A transportable system for monitoring airborne radionuclides.

Abstract

A transportable system for measuring radionuclides in air from a target environment may include a primary gas flow path including a cartridge dock. At least a first filter cartridge may be connectable to the cartridge dock, the filter cartridge may include a cartridge gas inlet sealingly connectable to a sample supply port, a cartridge gas outlet sealingly connectable to an exhaust port, and a cartridge flow path extending therebetween. The cartridge may include first and second filter chambers housing the first and second filters. A gamma radiation detector device may be positionable adjacent to the first filter cartridge when the first filter cartridge is connected to the cartridge dock, and is configured to detect radiation emitted from the first filter and to detect radiation emitted from the second filter, and to generate a sensor output signal based on the detected radiation.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of and priority to pending U.S. Provisional Application No. 63 / 223,903, filed July 20, 2021, entitled Portable System for Monitoring Airborne Radionuclides, which is incorporated by reference herein in its entirety.

[0002] The current subject matter of the teachings herein relates generally to transportable radiation detection devices and, more particularly, to transportable systems for monitoring airborne radionuclides. [Background technology]

[0003] US Patent No. 10,585,197 discloses a transportable detection device including a fluid inlet for acquiring a flow of fluid, a fluid outlet, and a fluid flow path therebetween. A pump circulates the fluid through the fluid flow path. A gamma ray spectrometer and a mercury analyzer are engaged with the fluid flow path for analyzing and detecting radiation emitted by the fluid. A filter trap is located in the fluid flow path downstream of the gamma ray spectrometer and the mercury analyzer. The filter trap includes a valve assembly and at least first and second filters for collecting gaseous components from the fluid. Each filter is removably connected to the first valve assembly. The valve assembly has a first configuration in which the first filter is fluidly connected to the fluid flow path and the second filter is fluidly isolated from the fluid flow path, and a second configuration in which the second filter is fluidly connected to the fluid flow path and the first filter is fluidly isolated from the fluid flow path.

[0004] No. 7,824,479 discloses an apparatus for sampling air in an aircraft cabin, comprising a sensor for detecting air contaminants, a processor, a data logger, means for detecting when the apparatus is airborne, a control unit, a manual trigger, at least one sorbent tube, a valve or other means for isolating the sorbent tube from contamination, and a pump for drawing air through the sorbent tube. An alternative apparatus uses Tedlar® bags. A method and use of the apparatus for sampling air is also disclosed.

[0005] Canadian Patent Publication No. 2,341,870 discloses a system for ambient air quality monitoring that can establish background levels of target contaminants in the ambient air prior to the start of remediation activities. The system can develop public health protection remediation action levels for dusts and vapors at the remediation facility and can monitor and document air levels of target contaminants around the fence line during remediation activities. The system and process therefore allows for the assessment of the need for dust or vapor control measures to reduce airborne containment levels below levels of concern. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 10,585,197 [Patent Document 2] U.S. Patent No. 7,824,479 [Patent Document 3] Canadian Patent Publication No. 2,341,870 [Non-patent literature]

[0007] [Non-Patent Document 1] S. Mukhopadhyay, R. Maurer, P. Guss, "Modern Trends in gamma detection systems for emergency response", Proc.SPIE 11494, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XXII, 114940B (2020); doi: 10.1117 / 12.2560115) [Non-Patent Document 2] WC Evans, "Quantitative methods for continuous particulate air monitoring", IEEE Transactions on Nuclear Science, vol. 48(5), pp. 1639-1657 (2001) Summary of the Invention [Problem to be solved by the invention]

[0008] This Summary is intended to guide the reader to the more detailed description that follows, and is not intended to limit or define any claimed or yet unclaimed inventions. One or more inventions may exist as any combination or subcombination of the elements or process steps disclosed in any part of this document, including the claims and figures.

[0009] Environmental monitoring systems and devices may be used in a variety of situations to measure potential contaminant and emission levels. To properly assess the environmental situation, detect emissions, and profile the emission stream, it may be necessary to measure and analyze acquired fluid samples using a series of different techniques or a sequence of different techniques and analytical equipment. In some cases, analytical and monitoring equipment may be used on-site, one-time only, to investigate contamination and emissions from a recent unplanned release, for example one caused by an accident, disaster, or emergency.

[0010] For example, in the case of a nuclear emergency, useful information can be obtained from radiation monitoring stations around a nuclear reactor. These information can help to confirm that radioactivity is being released into the environment and can help to quantify the dose rate to which nearby people may be exposed. Currently, two types of radiation monitoring stations are used. The first, which constitutes the majority of monitoring stations, measure the ambient radiation dose rate. These can provide real-time data on dose rates. However, they cannot provide any detailed information on the individual radionuclides present in the air. This is often addressed by employing air samplers. In this case, the missing information on the composition of the radionuclides present in the air can be obtained by capturing the radionuclides in the air on a filter and then analyzing them later by gamma spectrometry.

[0011] In a nuclear event where there is an unwanted / uncontrolled release of radioactive material into the environment, various different materials may be released in various concentrations. Having generally reliable and timely information on the nature and quantity of radioactive material may help in coordinating the response. For example, in a severe accident at a nuclear power plant, dozens of different radionuclides may be released. One such event was the Fukushima Daiichi accident in March 2011. In this event, the important / notable releases from the Fukushima accident were, for example, radioisotopes of Xe, I, Te, Cs, Tc, La, Sb, Ba, and Ag. Each radionuclide emits gamma rays with different energies, and thus they all contribute to different degrees to the overall environmental gamma dose rate. Using the techniques mentioned above, it is not possible to distinguish between different radioisotopes in environmental gamma radiation measurements. Without a priori assumptions about the radionuclides present, it is very difficult to even make inferences about the radioactivity concentrations in the vicinity of the measurement site. The limited availability of on-site real-time monitoring and measurement systems contributes to this lack of available information. For example, on-site air sampling measurements during the Fukushima Daiichi accident in March 2011 were limited in duration and location because an on-site team had to be dispatched to operate the sampling system and retrieve filters for gamma spectrometry analysis in another laboratory. The start of air sampling was delayed, making timely information about the composition of radionuclides in the air unavailable to emergency responders.

[0012] In such situations, it may be beneficial to have a transportable detection device capable of performing one or more different measurements and analyses, and preferably be able to perform measurements on-site, optionally in real time or at least near real time, rather than requiring samples to be taken from the site and transported to a laboratory or other off-site facility for analysis. For example, it may be useful to have real time or near real time data on radionuclide emissions by radioisotope, at least in part because different radioisotopes have very different radiotoxicity profiles. For example, radioactive iodine is of particular importance in considering human exposure, as it tends to accumulate in the thyroid gland. Isotopes 132 Te is also important because it has similar radiotoxicity to other radioactive iodine nuclides. 132 Radioactive iodine also exists in the environment in several chemical forms, including aerosols, I vapor, and volatile organic iodines. Radioactive cesium, on the other hand, may be of less importance in the context of first responders due to its relatively low direct radiotoxicity in the early stages of an accident, but its two long-lived radioisotopes 134 Cs and 137 There is a possibility of longer term effects due to Cs. [Means for solving the problem]

[0013] To help address at least some of the shortcomings of existing radiation monitoring systems, the teachings herein relate to a system that can be used to measure in situ, i.e., on-site, airborne radioactivity concentrations in the environment during severe accidents, preferably including events that may be expected to be as severe as the environmental events during the 2011 Fukushima accident. Preferably, the systems described herein may be configurable to provide raw, near real-time information regarding the concentrations of various radionuclides in the air without relying on human intervention to replace filters, collect samples, or perform gamma spectrometry measurements in a laboratory. The systems may optionally utilize a suitable sensor device, e.g., a spectrometer, that can be combined with a novel filter cartridge device that can capture and sequester the radionuclides in the air and provide a view factor sufficient for the sensor device to obtain a useful reading. That is, the systems and methods described herein may preferably be configured to measure the concentrations of various radionuclides in the air surrounding a given target location (such as the location of a suspected nuclear event) without having to rely on human intervention.

