Modeling and Qualification of a Modified Emission Unit for Radioactive Air Emissions Stack Sampling Compliance

A planned laboratory space and exhaust system modification to the Pacific Northwest National Laboratory Material Science and Technology Building indicated that a new evaluation of the mixing at the air sampling system location would be required for compliance to ANSI/HPS N13.1-2011. The modified exhaust system would add a third fan, thereby increasing the overall exhaust rate out the stack, thus voiding the previous mixing study. Prior to modifying the radioactive air emissions exhaust system, a three-dimensional computational fluid dynamics computer model was used to evaluate the mixing at the sampling system location. Modeling of the original three-fan system indicated that not all mixing criteria could be met. A second modeling effort was conducted with the addition of an air blender downstream of the confluence of the three fans, which then showed satisfactory mixing results. The final installation included an air blender, and the exhaust system underwent full-scale tests to verify velocity, cyclonic flow, gas, and particulate uniformity. The modeling results and those of the full-scale tests show agreement between each of the evaluated criteria. The use of a computational fluid dynamics code was an effective aid in the design process and allowed the sampling system to remain in its original location while still meeting the requirements for sampling at a well mixed location.

Simplified Solutions for Activity Deposited on Moving Filter Media

Simplified numerical solutions for particulate activity viewed on moving filter continuous air monitors are developed. The monitor configurations include both rectangular window (RW) and circular window (CW) types. The solutions are demonstrated first for a set of basic airborne radioactivity cases, for a series of concentration pulses, and for indicating the effects of step changes in reactor coolant system (RCS) leakage for a pressurized water reactor. The method is also compared to cases from the prior art. These simplified solutions have additional benefits: They are easily adaptable to multiple radionuclides, they will accommodate collection and detection efficiencies that vary in known ways across the collection area, and they also ease the solution programming.

Interactions between Silicon Oxide Nanoparticles (SONPs) and U(VI) Contaminations: Effects of pH, Temperature and Natural Organic Matters

The interactions between contaminations of U(VI) and silicon oxide nanoparticles (SONPs), both of which have been widely used in modern industry and induced serious environmental challenge due to their high mobility, bioavailability, and toxicity, were studied under different environmental conditions such as pH, temperature, and natural organic matters (NOMs) by using both batch and spectroscopic approaches. The results showed that the accumulation process, i.e., sorption, of U(VI) on SONPs was strongly dependent on pH and ionic strength, demonstrating that possible outer- and/or inner-sphere complexes were controlling the sorption process of U(VI) on SONPs in the observed pH range. Humic acid (HA), one dominated component of NOMs, bounded SONPs can enhance U(VI) sorption below pH~4.5, whereas restrain at high pH range. The reversible sorption of U(VI) on SONPs possibly indicated that the outer-sphere complexes were prevalent at pH 5. However, an irreversible interaction of U(VI) was observed in the presence of HA (Fig 1). It was mainly due to the ternary SONPs-HA-U(VI) complexes (Type A Complexes). After SONPs adsorbed U(VI), the particle size in suspension was apparently increased from ~240 nm to ~350 nm. These results showed that toxicity of both SONPs and U(VI) will decrease to some extent after the interaction in the environment. These findings are key for providing useful information on the possible mutual interactions among different contaminants in the environment.

Analysis of radon and thoron progeny measurements based on air filtration

Measuring of radon and thoron progeny concentrations in air, based on air filtration, was analysed in order to assess the reliability of the method. Changes of radon and thoron progeny activities on the filter during and after air sampling were investigated. Simulation experiments were performed involving realistic measuring parameters. The sensitivity of results (radon and thoron concentrations in air) to the variations of alpha counting in three and five intervals was studied. The concentration of (218)Po showed up to be the most sensitive to these changes, as was expected because of its short half-life. The well-known method for measuring of progeny concentrations based on air filtration is rather unreliable and obtaining unrealistic or incorrect results appears to be quite possible. A simple method for quick estimation of radon potential alpha energy concentration (PAEC), based on measurements of alpha activity in a saturation regime, was proposed. Thoron PAEC can be determined from the saturation activity on the filter, through beta or alpha measurements.

