WO2020118340A1

WO2020118340A1 - Device and method for the non-destructive assay of a radioactive waste package

Info

Publication number: WO2020118340A1
Application number: PCT/AT2019/060434
Authority: WO
Inventors: Dusan LEXA
Original assignee: Lexa Dusan
Priority date: 2018-12-12
Filing date: 2019-12-12
Publication date: 2020-06-18
Also published as: AT521936A1; AT521936B1

Abstract

Device (1) for the non-destructive assay of a radioactive waste package (2) comprising a spectrometer (3), wherein the device (1) comprises an at least four-axis articulated robotic arm (4) and the spectrometer (3) is fixed to the robotic arm (4). Furthermore, method for the non-destructive assay of a radioactive waste package (2), comprising the steps: providing a radioactive waste package (2); moving a spectrometer (3) fixed to an at least four-axis, preferably six-axis, articulated robotic arm (4) into a measurement position; and acquiring measurement data with the spectrometer (3).

Description

Device and method for the non-destructive assay of a radioactive waste package

The disclosure concerns a device for the non-destructive assay of a radioactive waste package comprising a spectrometer. Fur thermore, the disclosure relates to a method for the non

destructive assay of a radioactive waste package.

Non-destructive assay (NDA) is routinely performed by radioac tive waste producers, intermediate and final storage facilities, and regulatory authorities. As such, there are some commercial NDA systems available comprising a spectrometer, which is fixed at some point or movable along a rail. However, they are typi cally limited to a single waste package size and assay type, e.g. segmented gamma scanners for the characterization of 200 1 drums. Any changes in waste package size and assay type require either a new NDA system or a re-engineering of an existing one. The cost of the currently available commercial NDA systems tends to be commensurate with their single-purpose machine character istics, which also results in long delivery times due to the ne cessity of conducting the necessary individual modification for the contemplated type of waste packages to be assayed.

JP S57206875 A shows a system for the remote and automatic meas urement of the radioactivity distribution of a radioactive waste container comprising a rotary table and a gamma spectrometer.

US 2008/0084960 A1 discloses a method for automating and extend ing the density range for gamma ray attenuation correction algo rithms for supposedly all classes of non-destructive assay sys tems. The method comprises imaging an object with a low- intensity and with a high-intensity beam and by collecting pas sive emissions and obtaining a quantitative radiation map of the obj ect .

WO 2017/140870 A1 shows a method for conditioning radioactive waste using a radioactive waste conditioning robot, the robot being able to move and comprising at least one vibrating needle.

It is an objective of the present disclosure to alleviate or mitigate some or all of the above problems. In particular it is an objective of the present disclosure to provide for a device for the non-destructive assay of a radioactive waste package that is compatible with any waste package type and size (up to a reasonable maximum size) , has the ability to perform any assay type, following existing or novel measurement protocols, is able to perform additional automated operations not possible with current systems, has a lower production cost and shorter produc tion time or less or no modification time, has a better adapta bility to changing operational requirements, has a higher relia bility and/or has a lower maintenance need.

This is achieved by a device for the non-destructive assay of a radioactive waste as described in the outset, wherein the device comprises an at least four-axis articulated robot arm and the spectrometer is fixed to the robotic arm. Furthermore, this is achieved by a method for the non-destructive assay of a radioac tive waste package, the method comprising the steps:

- providing a radioactive waste package,

- moving a spectrometer fixed to an at least four-axis, prefera bly six-axis, articulated robotic arm into a measurement posi tion, and

- acquiring measurement data with the spectrometer.

