Charles A. Waggoner

High-efficiency particulate air filter test stand and aerosol generator for particle loading studies

This manuscript describes the design, characterization, and operational range of a test stand and high-output aerosol generator developed to evaluate the performance of 30 x 30 x 29 cm(3) nuclear grade high-efficiency particulate air (HEPA) filters under variable, highly controlled conditions. The test stand system is operable at volumetric flow rates ranging from 1.5 to 12 standard m(3)/min. Relative humidity levels are controllable from 5%-90% and the temperature of the aerosol stream is variable from ambient to 150 degrees C. Test aerosols are produced through spray drying source material solutions that are introduced into a heated stainless steel evaporation chamber through an air-atomizing nozzle. Regulation of the particle size distribution of the aerosol challenge is achieved by varying source solution concentrations and through the use of a postgeneration cyclone. The aerosol generation system is unique in that it facilitates the testing of standard HEPA filters at and beyond rated media velocities by consistently providing, into a nominal flow of 7 standard m(3)/min, high mass concentrations (approximately 25 mg/m(3)) of dry aerosol streams having count mean diameters centered near the most penetrating particle size for HEPA filters (120-160 nm). Aerosol streams that have been generated and characterized include those derived from various concentrations of KCl, NaCl, and sucrose solutions. Additionally, a water insoluble aerosol stream in which the solid component is predominantly iron (III) has been produced. Multiple ports are available on the test stand for making simultaneous aerosol measurements upstream and downstream of the test filter. Types of filter performance related studies that can be performed using this test stand system include filter lifetime studies, filtering efficiency testing, media velocity testing, evaluations under high mass loading and high humidity conditions, and determination of the downstream particle size distributions.

Evaluation of the Effect of Media Velocity on Filter Efficiency and Most Penetrating Particle Size of Nuclear Grade High-Efficiency Particulate Air Filters

High-efficiency particulate air (HEPA) filters are widely used to control particulate matter emissions from processes that involve management or treatment of radioactive materials. Section FC of the American Society of Mechanical Engineers AG-1 Code on Nuclear Air and Gas Treatment currently restricts media velocity to a maximum of 2.5 cm/sec in any application where this standard is invoked. There is some desire to eliminate or increase this media velocity limit. A concern is that increasing media velocity will result in higher emissions of ultrafine particles; thus, it is unlikely that higher media velocities will be allowed without data to demonstrate the effect of media velocity on removal of ultrafine particles. In this study, the performance of nuclear grade HEPA filters, with respect to filter efficiency and most penetrating particle size, was evaluated as a function of media velocity. Deep-pleat nuclear grade HEPA filters (31 cm × 31 cm × 29 cm) were evaluated at media velocities ranging from 2.0 to 4.5 cm/sec using a potassium chloride aerosol challenge having a particle size distribution centered near the HEPA filter most penetrating particle size. Filters were challenged under two distinct mass loading rate regimes through the use of or exclusion of a 3 μ m aerodynamic diameter cut point cyclone. Filter efficiency and most penetrating particle size measurements were made throughout the duration of filter testing. Filter efficiency measured at the onset of aerosol challenge was noted to decrease with increasing media velocity, with values ranging from 99.999 to 99.977%. The filter most penetrating particle size recorded at the onset of testing was noted to decrease slightly as media velocity was increased and was typically in the range of 110–130 nm. Although additional testing is needed, these findings indicate that filters operating at media velocities up to 4.5 cm/sec will meet or exceed current filter efficiency requirements. Additionally, increased emission of ultrafine particles is seemingly negligible.

