Joseph W. Talnagi

Accumulation and cellular distribution of uranium in Thiobacillus ferrooxidans

The uptake and cellular distribution of UO22+were investigated in washed cell suspensions of Thiobacillus ferrooxidans. The uptake was dependent on external concentration of uranium (0.01–10.0 mM) and was influenced by the pH of the reaction mixture, but not by 1 mM transition metals ions or by the previous growth history of the cells. Cells inactivated by either ultraviolet radiation or potassium cyanide accumulated about 40% more uranium than did viable cells especially at a high, toxic UO22+concentration. Most of the uranium was associated with the cell wall and membrane fractions and relatively little uranium was detected in the cytoplasmic, lipopolysaccaride and periplasmic space material fractions. Cells poisoned with potassium cyanide were found to have an 8 to 11-fold increase in the cytoplasmic concentration of uranium.

Additional experimental evidence for a solar influence on nuclear decay rates

Abstract Additional experimental evidence is presented in support of the recent hypothesis that a possible solar influence could explain fluctuations observed in the measured decay rates of some isotopes. These data were obtained during routine weekly calibrations of an instrument used for radiological safety at The Ohio State University Research Reactor using 36 Cl. The detector system used was based on a Geiger–Muller gas detector, which is a robust detector system with very low susceptibility to environmental changes. A clear annual variation is evident in the data, with a maximum relative count rate observed in January/February, and a minimum relative count rate observed in July/August, for seven successive years from July 2005 to June 2011. This annual variation is not likely to have arisen from changes in the detector surroundings, as we show here.

Effect of Space Radiation on the Leakage Current of MEMS Insulators

The effect of space radiation on the reliability of microelectromechanical systems (MEMS) devices is an important consideration for future upper atmosphere and space applications. MEMS capacitors with insulator materials of silicon nitride (Si₃N₄), silicon oxide (SiO₂), and ultrananocrystalline diamond (UNCD) were selected for radiation and leakage current studies. Leakage current was used as a measure of insulator performance and reliability, and is suggested here as a method to detect charge trapping, which also affects reliability. UNCD capacitors were orders of magnitude leakier than Si₃N₄ and SiO₂, with Si₃N₄ being leakier than SiO₂. SiO₂ devices exhibited unstable leakage current with accumulated electric field stress, and were not utilized in radiation studies. Si₃N₄ capacitors exhibited leakage current decay (with a time constant of 190 s) under constant voltage stress above 2 MV/cm due to charge injection from the electrodes and trapping in the insulator. Si₃N₄ and UNCD capacitors were more sensitive to ionizing gamma radiation than to displacement damage from fast neutrons. Both Si₃N₄ and UNCD devices survived total doses of radiation representative of 20-100 years in the Van Allen radiation belts with 4 mm Al equivalent shielding. Capacitor equivalent circuit and resistor capacitor (RC) circuit charging models are developed to explain leakage current behavior of Si₃N₄ capacitors subjected to constant voltage stress and/or irradiation. In situ monitoring of Si₃N₄ capacitors placed next to the nuclear reactor core did not yield any single event effects at electric field strength of 1 MV/cm with a fast neutron fluence of 2×10¹² n/cm². Si₃N₄ MEMS capacitors appear best suited for upper atmosphere and space applications with their relatively low leakage current (low power consumption) and apparent radiation hardness.

Performance evaluation of Fabry-Perot temperature sensors in nuclear power plant measurements

Abstract The Fiso Fabry-Perot fiber-optic temperature sensor was selected for performance evaluation and for potential application in nuclear power plants because of its unique interferometric sensing mechanism and data-processing technique, and its commercial availability. It employs a Fizeau interferometer and a charge-coupled device array to locate the position of the maximum interference fringe intensity, which is directly related to the environmental temperature. Consequently, the basic sensing mechanism is independent of the absolute transmitted light intensity, which is the most likely parameter to be affected by external harsh environments such as nuclear irradiation, high pressure/temperature, and cyclical vibration. This paper reports research on the performance of two Fiso Fabry-Perot temperature sensors in environmental conditions expected in nuclear power plants during both normal and abnormal (i.e., accident) conditions. The environmental conditions simulated in this paper include gamma-only (60Co) irradiation, pressure/temperature environmental transient, and mixed neutron/gamma field, respectively. The first sensor exhibited no failure or degradation in performance during and following gamma-only irradiation in which a total dose of 15 kGy was delivered at a dose rate of 2.5 kGy/h. Following gamma irradiation, this sensor was then tested for 10.75 days in a thermohydraulic environment prescribed by the Institute of Electrical and Electronics Engineers IEEE323-1983. Intermittent behavior was observed throughout the latter portions of this test, and degradation in performance occurred after the test. Visual evaluation after opening the sensor head indicated that the internal welding methodology was the primary contributor to the observed behavior during this test. Further consultation with the vendor shows that the robustness and reliability of Fiso sensors can be substantially improved by modifying the internal welding methods. The second Fiso temperature sensor was tested in a mixed neutron/gamma environment, in which the total neutron fluence was 2.6 × 1016 neutrons/cm2 and the total gamma dose was 1.09 × 108 rads. During the initial calibration following completion of the test, the sensor exhibited a fixed offset of 18.9°C (34°F offset) but responded linearly to change in temperature. An annealing phenomenon was observed as the temperature increased, which reduced the offset by ~63%. This observed phenomenon will be very valuable in the model building for on-line maintenance and calibration of the Fiso temperature sensor in a mixed neutron/gamma irradiation field. Fiso Technologies in Canada has suggested that the temperature offset may also be reduced by improved welding methods. If these shifts can be compensated in the on-line sensing or calibration model of the Fiso sensor, then this type of fiber optic sensor will be competitive in nuclear power plant applications.