The use of a robotic arm makes it possible to freely move the spectrometer to positions within a reasonable range of motion of the robotic arm and/or to orient the spectrometer at different angles, thus solving the problems stated above. For example, it allows not only measurement from the sides, but also from above. This can be necessary, for instance, if the waste package con tainer is made out of metal and is open at its upper side. Fur thermore, this allows, e.g., measurement from all four sides and from the top, which might be necessary for non-cylindrical waste packages, e.g. FIBCs . The device and the method enable the meas urement of waste packages including for example drums, e.g. 100- 1, 200-1 and 400-1 drums, crates, e.g. a 1.2 m times 0.8 m times 0.8 m crate, 1 m³ FIBCs, and a wide range of others. In general, it allows the measurement from various positions, i.e. also dis tances, and angles. Thus, for example, reconfiguration of the device for a new task can be a matter of software changes only. Four-axis (or, x-axis, respectively) articulated refers to the robot arm having at least four (or, x, respectively) joints with each joint allowing rotary movement about an axis, wherein all axes are different. Furthermore, there can be provided for one or more joints allowing translational (linear) displacement. The spectrometer is usually provided as end effector of the robotic arm, i.e. it is provided at the end of the robotic arm or at least at a position at the robotic arm which is further away along the robotic arm from the point of origin of the robotic arm than the four rotary joints. Three rotary joints combined allow for example either free positioning or free orienting of the end effector of a robotic arm. However, the spectrometers measurement might be rotation invariant in respect to an axis in the measurement direction of the spectrometer, such that two ax is of rotation can be enough for orienting the spectrometer. Further, there might not be the need for completely free move ment of the spectrometer, such that two axis of rotation can be enough for positioning the spectrometer. Preferably, the robotic arm is mounted at a pedestal, wherein the mass of the pedestal is at least equal to, preferably 2 times, higher than the mass of the robotic arm. Thus the maximum horizontal reach of the ro botic arm can be increased. Preferably, the maximum wrist pay- load of the robotic arm used is at least 1.5 times, preferably 3 times, higher than the mass of the spectrometer. This corre sponds to a larger working area and more precise steering. Fur thermore, it enables the optional use of additional spectrometer shielding and/or of a second spectrometer and it reduces wear and maintenance.

It is preferable, if the robotic arm is a (in particular: at least) six-axis articulated robotic arm. At least six degrees of freedom are required to enable the end effector, i.e. the spec trometer, to reach an arbitrary pose (an arbitrary position and orientation in the workspace of the robotic arm) in three dimen sional space. Additional degrees of freedom allow to change the configuration of some link on the arm (e.g., an "elbow" of the robotic arm to move up/down), while keeping the end effector in the same pose. Thus, the robotic arm can be compatible with an even larger amount of different radioactive waste packages and protocols .

In an advantageous embodiment, the spectrometer is a gamma spec trometer, in particular a high-purity germanium (HPGe) gamma spectrometer. This allows better characterization of the radio active waste package.

In a preferred embodiment of the device, it comprises a waste package platform for holding the waste package. For starting the assay of the radioactive waste package, the waste package is placed onto the waste package platform or the waste package platform holds the waste package. During the assay, the waste package platform is located such that the spectrometer's meas urement position is within the reachable working area of the ro botic arm.

It is advantageous if the waste package platform is movable, in particular by an actuator. Thus, the waste package placed onto the waste package platform can for example be moved into and out from a working area of the robotic arm. The waste package plat form can in particular be movable along a rail. The waste pack age platform can be movable in a linear manner, or the movement can have two or three degrees of freedom.

Preferably, waste package platform comprises means for rotating the waste package. This adds to the system another degree of freedom and can further reduce the amount of movement necessary for the robotic arm. For example, a waste package platform's up per plane, onto which the waste package can be placed, can be rotatable .

It is preferably if the device comprises a means of optical identification, in particular a bar code reader, wherein the means of optical identification is fixed to the robotic arm.

This allows further automation of the device, since it can iden tify the type of waste package on its own. After the means of optical identification has been brought to an appropriate iden tification position by the robotic arm (e.g. adjacent to and oriented towards a side of the waste package) , the waste package can for example be rotated by the waste package platform, such that an identification marking on the waste package can be read by the means of optical identification at some point of orienta tion of the waste package. Also, machine vision can be used if waste package identification markings are not affixed in a re producible position and/or orientation.

In a preferred embodiment, the device comprises a weighing scale for weighing the radioactive waste package, wherein preferably the waste package platform comprises the weighing scale. This can improve the characterisation of the waste package and can enable further automation.

It is advantageous if the device comprises a control unit, in particular a C5G control unit with a TP5 teach pendant, for con trolling the robotic arm and preferably for controlling and/or receiving data from the spectrometer and/or for controlling the waste package platform. This allows the control of the other components of the device and allows further automation, as well as user input regarding e.g. parameters for the measurement pro cess. Alternatively, the spectrometer can be controlled and data can be received from the spectrometer by a separate PC or a software running on a separate PC, respectively.