[0014] The systems described herein may include a main system housing or frame that can house various system components, including a gamma radiation sensor device operable to detect one or more target radioactive materials in real time, a filter cartridge that may include one or more filters for capturing airborne radionuclides (which may include particulate and / or vapor species) and that may be physically positioned relative to the gamma radiation sensor device to enable useful radiation measurements using the gamma radiation sensor device, and may further include a suitable power source (optionally an internal battery and / or a connection to an external power source), a controller or other suitable device for regulating the operation of the gamma radiation sensor device, and any other hardware (such as a transmitter and / or receiver) for communicating sensor measurements to a remote user for monitoring / analysis. The systems may also include other components as desired, including those described herein.

[0015] One example of a suitable sensor device can include a Cd-Zn-Te (CZT) spectrometer (e.g., as described in S. Mukhopadhyay, R. Maurer, P. Guss, "Modern Trends in gamma detection systems for emergency response," Proc. SPIE 11494, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XXII, 114940B (2020); doi: 10.1117 / 12.2560115, incorporated herein by reference), which can provide a reasonably high resolution spectrum for a room temperature sensor and can help facilitate performing measurements in the field. Examples of suitable filter cartridges are described herein, but they can be preferably configured to include separate aerosol and iodine filters, the aerosol and iodine filters being in a common filter unit and having internal air flow passages that can help direct air flow between the two filters. The filter cartridge is also preferably configured to provide a sufficient geometric factor between the filter and the CZT sensor to aid in improving measurement accuracy, while allowing for placement of the sensor relatively close to the filter.

[0016] Optionally, an automated system can be used to remove used / saturated cartridges from the sampling area and, preferably, supply new cartridges from a cartridge bank or other suitable source. This may allow the system to continue to operate for a longer period of time, and in particular to have a longer period of operation than the operational life / capacity of any one given sampling cartridge.

[0017] Preferably, to help facilitate replacement of multiple filter cartridges, the system may be configured to include a coupling mechanism that allows the filter to be inserted into the system (and into the desired airflow communication) in a generally unidirectional or linear insertion motion, rather than requiring a more complicated range of motion or orientation of the cartridge. This may help simplify the requirements of the automated filter replacement system. Preferably, the desired airflow connection may also be generally automatically established upon literally inserting the cartridge into the corresponding housing or other part of the overall system, eliminating the need for a separate step of engaging a coupling or otherwise establishing an airflow path connection. For example, the fittings on the cartridge and the corresponding fittings on the system housing may include ball joints, interference or friction fits, or other types of complementary sealing mechanisms that may automatically establish the desired airflow connection when the filter cartridge is physically aligned with the system housing. This may simplify the cartridge installation process (i.e., avoiding a separate airflow path coupling / connection step) and / or reduce the complexity of the automated cartridge replacement process. This may also facilitate relatively easy removal of a used cartridge from the system, since the cartridge may simply be grasped and then translated in a generally linear motion away from the system housing, thereby simultaneously blocking airflow communication between the used cartridge and the system and removing the cartridge from the housing (e.g., without requiring an initial uncoupling step prior to the physical removal step). Alternatively, in some embodiments of the system, the airflow path coupling / uncoupling operation may be a separate step other than linear insertion and / or removal of the cartridge. Similarly, in some instances of the system, the cartridge may be inserted using at least two degrees of freedom (instead of a simple translation in a substantially linear manner), and the coupling mechanism may be configured for such purposes.

[0018] In one example of the teachings described herein, the system may include a Cd-Zn-Te spectrometer, which may provide reasonably high resolution spectroscopic measurements at room temperature sensors, allowing measurements to be performed in situ. One example of an improved filter cartridge is configured to hold an aerosol filter and an iodine filter pair in place in a common cartridge, while keeping the gamma spectrometer as close as possible for high count rate efficiency. A single cartridge may preferably hold both filters, and may have internal channels to direct air flow between the filters. The cartridge design also facilitates replacement of the filters when the radioactivity builds up on the filters becomes too high. For example, an automated system may move the filter cartridges from a new cartridge storage bank to the sampling location (filtration and gamma spectroscopy) and return the used filter cartridges to the used cartridge storage bank. Because gamma spectrometry measurements are performed in situ with relatively good resolution, and the system may be automated, it may be possible for the system to transmit data immediately (or at least in near real time) back to a remote user, such as an emergency operations center, rather than having to wait for physical collection and transportation of used filter cartridges and additional analysis time in a laboratory.

[0019] Transportable detection equipment may provide relatively rapidly deployable monitoring and analysis capabilities for emergency response, and it may also be useful for the detection equipment to be modular in nature so as to allow modification depending on the particular environmental assessment required.

[0020] According to one broad aspect of the teachings disclosed herein, a transportable system for measuring radionuclides in air from a target environment may be deployable within the target environment, the system may include a main gas flow path extending between a system gas inlet configured to draw a gas sample and a system gas outlet downstream from the system gas inlet. A cartridge dock may be disposed within the main gas flow path, which may include a sample supply port in fluid communication downstream of the system gas inlet and an exhaust port in fluid communication upstream of the system gas outlet. At least a first filter cartridge may be connectable to the cartridge dock. The first filter cartridge may include a cartridge gas inlet sealingly connectable to the sample supply port, a cartridge gas outlet sealingly connectable to the exhaust port, and a cartridge flow path extending between the cartridge gas inlet and the cartridge gas outlet. The first filter cartridge may be connected to the cartridge dock to provide fluid communication between the sample supply port and the exhaust port, completing the main gas flow path. A first filter chamber may be disposed in the cartridge flow path downstream of the cartridge gas inlet, which may house a first filter. A second filter chamber may be disposed in the cartridge flow path between the first filter chamber and the cartridge gas outlet, which may house a second filter.

[0021] The gamma radiation detector device may be positionable adjacent to the first filter cartridge when the first filter cartridge is connected to the cartridge dock and is configured to detect radiation emitted from the first filter and to detect radiation emitted from the second filter, and to generate a sensor output signal based on the detected radiation.

[0022] The system controller may be configured to receive the sensor output signals and generate corresponding user outputs.

[0023] The first filter cartridge may be removable from the cartridge dock. By removing the first filter cartridge from the cartridge dock, the primary gas flow path may be blocked.

[0024] The first filter may be of a first filter type and the second filter may be of a different second filter type.

[0025] The first filter may include an aerosol filter configured to capture particles in the gas sample, and the second filter may include an iodine filter.

[0026] The filter cartridges may be connectable to the cartridge dock by translating a first filter cartridge in an insertion direction.

[0027] When a first filter cartridge is connected to the cartridge dock, the cartridge gas inlet may be aligned with the outlet port such that a fluid seal is formed between the first cartridge and the cartridge dock.

[0028] The first filter chamber may be sealed when the first cartridge is connected to the cartridge dock and is opened by removing the first filter cartridge from the cartridge dock.

[0029] The first filter may be exposed when the first filter cartridge is removed from the cartridge dock.

[0030] The first filter may be removable in an insertion direction from the first filter chamber when the first filter cartridge is removed from the cartridge dock.

[0031] The second filter chamber may be sealed when the first cartridge is connected to the cartridge dock and may be opened by removing the second filter cartridge from the cartridge dock.

[0032] The second filter may be exposed when the first filter cartridge is removed from the cartridge dock.

[0033] The second filter may be removable in an insertion direction from the second filter chamber when the first filter cartridge is removed from the cartridge dock.

[0034] The system may include a cartridge handling device controllable by the system controller and configured to remove the first filter cartridge from the cartridge dock upon expiration of the first cartridge usage period.

[0035] The system may include a second filter cartridge connectable to the cartridge dock, the second filter cartridge having a cartridge gas inlet sealingly connectable to the sample supply port, a cartridge gas outlet sealingly connectable to the exhaust port, and a cartridge flow path extending between the cartridge gas inlet and the cartridge gas outlet, where connecting the first filter cartridge to the cartridge dock provides fluid communication between the sample supply port and the exhaust port and completes the primary gas flow path. A first filter chamber disposed in the cartridge flow path downstream of the cartridge gas inlet and housing a first filter. A second filter chamber may be disposed in the cartridge flow path between the first filter chamber and the cartridge gas outlet, which may house a second filter. The cartridge handling device may be controllable by the system controller to connect the second filter cartridge to the cartridge dock after the first filter cartridge is removed from the cartridge dock.

[0036] The system may further include at least one new cartridge bank configured to store unused filter cartridges and containing at least a second filter cartridge. The cartridge handling device may be configured to retrieve the second filter cartridge and move the second filter cartridge into alignment with the cartridge dock after the first filter cartridge is removed from the cartridge dock.

