Roland R. Benke

Effect of biogas generation on radon emissions from landfills receiving radium-bearing waste from shale gas development

Dramatic increases in the development of oil and natural gas from shale formations will result in large quantities of drill cuttings, flowback water, and produced water. These organic-rich shale gas formations often contain elevated concentrations of naturally occurring radioactive materials (NORM), such as uranium, thorium, and radium. Production of oil and gas from these formations will also lead to the development of technologically enhanced NORM (TENORM) in production equipment. Disposal of these potentially radium-bearing materials in municipal solid waste (MSW) landfills could release radon to the atmosphere. Risk analyses of disposal of radium-bearing TENORM in MSW landfills sponsored by the Department of Energy did not consider the effect of landfill gas (LFG) generation or LFG control systems on radon emissions. Simulation of radon emissions from landfills with LFG generation indicates that LFG generation can significantly increase radon emissions relative to emissions without LFG generation, where the radon emissions are largely controlled by vapor-phase diffusion. Although the operation of LFG control systems at landfills with radon source materials can result in point-source atmospheric radon plumes, the LFG control systems tend to reduce overall radon emissions by reducing advective gas flow through the landfill surface, and increasing the radon residence time in the subsurface, thus allowing more time for radon to decay. In some of the disposal scenarios considered, the radon flux from the landfill and off-site atmospheric activities exceed levels that would be allowed for radon emissions from uranium mill tailings. Implications: Increased development of hydrocarbons from organic-rich shale formations has raised public concern that wastes from these activities containing naturally occurring radioactive materials, particularly radium, may be disposed in municipal solid waste landfills and endanger public health by releasing radon to the atmosphere. This paper analyses the processes by which radon may be emitted from a landfill to the atmosphere. The analyses indicate that landfill gas generation can significantly increase radon emissions, but that the actual level of radon emissions depend on the place of the waste, construction of the landfill cover, and nature of the landfill gas control system.

Microchannel Plate Detector Detection Efficiency to Monoenergetic Electrons Between 0.4 and 2.6 MeV

An unshielded microchannel plate detector was irradiated by an electron beam to determine the detection efficiency of electrons to create a detector signal or counts. Tested electron energies spanned a range of 400 kiloelectron volts to 2.6 million electron volts (MeV). Detection efficiency was found to decrease as the electron energy increased and ranged between 0.18 and 0.05 counts per incident electron, at 0.4 and 2.6 MeV, respectively. Simulations of beam losses over the experimental geometry were performed with MCNP6, and found to be similar in magnitude and possess a similar dependence over incident electron energy as the experimentally determined beam loss from beam current measurements. Detection efficiency as a function of incident angle of the electrons was also tested and relatively insignificant changes were observed. For the three beam energies and angles tested, deviation of the measured detection efficiency was 16%-22% (basically within the overlapping error bars of each measurement).

Comparison of Radiation Induced Noise Levels in Two Ion Detectors for Shielded Space Instruments in High Radiation Fields

Radiation shielding performance and radiation induced noise levels in ion detection instruments were investigated for a high radiation field. The intensity of primary and secondary radiation behind simple shields of aluminum and tantalum were determined by Monte Carlo computer simulations. Two ion detectors were evaluated: a micro-channel plate and a custom discrete dynode electron multiplier. Europa, an icy moon of Jupiter, was selected because it is one of the most intense radiation environments in our solar system. Based on the combination of computer simulation results and experimental measurements of detector responses to electron and photon radiation, the relative radiation induced background noise was assessed to inform further instrument design considerations and performance optimization, such as anticipated signal-to-noise ratio and minimum detectable concentrations for mass spectroscopy during specific missions. Radiation detection efficiencies between the two detectors were comparable for photons and higher energy electrons, but significant differences were found for electrons with energies less than 0.5 MeV. Higher radiation induced count rates are expected for the micro-channel plate detector owing to its larger cross-sectional area. Superior instrument performance is anticipated for the custom discrete dynode electron multiplier detector in high radiation environments with the same or slightly less shielding.

Microchannel plate detector detection efficiency to monoenergetic electrons between 3 and 28 keV

An unshielded microchannel plate (MCP) detector with an ultrafine pore diameter of 2 μm was irradiated by an electron beam to determine the detection efficiency of electrons for creating detector signals, or counts. Tested electron energies spanned a range of 3 kiloelectron volts (keV) to 28 keV. Higher detection efficiencies were measured at the lower end of this energy range, 0.376 counts per incident electron at 3 keV down to 0.155 at 15 keV with an increase to 0.217 at 18 keV and then another decrease down to 0.15 counts per incident electron at 28 keV. The increase at 18 keV is attributed to primary electron interaction with the L shell electrons of lead (Pb), leading to an increase in secondary electron and X-ray generation within the MCP and thus an increase in detection efficiency. For the electron beam directed normal to the MCP surface, the lowest efficiency of 0.15 counts per incident electron was observed at 28 keV. Detection efficiency was also tested as a function of incident angle with angular steps of 5°. Detection efficiency was more sensitive to the angle of incidence as the incident electron energy decreased. The detection efficiency at 3 keV decreased from 0.376 counts per electron at the zero degree angle (normal incidence to MCP surface) to 0.027 counts per electron at an incident angle of 50° (average in both orientations). At 28 keV, the decrease in detection efficiency as a function of increasing angle was less pronounced, ranging from 0.15 counts per electron at zero degrees to 0.08 counts per electron at 50° (average in both orientations). Experimental data showed lower detection efficiencies compared with previously published data.

Analytical and numerical solutions of the expected number of occurrences for combinations of event sequences due to variability

This paper investigates variability in the occurrence of different event sequences on an annual basis during the operation of a proposed nuclear facility. During the operational period of a nuclear facility, the annual radiological dose received by workers or members of the public depends on the number of event sequence occurrences. Based on the facility design, some combinations of event sequences will be expected to occur at least once during the operational period, and some combinations will not. This paper provides analytical solutions for calculating the expected number of combinations of independent event sequences. These analytical solutions agree with numerical solutions for an example problem. Although uncertainties can be incorporated into the method, only point-estimate parameter values are used in the example problem presented. The main objectives of this paper are to present calculational approaches to (i) identify which combinations of event sequences within the same year are expected to occur at least once during the operational life of a proposed facility and (ii) determine the annual doses from those identified combinations. Facility performance based on some proposed design is evaluated against the operational dose limits. Because the operational dose limits tend to be annual quantities that may not be exceeded in any year of operation, calculation of the doses resulting from combinations of event sequences that are expected to occur at least once can provide insight on the maximum annual dose expected during the operation of a proposed facility.