Richard Thomas Wood

Robust dynamic sensor fault detection and isolation of helical coil steam generator systems using a subspace identification technique

Abstract A design approach to sensor fault detection and isolation (FDI) of helical coil steam generator (HCSG) systems of the International Reactor Innovation Secure (IRIS) reactor is presented. In the design phase, a physical model is first developed to provide a realistic simulation and generate data characterizing the system dynamics. A subspace identification technique is then used to extract a low-order linear state-space model from the data. Finally, a robust dynamic parity space approach is utilized to design residual generators for FDI. This design approach is able to achieve fault isolation following a predetermined logic without the need to use data during fault conditions, which is an unrealistic assumption of many FDI approaches studied for nuclear power plants. The results of the HCSG application show that the approach is robust to not only measurement and process noises but also operation condition changes and has the capability of correct FDI during reactor power transients and during the propagation of sensor faults in a control loop.

Development of an automated approach to control system design

Abstract A research effort to develop methods for automated generation of control systems that can be traced directly to the design requirements is documented. This research is being conducted under the Nuclear Energy Research Initiative for the U.S. Department of Energy. The final goal is to allow the control designer to specify only high-level requirements and stress factors that the control system must survive (e.g., a list of transients or a requirement to withstand a single failure). To this end, the “control engine” automatically selects and validates control algorithms and parameters that are optimized to the current state of the plant, and that have been tested under the prescribed stress factors. The control engine then automatically generates the control software from validated algorithms. The automated design approach also lends itself to a control system structure that captures the design requirements and permits the optimum control solution to be maintained during the plant life.

U.S. Department of Energy Instrumentation and Controls Technology Research for Advanced Small Modular Reactors

Instrumentation, controls, and human–machine interfaces (ICHMI) are essential enabling technologies that strongly influence nuclear power plant performance and operational costs. The U.S. Department of Energy (DOE) has recognized that ICHMI research, development, and demonstration (RD&D) is needed to resolve the technical challenges that may compromise the effective and efficient utilization of modern ICHMI technology and consequently inhibit realization of the benefits offered by expanded utilization of nuclear power. Consequently, key DOE programs have substantial ICHMI RD&D elements to their respective research portfolio. This article describes current ICHMI research to support the development of advanced small modular reactors.

Advanced Reactor Licensing: Experience with Digital I&C Technology in Evolutionary Plants

This report presents the findings from a study of experience with digital instrumentation and controls (I&C) technology in evolutionary nuclear power plants. In particular, this study evaluated regulatory approaches employed by the international nuclear power community for licensing advanced l&C systems and identified lessons learned. The report (1) gives an overview of the modern l&C technologies employed at numerous evolutionary nuclear power plants, (2) identifies performance experience derived from those applications, (3) discusses regulatory processes employed and issues that have arisen, (4) captures lessons learned from performance and regulatory experience, (5) suggests anticipated issues that may arise from international near-term deployment of reactor concepts, and (6) offers conclusions and recommendations for potential activities to support advanced reactor licensing in the United States.

Technical basis for environmental qualification of microprocessor-based safety-related equipment in nuclear power plants

This document presents the results of studies sponsored by the Nuclear Regulatory Commission (NRC) to provide the technical basis for environmental qualification of computer-based safety equipment in nuclear power plants. The studies were conducted by Oak Ridge National Laboratory (ORNL), Sandia National Laboratories (SNL), and Brookhaven National Laboratory (BNL). The studies address the following: (1) adequacy of the present test methods for qualification of digital I and C systems; (2) preferred (i.e., Regulatory Guide-endorsed) standards; (3) recommended stressors to be included in the qualification process during type testing; (4) resolution of need for accelerated aging for equipment to be located in a benign environment; and (5) determination of an appropriate approach for addressing the impact of smoke in digital equipment qualification programs. Significant findings from the studies form the technical basis for a recommended approach to the environmental qualification of microprocessor-based safety-related equipment in nuclear power plants.

Autonomous Control Capabilities for Space Reactor Power Systems

The National Aeronautics and Space Administration’s (NASA’s) Project Prometheus, the Nuclear Systems Program, is investigating a possible Jupiter Icy Moons Orbiter (JIMO) mission, which would conduct in‐depth studies of three of the moons of Jupiter by using a space reactor power system (SRPS) to provide energy for propulsion and spacecraft power for more than a decade. Terrestrial nuclear power plants rely upon varying degrees of direct human control and interaction for operations and maintenance over a forty to sixty year lifetime. In contrast, an SRPS is intended to provide continuous, remote, unattended operation for up to fifteen years with no maintenance. Uncertainties, rare events, degradation, and communications delays with Earth are challenges that SRPS control must accommodate. Autonomous control is needed to address these challenges and optimize the reactor control design. In this paper, we describe an autonomous control concept for generic SRPS designs. The formulation of an autonomous control concept, which includes identification of high‐level functional requirements and generation of a research and development plan for enabling technologies, is among the technical activities that are being conducted under the U.S. Department of Energy’s Space Reactor Technology Program in support of the NASA’s Project Prometheus. The findings from this program are intended to contribute to the successful realization of the JIMO mission.