[0037] The system may further include at least one used cartridge bank that may be configured to receive and store used filter cartridges. The cartridge handling device is configured to retrieve a first filter cartridge from the cartridge dock and place the first filter cartridge in the used cartridge bank.

[0038] The cartridge handling device can include an end effector configured to selectively grasp the first filter cartridge and movable with at least two degrees of freedom.

[0039] The cartridge handling device includes a carriage movable along a carriage rail, and an extension unit mounted to the carriage and configured to support and move the end effector along an extension axis.

[0040] The carriage rail may be substantially straight.

[0041] The extension axis may be substantially linear and may be substantially perpendicular to the carriage rail.

[0042] The gamma ray detector device may include a sensor portion movable between:

[0043] a measurement position in which the gamma ray detector device is adjacent to the first filter cartridge and the sensor portion prevents removal of the first filter cartridge from the cartridge dock, and a replacement position in which the sensor portion is spaced apart from the first filter cartridge and the first filter cartridge can be removed from the cartridge dock.

[0044] The gamma radiation detector device may include a detector actuator communicatively coupled to the controller and configured to support the sensor portion, the detector actuator being configured to selectively move the sensor portion between a measurement position and a replacement position.

[0045] The detector actuator comprises a linear actuator configured to linearly translate the sensor portion along the detector axis between the measurement position and the exchange position.

[0046] The detector actuator may be operable independently of the cartridge handling device.

[0047] The gamma ray detector apparatus may include at least a first detector aligned with the first filter and a second detector spaced apart from the first detector and aligned with the second filter, the first detector may be configured to generate a first detection signal based on the gamma radiation in the first filter, and the second detector may be configured to generate a second detection signal based on the gamma radiation in the second filter.

[0048] At least one of the first detector and the second detector may include a gamma ray spectrometer, preferably a CZT gamma ray spectrometer, that is at least partially surrounded laterally by radiation shielding to limit exposure to background radiation not emitted from the filter cartridge.

[0049] The sample supply port may include a sample dock coupler having a curved supply sealing surface, and the cartridge gas inlet includes a complementary curved inlet sealing surface configured to seal against the supply sealing surface.

[0050] The supply sealing surface may be convex and the curved inlet sealing surface may be concave.

[0051] When the first cartridge is connected to the cartridge dock, the supply sealing surface may be pressed against the inlet sealing surface to seal the first filter chamber, and the first cartridge may be translated away from the cartridge dock such that the supply sealing surface and the inlet sealing surface are separated without releasing the fastener.

[0052] The exhaust port may include an exhaust dock coupler having a curved exhaust sealing surface, and the cartridge gas outlet may include a complementary curved outlet sealing surface configured to seal against the exhaust sealing surface.

[0053] The exhaust sealing surface may be convex and the curved outlet sealing surface may be concave.

[0054] When the first cartridge is connected to the cartridge dock, the exhaust sealing surface may be pressed against the outlet sealing surface to seal the second filter chamber, and the first cartridge may be translated away from the cartridge dock such that the exhaust sealing surface and the outlet sealing surface are separated without releasing the fastener.

[0055] Other aspects and features of the teachings disclosed herein will become apparent to those of ordinary skill in the art upon review of the following description of specific examples of the disclosure.

[0056] The drawings included herein are for the purpose of illustrating various examples of the articles, methods, and apparatus of the teachings herein and are not intended to limit the scope of the teachings in any way. [Brief description of the drawings]

[0057] [Figure 1] 1 is a graph showing options for the operating envelope associated with the predicted count rate of a filter for a given airborne radionuclide concentration for various sampling times (line style) and energy-dependent detector efficiency (line color). [Diagram 2] FIG. 1 is a schematic diagram of one example of a system for measuring radionuclides in air. [Diagram 3] FIG. 2 is a top view of one example system of filter cartridges. [Figure 4] FIG. 4 is a side view of the filter cartridge of FIG. 3. [Diagram 5] 5 is a cross-sectional view of the filter cartridge of FIG. 3 taken along line 5-5n. [Figure 6] 1 is a partial cross-sectional view of a portion of a system for measuring radionuclides in air; [Figure 7] FIG. 7 is an enlarged view of a portion of FIG. [Figure 8] 3 is a diagram of the system for measuring radionuclides in air of FIG. 2 in various configurations; [Figure 9] 3 is a diagram of the system for measuring radionuclides in air of FIG. 2 in various configurations; [Figure 10] 3 is a diagram of the system for measuring radionuclides in air of FIG. 2 in various configurations; [Figure 11] 3 is a diagram of the system for measuring radionuclides in air of FIG. 2 in various configurations; [Figure 12] 1 is a photograph showing a portion of a prototype example of a system for measuring airborne radionuclides from a target environment. [Figure 13a] 1 is a graph showing the in situ gamma ray counting efficiency of an aerosol filter detector and an iodine filter detector evaluated using 152Eu and 137Cs / 241Am. [Figure 13b]7 is a graph showing simulated detector count rates for 131I, 137Cs, and 103Ru during a hypothetical nuclear emergency when an air sampler is used according to the sampling time-based algorithm for filter replacement given in Equation 7. [Figure 14] 1 is a graph showing reconstruction of air concentrations of 131I, 137Cs, and 103Ru in a hypothetical nuclear emergency. [Figure 15] FIG. 1 is a schematic diagram of a test apparatus for evaluating particle retention efficiency. [Figure 16] FIG. 16 is a CAD drawing of the test setup of FIG. [Figure 17a] 1 is a photograph of the filter used in the test. [Figure 17b] 1 is a photograph of the filter used in the test. [Figure 18] 1 is a graph showing pressure drop versus flow rate for a paper filter only. [Figure 19] 1 is a graph showing pressure drop versus flow rate for the activated carbon filter only. [Figure 20] 1 is a graph showing pressure drop versus flow rate for a combination paper and activated carbon filter. [Figure 21] 1 is a histogram of the aerosol particle size that passed through the filter during testing compared to a control (no filter installed). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Various devices or processes are described below to provide illustrations of embodiments of each claimed invention. The embodiments described below are not intended to limit any claimed invention, and any claimed invention may encompass processes or devices different from those described below. The claimed invention is not limited to a device or process having all the features of any one device or process described below, or to features common to more than one or all of the devices described below. A device or process described below may not be an embodiment of any claimed invention. Any inventions disclosed in the devices or processes described below that are not claimed in this document may be the subject of other means of protection, such as a continuing patent application, and it is not the intention of the applicant, inventor, or owner to abandon, partially abandon, or dedicate such inventions to the public by disclosing them in this document.

[0059] Emergency response situations involving unplanned releases of radioactive material may require monitoring or analysis. Such situations include road accidents involving radioactive transports and unplanned releases to liquids or air. Environmental remediation and decommissioning are other examples of situations where environmental monitoring systems may be utilized. Analysis of environmental materials may require relatively long processing times (in some cases up to several weeks) to accommodate the collection and transportation of physical filters and samples to off-site laboratories, the conduct of the tests themselves, and the subsequent delivery and receipt of the results. On-site analysis and monitoring of airborne contaminants, doses, and contaminant dispersion may all be useful in the event of an unplanned release of radioactive material.

[0060] As described herein, a transportable system has been developed to perform real-time or near real-time measurements utilizing an in-situ gamma ray spectrometer. Gamma ray spectrometers suitable for use in the systems described herein are preferably configured to measure large releases from the initial stage of an accident and persistent background from smaller leaks, and therefore can measure up to 102 Bq / m 3~108Bq / m 3 A wide range of potential radioactivity concentrations C on the order of a,i Gamma spectrometers have a fairly large dynamic measurement range before saturation, but this range can be further extended, for example by sampling the air for a shorter or longer period of time.