It is preferable, if the robotic arm comprises a mounting means for exchangeably mounting at least one collimator (such that it collimates the radiation reaching the spectrometer) and if the device comprises a tray for storing unused collimators not mounted on the robotic arm. This allows further automation, since the robotic arm can thus change the collimator by itself, in case this is required by the measurement. The tray for stor ing an unused collimator, preferably for storing at least two collimators, should be located within the reachable workable ar ea of the robotic arm. Preferably, the device comprises a 90°- opening collimator and a 30°-opening collimator. Preferably, the device comprises one collimator mounted at the robotic arm, in particular the 90°- or 30°-opening collimator. The angle refers to an opening angle, i.e. visual angle, of the collimator. Pref erably, the collimator limits/constricts the view field of the spectrometer such that in a measurement position of the spec trometer it contains only the waste package, or more generally that it contains the waste package and as little non-relevant objects as possible. The collimator acts to minimize the back ground .

In a preferred embodiment, the spectrometer is a liquid nitrogen cooled spectrometer. Preferably, the robotic arm comprises a first liquid nitrogen container (e.g. a cryostat) and the device comprises a second liquid nitrogen container (e.g. a Dewar con tainer) , wherein the first and the second liquid nitrogen con tainers can be connected via a docking station. Since the first liquid nitrogen container is mounted to the robotic arm, it can be directly connected to the spectrometer, and when the first liquid nitrogen container is empty or almost empty, the robotic arm can couple the first and the second liquid nitrogen contain ers via the docking station with one another and refill the first liquid nitrogen container. The docking station is prefera bly permanently connected with the second liquid nitrogen con tainer (e.g. via an insulated pipe) . The docking station should be located in the reachable working area of the robotic arm and/or outside a space that is during usual operation used by the spectrometer and waste package. Advantageously, the docking station and the first liquid nitrogen container comprise cou plings for coupling with each other. Alternatively, the spec trometer can be an electrically cooled spectrometer.

It is preferable, if the device further comprises a reference radioactive source. This reference radioactive source can be used to calibrate and, if necessary, adjust the spectrometer. Advantageously, the reference radioactive source is placed with in the (reachable) working area of the robotic arm or close to it, such that the robotic arm can bring the spectrometer into a suitable position for a measurement of and calibration with the reference radioactive source. This can be performed e.g. daily before the usual measurements with the spectrometer are started. Preferably, the reference radioactive source comprises one or more radionuclides with well-defined gamma emissions peaks, in particular covering the entire (relevant) energy range, e.g. Na- 22 and Eu-155 with an activity of 37 kBq.

In an advantageous embodiment, the device comprises a, in par- ticular gamma, radiation source, preferably comprising a radio nuclide composition and an activity suitable for penetrating the waste package and more preferably for obtaining a spectrum with in a reasonable time. The radiation source could, e.g., comprise Eu-152 with an activity of 3.7 GBq. The radiation source has an activity of preferably between 0.01 and 1000 GBq, more prefera bly between 0.1 and 100 GBq, even more preferably between 1 and 10 GBq. Preferably, the radiation emitted by the radiation source covers the entire energy range and does not interfere with radionuclides expected to be present in the waste package. This radiation source can be used for radiography, in particular tomography, of object, wherein the spectrometer is used as de tector. The density and in particular density distribution of the object to be examined can thus be determined. It is advanta geous if the device comprises a second robotic arm, preferably an at least four-axis articulated robotic arm, more preferably a six-axis articulated robotic arm, wherein the radiation source is mounted to said second robotic arm. Thus, an object to be ex amined can be radiographed in various directions.

In another embodiment of the device, the device comprises one or more further (gamma) spectrometer ( s ) , in particular a second spectrometer and preferably a third sepctrometer . Preferably, also the further spectrometer ( s ) are mounted to the robotic arm. They can be used, together with the aforementioned spectrometer, for clearance ( free-release ) measurement of a waste package, i.e. for determining if the radioactivity of the waste package is below a predetermined limit, in particular below the applica ble regulatory limits and can, thus, be de iure treated as non radioactive material.

Referring to the inventive method, moving the spectrometer com prises translationally moving the spectrometer in along one, preferably two, even more preferably three, degrees of freedom in 3d-space and/or changing the orientation of the spectrometer with regard to one, preferably two, even more preferably three, degrees of freedom by rotating the spectrometer.

It is preferable if the method further comprises one or more of the following steps: placing the waste package on a waste package platform, in particular while the robotic arm and/or the waste package plat form is/are in a predefined home position,

selecting one of a set of predefined waste package types and/or measurement protocols in a user application, and/or

adjusting on or more additional parameters, in particular the data acquisition time and/or the maximum detector dead time, in particular if the default values of the respective additional parameter is not suitable, in the user application,

It is advantageous if the method further comprises one or more of the following steps:

moving and/or turning the platform and/or moving the robotic arm to an optical identification position, in particular a bar code reading position,

activating a means of optical identification, in particular a bar code reader or a camera,

reading an optical identification feature with the means of optical identification, in particular a bar code with the bar code reader, and/or

determining a weight of the waste package.

