Reactor Regulation Research Articles

A differentiator based second-order sliding-mode control of a pressurized water nuclear research reactor considering Xenon concentration feedback

This paper presents the Twisting control algorithm with a differentiator to extend the applicability of the second-order sliding-mode control scheme in a nuclear reactor power control and regulation. Application of the second-order sliding-mode control in the power tracking control of a nuclear reactor is vital because it addresses the challenges of chattering and relative degree restriction faced in conventional-sliding mode control. A differentiator is designed to realize the exact robust differentiation of the sliding variable required in the second-order sliding-mode control. The nuclear reactor core is simulated based on the point kinetics equation with a single delayed neutron group. Using the Twisting algorithm, the simulation results show that the closed-loop control system is stable, robust against external disturbance, insensitive to parametric variation, and achieved the desired performance specifications. Moreover, it is found that the Twisting controller can adequately replace the super-Twisting controller without compromising any of the performance indices.

Observer based adaptive robust Feedback-linearization control for VVER-1000 nuclear reactors with bounded axial power distribution based on the validated multipoint kinetics reactor model

In nuclear reactor, spatial oscillations in neutron flux distribution resulting from xenon reactivity feedback are a matter of concern. If the oscillations in power distribution are not controlled, power density and rate of change of power at some locations in the reactor core may exceed their respective limits causing the nuclear power plant instability. Therefore, during the design stages of any Pressurized Water Nuclear Reactor (P.W.R), it is necessary to identify the existence of xenon oscillation and to design suitable control strategy for regulating the spatial power distribution. In each nuclear power plant, Load-following control is one of the most important techniques for nuclear reactor regulation. A novel nonlinear controller called observer-based adaptive robust feedback-linearization controller for VVER-1000 nuclear reactors is presented in this paper. This novel control strategy is then applied to the Axial power distribution control during load following operation in the VVER-1000 nuclear reactors.The reactor core is simulated based on the validated four nodes kinetics reactor model and three groups of delayed neutron precursor’s concentration based on the Skinner-Cohen model. Considering the limitations of the xenon concentrations and delayed neutrons precursor’s densities physical measurement, an adaptive sliding mode observer is designed to estimate their values and finally adaptive robust feedback-linearization based on the adaptive sliding mode observer and nodal kinetics reactor model is presented to AO control during load following operation for nuclear reactors. The stability analysis is given by means Lyapunov approach, thus the designed control system is guaranteed to be stable within a large range.Simulation results show that robust control and state estimation with adaptive robust feedback-linearization and adaptive Sliding mode methodologies can be achieved in nuclear plant systems with diverse applications including control and estimation in the presence of model uncertainties and external disturbances. One significant finding to emerge from this paper is that the Observer based Adaptive robust feedback-linearization control method provides a robust, high-performance and automatic control mechanism at all the power ranges of operation for P.W.R control system.

Risk-Deformed Regulation: What Went Wrong with NFPA 805

National Fire Protection Association (NFPA) Standard 805 was incorporated into Title 10 of the U.S. Code of Federal Regulations to allow commercial nuclear plants to transition their existing, deterministic fire protection licensing bases to ones that are “performance-based and risk-informed.” Both the US Nuclear Regulatory Commission (NRC) and the commercial reactor industry championed this major leap forward in “risk-informed regulation.” However, hidden behind all the “success” are compromises and manipulations that were necessary to make this “work,” as revealed in this article. It is written by a former employee of the NRC (views do not nor ever did represent an official position), the first to receive a PhD on a thesis specifically related to fire probabilistic risk assessment (PRA) in nuclear plants, and later hired in 2003 as the expert in fire PRA for the Office of Nuclear Reactor Regulation (NRR). He participated in the NFPA-805 program from the start in 2005 until mid-2014. The perspectives here cover that time period, with some extended time specific to issues that the interested reader can find detailed in “Risk-Deformed Regulation: What Went Wrong with NFPA 805” http://vixra.org/pdf/ (access latest version of entry 1805.0403).NFPA 805 will have been “successful” in that adopting plants are as safe as or safer than before, at a minimum having at least become more knowledgeable of potential safety weaknesses. Plants that made effective changes will be safer than before, although “effective” conveys that some changes only may have “seemingly” reduced risk. If such changes were prompted by questionable risk-reduction credits such as those cited later in this paper, then perhaps actual risk-reduction changes that could have been made were not. At worst, the plant merely missed an opportunity to become “safer,” a consequence of the problems with “risk-deformed regulation.”