Influences of U Sources and Forms on Its Bioaccumulation in Indian Mustard and Sunflower

Anthropogenic activities, such as ore mining and processing, nuclear power generation, and weapon tests, have generated uranium (U) contamination to soils and waters. The mobility and bioavailability of U are influenced by its sources, speciation, and plant species. Phytoremediation has emerged as an environmentally friendly, cost-effective green technology to remediate radioisotope- and metal-contaminated soils. The main objective of this study was to explore the feasibility using sunflower (Helianthus annuus) and Indian mustard (Brassica juncea) in cleaning up soils with UO2, UO3, and UO2(NO3)2. Uranium was found to be bioaccumulated in plant roots more than plant shoots. Uranium uptake by both plant species was significantly higher from the UO3- and uranyl-contaminated soils than from UO2-contaminated soils. UO3- and UO2(NO3)2-contaminated soils showed higher exchangeable, weak acid extractable, and labile U than the UO2-contaminated soils. After a growing season, three U forms decreased as redistribution/transformation of U resulted in U species with lower extractability. This study indicates the importance of U speciation in soil with regard to the potential use of sunflower and Indian mustard for phytoremediation of U-contaminated soils.

Development and characterization of small-scale washing systems for removal of depleted uranium oxides

Researchers from the Mississippi State University Institute for Clean Energy Technology (MSU-ICET) and the U.S. Army Engineer Research and Development Center (ERDC) have identified procedures and methodologies for identifying leaching solutions to assist in the removal of depleted uranium (DU) oxides from contaminated soils. They developed a benchscale leach system to optimize leaching procedures and methodologies. This study identified that a 2 molar (M) acetic-acid solution with a 15% (v/v) 0.3 M hydroxylamine hydrochloride solution could remove approximately 70% of the uranium in the soil sample. Pretreating the soil with 3 M hydrochloric acid improved leaching efficiency to approximately 90%. The MSU-ICET research team developed the preliminary design of a mobile leaching system based on the hydrochloric-acid pretreatment followed by 2 M acetic acid / 15% (v/v) 0.3 M hydroxylamine hydrochloride leaching method. The trailer heap leach system is designed to be used on-site, eliminating the need for additional transport of radioactive, contaminated soils. This will reduce the risk of radioactive exposure for personnel and will eliminate potentially serious transportation accidents. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.

Evaluating Performance of High Efficiency Mist Eliminators

Processing liquid wastes frequently generates off gas streams with high humidity and liquid aerosols. Droplet laden air streams can be produced from tank mixing or sparging and processes such as reforming or evaporative volume reduction. Unfortunately these wet air streams represent a genuine threat to HEPA filters. High efficiency mist eliminators (HEME) are one option for removal of liquid aerosols with high dissolved or suspended solids content.HEMEs have been used extensively in industrial applications, however they have not seen widespread use in the nuclear industry. Filtering efficiency data along with loading curves are not readily available for these units and data that exist are not easily translated to operational parameters in liquid waste treatment plants.A specialized test stand has been developed to evaluate the performance of HEME elements under use conditions of a US DOE facility. HEME elements were tested at three volumetric flow rates using aerosols produced from an iron-rich waste surrogate. The challenge aerosol included submicron particles produced from Laskin nozzles and super micron particles produced from a hollow cone spray nozzle. Test conditions included ambient temperature and relative humidities greater than 95%.Data collected during testing HEME elements from three different manufacturers included volumetric flow rate, differential temperature across the filter housing, downstream relative humidity, and differential pressure (dP) across the filter element. Filter challenge was discontinued at three intermediate dPs and the filter to allow determining filter efficiency using dioctyl phthalate and then with dry surrogate aerosols. Filtering efficiencies of the clean HEME, the clean HEME loaded with water, and the HEME at maximum dP were also collected using the two test aerosols.Results of the testing included differential pressure vs. time loading curves for the nine elements tested along with the mass of moisture and solid material on each element at final dP. Plots of overall filtering efficiencies for DOP (spherical aerosol) and dry surrogate (aspherical aerosols) at specified dPs were computed for each filter. Filtering efficiencies were determined as a function of particle size. Curves were also generated showing the most penetrating particle size as a function of dP.A preliminary set of tests was conducted to evaluate spray location, duration, pressure, and wash volume for in-place cleaning the interior surface (reducing dP) of the HEME element. A variety of nozzle designs were evaluated and test results demonstrated the potential to overload the HEME (saturate filter medium) resulting in very high dPs and extensive drain times. At least one combination of spray nozzle design, spray location on the surface of the element, and spray time/pressure was successful in achieving extension of operational life.© 2013 ASME