[0061] Gamma ray spectrometers measure the physical counting rate of nuclides.

number

number

[0062] The radioactivity on the filter is expressed as the air volume flow rate F and the filter efficiency Φ f , and the amount of time the filter was used t f Furthermore, the radioactivity of the filter is also related to the amount of trapped radioactivity by the decay constant λ i Therefore, the counting rate is affected by the air concentration C a,i and the following relationships:

number

[0063] Equation 2 assumes that both the air activity concentration and the air sample flow rate are constant. For the purposes of measuring the count rate, the gamma spectrometer calculates the sum of counts ΔC above the background level. i In order to obtain the specified time (detection period), Δt aqData can be acquired over a period of time that is preferably long enough to provide a relatively useful / acceptable signal-to-noise ratio for purposes of identifying peaks, yet short enough compared to the increase in radioactivity captured by the filter to approximate the transient count rate.

number

[0064] Using algorithms such as those presented in W. C. Evans, "Quantitative methods for continuous particulate air monitoring," IEEE Transactions on Nuclear Science, vol. 48(5), pp. 1639-1657 (2001), it is possible to calculate the air concentration, including the effects of radioactive decay, which is given by:

number

[0065] For design and study purposes, some assumptions can be made about the system, e.g., the filter efficiency Φ f can be assumed to be close to 1. Although the activity of short-lived radioisotopes on the filter will eventually plateau and possibly decrease over time, for at least some of the radioisotopes of interest herein ( 131 I, 137 Cs, 132 Te, 103 Ru) either has a half-life of greater than about 6 hours or is in equilibrium with a longer-lived isotope. For purposes of the teachings herein, this allows Equation 2 to be reduced to the following, which suggests that the count rate increases approximately linearly the longer the filter is in place:

number

[0066] For a sampling flow rate of 5 L / min, several curves were calculated using Equation 5 and are shown in Figure 1. The relationship between air activity concentration and expected count rate on the filter is shown for several combinations of filter collection time and detector efficiency (e.g., various gamma ray energies). The plot also illustrates some of the constraints associated with detecting radioactivity on the filter. If the count rate of a particular radioisotope is less than about 10 counts per minute (cpm), it is relatively unlikely that that radioisotope can be observed unless very long acquisition times are used, especially if there is a relatively high background due to other radioisotopes trapped on the filter. If the overall count rate is less than about 10 6 If cpm is exceeded, the detectors described herein may begin to saturate and may not operate in a desired manner.

[0067] As shown in the exemplary FIG. 2 Bq / m 3 From 10 8 Bq / m 3 The air concentration can be measured over a period of time, but not necessarily at a set sampling period. With a conventional fixed filter configuration, filter replacement can be expected at most once every 24 hours in an emergency and at most once every 5-7 days during routine monitoring. If one of the fixed periods in Figure 1 is used, the measurable concentration range is reduced by nearly three orders of magnitude in this example. However, the inventors have determined that if the filter cartridges could be replaced dynamically in the field, preferably without human intervention, the frequency of filter cartridge replacement could be much higher, and therefore the system as a whole could potentially obtain useful measurements over a wider range of air concentrations.

[0068] Another design consideration for the system is the degradation of the detector's sensitivity over time due to the radioactivity accumulated in a given filter. For example, releases from nuclear power plants during accidents or other similar events may tend to be explosive, meaning that a cloud containing a relatively high concentration of radioactivity may pass through in a relatively short time, after which the amount of radioactivity in the air may drop significantly. In traditional measurements with fixed filters, all the accumulated radioactivity remains in the common filter media until the user manually replaces / collects it. In spectroscopy, the signal error (inherent in the signal and other uncertainties due to Compton background or peak interferences) is taken for the purposes of this description to be equal to the square root of the count rate for the signal, in this case the filter, and thus:

number

[0069] Under these conditions, count rates measured with conventional systems would remain high unless, for example, filters were replaced or radioactive decay was waited for, and this error would tend to increase the variability in data taken at the end of the high concentration event, after airborne radioactivity concentrations had fallen again.

[0070] In contrast, the systems described herein can be configured to automatically use more than one filter during a given detection period, which may help improve the time resolution of the measurements and address some of these known challenges. The system also preferably includes at least two different types of filters that can be configured to capture different radionuclides from the incoming air sample, such as at least one aerosol filter and at least one iodine filter. Preferably, the system is configured to be able to individually detect the radionuclides captured in each filter, and more preferably to be able to distinguish between aerosol and vapor iodine species. In such a system, a second set of charcoal filters dedicated to iodine may also be used, as described herein. In situ measurements may then be performed using a pair of CZT gamma ray spectrometers (or other suitable detectors, one associated with each filter), which may collect data while the system is sampling from the air.

[0071] 2, a schematic diagram of one example of a transportable system 100 for measuring airborne radionuclides from a target environment is shown. The system 100 and its components are intended to be sufficiently transportable, and optionally generally self-contained, to allow the system 100 to be transported to an area or environment where measurement of airborne radionuclides is desired, such as an area surrounding a nuclear power plant or other potential source of airborne radionuclides. For purposes of the present teachings, such areas may be considered target environments, and placing the system within such environments is considered to be placing the system 100 in situ or on-site, which is generally understood to be distinct from a laboratory or other building / environment remote from an area where airborne radionuclides are expected / suspected.

[0072] In this schematic example, the system 100 includes a system housing 102 capable of supporting and / or housing other system components. The housing 102 may be a generally rigid housing, e.g., to help protect the internal components from rain, dust, and other air contaminants, and may have rigid or substantially rigid walls, preferably having one or more openable doors or panels to provide access to the interior of the housing 102. Alternatively, the housing 102 may be a generally open, frame-like structure having several support points for mounting and attaching other system components, but need not have a protective shell or the like. Although shown generally as a single continuous structure, in some examples the housing 102 may include two or more separate housings, modules, containers, or other such structures that may be collectively considered the housing of the overall system 100. Regardless of its overall configuration, the housing 102 may include a variety of suitable openings to accommodate air sampling as described herein, as well as to provide connections to any external modules capable of interfacing with the system 100, such as power, control, communication and data connections.

[0073] Housing 102 and the components it supports are preferably sized to be generally portable and transportable from a storage location to a target location where radioactivity is found when it is desired to use system 100. Thus, housing 102 is preferably sized so that it can be carried by a user, or alternatively, can be maneuvered using appropriate equipment (such as a lift truck or crane) and transported on a conventional vehicle (such as a car or van, pick-up truck, airplane, ship, transport truck, etc.) for deployment within the target environment.

[0074] In this example, the system 100 includes a system gas inlet 104, through which samples of air, and other gases from the surrounding target environment, can be drawn into the system 100 for measurement. In this illustrated example, the system gas inlet 104 is provided in the form of an open end of a conduit extending into the housing 102. The system 100 also includes a system gas outlet 106, through which air can exit the housing 102 upon completion of the measurements described herein. The gas outlet 106 may be connected to any suitable downstream processing equipment, if desired, or alternatively, as shown in this example, may be the end of a generally open air flow conduit that simply allows the exhausted air to be expelled back into the surrounding atmosphere.

[0075] A main system gas air flow path 108 extends between the system gas inlet 104 and the system gas outlet 106, providing a path by which air may flow through the system 100. In the example described herein, the system gas air flow path 108 includes multiple various sections of tubing / conduits that can be connected to one another during use of the system 100 to provide a generally continuous, unidirectional air flow path through the system 100. Preferably, at least some portions of the gas air flow path 108, including one or more of the conduits and other such structures, may be formed from a generally non-reactive material, such as glass, to help reduce chemical interactions between the incoming air sample and portions of the system 100 upstream of the filter cartridge. A variety of different air flow devices, such as pumps, compressors, valves, pressure sensors, flow sensors, temperature sensors, and other suitable devices and sensors, may be provided along the air flow path 108 to aid in the system 100 operating as described herein. The schematic example includes an air circulation pump 110 and flow and pressure gauges 112 as illustrative illustrations of such features.

[0076] In addition to the airflow device, the system 100 includes a cartridge dock 114 disposed within and serving to form a portion of the primary air flow path 108. The cartridge dock 114 is a portion of the system 100 that is configured to removably connect to a filter cartridge used to aid in the capture of airborne radionuclides and their retention for measurement and detection using the system 100 as described herein. The cartridge dock 114 may thus have any configuration suitable for connection with a given filter cartridge design, and will preferably have complementary mating and sealing features that aid in providing a substantially airtight connection between the cartridge dock 114 and the replaceable filter cartridge. Preferably, the system 100 is configured such that when a filter cartridge is mated to the cartridge dock 114, the filter cartridge aids in completing the primary air flow path 108 such that air can travel from the system gas inlet 104 to the system gas outlet 106 through both the cartridge dock 114 and the associated filter cartridge. In this configuration, the filter cartridge can block the primary air flow path 108 when removed from the cartridge dock 114 .