Reading the bar code and weighing the waste package allows char acterization and identification of the waste package. Since the bar code reader is attached to the robotic arm, this action can be performed completely automatic. Turning the platform refers to rotating the waste package.

In a preferable variant, the method further comprises one or more of the following steps:

moving the waste package platform and the robotic arm pref erably synchronously, in particular into a measurement position, and

pausing the robotic arm and the waste package platform in a measurement position while the spectrometer acquires measurement data .

Alternatively, only the robotic arm can be moved. Moving the waste package platform can also comprises rotating the waste package container. Rotation (during the measurement) can be em ployed to minimize the effects of matrix density and/or activity inhomogeneity. However, rotation of non-cylindrical waste pack- ages during measurement might not be useful in this case since the measurement efficiency changes with the relative position of the waste package and the spectrometer. Therefore, the measure ment can be conducting in several efficiency-equivalent geome tries. The individual spectra acquired can be summed and the sum spectrum evaluated. It is also possible, to evaluate individual spectra separately and use the differences in activities so ob tained as a measure of matrix density and/or activity inhomoge neity. Selecting efficiency-equivalent geometries is convenient, but not necessary. Also other geometries could be selected, e.g. measurement from the top. In this case, the corresponding spec tra can for example be evaluted using appropriate efficiencies.

Preferably, the method further comprises one or more of the fol lowing steps:

displaying a measurement progress by the user application, returning the waste package platform and/or the robotic arm to the home position,

unloading the waste package from the waste package platform, and/or

displaying measurement results and/or creating a spectrum and/or reporting files by the user application.

Thus the results of the measurement are easily available.

performing a pre-measurement of the waste package using a first collimator, in particular a 90°-opening collimator, mount ed to the robotic arm,

determining if a predefined detector dead time is exceeded, if the detector dead time is exceeded, unmounting the first collimator into a tray and mounting a second collimator, wherein the second collimator has a narrower opening angle than the first collimator, in particular a 30°-opening collimator,

wherein preferably the first and the second collimator are mounted to or unmounted from, respectively, the robot arm in particular by a movement of the robot arm and preferably by a bayonet mounting mechanism.

Thus, due to the use of a robotic arm carrying the spectrometer and the collimator, there can be provided for an automatic col- limator change. There is no need for an intervention by a per son, making the measurement process much easier and faster.

There can also be provided for three, four or more different collimators .

It is preferable if the robot arm performs an automatic liquid refill for the spectrometer, wherein the spectrometer is a liq uid nitrogen cooled spectrometer. This preferably comprises the following steps:

docking a first liquid nitrogen container comprised by the robotic arm with a second liquid nitrogen container advanta geously via a docking station, preferably at predefined time in tervals, by a movement of the robotic arm, and

flowing liquid nitrogen from the second liquid nitrogen con tainer to the first liquid nitrogen container, and

preferably stopping the flowing of liquid nitrogen as soon as a sensor detects a switch from gaseous to liquid nitrogen.

This makes overall operation of the system much easier and fast er. Concerning stopping the flowing of liquid nitrogen as soon as a sensor detects a switch from gaseous to liquid nitrogen: During filling, i.e. flowing liquid nitrogen from the second liquid nitrogen container to the first liquid nitrogen contain er, at first gaseous nitrogen escapes the (empty or partially empty) first liquid nitrogen container. Only when the first liq uid nitrogen container is filled up, liquid nitrogen escapes the first liquid nitrogen container.

Preferably, the method comprises an automatic calibration and if necessary adjustment of the spectrometer. For this purpose, the robotic arm moves the spectrometer into a position for measuring the radiation of a reference radioactive source. Subsequently, the spectrometer can be calibrated and if necessary adjusted. It is advantageous, if this calibration process is conducted auto matically and/or regularly, e.g. daily before the start of the regular measurements.

In another variant, the radioactive waste package can be any ob ject. The object shall be radiographed, in particular to- mographed. For this purpose, a radiation source is provided for, in particular behind the object in view of the spectrometer, i.e. opposite the spectrometer with the object in between. The radiation source is in particular brought into the position by a second robotic arm. The (first) robotic arm can move the spec trometer for measurement from different directions/angles, while the second robotic arm moves the radiation source into a corre sponding position behind the object.