Low-Enriched Uranium Conversion/Power Upgrade of The Ohio State University Research Reactor

The 10-kW, highly enriched uranium (HEU) fueled Ohio State University Research Reactor (OSURR) is being upgraded to operate at 500 kW under natural convection core cooling with the recently licenced lowenriched uranium (LEU), high-density U3Si2fuel. The OSURR will be the first university reactor to use standardized U3Si2 plates for a full-core conversion from HEU to LEU fuel. The activities toward conversion/power upgrade objectives include (a) a neutronic performance assessment of 15 LEU cores with 16 plate standard and 10 plate control elements under expected operating conditions; (b) simulation of OSURR threedimensional pool dynamics under various pool configurations to limit the pool top 16N activity (PTNA) to operationally allowable levels; (c) determination of a new correlation to predict onset of nucleate boiling (ONB) in thin, rectangular channels under low-velocity, upward flow conditions; and (d) design of a pool heat removal system (PHRS). These activities have identified three possible LEU cor...

Analysis of Random Neutron Sensor Fluctuations for Surveillance of Nuclear Instrumentation Channels in Nuclear Power Plant Protection Systems

The analysis of the random fluctuations from nuetron sensors operating in the current mode has been shown to be a feasible method for monitoring the dynamic state of neutron measurement channels. A laboratory evaluation of both boron-lined and uranium-lined neutron sensors with simulated sensor and signal cable degradation was completed. The experimental evaluation, supported by a theoretical analysis, has demonstrated the potential for using the power spectral density of the random fluctuations on the detection process as an indicator of change in transient response of a neutron measurement channel.

The application of radiation detection noise as an in situ method of surveillance and performance verification of nuclear instrumentation channels for reactor protection systems

Abstract The monitoring of “detection noise” as a method of surveillance of power plant nuclear instrumentation has been theoretically and experimentally evaluated. The evaluation employed simulated degradations and malfunctions of the neutron sensor and the signal cable to assess the change in the high frequency power spectral density of the random fluctuations in the current signal from the neutron sensor. The experimental measurements were completed with plant instrumentation channels installed in The Ohio State University Research Reactor and in an operating Pressurized Water Reactor. The results of this research demonstrate the feasibility of using detection noise “signatures” to detect degradation and malfunctions in power plant nuclear instrumentation.

The High Voltage Perturbation Technique for Testing the Response of Neutron Sensors of the Type Used in Nuclear Reactors

Perturbation of the high voltage bias supply of neutron sensors of the type used in nuclear reactor protection systems has been demonstrated in a laboratory environment to be a potential method for response time measurement. The laboratory evaluation used simulated sensor and signal cable degradation with boron lined and uranium lined chambers operating in current mode. The investigations have demonstrated the sensitivity of the technique for detecting simulated degradations of the time response of the simulated detector-cable system.

An experimental method to dynamically test pressure sensors using a rupture disk

The response time of a pressure sensor is required when it is used in control systems and in some measurement applications. It is often difficult to measure the response time of a pressure sensor since it is difficult to obtain changes in fluid pressure sufficient to characterize the sensor dynamic response. In this article we describe a relatively simple system for measuring or validating the response time of pressure sensors with fast dynamic response. The system consists of two chambers isolated by a graphite rupture disk, a device that fully and rapidly opens at a known rupture or break pressure. A pressure transient in the second chamber is initiated by slowly increasing the pressure in the first chamber until reaching the nominal break pressure of the rupture disk. Performance of the system was validated by comparing the rise time predicted by a theoretical model with the rise time of the pressure transient measured by a piezoelectric pressure transducer. The method was evaluated by comparing the re...

A Comparison of Measurements and Calculations of the Effects of Scattered Radiation on Dosimeter Calibration in a Calibration Range

Abstract The method presented provides an alternative to the shadow shield method for experimentally measuring the contribution due to scattering radiation in a calibration range. Scattering of 0.6616 MeV photons from a 137Cs irradiator in a calibration range does not only occur due to the walls and floor of the range. It also occurs due to the source material itself, its encapsulation, the brass cup that holds the source, the two stainless tubes that surround the source capsule and the brass cup, and the irradiator structure that surrounds the aforementioned objects. The shadow shield method underestimates this scattering radiation that originates in the irradiator. By measuring the uncollided effective activity using a CZT detector and a total effective activity using a survey meter, the contribution of scattered radiation (including all of the abovementioned sources of scatter) to the effective source activity is able to be measured. In this paper, the measured mean effective source activities for a 137Cs irradiator in a calibration range are reported for a CZT detector and a survey meter. The measured activities are compared among themselves and with the results of MCNP calculations. From these comparisons, the new alternative method for measuring the scatter contribution was validated by agreement in both the MCNP calculations and experimental measurements that scattering contributed about 28% to the overall effective activity of the range.