[0077] To capture airborne radionuclides, system 100 includes at least one filter cartridge, and preferably may include a plurality of replaceable filter cartridges, as described herein, that are connectable to cartridge dock 114 for a detection period during use of system 100. In the illustrated example, a plurality of suitable filter cartridges 120 are shown as being part of the system, including a plurality of new or unused cartridges 120 and a plurality of used cartridges that have captured at least a certain amount of airborne radionuclides and / or other contaminants as generally indicated by the presence of one or more small circles on cartridge 120.

[0078] 3-6, one example of a filter cartridge 120 suitable for use with the system 100 described herein includes a cartridge housing 122, which in this example includes an upper wall 124, an opposing lower wall 126 spaced from the upper wall 124 by a cartridge thickness 128, and a sidewall 130 extending between the upper wall 124 and the lower wall 126. Together, the walls 124, 126, and 130 cooperate to enclose an interior airflow passage or cartridge flow path 133 within the filter cartridge 120.

[0079] The filter cartridge 120 is configured to hold two filters and to allow air to pass through the body of the filter cartridge 120 such that during use of the filter cartridge 120 it forms part of the overall primary air flow path 108. In this example, the filter cartridge 120 includes an air inlet 132 connectable in a generally airtight manner to air flow conduits that form part of the primary air flow path 108 (e.g., to a sample supply port and an exhaust port, respectively, as described herein) to allow air to enter the filter cartridge 120. In this example, the air inlet 132 is a hole / opening formed in the upper wall 124 of the filter cartridge 120, but may have different configurations in different examples.

[0080] The filter cartridge 120 also includes an air outlet 134 that is connectable to another conduit that forms part of the primary air flow path 108 during use of the cartridge 120. A cartridge internal flow path 136 extends between the air inlet 132 and the air outlet 134 (see FIG. 5 ), thereby providing airflow communication through the cartridge 120.

[0081] The filter cartridge 120 of this example is configured to hold two filters that will be placed in the main air flow path 108 so that materials traveling through the air flow path 108 with the air sample will be captured by the filters and held for measurement and analysis. For example, the air pump 110 may be configured to turn on when the cartridge 120 is installed and begin drawing air (e.g., at about 5 L / min as shown), and a flow meter and pressure sensor 112 may be used to monitor the air sampling rate. The gamma spectrometer may begin counting when the air pump 110 is turned on, and in conjunction with the controller 186, may track radionuclide activity as it accumulates in the filters in the cartridge 120 as described herein. Other devices, valves, etc. may be provided in other examples.

[0082] The filters may be located anywhere within the cartridge air flow path 136 and may be arranged in parallel or preferably in series with one another. In this example, the cartridge 120 includes a first filter chamber 138 defined by a portion of the housing / body of the cartridge 120 and configured to house a first filter 140 (FIG. 5). The first filter chamber 138 in this example is located at the air inlet 132 (although it may be located elsewhere in other examples).

[0083] Preferably, the first filter 140 is sized to generally match the dimensions and shape of the first filter chamber 138 and is exposed to the incoming airflow. The first filter 140 may be any suitable type of filter media suitable for capturing target contaminants in the air, and is preferably an aerosol filter formed from a suitable material, such as cellulose, and operable to capture particles from the air passing therethrough. One example of a suitable aerosol filter is Whatman® Qualitative Filter Paper, Grade 1 (WHA1001047). Optionally, the first filter chamber 138 may be openable to allow the first filter 140 to be inserted and removed as desired. In some instances, a used filter may be removed from the filter cartridge 120 and replaced with a new filter media. This may allow a given filter cartridge 120 to be used multiple times.

[0084] The cartridge 120 also includes a second filter chamber 142 downstream of the first filter chamber 138, located at the air outlet 134 in this example (although it may be located elsewhere in other examples). The second filter chamber 142 is configured to hold a second filter 144. The second filter 144 may be the same type of filter as the first filter 140, but is preferably a different type of filter configured to capture a different type of airborne contaminant than the first filter 140, such as a charcoal filter specifically for iodine. In this configuration, the filter cartridge 120 may be considered a two-stage filter, with different types of contaminants captured by the different filters 140 and 144, which are located at different locations. This helps facilitate independent measurement of contaminants on the filters 140 and 144, which may enable the system 100 to separately monitor:

[0085] Because each filter cartridge 120 is intended to be used for a predetermined period of use, it may be advantageous to be able to connect and disconnect the cartridge 120 to and from the air flow path 108 in a relatively easy manner, preferably in a generally one-step process that does not require separate actuation or manipulation of fasteners, connectors, or the like to establish a desired airtight seal. For example, in some implementations of the system 100, it may be preferable to be able to connect the cartridge 120 to a corresponding portion of the system (such as the cartridge dock 114 as described herein) via movement in a single mating direction, such as translation of the cartridge in an insertion / removal direction. Optionally, the insertion / removal direction may be a generally linear path of movement, with the cartridge 120 moved via a suitable linear actuator or the like. This may help facilitate automated installation and removal of the cartridge 120, and may reduce or possibly eliminate the need for a user to manually install or remove the cartridge. Enabling this type of relatively easy installation and removal may include suitable mating and sealing mechanisms in the filter cartridge 120 and complementary mating and sealing mechanisms in other portions of the system 100. Any suitable, complementary set of mechanisms may be used.

[0086] 6 and 7, there is shown an enlarged view of a portion of the system 100 illustrating some of the features of the cartridge dock 114. In this example, the cartridge dock 114 includes at least a portion of a filter supply conduit 150 terminating in an air sample supply port and a filter exhaust conduit 152 terminating in an exhaust port that form part of the primary air flow path 108. Each conduit 150 and 152 terminates in an open free end with a dock coupler 154. In this example, the dock coupler includes a generally rounded ball joint mechanism at the sample supply and exhaust ports at the ends of the conduits 150 and 152. The ball joints at the ports may have generally smooth convex outer surfaces, such as a lower convex sealing surface 156 as shown in FIG. 7. These surfaces may form at least a portion of the seal with the cartridge 120. To provide a complementary concave sealing surface that can engage and seal against the sealing surface 156, the filter cartridge 120 illustrated in this example includes a cartridge coupling member 158 provided in the form of a generally annular sealing member having a concave sealing surface 160 configured to seal against the convex sealing surface 156 when the cartridge 120 is docked as shown in FIG. 7. To disconnect the cartridge 120, it can be moved linearly downwardly, as shown in FIG. 7, away from the cartridge dock 114 to disengage the concave sealing surface 160 configured to seal against the convex sealing surface 156. In this example, the cartridge coupling member 158 laterally surrounds the gas inlet 132 and gas outlet 134, and the first and second filter chambers 138 and 142.

[0087] In the illustrated example, moving the cartridge 120 linearly away from the cartridge dock 114 will automatically interrupt the airflow connection between the cartridge 120 and the primary air flow path 108 and may also expose the filters 140 and 144 housed within the corresponding filter chambers 138 and 142. This may eliminate the need to touch or open chamber doors or other such structures to inspect or access the filters 140, 144.

[0088] When the cartridge 120 is connected to the cartridge dock 114 and the system 100 is in use, airborne contaminants entrained in the air drawn into the primary air flow path 108 may be trapped by the filters 140 and 144. As the contaminants accumulate on the filters 140 and 144, the amount and / or type of contaminant may be measured by the system using an appropriate sensor, such as a gamma radiation detector as described herein. Because different types of contaminants may be retained in the different filter types 140 and 144, by individually measuring the gamma radiation emitted from each filter 140 and 144, the system 100 may be able to simultaneously detect and / or measure the concentration of two or more different types of airborne contaminants.

[0089] 2 and 6, in the illustrated embodiment, the system 100 includes a gamma radiation detector device 170 having a sensor portion 172 that may be positioned adjacent to the filter cartridge 120 and aligned or registered with the corresponding filters 140 and 144 during use of the system 100, as shown diagrammatically in FIG. 6. The sensor portion 172, and optionally other portions of the gamma detector device 170, are preferably movable such that they may be moved between a measurement position, as shown in FIG. 6, in which it is adjacent to the first filter cartridge, and a replacement position (see FIG. 8), in which the sensor portion 172 is spaced from the filter cartridge 120 a sufficient distance to vertically remove and install the filter cartridge 120 from the cartridge dock 114. While the sensor portion 172 is in the replacement position, the used cartridge 120 may be removed from the cartridge dock and replaced with a new cartridge 120. With the new cartridge 120 installed, the sensor portion 172 may be moved back to the measurement position (see also FIG. 10).