A Review of Safety Analysis Philosophies for Nuclear Reactors

Various questions can be examined when discussing safety in general. Among these, some key issues are the attitude toward risk and its acceptance, the ways of identifying, analyzing, and quantifying risks, and societal factors and public opinion toward risks. The identification and quantification of risks are central in the regulatory framework and decision making and will be the focus of this article. Various approaches have been used for safety analysis over the years. This paper will survey some of the central attitudes in the nuclear reactor regulation philosophy and discuss the historical background surrounding them. Among these, we mention the “defense-in-depth” approach, the design basis accident (DBA), and beyond design basis accident (BDBA) analyses and discuss the rather subjective nature of their associated decision making. We maintain that it has long been recognized that the natural approach that comes out of the scientific method of inquiry is the probabilistic one, which in today's tools is conducted through the probabilistic safety analysis (PSA) method. This approach unlike the deterministic one, which produced concepts like DBA and defense-in-depth, enables us to put risks into context and to compare different risks such as those posed by different activities in particular or by other industries in general. It has consequently been gaining wide acceptance in regulatory bodies around the world as an effective tool in the inspection and regulation of nuclear reactors. Yet, it is also recognized that despite significant development over the past few decades, PSA still suffers from some well-known deficiencies. Its main benefit at this point is its contribution to identification and prioritization of design features, maintenance, management, and quality assurance (QA) important to safety. PSA has mostly been used in the nuclear power industry, but in recent years it has also started to be incorporated in research reactor (RR) safety analysis, and we therefore cover the subject of PSA usage for this purpose as well.

Perspectives on CFD analysis in nuclear reactor regulation

The U.S. Nuclear Regulatory Commission is tasked with ensuring that the commercial use of nuclear materials in the United States is safe. This includes the review and evaluation of submitted analyses that support the safety justification for specific reactor-system components or scenarios. Typically these analyses involve the use of codes that have a proven history of validation and acceptance for the specific application of interest. The use of computational fluid dynamics (CFD) has not been as widespread in regulatory activities and the experience level with acceptance is more limited. The ever-increasing capacity of computers, along with the growing number of capable analysts, ensures us that CFD applications will continue to grow in usage for nuclear safety analysis. The challenge ahead is to ensure that these tools are properly validated and applied in order to build up the necessary evidence for more common acceptance in regulatory processes. The challenges include a continuation of the development and maintenance of best-practice guidance, development of problem-specific CFD-grade benchmark studies, the application of verification and validation techniques, and the development of practical treatments for uncertainties and scaling. Through these efforts, it is anticipated that CFD methods will continue to gain acceptance for use in nuclear reactor safety applications.

Precursor Analysis for Offshore Oil and Gas Drilling: From Prescriptive to Risk-Informed Regulation

The Oil Spill Commission’s chartered mission—to “develop options to guard against … any oil spills associated with offshore drilling in the future” (National Commission 2010)—presents a major challenge: how to reduce the risk of low-frequency oil spill events, and especially high-consequence events like the Deepwater Horizon accident, when historical experience contains few oil spills of material scale and none approaching the significance of the Deepwater Horizon. In this paper, we consider precursor analysis as an answer to this challenge, addressing first its development and use in nuclear reactor regulation and then its applicability to offshore oil and gas drilling. We find that the nature of offshore drilling risks, the operating information obtainable by the regulator, and the learning curve provided by 30 years of nuclear experience make precursor analysis a promising option available to the U.S. Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) to bring costeffective, risk-informed oversight to bear on the threat of catastrophic oil spills.

The Investigation of Prevention of a Disaster, and a Proposal for the Revision of the Nuclear Reactor Regulation Law

昭和30年代初頭において，原子炉等規制法は，放射線障害の防止に関する法律を上位法とし，「障害の防止」を法目的とすることから議論が始まった。この法律の法目的が「災害の防止」となった過程を明らかにするとともに，法制定当初の議論に返り，諸外国の原子炉規制と同様に，放射線障害の防止を直接の法目的とするための原子炉等規制法の改正について考察する。

A Study about Improvement of the Nuclear Reactor Regulation Law and the Regulatory System of Japan

福島第一原子力発電所の事故について，現在，政府の事故調査・検証委員会が事故原因などの調査中であり，教訓はこの結果を踏まえて検討すべきではあるが，本稿では，政府がIAEA閣僚理事会へ提出した報告書や過去の原子力法制に関する研究を踏まえつつ，我が国の原子力の法規制と組織に関する分析・考察を行う。

Nonlinear Observer-Based Feedback Dissipation Load-Following Control for Nuclear Reactors

Nuclear fission reaction provides more and more energy required for generating electrical power in the world, and therefore load-following control has become an important technique for nuclear reactor regulation. A novel nonlinear controller called observer-based feedback dissipation controller for single-output-single-input (SISO) generalized Hamiltonian systems is presented in this paper. The observer has a dissipative Hamiltonian structure, and sufficient condition for closed-loop asymptotical stability is also derived. This novel control strategy is then applied to the load following control for nuclear reactors. Simulation results show that the control performance is high, and parameters of the controller have direct and close relationship with the rod speed and transient response of the nuclear power and coolant temperature.

