Kofi Korsah

Harmonic frequency analysis of SAW resonator chemical sensors: application to the detection of carbon dioxide and humidity

Abstract We have investigated the possibility of increasing surface acoustic wave (SAW) gas sensor sensitivity and detection limit by operating a SAW device at its fundamental frequency (250 MHz for the devices used in this paper), while monitoring frequency changes at a higher harmonic. In particular we have compared frequency changes at the third harmonic with that of the fundamental mode, using carbon dioxide (CO2) and water vapor as our test gases. The results showed that sensitivity is increased by a factor of three and the detection limit is improved by a factor of two. Three different polymers were used in our investigations. Of the three polymer coatings studied—BMBT, PEI and Versamid 900—PEI gave the greatest frequency change per unit change in humidity, followed by Versamid 900 and BMBT, in that order. The frequency change yielded by PEI (5.7 kHz per percent change in humidity) was about a factor of ten increase compared with the other two polymers. PEI was also found to be relatively more sensitive to CO2 compared with the other polymers. A frequency shift of about 1 kHz was measured for 240 ppm of CO2 in nitrogen. This was comparable to the frequency shift obtained for Versamid 900. The corresponding frequency shift for BMBT was about 700 Hz.

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.

Evaluating ‘new’ instrumentation and control technologies for safety-related applications in nuclear power plants

Abstract As obsolescence and spare parts issues drive nuclear power plants to upgrade with new technologies (such as optical fiber communication systems), the ability of the new technologies to withstand environmental stresses that act at the installation location needs to be determined. New standards may be required to address environmental qualification and their application to the nuclear power plants of tommorow. This article discusses the failure modes and age-related degradation mechanisms relevant to fiber-optic communication systems in particular, and suggests a methodology for identifying conditions under which accelerated aging should be performed during qualification testing. While optical fiber communication systems have been used as the basis for discussion, the methodology presented should be applicable to any safety-related instrumentation and control equipment not covered under Title 10 of the Code of Federal Regulations (10 CFR 50.49).

Options for shielding Tokamak Cooling Water electrical components against high magnetic fields

The Tokamak Cooling Water System (TCWS) Instrumentation and Control (I&C) components of ITER will be located in areas of relatively high magnetic fields. Previous tests on electrical and I&C components have indicated that shielding will be required to protect these components from such magnetic fields. To accomplish this, studies were performed by AREVA Federal Services (AFS) in support of the TCWS Design project with the intent of identifying an optimal solution for shielding I&C components. This paper presents a summary of these studies and presents design options for providing magnetic shielding to ITER TCWS I&C components and electrical equipment that are susceptible to the magnetic fields present.

Fusion Nuclear Science Facility (FNSF)

A compact (R0∼1.2–1.3m), low aspect ratio, low-Q (<3) Fusion Nuclear Science Facility (FNSF) was recently assessed to provide a fully integrated, D-T-fueled, continuously driven plasma, volumetric nuclear environment of copious neutrons. This environment would be used, for the first time, to carry out discovery-driven research in fusion nuclear science and materials, in parallel with and complementary to ITER. This research would aim to test, discover, and understand new nuclear-nonnuclear synergistic interactions involving plasma material interactions, neutron material interactions, tritium fuel breeding and transport, and power extraction, and innovate and develop solutions for DEMO components. This facility properly designed could provide, initially using conservative JET-level D-T plasmas in Hot-Ion H-Mode, and an outboard fusion neutron flux of ∼0.33 MW/m2. If the research, facility operation, and component solutions were successful, the performance could be raised to 1 MW/m2 (fusion power ∼76 MW) by reaching for twice the JET plasma pressure and Q. Stable high-safety factor q and ² plasmas would be chosen to minimize plasma-induced disruptions, and deliver reliably a neutron fluence of 1 MW-yr/m2, if duty factors of ∼10% (accumulated plasma burn time in a year) can be achieved. Such duty factors would therefore require time-efficient installation and replacement of all components using remote handling (RH). These in turn would require RH-compatible modular designs for all internal components, a single-turn toroidal field coil center-post, and placement of support structures and vacuum seal welds behind the internal and shielding components. RH-enabled hot-cell laboratories would enable preparation and investigations of damages of the internal test components. The scientific and technical basis for such an FNSF, and the research needed in the next decade to manage the potential risks in its research capabilities, will be described.