It is advantageous if the method is used for clearance (free re lease) measurement. In this case, the aforementioned radioactive waste package is typically only slightly radioactive or not ra dioactive. For this purpose, one or more further spectrometers are moved together with the spectrometer and collect data (sim ultaneously) . This leads to higher measurement efficiency and, thus, lower minimum detectable activity (MDA) for a given dura tion of measurement compared to a single spectrometer.

The invention will now be explained in more detail with refer ence to the accompanying exemplary embodiments; the invention is not, however, limited thereto.

Fig. 1 shows an exemplary embodiment of the device for the non destructive assay of a radioactive waste package;

Fig. 2 shows the working areas of the robotic arm of an exempla ry embodiment of the device;

Fig. 3 shows the tray for collimators in an exemplary embodiment of the device;

Fig. 4 illustrates the refill of liquid nitrogen via a docking station;

Fig. 5 and 6 illustrate the measurement of efficiency equivalent geometries .

Fig. 1 shows a preferred embodiment of the device 1 for the non destructive assay of a radioactive waste package 2. The device 1 comprises a gamma spectrometer 3 and a six-axis articulated ro botic arm 4. The gamma spectrometer 3 is mounted at the end of the robotic arm 4, at the position where usually the end effec- tor is mounted. The waste package 2 is placed on a waste package platform 5, which is movable along a rail and which has an upper plate that is rotatable, such that the waste package container 2 placed on top of it rotates with it. Integrated into the waste package platform 5 is a weighing scale. The robotic arm 4 com prises mounting means 6 for exchangeably mounting a collimator 7. Furthermore, the device 1 comprises a tray 8 for storing a second, unused collimator (7') . In this embodiment, the tray 8 has space for storing two collimators, such that the robotic arm 4 can unmount and place one collimator at the tray 8 and subse quently can pick up and mount the other collimator to it (and vice versa) . The spectrometer 3 is liquid nitrogen cooled. The robotic arm 4 comprises a first liquid nitrogen container 9 (see Fig. 4) and the device 1 comprises a second liquid nitrogen con tainer 10. The first and the second liquid nitrogen container 9, 10 can be connected via a docking station 15. The waste package platform 5 comprises means 11 for rotating the waste package 2 and a weighing scale 13. Furthermore, there is provided for a control unit 14 for controlling the robotic arm 4, for control ling and receiving data from the spectrometer 3 and for control ling the waste package platform 5.

Fig. 2 illustrates the working area of an exemplary robotic arm, which is a six-axis articulated robotic arm 4 and in this exem plary embodiment is a Comau NJ-220-2.7 industrial robotic arm.

Fig. 3 shows the tray 8 for storing collimators of Fig. 1 in more detail.

Fig. 4 shows the coupling of the first liquid nitrogen container 9 and with a docking station 15, with a piping leading from the docking station 15 to the second liquid nitrogen container 10 (not visible), in more detail. Fixed to the robotic arm 4 (or the spectrometer 3) is a means of optical identification 12.

Fig. 5 and 6 illustrate the measurement in efficiency-equivalent geometries. In the case of Fig. 5, the waste package 2 is as sumed to be a crate. Four measurements are performed with the detector axis normal to the long side of the crate at 1/2 its height and at 1/4 and 3/4 of its length, respectively. The de- tector end cap to crate side distance is 30 cm with the 90° col limator and 120 cm with the 30° collimator, respectively. The filling grade is assumed to be 100% with lower actual values taken into account in the course of data analysis. In the case of Fig. 6, the waste package 2 is a FIBC. Four measurements are performed with the detector axis normal to the side of the FIBC at the middle. The detector end cap to crate side distance is 40 cm with the 90° collimator and 160 cm with the 30° collimator, respectively. The filling grade is assumed to be 60% with dif fering actual values taken into account in the course of data analysis .