[0090] In this example, the sensor portion 172 includes two separate gamma ray spectrometers 174, each housed within a corresponding shielded housing 176, which may be a tungsten shield or the like, to reduce detection of false radioactivity readings from the surrounding environment. Such shielding may be important in some situations where the environment surrounding the system 100 may be contaminated, such as when the system 100 is deployed near a nuclear power plant during an emergency. Optionally, a tungsten collimator (e.g., 20 mm high, 35 mm inside diameter in some examples) may be placed between the spectrometers 174 and the cartridge 120 to help further narrow the field of view. This type of directionality and exposure limitation for each spectrometer 174, for example by using the collimators described or other such hardware, may help prevent, for example, radioactivity from the aerosol filter 140 from being viewed by a spectrometer 174 that is focused on the iodine filter 144, and vice versa.

[0091] To help reduce the possibility of such mixed readings between spectrometers 174, filter chambers 138 and 142 and filters 140 and 144 therein are preferably spaced laterally (e.g., in the horizontal direction as illustrated in FIG. 5) from one another by an offset distance 180 ( FIG. 5 ) that is between about 2 cm and about 50 cm, and which may be between about 5 cm and about 20 cm.

[0092] When the sensor portion 172 is in the measurement position, each spectrometer 174 is aligned with a corresponding one of the filters 140 and 144. In this configuration, one of the spectrometer detectors 174 can generate a first detection signal based on the gamma radiation in the first filter, and a second one of the spectrometer detectors 174 can generate a second detection signal based on the gamma radiation in the second filter. These signals can be sent to the system controller 186 for processing. The controller 186 can then generate appropriate user outputs and / or output signals. The first and second detection signals can be different if different amounts of radiation are detected at the filters 140 and 144.

[0093] Similarly, placing the spectrometer 174 axially (e.g., vertically as illustrated in FIG. 6) relatively close to the filters 140 and 144 may help improve the quality and / or accuracy of the measurements. One factor that may affect the vertical / axial spacing between the spectrometer 174 and the filters 140 and 144 is the thickness 128 of the cartridge 120. Preferably, the thickness 128 of the cartridge is relatively small so that a gamma ray spectrometer located adjacent the lower wall 126 can still get close enough to the filters in the cartridge to obtain useful measurements. Optionally, the thickness 128 may be less than about 20 cm, preferably less than about 10 cm, and may be about 3-6 cm. The spectrometer 174 is preferably placed as close as possible to the filters 140, 144, as this may help improve signal quality.

[0094] To aid in moving the sensor portion 172 in this manner, the gamma ray detector device 170 may also include any suitable type of actuator, such as a detector actuator 178, shown generally in FIGS. 2, 8-9, and 11, that can support and move the sensor portion 172 between a measurement position (FIGS. 2 and 11) and a replacement position (FIG. 9). The detector actuator 178 can include a linear actuator, and may be pneumatic, hydraulic, or electric, or any other suitable device. The detector actuator 178 is preferably communicatively coupled to the controller 186, for example by a wired or wireless connection, to support the sensor portion 172.

[0095] Preferably, the detector actuator 178 may be controlled independently from the cartridge handling devices described herein, although optionally, the movement of the different actuators may be coordinated, for example by the controller 186, to help facilitate cartridge exchange as described herein.

[0096] To help facilitate replacement of the cartridges 120 and operation of the system 100 in a generally autonomous manner, the system may include a suitable cartridge handling device 190 controllable by the controller 186. The cartridge handling device 190 is preferably configured to allow a used filter cartridge 120 to be removed from the cartridge dock 144 at the end of its cartridge life, and a new replacement filter cartridge 120 to be subsequently connected to the cartridge dock 114 without the need for intervention by a human user / operator.

[0097] Preferably, to aid in managing the supply of cartridges 120, system 100 may include at least one fresh cartridge bank, shown generally in FIG. 8 as new bank 192, that can hold one or more unused cartridges. Similarly, system 100 preferably includes at least one used cartridge bank, shown generally in FIG. 8 as used bank 194, that can hold one or more used cartridges.

[0098] In this example, the cartridge handling device 190 is therefore preferably configured to retrieve the used cartridge 120 from the cartridge dock 114 (see Figures 2, 8 and 9 where the sensor portion 172 has been moved to the exchange position) and transport it towards the used bank 194. An unused cartridge can then be obtained from a new bank 192 which the cartridge handling device 190 can connect to the cartridge dock 114 (Figure 10). The sensor portion 172 can then be returned to the measurement position (Figure 11) for the appropriate cartridge use period. A variety of devices can be used for this purpose.

[0099] In the illustrated example, the cartridge handling apparatus 190 is shown generally as including an end effector portion, e.g., a pneumatic gripper 196 capable of grasping the cartridge 120. The pneumatic gripper 196 is preferably movable in at least two degrees of freedom to aid in achieving a desired cartridge handling operation. For example, in this case, the cartridge handling apparatus 190 includes a carriage 198 mounted to a rail 200 and slidable in a first lateral translation direction 202 along the rail 200. In this example, the rail 200 is shown as linear / straight, but in other examples may have other shapes (e.g., curved, angled, etc.).

[0100] An extension unit 204 is mounted which is translatable with the carriage 198 and can extend in a second direction to support the pneumatic gripper 196 (FIG. 9) and move the cartridge 120 towards and away from the cartridge dock 114. This can include pneumatic piston / cylinders, ball screws, scissor lifts, linear rails, or other hardware. In this example, the extension of the extension unit 204 is generally perpendicular to the movement of the carriage 198, but can be of different configurations in other examples.

[0101] System controller 186 is illustrated generally in the examples herein, but may be any suitable computer, processor, programmable logic controller, etc., capable of connecting to components of system 100, such as the cartridge handling system, gamma spectrometer, gas handling equipment, etc. The system controller may be communicatively coupled to these various components using any suitable communications hardware / protocol, including wired, wireless connections (such as BlueTooth or WiFi), infrared communications devices, radio transmitters / receivers, etc.

[0102] The system controller may include any suitable input and output devices to allow a user to interface with the system, including a keyboard, mouse, track pad, or other input devices, a monitor / screen, speakers or other sound generating transducers, lights, audio / speech capabilities, interfaces with apps or other similar software running on parallel devices (e.g., smart phones, tablets, etc.), and other suitable devices.

[0103] Although shown generally as a single unit, the system controller may in some instances include multiple different physical devices that are separate from each other but in communication with each other and may function together to perform the functions of the system controller described herein.

[0104] During use of the system 100, the gamma ray spectrometers 174 can each generate a corresponding sensor output signal proportional to the number of radionuclides captured / present within the filters 140 or 144 to which they are aligned. These signals can be in any suitable format and provided to the controller 186. The controller 186 can then generate an appropriate output based on the received sensor data. This output can include recorded data associated with the sensor, such as radiation levels, identification or classification data that can help identify specific airborne contaminants present in the sample, etc. The controller 186 can also utilize other incoming received data / information, such as weather data, temperature, time, location data, and other suitable data. These various data sources can be utilized by the controller 186 to generate one or more desired user outputs, such as a time-based record of measured radiation levels, graphs, reports, on-screen displays, warnings or alerts (e.g., when the recoded values ​​exceed a predefined alarm threshold), and other such outputs. A user output may be generated locally by the controller, for example by sounding an alarm or triggering a light, and / or information may be communicated to an external or remote device that is physically separate from the housing 102, such as a computer, tablet, smart phone, etc.

[0105] To verify operation of the system 100 described herein, a prototype system was constructed for testing purposes. Referring to FIG. 12, a photograph of a portion of the prototype device is shown. Portions of the prototype are similar to portions of the system 100, and similar features have been identified using similar reference characters. FIG. 12 shows an example of a test cartridge 120 connected to the cartridge dock 114 with the sensor portion 172 positioned in a measurement position.

[0106] The two gamma spectrometers in this example are Kromek GR1 CZT detectors, and the system controller 186 employs Kromek MultiSpect Analysis software to capture and record gamma spectrometry measurements. The tungsten shield 176 was from a Canberra CSM-GR1 system. An initial prototype of the filter cartridge 120 was 3D printed from polylactic acid (PLA), with other versions fabricated from PTFE. The linear axis slide, pneumatic piston, and pneumatic gripper that are part of the detector actuator 178 and cartridge handling device 190, as well as the control software and other accessories, were Festo components.

