment of existing plants. Its success has been demonstrated in several domestic and international I&C projects.

The brazing of nickel alloys for nuclear reactor with the using of the rapidly-quenched filler metals

The possibility to apply amorphous nickel-based braze alloys for junction of nickel-alloy products used in the control and protection devices of nuclear power plants is demonstrated. Mechanical tests and investigations of the structural phase state of brazed junctions are carried out.

Schutzzielorientiertes Design der Sicherheitsleittechnik

Safety instrumentation and control in nuclear power plants has to be systematically designed and revisable in order to meet the highest safety requirements. A safety objective oriented design process is presented in combination with the defence in depth philosophy. The approach is applicable for the construction of new plants like the European Pressurized Reactor (EPR) and for the comprehensive refurbishment of existing plants. Its success has been demonstrated in several domestic and international I&C projects.

The influence of dispositional mindfulness on safety behaviors: A dual process perspective

Based on the dual process model of human cognition, this study investigated the influence of dispositional mindfulness on operators’ safety behaviors and its boundary conditions. In a sample of 212 nuclear power plant control room operators, it was found that both safety compliance and safety participation behaviors were positively influenced by dispositional mindfulness as measured by the 14-item Freiburg Mindfulness Inventory. This effect was still positive after controlling for age, intelligence, work experience and conscientiousness. Moreover, two boundary conditions were identified: the impact of dispositional mindfulness of safety behaviors was stronger among operators who were either more experienced or more intelligent. Theoretically, the framework we used to understand the benefit of mindfulness on safety behaviors has been proved to be useful. Practically, it provides a new and valid criterion that could be used in operators’ selection and training program to improve organizational safety.

A preliminary approach to the ALFRED reactor control strategy

In this paper, a preliminary approach to the definition of a suitable control strategy for the Advanced Lead Fast Reactor European Demonstrator (ALFRED), developed within the European 7th Framework Program, has been undertaken. The Generation IV reactors offer new challenges for what concerns the nuclear power plant control since several constraints both on primary and secondary loops have to be faced, differently from the conventional Light Water Reactors. A simulator of the ALFRED plant has been developed in a previous work (Ponciroli et al., 2014) with the main purpose of studying the system free dynamics and stability features in a control-oriented perspective. Based on the outcomes of these investigations, in the present work, the possibility of adopting decentralized control schemes has been investigated. Accordingly, Single Input Single Output control laws have been applied directly to the selected couples of input–output variables, which have been identified first on the basis of the preliminary plant dynamics analyses, and then confirmed by the indications of the Relative Gain Array method. Afterwards, two different control schemes have been studied depending on the number of available inputs, and then implemented and compared in order to evaluate the effect of each control action on the associated potential control strategy effectiveness. As a last step, the ALFRED control system has been finalized. The regulator design has been set up based on a simultaneous feedforward-feedback scheme incorporating four closed feedback loops. A controlled power reduction and a controlled overpower transient have been simulated in order to assess the performance of the two proposed control schemes. Results show that both the adopted control strategies can assure an efficient control of the thermal power while guaranteeing an effective control of lead and steam temperatures as well. In addition, some non-negligible differences between the two schemes have been observed and discussed in the simulation results of control and controlled variables.

Cost evaluation of I&C upgrade approach in nuclear power plants

Utilities have recently been debating the respective pros and cons of implementation of a multi-phase upgrade during several normal outages versus a single major upgrade implementation during a prolonged outage. We have studied these approaches and have been developing the basic design of nuclear power plants (NPPs) instrumentation and control (I&C) upgrade since early 2008. As part of this study, analyses of the NPPs I&C systems were conducted and the need for upgrading the systems was raised. One of the primary concerns regarding the system upgrade is a cost-benefit implementation, which will influence the upgrade approach. From this viewpoint, the I&C upgrade must consider economic factors such as I&C vendor cost, architecture engineering cost, installation cost, utility cost, and other transition costs such as training and procedure development. This paper presents a comparison study of economical aspects including cost evaluation between the aforementioned upgrade implementations and suggests a solution for I&C upgrade approach.