Radon mitigation in cold climates at Kitigan Zibi Anishinabeg

Available radon mitigation results were gathered for 85 houses mainly by installing sub-slab depressurization systems (SSDS) with two types of discharge and fan locations: Above ground level discharge with the fan located in the basement (AGL) or above roof line discharge with the fan located in the attic (ARL). A comparative analysis was made of mitigation efficiency and of exhaust icing. Results show that both SSDS scenarios reduced radon levels similarly. The results of SSDS with AGL show that a sealed radon fan having proper fittings and sealed piping was able to reduce the radon to acceptable levels, and that these installations were less subject to obstructive icing of the exhaust in cold climates.

Particulate activity accumulated on a moving filter and RCS leak detection

Analytical equations for calculating the particulate activity accumulated on a moving filter of a containment air particulate radiation monitor due to a reactor coolant system leak in the containment, including the noble gas decay products, were presented. The particulate airborne concentration in the containment was treated by assumptions of a constant reactor coolant leak rate at a constant concentration, a given aerosolizing fraction, a constant removal coefficient to account for the loss due to diffusion, settling, diffusiophoresis, and containment air recirculation operation. The ratio of moving-to-fixed filter activity was presented for radionuclide of various half-lives and for different filter moving speeds. The monitor response at one hour after the initiation of a 1-gallon per minute leak at measured reactor coolant concentrations was compared to the standard deviation of the background count rate for an operating pressurized water reactor. The detectability of a 1-gallon per minute leak in an hour can be demonstrated if the aerosolization percentage of the radionuclide in the leaked coolant is at least a few percent.

Revision of testing criteria for air cleaning unit of renovated APR-1000 and APR-1400 NPPS

Designing Air Cleaning Units (ACU) of an Engineered Safety Feature and normal atmosphere clean-up system at the renovated APR-1000 and APR-1400 NPP, and fuel cycle facilities in Korea, is required to meet the standards of ASME AG-1 (1997), ASME N509/N510 (1989) and KEPIC-MH (2001) to enhance the removal efficiency of aerosols and particulates from the effluents. The revised ACU testing criteria are allowed to use alternative challenge agents of the dioctyl phthalate and Refrigerant-11 for in situ testing of high efficiency particulate air filters and adsorption banks. The operability testing time of engineered safety feature (ESF) trains was changed from 10 h to 15 min. The activated carbon in adsorption banks should undergo laboratory tests at a temperature of 30 °C and relative humidity 95 %. The removal criteria of methyl iodide should be over 99.5 % for ESF and 99 % for normal systems. This paper provides the background of the changed criteria for designing and testing of the ACU system in nuclear facilities.

Wire-mesh capped deposition sensors: novel passive tool for coarse fraction flux estimation of radon thoron progeny in indoor environments

Deposition-based (222)Rn and (220)Rn progeny sensors act as unique, passive tools for determining the long time-averaged progeny deposition fluxes in the environment. The use of these deposition sensors as progeny concentration monitors was demonstrated in typical indoor environments as conceptually superior alternatives to gas-based indirect monitoring methods. In the present work, the dependency of these deposition monitors on various environmental parameters is minimized by capping the deposition sensor with a suitable wire mesh. These wire-mesh capped deposition sensors measure the coarse fraction deposition flux, which is less dependent on the change in environmental parameters like ventilation rate and turbulence. The calibration of these wire-mesh capped coarse fraction progeny sensors was carried out by laboratory controlled experiments. These sensors were deployed both in indoor and in occupational environments having widely different ventilation rates. The obtained coarse fraction deposition velocities were fairly constant in these environments, which further confirmed that the signal on the wire-mesh capped sensors show the least dependency on the change in environmental parameters. This technique has the potential to serve as a passive particle sizer in the general context of nanoparticles using progeny species as surrogates. On the whole, there exists a strong case for developing a passive system that responds only to coarse fraction for providing alternative tools for dosimetry and environmental fine particle research.