In the following, an exemplary embodiment of the inventive de vice and method are described:

Short summary

The robotic system for non-destructive assay (NDA) of radioac tive waste is based on an industrial 6-axis articulating robot platform, combined with a dedicated waste package platform and a high-resolution HPGe gamma spectrometer. The system enables measurement of waste packages including drums (100-1, 200-1, 400-1), crates (up to 1200 x 800 x 800 mm), 1 m3 FIBCs, and oth ers. Assay type can be freely defined, ranging from currently accepted protocols such as segmented gamma scan (SGS) or inte gral gamma scan (IGS) to new protocols developed for specific non-cylindrical waste packages, e.g., measurement of FIBCs from all four sides and the top. As a result of the robotic hardware flexibility, reconfiguration of the system for a new task is a matter of software changes only. In addition, while primarily geared towards waste characterization, the system can be config ured for free release (clearance) by installing a second detec tor and field-of-view shielding.

Additional features beyond the basic functionality have been im plemented such as an automatic lead collimator change based on measured HPGe detector dead time and an automatic liquid nitro gen refill, performed by the robot via a docking station at pre defined time intervals. (Use of electrically cooled HPGe detec tors is also possible.) INTRODUCTION

NDA is routinely used by radioactive waste producers, intermedi ate and final storage facilities, and regulatory authorities. So much so that commercial NDA systems are now widely available. However, they are typically limited to a single waste package size and assay type, e.g., segmented gamma scanners for charac terization of 200-1 drums. Any changes in waste package size and assay type require either a new NDA system or a re-engineering of an existing one. The cost of the commercial NDA systems tends to be commensurate with their single-purpose machine character istic as does the delivery time. The system mitigates all of the above shortcomings while simultaneously introducing novel fea tures .

SYSTEM DESCRIPTION

Building an NDA system around an industrial robot offers several advantages compared to the single-purpose machine approach. They include

compatibility with any waste package type and size limited only by robot working area;

ability to perform any assay type, following existing or novel measurement protocols;

ability to perform additional automated operations;

lower cost and shorter delivery time compared to single purpose units;

adaptability to changing operational requirements;

high reliability and low maintenance.

The system consists of a robot carrying a gamma spectrometer, a waste package platform, auxiliary systems, and control PC, see Fig.1.

The system enables measurement of waste packages including drums (100-1, 200-1, 400-1), crates (up to 1200 x 800 x 800 mm), 1 m3 FIBCs, and others. Assay type can be freely defined, ranging from currently accepted protocols such as segmented gamma scan (SGS) or integral gamma scan (IGS) to new protocols developed for specific non-cylindrical waste packages, e.g., as is the case with the current unit, measurement of FIBCs on all four sides' axes and crates on the four axes of longer side vertical halves .

The typical measurement sequence starts with placing the waste package on the platform while both the robot and the platform are in their freely definable home positions. In the user appli cation, one of the pre-defined waste package types and measure ment protocols is selected. Additional parameters, such as data acquisition time, max. detector dead time, etc., can be adjusted if default values are not suitable. The measurement can then be started. The platform turns and the robot moves to the bar code reading position and the bar code reader is activated. At the same time, the weight of the waste package is determined. The platform and robot then synchronously move and pause in measure ment positions while the gamma spectrometer acquires data. After completing all measurements, the platform and robot return to the home position and the waste package can be unloaded. The us er application displays both measurement progress and its re sults and creates spectrum and report files. The spectra can be re-analyzed off line and/or the results made available to a su pervisory application.

Robot

The system is based on a Comau SpA industrial 6-axis articulat ing robot model NJ-220-2.7. The key robot technical specifica tions are shown below in TABLE I. Any other suitable 6-axis in dustrial robot could be used.

TABLE I. Comau NJ-220-2.7 Technical Specifications

The maximum wrist payload of 220 kg is significantly higher than the mass of the spectrometer it is carrying. This is intentional because higher payload corresponds to a larger working area (see Fig.2), enables the use of additional detector shielding and/or additional detectors as needed, and minimizes both wear and maintenance. Even if operated at maximum load, the wear and maintenance are expected to be minimal since the robot performs a few relatively leisurely motions during a typical assay com pared to hundreds of high-speed cycles per day in manufacturing operations it was primarily designed for.

The robot features a C5G control unit with a TP5 teach pendant. All robot motions can be performed manually from the teach pen dant which is also used for robot programming.

The robot is mounted on a custom massive steel pedestal which increases its effective maxi mum horizontal reach.

Gamma Spectrometer

The spectrometer is a Canberra Industries, Inc., unit featuring a single GC2020 high-purity germanium (HPGe) detector, 7 1 Big- MAC liquid nitrogen cryostat with a 5 day holding time, and a DSA-LX multi-channel analyzer with digital signal processing.