Current research results on the technical basis for environmental qualification of safety-related digital I&C hardware in nuclear power plants

Abstract This paper presents progress to date of an NRC-sponsored confirmatory research program initiated to address hardware issues associated with the use of safety-related digital instrumentation and control (I&C) hardware in nuclear power plants. In particular, the potential vulnerability of digital technology to environmental stress effects and means for establishing environmental compatibility for digital I&C systems were studied. The research approach involved evaluating existing military and industrial guidance, identifying the most significant environmental stressors and, for advanced I&C systems in nuclear power plants, investigating the likely failure modes—both at the integrated circuit and system level—for digital technologies under varying levels of environmental stress. Environmental stressors used in the studies included smoke exposure, electromagnetic and radio-frequency interference (EMI/RFI), temperature, and humidity. The insights gained from these studies are being used to recommend appropriate methods for qualifying safety-related digital equipment in nuclear power plants. To characterize the EMI/RFI environment at current LWRs and to estimate the expected environment at ALWRs, ORNL conducted a long-term survey of ambient electromagnetic conditions at several nuclear power plants. A representative sampling of power plant conditions (reactor type, operating mode, site location) were monitored over extended observation periods (e.g., continuous measurements for up to 5 weeks at a single location) were selected to more completely determine the characteristic electromagnetic environment for nuclear power plants. The results of this study contributed to the technical basis for a Nuclear Regulatory Commission Draft Regulatory Guide (DG-1029) issued for comment in 1998.

Common-Cause Failure Mitigation Practices and Knowledge Gaps

This technical report documents the findings from first phase of research activities by ORNL. Specifically, the report describes the results of the investigation of CCF mitigation practices and determination of knowledge gaps.

Impact of Smoke Exposure on Digital Instrumentation and Control

Abstract Smoke can cause interruptions and upsets in active electronics. Because nuclear power plants are replacing analog with digital instrumentation and control systems, qualification guidelines for new systems are being reviewed for severe environments such as smoke and electromagnetic interference. Active digital systems, individual components, and active circuits have been exposed to smoke in a program sponsored by the U.S. Nuclear Regulatory Commission. The circuits and systems were all monitored during the smoke exposure, indicating any immediate effects of the smoke. The results of previous smoke exposure studies have been reported in various publications. The major immediate effect of smoke has been to increase leakage currents and to cause momentary upsets and failures in digital systems. This paper presents new results from conformal coatings, memory chips, and hard drive tests. The best conformal coatings were found to be polyurethane, parylene, and acrylic (when applied by dipping). Conformal coatings can reduce smoke-induced leakage currents and protect against metal loss through corrosion. However conformal coatings are typically flammable, so they do increase material flammability. Some of the low-voltage biased memory chips failed during a combination of high smoke and high humidity. Typically, smoke along with heat and humidity is expected during fire, rather than smoke alone. Thus, due to high sensitivity of digital circuits to heat and humidity, it is hypothesized that the impact of smoke may be secondary. Low-voltage (3.3-V) static random-access memory (SRAMs) were found to be the most vulnerable to smoke. Higher bias voltages decrease the likelihood of failure. Erasable programmable read-only memory (EPROMs) and nonvolatile SRAMs were very smoke tolerant. Failures of the SRAMs occurred when two conditions were present: high density of smoke and high humidity. As the high humidity was present for only part of the test, the failures were intermittent. All of the chips that failed during the test recovered after enough venting. Hard disks were tested in severe environments but did not fail during the 2 h of monitoring. While the results of the tests documented in this report confirm that digital circuits can indeed be vulnerable to smoke, there is currently no practical, repeatable testing methodology, so it is not feasible to assess smoke susceptibility as part of environmental qualification. As a result, the most reasonable approach to minimizing smoke susceptibility is to employ design, implementation, and procedural practices that can reduce the possibility of smoke exposure and enhance smoke tolerance. Traditional approaches to mitigate its effects in digital safety instrumentation and control, such as redundancy, separation, defense in depth, as well as adherence to standards (e.g., the Institute of Electrical and Electronics Engineers’ IEEE 384) and the Code of Federal Regulations Appendix R of 10 CFR 50, should continue to be applied.

DEVELOPMENT OF A SUPERVISORY CONTROL SYSTEM CONCEPT FOR ADVANCED SMALL MODULAR REACTORS

Small modular reactors (SMRs) can provide the United States with a safe, sustainable, and carbon-neutral energy source. Because of their small size and, in many cases, simplified nuclear island configurations, it is expected that capital costs will be less for SMRs compared to that of large, Generation III+ light-water reactors. Advanced SMRs (AdvSMRs), which use coolants other than water as the primary heat transport medium, introduce several passive safety concepts and controls features that further reduce the complexity of primary system designs by eliminating redundant components and systems.Under U.S. Department of Energy (DOE) Office of Nuclear Energy (NE), the Supervisory Control of Multi-Modular SMR Plants project was established to enable innovative control strategies and methods to supervise multi-unit plants, accommodate shared systems, identify opportunities to increase the level of automation, define economic metrics based on the relationship between control and staffing levels, and permit flexible co-generation operational regimes.This paper documents current findings from the Supervisory Control project. Specifically, it defines and documents strategies, functional elements, and an architectural structure for supervisory control of a representative generic AdvSMR plant. More specifically, this research advances the state-of-the art by incorporating decision making into the supervisory control system architectural layers through the introduction of tiered taxonomy of plant systems and subsystems.The proposed architecture has the features of planning and scheduling, analyzing plant status, diagnosing problems as they develop and predicting potential future problems, making decisions based on these features, and generating validated commands to lower control layers in the architecture.Copyright