Development of tritiated vapor absorbent applicable to the atmospheric detritiation system in a nuclear facility

The combination of hydrogen oxidation reactor packed noble metal catalysts and water vapor absorber has been applied to the atmospheric detritiation system of the tritium handling facility. Commercial synthetic zeolite such as molecular sieve 5A has been used as an adsorbent of ADS absorber. In the case of application of molecular sieve 5A to the ADS absorber of a large-scale tritium handling facility such as a future fusion plant, an absorber becomes huge due mainly to the difficulty in dehydration from molecular sieve 5A. Hence, application of CaY Faujasite-type zeolite with a high framework silica-to-alumina ratio to the adsorbent for atmospheric detritiation system was investigated. It was clear that the dehydration behavior at room temperature was significantly improved using CaY zeolite. In contrast, detritiation factor for CaY zeolite with a high framework silica-to-alumina ratio depended strongly on the space velocity through the absorber. To apply CaY zeolite with a high framework SiO(2)/Al(2)O(3) ratio to the ADS absorbent, the space velocity less than 250h(-1) was recommended to maintain the detritiation factor more than 1000. The steep increase in water adsorption at the relative pressure lower than 0.05 is a feature of synthetic zeolite with calcium cation. However, such an increase was not observed in water adsorption on CaY zeolite with a framework SiO(2)/Al(2)O(3) ratio more than 7.0. Consequently, the CaY zeolite with the framework SiO(2)/Al(2)O(3) ratio of 5.0 is a promising candidate as absorbent of ADS absorber.

Results of a self-absorption study on the Versapor 3000 47-mm filters for radioactive particulate air stack sampling

Since the mid-1980's the Pacific Northwest National Laboratory (PNNL) has used a value of 0.85 as a correction factor for the self absorption of activity for particulate radioactive air samples collected from building exhaust for environmental monitoring. More recently, an effort was made to evaluate the current particulate radioactive air sample filters (Versapor 3000, 47-mm diameter) used at PNNL for self absorption effects. There were two methods used to characterize the samples. Sixty samples were selected from the archive for acid digestion to compare the radioactivity measured by direct gas-flow proportional counting of filters to the results obtained after acid digestion of the filter and counting again by gas-flow proportional detection. Thirty different sample filters were selected for visible light microscopy to evaluate filter loading and particulate characteristics. Mass-loading effects were also considered. Large error is associated with the sample filter analysis comparison and subsequently with the estimation of the absorption factor resulting in an inadequate method to estimate losses from self-absorption in the sample filter. The mass loading on the sample filter as determined after digestion and drying was approximately 0.08 mg cm; however, this value may not represent the total filter mass loading given that there may be undetermined losses associated with the digestion process. While it is difficult to determine how much material is imbedded in the filter, observations from the microscopy analysis indicate that the vast majority of the particles remain on the top of the filter. In comparing the results obtained, the continued use of 0.85 as a conservative correction factor is recommended.

Radon control systems in existing and new construction: a review

In support of the implementation of the new Canadian radon guideline, a comprehensive review of radon mitigation techniques used in countries around the world was undertaken, with particular emphasis on North America and Europe that have climates and construction techniques similar to Canada. The results of this review are presented here as an aid to administrators of radon control programmes, companies offering radon testing and mitigation services and other concerned parties, both in Canada and elsewhere, who are facing issues of implementing a radon control strategy. A wide variety of radon mitigation strategies have been employed worldwide and all have achieved some success in reducing radon concentrations. Generally, active mitigation techniques involving physical alterations to a house (e.g. sub-slab depressurisation) are more effective in achieving a sustained and substantial radon reduction than passive techniques (e.g. improved ventilation or sealing of cracks). To a large extent, the choice of an optimal mitigation strategy will depend on the building type, soil conditions and climate. Radon levels should be measured at periodic intervals after remediation, perhaps once every 5 y, to ensure that concentrations continue to remain at acceptable levels.

Aerosol sampling system for collection of Capstone depleted uranium particles in a high-energy environment