[0107] The efficiency of this prototype in-situ detector was evaluated using a set of fixed counting sources placed on an aerosol filter or an iodine filter to simulate collected radioactivity. Two different sources, i.e., 6.47 x 10 counts with gamma ray energies of 40.1 keV, 121.8 keV, and 344.3 keV, were used. 3 Bq 152 Eu source and 5.86×10 3 Bq 241 Am and 1.31×10 4 Bq 137 A mixed source of Cs, 1000 and 10000Cs was employed. Both sources were 40 mm diameter disks that fit into the filter chamber. Four measurements were made with each source placed on either the aerosol filter or the iodine filter, each for 5 min. The in situ efficiency could be assessed by comparing the net count rate over the period with the known activity of each radionuclide and the relative intensity of the gamma rays. This is shown in Figure 13a as a function of gamma energy for the aerosol filter detector and the iodine filter detector. In this test, the filter was at a height of 56 mm from the top of the CZT spectrometer.

[0108] Using the measured detector efficiencies as described herein, the expected performance of the proposed air sampling system was modeled for a hypothetical mix of radionuclides in an air sample. Detector count rates over time and cartridge replacement frequency (e.g., for a given length of cartridge life) were specifically subject to this evaluation.

[0109] A sampling time based algorithm is used to determine when to replace the cartridge. Maximum allowable count rate

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[0110] Time-varying atmospheric radioactive materials released from nuclear power plant accidents 131 I, 137 Cs, and 103 A hypothetical case involving a mixture of Ru and Cr was simulated. The simulated count rates of the detector facing the aerosol filter are shown in Figure 13b, and the real and reconstructed air concentrations of each radioisotope are shown in Figure 14. To get closer to reality, the noisy count rates were calculated using the expected

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[0111] Based on our analysis of the model including FIG. 13b, it was determined that during large spikes it may be desirable to replace the filter cartridge 120 quite frequently. In both spikes, the sampling period was only about 30-40 minutes. As shown in FIG. 14, the reconstructions of the airborne concentrations generally agreed well with the actual concentrations simulated. They are given in 10 minute increments in this figure, which allows a relatively higher time resolution for data reporting than would normally be possible for stationary filters that are manually collected and analyzed in an external laboratory. In this test 137 The data for Cs is 131 I and 103 The count rate signal was noisier than the Ru data, likely due to the smaller count rate and lower outdoor concentrations. There were also some periods of overprediction after a large decrease in air concentrations, which may be the result of noise in the count rate signal masking a plateau of decreasing amounts of new activity accumulating on the filter. This may have been caused by higher activity on the filter from earlier on, when air concentrations were higher, and this overprediction often lasted until the filter 120 was replaced. While these differences were relatively small and did not appear to significantly change the performance of the system 100, it clearly illustrates the need to have a good set of metrics for filter replacement.

[0112] Several additional tests of the system 100 were performed to determine the aerosol retention efficiency and pressure drop across the selected filter cartridge 120 design. This testing included testing the pressure drop across paper (aerosol) and activated carbon (iodine) filters at multiple flow rates, testing aerosol density measurements across each filter at multiple flow rates, performing seal tests to determine whether the cartridge or associated connections would function as intended, and testing to failure to determine the pressure and flow limits of the filters used in this first example. This testing was performed in a suitable laboratory at Chalk River Laboratories operated by the Canadian Nuclear Laboratories in Ontario, Canada.

[0113] In some of the tests, a Whatman® aerosol filter was installed as the first filter 140 at the inlet 132 and an activated charcoal iodine filter was installed as the second filter 144 at the cartridge outlet 134. To monitor the radioactivity captured by each filter unit, a gamma spectrometer 174 was placed in the cartridge 120 directly below the filter chambers 138 and 142, as shown diagrammatically in FIG.

[0114] 15 and 16 are diagrams of the test apparatus used to perform the tests described herein. The test apparatus includes an aluminum extrusion frame supporting a tubing assembly, various instruments, and an air input. A compressed air line 150 is split, one side leading to an aerosol generator 220 and the other to the main air inlet of the tubing assembly. The aerosol generator 220 delivers into the tubing assembly to which a pressure transducer 222 is connected. The flow from the tubing assembly is then directed through a glass tube with a seal 154 into the test cartridge 120 where a filter captures the aerosol. The air is then discharged through a second glass tube 152 where sampling for the optical particle size analyzer 224 is performed. Aerosol sampling for the optical particle size analyzer 224 was performed at the output of the first glass tube to obtain a baseline concentration. Various aspects of the test apparatus are listed below.

[0115] In this configuration, the aerosol generator 220 receives approximately 200 kPa of compressed air and uses it to generate a water aerosol at a rate of approximately 3 mL / min. The liquid in the aerosol generator 220 is a 5 wt% solution of NaCl in water. The water in the generated aerosol evaporates after mixing with the main air flow, leaving behind a residual NaCl aerosol. Varying the pressure and flow rate of the air to the main input allows for testing of the filter efficiency under a variety of conditions. The tubing assembly is a series of straight sections and "tees" that allow for the connection of various inputs and sensors, as seen in Figures 15 and 16.

[0116] Table 1 shows a list of the instruments and gauges installed in the test equipment. [Table 1]

[0117] Data recorded during testing included aerosol particle size distribution, intake volumetric flow rate, and differential pressure across the cartridge 120, upstream and downstream of the cartridge without a filter and downstream of the cartridge 120 with various filters.

[0118] Tests were conducted using two different aerosol filters, Whatman® charcoal-filled paper, Grade 72, and Whatman® glass microfiber filter, Grade GF / A, as shown in FIG. 17. The experimental design conditions are shown in Table 2. These tests included maintaining the input flow rate to the aerosol generator 220 substantially constant (193 kPa and 5 SLPM), where "SLPM" stands for standard liters per minute. The flow rate into the fittings was varied as much as possible from 5 SLPM to 55 SLPM. [Table 2]

[0119] The procedure for these experiments was to assemble the cartridge 120 with the filter configuration for a given test. The cartridge 120 was inserted into the test fixture, ensuring that the test preparation steps were completed with the PVC air being charged at the desired rate and the system at a sufficiently stable steady state. The flow rate through the PVC air line was then set to the first value in Table 2. After allowing time for the pressure to reach a steady state, the OPS was run for a standard 1 minute collection time and the pressure seen by the transducer was recorded. The air flow rate was then increased by 5 SLPM and these test steps were repeated until either the maximum flow rate listed in Table 2 was reached or the filter broke.

[0120] No significant leakage was detected during any of the tests. This was confirmed by applying a soapy solution to the interface between the glass ball joint and the cartridge, and further to the cartridge-to-cartridge joints. No air bubbles were observed throughout the duration of each test run. These observations, combined with the pressure readings, qualitatively indicate that the seal leakage remains sufficiently low and that the cartridge 120 and cartridge dock 114 design is performing as intended.

[0121] Raw data from the pressure drop test measurements are shown in Tables 3-6. Plots of pressure drop across the filter versus flow rate for the paper filter only, the activated carbon filter only, and both filters installed are shown in Figures 18-20 along with a second order polynomial fit to the data. The paper filters tested began to break at a pressure differential of approximately 10 kPa, indicating an upper pressure limit for use in an automation system. An example of a broken paper filter is shown in Figure 17(b), which showed a tendency to rupture. The activated carbon filter tended to slide off its frame rather than tear. Therefore, it is recommended that the final radionuclide monitoring system 100 be operated with both the paper and activated carbon filters installed, preferably at a total pressure differential of less than about 10 kPa, which may correspond to a flow rate of approximately 25 SLPM (see Table 6). [Table 3] [Table 4] [Table 5] [Table 6] [Table 7]

[0122] The raw data from the filter efficiency test measurements are shown in Tables 3 to 6. The filter efficiency can be determined from the ratio of the aerosol concentration at the outlet of the cartridge with and without the filter installed according to Equation 8.

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[0123] The aerosol generator 220 produced NaCl aerosol with a mass median diameter of about 3.3 μm and a geometric standard deviation of 1.3. The measured particle size distribution histograms are shown in FIG. 21, which compare the results without a filter with the results when either the paper filter or the activated carbon filter is in place in the cartridge, but the other type of filter is not present. There is a large downward shift in the particle size distribution, which means that the filter is more efficient for particles >0.7 μm. As shown in Table 7, the overall efficiency of the paper filter was about 99.996%, while the overall efficiency of the activated carbon filter was 99.98%. When combined, the overall filtration efficiency when both filters were installed was about 99.999%. When implemented in the final radionuclide monitoring system, this means that nearly all of the aerosol is assumed to be effectively captured by the paper filter, and there is limited bypass of the aerosol to the activated carbon filter.