The detector end cap is placed in a 5 cm thick cylindrical modu lar lead shield. The standard manually exchangeable collimator set (90° or 30° conical opening) has been modified for automatic collimator change, see Auxiliary Systems. Since the current unit is primarily geared towards waste characterization, one HPGe de tector is sufficient. However, for free release (clearance) or to increase material throughput, the system can be re-configured by installing a second HPGe detector and, optionally, field-of- view shielding. Any other suitable spectrometer could be used.

Waste Package Platform

The waste package platform is an optional system component. How ever, it significantly expands the system functionality provid ing waste package weighing and positioning (rotation) . The rota- tion motion is seamlessly integrated into the robot control ar chitecture as a seventh axis. The integrated balance has a maxi mum load of 2500 ± 1 kg.

Auxiliary Systems

Additional features beyond the basic spectrometry functionality have been implemented such as a bar code reader, automatic col limator change, and automatic liquid nitrogen refill.

A Sick AG CLV620-2000 bar code reader is attached to the detec tor shield and is configured to read bar codes from pre

determined positions on the waste packages. If bar code place ment is not reproducible, reading during rotation and/or robot movement can be implemented. Any other suitable bar code reader could be used.

Waste packages containing high activities could cause the HPGe detector incoming count rate to exceed the maximum throughput of the spectrometry chain, leading to increased detector dead time and, thus, inaccurate results. A pre-measurement of the waste package is performed with a 90o opening collimator. If the de tector dead time preset is exceed, the robot will select the narrower 30o collimator and perform a full measurement. The un used collimator is stored in a tray (Fig. 3) which, together with the bayonet mounting mechanism, are designed for mechanical operation without the need for electrical or pneumatic elements. The number and type of additional collimators could be increased if needed.

The system also features an automatic liquid nitrogen refill, performed by the robot via a docking station (Fig. 4) at prede fined time intervals. The detector and docking station feature special cryogenic male and female couplings, respectively. The fill and vent coupling of the detector are connected to the in let and outlet of the HPGe detector Dewar, respectively. The fill coupling of the docking station is connected to a 35 1 sup ply Dewar via a Norhof #900 micro-dosing pump, providing a ~25 day effective holding time. The vent coupling of the docking station exhausts into the atmosphere through a Pt resistance sensor connected to the pump. Flow of liquid nitrogen is inter rupted as soon as the sensor detects the switch from gaseous to liquid nitrogen. Larger supply Dewars could be used to further extend the effective holding time, e.g., ~75 days with a 100 1 supply Dewar. Any other suitable liquid nitrogen dosing system could be used. Use of electrically cooled HPGe detectors, elimi nating liquid nitrogen entirely, is also possible.

Software

The control PC, connected to the C5G control unit by an IEEE 802.3 cable, runs the user application developed specifically for the system. The application communicates with the robot, the waste package platform balance, the bar code reader, and the gamma spectrometer. It also provides a GUI for system setup and operation. For gamma spectrometer data acquisition and analysis, the application integrates the Canberra Industries, Inc., Genie™ 2000 software suite. Genie™ 2000 can also be used independently, e.g., for calibration and data re-analysis. The user application architecture is such that other commercially available gamma spectrometry hardware and software can be integrated.

Safety

Personnel safety is of utmost importance in industrial settings involving heavy automated machinery such as an industrial robot In addition to standard emergency stop buttons on both the con trol unit and the teach pendant, the perimeter of the System working area is protected by a Sick AG C4000 light barrier. Any other suitable safety barrier or safety scanner could be used.

DISCUSSION

A robotic system for non-destructive assay (NDA) of radioactive waste has been designed and manufactured. The development and testing confirmed the expected advantages of a robotic system over single-purpose NDA units.

CONCLUSIONS The system is a universal NDA unit best suited for operators en countering variable waste packages, needing to apply existing as well as specialized measurement protocols. The industrial robot platform is over-dimensioned, ensuring maintenance-free opera tion and the possibility to use additional detectors and shield ing for free release (clearance) operations.

Claims

Claims :

1. Device (1) for the non-destructive assay of a radioactive waste package (2) comprising a spectrometer (3), characterized in that the device (1) comprises an at least four-axis articu lated robotic arm (4) and the spectrometer (3) is fixed to the robotic arm ( 4 ) .

2. Device (1) according to claim 1, characterized in that the robotic arm (4) is a six-axis articulated robotic arm (4) .

3. Device (1) according to any of the previous claims, charac terized in that the spectrometer (3) is a gamma spectrometer

(3), in particular a HPGe gamma spectrometer.