The Capstone Depleted Uranium (DU) Aerosol Study was undertaken to obtain aerosol samples resulting from a large-caliber DU penetrator striking an Abrams or Bradley test vehicle. The sampling strategy was designed to (1) optimize the performance of the samplers and maintain their integrity in the extreme environment created during perforation of an armored vehicle by a DU penetrator, (2) collect aerosols as a function of time post perforation, and (3) obtain size-classified samples for analysis of chemical composition, particle morphology, and solubility in lung fluid. This paper describes the experimental setup and sampling methodologies used to achieve these objectives. Custom-designed arrays of sampling heads were secured to the inside of the target in locations approximating the breathing zones of the crew locations in the test vehicles. Each array was designed to support nine filter cassettes and nine cascade impactors mounted with quick-disconnect fittings. Shielding and sampler placement strategies were used to minimize sampler loss caused by the penetrator impact and the resulting fragments of eroded penetrator and perforated armor. A cyclone train was used to collect larger quantities of DU aerosol for measurement of chemical composition and solubility. A moving filter sample was used to obtain semicontinuous samples for DU concentration determination. Control for the air samplers was provided by five remotely located valve control and pressure monitoring units located inside and around the test vehicle. These units were connected to a computer interface chassis and controlled using a customized LabVIEW engineering computer control program. The aerosol sampling arrays and control systems for the Capstone study provided the needed aerosol samples for physicochemical analysis, and the resultant data were used for risk assessment of exposure to DU aerosol.

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 x 31 cm x 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 microm 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.

Radon remediation of a two-storey UK dwelling by active sub-slab depressurisation: effects and health implications of radon concentration distributions

Radon concentration levels in a two-storey detached single-family dwelling in Northamptonshire, UK, were monitored continuously throughout a 5-week period during which active sub-slab depressurisation remediation measures were installed. Remediation of the property was accomplished successfully, with both the mean radon levels and the diurnal variability greatly reduced both upstairs and downstairs. Following remediation, upstairs and downstairs radon concentrations were 33% and 18% of their pre-remediation values respectively: the mean downstairs radon concentration was lower than that upstairs, with pre- and post-remediation values of the upstairs/downstairs concentration ratio, R(U/D), of 0.81 and 1.51 respectively. Cross-correlation between upstairs and downstairs radon concentration time-series indicates a time-lag of the order of 1 h or less, suggesting that diffusion of soil-derived radon from downstairs to upstairs either occurs within that time frame or forms a relatively insignificant contribution to the upstairs radon level. Cross-correlation between radon concentration time-series and the corresponding time-series for local atmospheric parameters demonstrated correlation between radon concentrations and internal/external pressure difference prior to remediation; this correlation disappears following remediation. Overall, these observations provide further evidence that radon concentration levels within a dwelling are not necessarily wholly determined by the effects of soil-gas advection, and further support the suggestion that, depending on the precise content of the building materials, upstairs radon levels, in particular, may be dominated by radon exhalation from the walls of the dwelling, especially in areas of low soil-gas radon.

High-temperature sorption of cesium and strontium on dispersed kaolinite powders

Sorption of cesium and strontium on kaolinite powders was investigated as a means to minimize the emissions of these metals during certain high-temperature processes currently being developed to isolate and dispose of radiological and mixed wastes. In this work, nonradioactive aqueous cesium acetate or strontium acetate was atomized down the center of a natural gas flame supported on a variable-swirl burner in a refractory-lined laboratory-scale combustion facility. Kaolinite powder was injected at a postflame location in the combustor. Cesium readily vaporized in the high-temperature regions of the combustor, but was reactively scavenged onto dispersed kaolinite. Global sorption mechanisms of cesium vapor on kaolinite were quantified, and are related to those available in the literature for sodium and lead. Both metal adsorption and substrate deactivation steps are important, so there is an optimum temperature, between 1400 and 1500 K, at which maximum sorption occurs. The presence of chlorine inhibits cesium sorption. In contrast to cesium, and in the absence of chlorine, strontium was only partially vaporized and was, therefore, only partially scavengeable. The strontium data did not allow quantification of global kinetic mechanisms of interaction, although equilibrium arguments provided insight into the effects of chlorine on strontium sorption. These results have implications for the use of sorbents to control cesium and strontium emissions during high-temperature waste processing including incineration and vitrification.

Calibration of diffusion barrier charcoal detectors using a semi-empirical expression

Several calibration settings of diffusion barrier charcoal canister (DBCC) detectors for measuring radon concentration in air were studied. A set of functions and graphs were developed for relations between radon concentration in air and adsorbed activity in DBCC, when calibrated in small chambers. Both the integration time for 10% of DBCC of a batch, and the radon adsorption coefficient for the activated charcoal used in these detectors, were determined. Thus, a semi-empirical expression for detector calibration was applied.