Lifecycle Testing Results of Dimple Pleat Radial Flow HEPA Filters Under Ambient and Elevated Conditions

The Institute for Clean Energy Technology (ICET) at Mississippi State University (MSU) has developed testing capabilities for evaluating the American Society of Mechanical Engineers (ASME) Code on Nuclear Air and Gas Treatment (AG-1) section FK radial flow HEPA filters. These high efficiency particulate air (HEPA) filters are typically used at sites within the DOE complex to control particulate matter emissions. The goal of this testing was to provide information related to the performance of radial flow HEPA filters that use dimple pleat separators. Prior to this testing, insufficient data were available to determine the lifecycle performance of these filters. Two different types of dimple pleated radial flow HEPA filters were tested: a safe change design and a remote change design. Filters were tested at both ambient and elevated conditions of temperature and relative humidity. The challenge aerosols were Alumina (Al(OH)3), Carbon black, and Arizona road dust. The performance of these filters at ambient conditions was determined by the filters’ mass loading capacity and filtering efficiency. Elevated condition performance was evaluated by the filters’ resistance to elevated temperature and relative humidity. The results indicated that the challenge aerosol had a large impact on the total loading capacity of the filters. Testing at elevated conditions of temperature and relative humidity revealed an issue with the strength of the dimple pleats. The dimples softened when challenged with elevated conditions, which led to filter failure due to a cascading reduction in free flow area and increase in differential pressure. Copyright 2013 American Association for Aerosol Research

Large-scale generic test stand for testing of multiple configurations of air filters utilizing a range of particle size distributions.

The Institute for Clean Energy Technology (ICET) at Mississippi State University has developed a test stand capable of lifecycle testing of high efficiency particulate air filters and other filters specified in American Society of Mechanical Engineers Code on Nuclear Air and Gas Treatment (AG-1) filters. The test stand is currently equipped to test AG-1 Section FK radial flow filters, and expansion is currently underway to increase testing capabilities for other types of AG-1 filters. The test stand is capable of producing differential pressures of 12.45 kPa (50 in. w.c.) at volumetric air flow rates up to 113.3 m(3)/min (4000 CFM). Testing is performed at elevated and ambient conditions for temperature and relative humidity. Current testing utilizes three challenge aerosols: carbon black, alumina, and Arizona road dust (A1-Ultrafine). Each aerosol has a different mass median diameter to test loading over a wide range of particles sizes. The test stand is designed to monitor and maintain relative humidity and temperature to required specifications. Instrumentation is implemented on the upstream and downstream sections of the test stand as well as on the filter housing itself. Representative data are presented herein illustrating the test stands capabilities. Digital images of the filter pack collected during and after testing is displayed after the representative data are discussed. In conclusion, the ICET test stand with AG-1 filter testing capabilities has been developed and hurdles such as test parameter stability and design flexibility overcome.

A test stand for the evaluation of high efficiency mist eliminators

High efficiency mist eliminators (HEME) are airstream filtering elements primarily used to remove liquid and solid aerosols. HEME elements are designed to reduce aerosol load on downstream high efficiency particulate air filters and to have a liquid particle removal efficiency of 99.5% for aerosols as small as 1 μm in size. The test stand described herein is designed to evaluate the loading capacity and filtering efficiency of a single HEME element. The loading capacity was determined with or without use of a water spray cleaning system to wash the interior surface of the element. The HEME element is challenged with a liquid waste surrogate using Laskin nozzles and large dispersion nozzles. The waste surrogate used was a highly caustic solution with both suspended and dissolved solids representative of actual exposures at mixed, hazardous, and radiological, waste treatment facilities. The filtering efficiency performance was determined by challenging the element with a dried waste surrogate aerosol and di-octyl phthalate intermittently during the loading process. Capabilities of the test stand and representative results obtained during testing are presented.