[0124] The foregoing is intended to be illustrative and non-limiting of the present invention, and those skilled in the art will appreciate that other variations and modifications can be made without departing from the scope of the present invention, which is defined in the claims appended hereto.

Claims

1. A transportable system for measuring radionuclides in air from a target environment, said system being deployable within said target environment and a) a main gas flow path extending between a system gas inlet configured to draw in a gas sample and a system gas outlet downstream of said system gas inlet; and b) a cartridge dock disposed within said main gas flow path and having a sample supply port in fluid communication downstream of said system gas inlet and an exhaust port in fluid communication upstream of said system gas outlet; and c) at least a first filter cartridge connectable to said cartridge dock, i. a cartridge gas inlet sealably connectable to said sample supply port; ii. a cartridge gas outlet sealably connectable to said exhaust port; and iii. a cartridge flow path extending between said cartridge gas inlet and said cartridge gas outlet, said cartridge flow path effecting fluid communication between said sample supply port and said exhaust port and completing said main gas flow path when said first filter cartridge is connected to said cartridge dock; iv. a first filter chamber disposed downstream of said cartridge gas inlet within said cartridge flow path and housing a first filter; v. a second filter chamber disposed between said first filter chamber and said cartridge gas outlet within said cartridge flow path and housing a second filter, said at least first filter cartridge; and d) a gamma ray detector device configured to be disposed adjacent to said first filter cartridge when said first filter cartridge is connected to said cartridge dock and to detect radiation emitted from said first filter and radiation emitted from said second filter and to generate a sensor output signal based on the detected radiation; and e) a system control device configured to receive said sensor output signal and generate a corresponding user output, a transportable system.

2. The system according to claim 1, wherein the first filter cartridge is removable from the cartridge dock, and the main gas flow path is blocked by removing the first filter cartridge from the cartridge dock.

3. The system according to claim 1, wherein the first filter is of a first filter type and the second filter is of a different second filter type.

4. The system according to claim 1, wherein the first filter comprises an aerosol filter configured to capture particles in the gas sample, and the second filter comprises an iodine filter.

5. The system according to claim 1, wherein the filter cartridge is connectable to the cartridge dock by translating the first filter cartridge in a direction parallel to the insertion direction.

6. The system according to claim 5, wherein when the first filter cartridge is connected to the cartridge dock, the cartridge gas inlet is aligned with the exhaust port, and a fluid seal is formed between the first cartridge and the cartridge dock.

7. The system according to claim 6, wherein the first filter chamber is sealed when the first cartridge is connected to the cartridge dock and is opened by removing the first filter cartridge from the cartridge dock.

8. The system according to claim 7, wherein the first filter is exposed when the first filter cartridge is removed from the cartridge dock.

9. The system according to claim 8, wherein the first filter is removable from the first filter chamber in the insertion direction when the first filter cartridge is removed from the cartridge dock.

10. The system according to claim 9, wherein the second filter chamber is sealed when the first cartridge is connected to the cartridge dock and is opened by removing the first filter cartridge from the cartridge dock.

11. The system according to claim 10, wherein the second filter is exposed when the first filter cartridge is removed from the cartridge dock. Claim 12 The system according to claim 11, wherein the second filter is removable from the second filter chamber in the insertion direction when the first filter cartridge is removed from the cartridge dock. Claim 13 The system according to claim 1, further comprising a cartridge handling device that is controllable by the system control device and is configured to remove the first filter cartridge from the cartridge dock at the end of a first cartridge usage period. Claim 14 The system further comprises a second filter cartridge connectable to the cartridge dock, the second filter cartridge comprising: i. a cartridge gas inlet sealably connectable to the sample supply port; ii. a cartridge gas outlet sealably connectable to the exhaust port; iii. a cartridge flow path extending between the cartridge gas inlet and the cartridge gas outlet, wherein fluid communication between the sample supply port and the exhaust port is achieved by connecting the first filter cartridge to the cartridge dock, and the main gas flow path is completed, the cartridge flow path; iv. a first filter chamber disposed downstream of the cartridge gas inlet in the cartridge flow path and containing a first filter; v. a second filter chamber disposed between the first filter chamber and the cartridge gas outlet in the cartridge flow path and containing a second filter, The system according to claim 13, wherein the cartridge handling device is controllable by the system control device to connect the second filter cartridge to the cartridge dock after the first filter cartridge is removed from the cartridge dock. Claim 15 The system according to claim 14, further comprising at least one new cartridge bank configured to store unused filter cartridges and containing at least said second filter cartridge, wherein said cartridge handling device is configured to remove said second filter cartridge after said first filter cartridge has been removed from said cartridge dock and to move said second filter cartridge into alignment with said cartridge dock.

16. The system according to claim 15, further comprising at least one used cartridge bank configured to receive and store used filter cartridges, wherein said cartridge handling device is configured to remove said first filter cartridge from said cartridge dock and to store said first filter cartridge within said used cartridge bank.

17. The system according to claim 13, wherein said cartridge handling device comprises an end effector configured to selectively grip a first filter cartridge and movable in at least two degrees of freedom.

18. The system according to claim 17, wherein said cartridge handling device comprises a carriage movable along a carriage rail and an extension unit mounted to said carriage and configured to support said end effector and move it along an extension axis.

19. The system according to claim 18, wherein said carriage rail is substantially linear.

20. The system according to claim 19, wherein said extension axis is substantially linear and substantially orthogonal to said carriage rail.

21. Said gamma ray detector device comprises a sensor portion, said sensor portion a) a measurement position where said sensor portion is adjacent to said first filter cartridge and removal of said first filter cartridge from said cartridge dock is blocked by said sensor portion, b) The system according to any one of claims 13 to 20, wherein the sensor part is spaced apart from the first filter cartridge and is movable between an exchange position where the first filter cartridge can be removed from the cartridge dock.

22. The system according to claim 21, wherein the gamma ray detector device further comprises a detector actuator communicably coupled to the control device and supporting the sensor part, and the detector actuator is configured to selectively move the sensor part between the measurement position and the exchange position.

23. The system according to claim 22, comprising a linear actuator, wherein the detector actuator is configured to linearly translate the sensor part along a detector axis between the measurement position and the exchange position.

24. The system according to claim 22, wherein the detector actuator is operable independently of the cartridge handling device.

25. The system according to claim 1, wherein the gamma ray detector device includes at least a first detector aligned with the first filter and a second detector spaced apart from the first detector and aligned with the second filter, the first detector being configured to generate a first detection signal based on gamma radiation in the first filter, and the second detector being configured to generate a second detection signal based on gamma radiation in the second filter.

26. The system according to claim 25, comprising a gamma ray spectrometer, preferably a CZT gamma ray spectrometer, wherein at least one of the first detector and the second detector is at least partially laterally surrounded by a radiation shield to limit exposure to background radiation not emitted from the filter cartridge.

27. The system according to claim 1, wherein the sample supply port comprises a sample dock coupler having a curved supply sealing surface, and the cartridge gas inlet comprises a complementary curved inlet sealing surface configured to seal against the supply sealing surface.

28. The system according to claim 27, wherein the supply sealing surface is convex and the curved inlet sealing surface is concave.

29. The system of claim 27, wherein when the first cartridge is connected to the cartridge dock, the supply seal surface is pressed against the inlet seal surface to seal the first filter chamber, and the first cartridge is movable in parallel away from the cartridge dock such that the supply seal surface and the inlet seal surface are separated without releasing a fastener.

30. The system of claim 1, wherein the exhaust port comprises an exhaust dock coupler having a curved exhaust seal surface, and the cartridge gas outlet comprises a complementary curved outlet seal surface configured to seal against the exhaust seal surface.

31. The system of claim 30, wherein the seal surface is convex and the curved outlet seal surface is concave.

32. The system of claim 30, wherein when the first cartridge is connected to the cartridge dock, the exhaust seal surface is pressed against the outlet seal surface to seal the second filter chamber, and the first cartridge is movable in parallel away from the cartridge dock such that the exhaust seal surface and the outlet seal surface are separated without releasing a fastener.

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