4. Device (1) according to any of the previous claims, charac terized by a waste package platform (5) for holding the waste package ( 2 ) .

5. Device (1) according to claim 4, characterized in that the waste package platform (5) is movable.

6. Device (1) according to claim 4 or 5, characterized in that the waste package platform (5) comprises means (11) for rotating the waste package (2) .

7. Device (1) according to any of the previous claims, charac terized by a means (12) of optical identification, in particular a bar code reader, wherein the means of optical identification is fixed to the robotic arm (4) .

8. Device (1) according to any of the previous claims, charac terized by a weighing scale (13), wherein preferably the waste package platform (5) comprises the weighing scale.

9. Device (1) according to any of the previous claims, charac terized by a control unit (14) for controlling the robotic arm

(4) and/or for controlling the waste package platform (5) .

10. Device (1) according to any of the previous claims, charac- terized in that the robotic arm (4) comprises a mounting means (6) for exchangeably mounting at least one collimator (7) and that the device (1) comprises a tray (8) for storing unused col limators (7') not mounted on the robotic arm (4) .

11. Device (1) according to any of the previous claims, charac terized in that the spectrometer (3) is a liquid nitrogen cooled spectrometer, that the robotic arm (4) comprises a first liquid nitrogen container (9) and the device (1) comprises a second liquid nitrogen container (10), wherein the first and the second liquid nitrogen container (9, 10) are connectable via a docking station ( 15) .

12. Device (1) according to any of the previous claims, charac terized by a further spectrometer ( 3 '), wherein also the further spectrometer (3') is fixed to the robotic arm (4) .

13. Method for the non-destructive assay of a radioactive waste package (2), comprising the steps:

providing a radioactive waste package (2),

moving a spectrometer (3) fixed to an at least four-axis, preferably six-axis, articulated robotic arm (4) into a measure ment position, and

acquiring measurement data with the spectrometer (3) .

14. Method according to claim 13, comprising the steps:

placing the waste package (2) on a waste package platform

(5), in particular while the robotic arm (4) and/or the waste package platform (5) is/are in a predefined home position,

adjusting one or more additional parameters, in particular the data acquisition time and/or the maximum spectrometer dead time, in particular if the default values of the respective ad ditional parameter is not suitable, in the user application,

15. Method according to claim 13 or 14, comprising the steps: turning the platform and/or moving the robotic arm (4) to an optical identification position, in particular a bar code read ing position, activating a means (12) of optical identification, in par ticular a bar code reader,

reading an optical identification feature with the means (12) of optical identification, in particular a bar code with the bar code reader, and/or

determining a weight of the waste package (2) .

16. Method according to any of claims 13 to 15, comprising the steps :

moving the waste package platform (5) and the robotic arm

(4) preferably synchronously, in particular into a measurement position, and

pausing the robotic arm (4) and the waste package platform

(5) in a measurement position while the spectrometer (3) ac quires measurement data.

17. Method according to any of claims 13 to 16, comprising the steps :

displaying a measurement progress by the user application, returning the waste package platform (5) and/or the robotic arm (4) to the home position,

unloading the waste package (2) from the waste package plat form ( 5 ) , and/or

18. Method according to any of claims 13 to 17, comprising the steps :

performing a pre-measurement of the waste package (2) using a first collimator (7), in particular a 90°-opening collimator, mounted to the robotic arm,

determining if a predefined spectrometer dead time is ex ceeded,

if the spectrometer dead time is exceeded, unmounting the first collimator (7) into a tray (8) and mounting a second col limator (7 ' ) , wherein the second collimator (7') has a narrower opening angle than the first collimator, in particular a 30°- opening collimator,

wherein preferably the first (7) and the second collimator (7') are mounted to or unmounted from, respectively, the robotic arm (4) in particular by a movement of the robotic arm (4) and preferably by a bayonet mounting mechanism.

19. Method according to any of claims 13 to 18, characterized in that the robotic arm (4) performs an automatic liquid refill for the spectrometer (3), wherein the spectrometer (3) is a liquid nitrogen cooled spectrometer, preferably comprising the steps: docking a first liquid nitrogen container (9) comprised by the robotic arm (4) with a second liquid nitrogen container (10), preferably at predefined time intervals, by a movement of the robotic arm (5), and

flowing liquid nitrogen from the second liquid nitrogen con tainer (10) to the first liquid nitrogen container (9), and