The effect of moisture on the adsorption of xenon by activated carbon

The following procedure was used to determine the effect of moisture on the adsorption of xenon from air onto activated carbon: A known amount of water is added to a sample of dried activated carbon and allowed to equilibrate. This activated carbon is then split between two cylindrical beds placed in a temperature controlled water bath, and air is passed through the beds sequentially. Because the beds contain pre-moistened activated carbon from the same sample, the first bed acts as a buffer, maintaining a constant humidity in the second. The mean holdup time of a pulse of 133Xe injected into the second bed is used to determine the adsorption coefficient for xenon under these conditions. Measurements were made for three carbons activated to 35, 40, and 59%, respectively, at temperatures of 25 degrees C and 55 degrees C. The effect of moisture on the same activated carbon at these two temperatures shows an affine relationship that could be helpful in extending these results to other temperatures. At low moisture uptakes, a plot of the log(adsorption coefficient) vs. moisture uptake gives a straight line.

Mitigation of indoor radon in an area with unusually high radon concentrations

In an area of unusually high indoor radon concentrations of up to 270,000 Bq m-3, four houses were selected for mitigation of indoor radon. Methods used were basement sealing, soil depressurization, a mechanical intake and outlet ventilation system with heat exchanger in the basement, and a multilayer floor construction using a fan to suck radon from a layer between bottom slab and floor. Basement sealing proved unsuccessful, the radon concentration remained unchanged after the mitigation attempt. The most successful remedial measure was soil depressurization using two fans and loops of drainage tubes to withdraw radon from the region under the floor and outside the walls of the basement and from soil under the part of the house without a basement. This method reduced the basement radon level in winter by about a factor of 200, i.e., from 100,000 Bq m-3 to 500 Bq m-3, and the ground-floor level by about a factor of 400. As regards the mechanical intake and outlet ventilation system with heat exchanger in the basement, it is essential to ensure that ventilation provides increased air pressure in the basement compared to outdoors. Unbalanced mechanical intake and outlet ventilation may decrease the air pressure indoors compared to outdoors, leading to increased radon concentrations. Optimization of this method reduced radon concentrations from 200,000 Bq m-3 to 2,000-3,000 Bq m-3 in winter. In one house with only a very small basement, a multilayer floor construction using a fan to suck radon from a layer between the bottom slab and floor was found to reduce radon concentrations on the ground floor from 25,000 Bq m-3 to about 1,700 Bq m-3 in winter. The results show that even in areas with extremely high radon concentrations, effective mitigation of indoor radon can be accomplished if suitable techniques are used. The evaluation of the different mitigation methods shows good coincidence with the ICRP 65 report.

Steady-state response of a charcoal bed to radon in flowing air with water vapor

Previously we have developed a mathematical model of radon adsorption in active air with water vapor on small U.S. Environmental Protection Agency charcoal canisters that are used for environmental measurements of radon. The purpose of this paper is to extend this mathematical model to describe the adsorption of radon by large charcoal beds with radon-laden air flowing through them. The resulting model equations are solved analytically to predict the steady-state adsorption of radon by such beds.

[Protection from radon emissions from a radon laboratory]

An absorbing chuck with activated coal has been suggested for absorbing radon and its daughter products' wastes from the air which are formed in the device YPP-1 in the process of preparation of radon water concentrate. Testing of such a device has shown that it is simple, reliable and efficient in functioning, thus it can be recommended to be used in radon laboratories.

[Separation of HT and HTO in the atmosphere with porous Vycor glass tube]

The continuous selective monitoring of tritium gas (HT) in the air containing HT and tritiated water vapor (HTO) was investigated by using the separation cell made of porous Vycor glass tube. On admitting the air containing HT or HTO into the separation cell, HT permeated immediately through the Vycor tube depending on the partial pressure, however, HTO permeated very slowly through the Vycor tube after initial induction period. The initial induction period was elongated with a rise of the temperature of separation cell and then the permeability of HTO decreased remarkably. In the air containing HT and water vapor, the permeation of HT through the Vycor tube was considerably restricted by the water vapor adsorbed on the Vycor tube at lower temperature (at 25 degrees C) but it was hardly affected by water vapor at higher temperature (greater than 50 degrees C) since water vapor was difficult to adsorb on the Vycor tube. These results indicated that HT in the air containing HT and water vapor can be continuously monitored by using the separation cell made of the porous Vycor glass tube.