核物質防護に関わる機微情報管理の現状と課題に関する考察

The confidentiality system concerning the physical protection of nuclear materials and nuclear facilities was enacted by revision of the Nuclear Reactor Regulation Law in 2005. We made a comparative analysis with the information security in governmental agencies or financial sectors, in order to consider the way the sensitive information management concerning the physical protection of nuclear materials and nuclear facilities should be. The considerations in this paper are as follows. (1) In order to secure a suitable level of security, close cooperation should be achieved among related governmental agencies. (2) A cycle that continuously evaluates whether suitable management is performed should be established. (3) Excessive secretiveness should be eliminated. (4) An information-sharing system among the related persons beyond the frame of governmental agencies and electricity companies should be established. (5) Improvement in the social acceptability of the sensitive information management is important. (6) Although it is important to perform evaluation by the consideration of suitable balance with information disclosure, it is also important that it is positively shown to society.

Problems and Study of Regulations on Nuclear Power Plants

The purpose of this paper is to extract problems of the regulations on nuclear power plants in Japan in order to indicate the direction of the solution as much as possible. This paper includes problems about the duplicated application of Nuclear Reactor Regulation Law and Electricity Utility Law, the examination criteria of nuclear reactor establishment permission, the relation between the establishment permission and the regulations, the double check evaluation system by the Minister of Economy, Trade and Industry, and Nuclear Safety Commission, fuel inspection and in-service inspection, management of the information about insignificant events, and so on.

Uncertainties and probabilities in nuclear reactor regulation

Nuclear reactor regulations in the USA originally specified deterministic criteria to be met by thermal/hydraulic codes. A set of results from a single run of the code was compared with a set of criteria. Codes are now becoming “realistic” with uncertainties incorporated into the process, usually requiring many runs of the code. The result is a range of results with associated probabilities. Regulations do not currently specify how such results should be evaluated against acceptance criteria. A suggestion has been made to use a level of confidence (e.g., 0.95) that the criteria are satisfied with at least some specified probability (e.g., 0.95). Some valid and invalid ways of doing this and their consequences are presented. It is suggested that an improved process would relate the thermal/hydraulic outputs to measures of core damage or some other suitable measure of risk. Furthermore, the uncertainties modeled in the code should be combined with uncertainties and probabilities, e.g., about functioning of equipment and operator actions, that are now represented in the probabilistic risk assessment (PRA). The task of combining thermal/hydraulic codes with PRA techniques to produce an effective and feasible technology presents a challenge to the technical community.

原子力発電施設の規制の課題と考察

The purpose of this paper is to extract problems of the regulations on nuclear power plants in Japan in order to indicate the direction of the solution as much as possible. This paper includes problems about the duplicated application of Nuclear Reactor Regulation Law and Electricity Utility Law, the examination criteria of nuclear reactor establishment permission, the relation between the establishment permission and the regulations, the double check evaluation system by the Minister of Economy, Trade and Industry, and Nuclear Safety Commission, fuel inspection and in-service inspection, management of the information about insignificant events, and so on.

Engineering initiatives in nuclear reactor regulation

In this paper relevant engineering initiatives that are currently being developed by the United States Nuclear Regulatory Commission (NRC) to enhance regulatory effectiveness are described. The broad issues addressed are: Piping Design and Non-Destructive Examination, Pressurized Thermal Shock, Containment Integrity During Severe Accidents, and Equipment Qualification.

A slow comeback: The optimists have been disappointed in the rate of progress in cleanup, but the outlook for its defueling may be brightening

?We've made so little progress in the cleanup in five years that it is literally a national disgrace,? Harold Denton, the U.S. Nuclear Regulatory Commission's director of nuclear reactor regulation, told Spectrum. Such a strong statement from the head of the office charged with regulating the industry ? and therefore the cleanup of the damaged Unit 2 reactor at Three Mile Island in Middletown, Pa. ? may not be surprising. But even Herman Dieckamp, the president and chief operating officer of General Public Utilities Corp. of Parsippany, N.J., which owns the facility, conceded that ?in 1979, I probably thought that the bulk of the job would be done in five years.?

Critical Human Factors Issues in Nuclear Power Generation and a Recommended Comprehensive Long Range Plan

A comprehensive long range human factors plan for nuclear reactor regulation was developed for the U.S. Nuclear Regulatory Commission by a Study Team of the Human Factors Society. This Study Team was selected by the Society to provide a balanced, experienced human factors perspective to the application of human factors scientific and engineering knowledge to nuclear power generation. The Study Team identified and analyzed areas of human factors concern in nuclear power generation. It reviewed and evaluated current and planned human factors activities and programs throughout industry and the Nuclear Regulatory Commission. The result was a recommended comprehensive human factors plan for the next ten years.

Human Factors Society Project for Development of a Comprehensive Human Factors Plan for Nuclear Reactor Regulation

Human Factors Society Project for Development of a Comprehensive Human Factors Plan for Nuclear Reactor Regulation

Geophysicists

Philip S. Justus has joined the Nuclear Regulatory Commission as a staff geologist in the Geosciences Branch, Division of Engineering, Office of Nuclear Reactor Regulation, which is based in Bethesda, Maryland.Delia Laura has been appointed chief of the U.S. Geological Survey's Office of International Hydrology. She had been the assistant chief of that office since July 1979.