Use of Lanthanum Bromide Detectors to Augment Site Surveys for Depleted Uranium

A variety of systems have now been described for use in surveying sites for anthropogenic radiological contamination. Virtually all of these include use of sodium iodide detectors and register detection data with global positioning satellite data. This paper demonstrates how lanthanum bromide detectors can be used to augment existing field surveys in a manner to reduce uncertainty in areas of low count rates and to discriminate between depleted uranium and naturally occurring uranium. The survey system described is equipped with large (20 × 20 × 100 cm) sodium iodide (Alpha Spectra) and 7.5 × 7.5 cm lanthanum bromide (Saint Gobain) detectors. Additional radiological detection equipment (DigiBase) was obtained from ORTEC with survey data collected in the List Mode. Data collected in surveys were then used to generate digital maps using GeoSoft’s Oasis Montaj. Software has been developed to automatically identify areas of increased count rates using user-defined thresholds. This software can collect the count data for the masked area and generate a composite spectrum that can be compared to a reference spectrum believed to represent an uncontaminated area. Ratios of counts attributed to protactinium-234m (Pa-234m) are compared to counts attributed to Bismuth-214 (Bi-214) for both the composite filed survey spectrum and the reference spectrum. Soil samples have been collected from selected sites over a range of soil and geology types for the purpose of collecting data comparing high purity germanium (HPGe) detector and lanthanum bromide (LaBr) detector spectra. These samples have come from areas believed to be devoid of depleted uranium contamination and from areas expected to have higher concentrations of naturally occurring uranium. A library of HPGe and LaBr spectra have been collected comparing: (1) background soil samples with, (2) spectra from the same samples that have been doped with half the remediation threshold activity of depleted uranium, and (3) the remediation threshold activity of depleted uranium. Ratios of the Pa-234m:Bi-214 for both HPGe and LaBr detectors are provided in this paper. This process can be repeated for any site of interest. Background soil samples can be obtained prior to surveying and an equivalent library of spectral ratios generated. Field data from three different sites will be used to show how LaBr detectors can be effectively used as an infield HPGe surrogate for rapid discrimination between DU contamination and areas of high naturally occurring uranium. Areas of maps of questionable contamination are selected and composite LaBr spectra are generated along with Pa-234m:Bi-214 ratio. This is compared to library data to determine the approximate activity of DU present. All areas suspected of DU contamination can also be selected and excluded from the remainder of map data. A composite spectrum from the areas believed to be uncontaminated can be generated and spectral ratios compared library data for clearance purposes.Copyright

An Integrated System for Conducting Radiological Surveys of Contaminated Sites

This paper describes an integrated detection system that has been developed to conduct radiological surveys of sites suspected of contamination of materials such as depleted uranium. This system utilizes cerium activated lanthanum bromide and thallium activated sodium iodide gamma detectors and can be easily adapted to include units for detecting neutrons. The detection system includes software controlling the collection of radiological spectra and GPS data. Two different platforms are described for conducting surveys, a modified zero turn radius (ZTR) mower and a three-wheeled cart that is manually pushed. The detection system software controlling data collection has components that facilitate completing a gridless survey on user specified spacings. Another package confirms that all data quality activities (calibrations, etc.) are conducted prior to beginning the survey and also reviews data to identify areas that have been missed for which data quality falls below user designated parameters. Advanced digital signal processing algorithms are used to enhance the interpretation of spectra for conducting background subtractions and for mapping. Data from radiation detection instruments and GPS antennae are merged and made compatible with mapping using Geosoft Oasis montaj software. A summary of system performance during field-testing is included in the paper. This includes survey rate, detection limits, duty cycle, supporting ancillary equipment/material, and manpower requirements. The rate of false positives and false negatives is discussed with the benefits of surveys conducted using synergetic detection systems such as electromagnetic induction imaging.Copyright