Monitoring

Abstract

The method includes providing the volume of waste in a monitoring space; providing a support, the support being provided with a plurality of detectors for radioactive material; monitoring the volume of waste for radioactive material, in one or more parts, to give a monitoring result; and correcting the monitoring result for geometry and/or attenuation to give a corrected result using a correction factor. The correction factor is obtained by a method that includes providing a simulation of an equivalent volume of waste free of radioactive material in an equivalent monitoring space, with equivalent detectors; providing a known activity radioactive source at one or more positions in the volume of waste; determining the detector response to the source in a position, a comparison of the response and known activity contributing to a correction function for that equal volume, one or more such correction functions providing the correction factor.

1 . A method of monitoring a volume of waste for radioactive material, the method comprising: 
 providing the volume of waste in a monitoring space;    providing a support, the support being provided with a plurality of detectors for radioactive material;    monitoring the volume of waste for radioactive material, in one or more parts, to give a monitoring result; and    correcting the monitoring result for geometry and/or attenuation to give a corrected result using a correction factor;    wherein the correction factor is obtained by a method comprising: 
 providing a simulation of an equivalent volume of waste free of radioactive material in an equivalent monitoring space, with equivalent detectors;  
 providing a known activity radioactive source at one or more positions in the volume of waste; and  
 determining the detector response to the source in a position, a comparison of the response and known activity contributing to a correction function for that equal volume, one or more such correction functions providing the correction factor.  
   
   
   
       2 . A method according to  claim 1  in which the simulation is a computer simulation.  
   
   
       3 . A method according to  claim 1  in which the simulation is a physical simulation.  
   
   
       4 . A method according to  claim 1  in wherein the correction factor is obtained by a method comprising: 
 providing an equivalent volume of waste free of radioactive material in an equivalent monitoring space, with an equivalent support provided with equivalent detectors;    dividing in one or more parts, the volume of waste into a plurality of equal volumes;    providing a known activity radioactive source at one or more positions in one or more of the equal volumes; and    monitoring the detector response to the source in a position in one of the equal volumes, a comparison of the response and known activity contributing to a correction function for that equal volume, one or more such correction functions providing the correction factor.    
   
   
       5 . A method according to  claim 4  in which one of the equal volumes is a core equal volume, the core equal volume being that volume to which the detectors are least sensitive.  
   
   
       6 . A method according to  claim 4  in which the other equal volumes are defined in layers around the core equal volume.  
   
   
       7 . A method according to  claim 4  in which the core equal volume is defined in terms of the volume bounded by a given minimum distance from all the detectors.  
   
   
       8 . A method according to  claim 5  in which the other equal volumes are defined as that volume which is all between a first given minimum distance and a second given minimum distance from all the detectors, the first and second distances varying for the different equal volumes.  
   
   
       9 . A method according to  claim 4  in which the shape of the equal volumes is defined relative to that location separated from all of the detectors by the greatest distance.  
   
   
       10 . A method according to  claim 9  in which the greatest distance is the greatest distance through the waste and/or container therefor.  
   
   
       11 . A method according to  claim 9  in which the equal volume containing that location is the core equal volume.  
   
   
       12 . A method according to  claim 4  in which the method is repeated with a number of different known activity sources.  
   
   
       13 . A method according to  claim 12  which includes the use of a Cs137 source and a Co60.  
   
   
       14 . A method according to  claim 4  in which the positions are evenly distributed throughout an equal volume.  
   
   
       15 . A method according to  claim 4  in which between 5 and 20 positions are provided for each equal volume.  
   
   
       16 . A method according to  claim 4  in which one or more of the positions are at locations equidistant from the boundary of the equal volume with the next equal volume out and the boundary of the equal volume with the next equal volume in.  
   
   
       17 . A method according to  claim 4  in which one or more of the positions are at locations equidistant from the boundary of the equal volume with the next equal volume out and the location with the greatest minimum distance from all detectors.  
   
   
       18 . A method according to  claim 4  in which one or more of the positions are at locations equidistant from the boundary of the equal volume with the next equal volume in and the outside boundary of the equal volume.  
   
   
       19 . A method according to  claim 4  in which the positions are accessed using one or more tubes provided in the waste.  
   
   
       20 . A method according to  claim 19  in which a tube provides access to one or more of the equal volumes.  
   
   
       21 . A method according to  claim 4  in which all equal volumes are considered using a source.  
   
   
       22 . A method according to  claim 4  in which the comparison is of the calculated or monitored response without the waste present compared with the waste present.  
   
   
       23 . A method according to  claim 4  in which the correction factor is a combination of all the correction functions.  
   
   
       24 . A method according to  claim 4  in which a single correction factor for each part or segment is provided.  
   
   
       25 . A method according to  claim 1  in which the simulation accounts for one or more of: detector type, detector sensitivity, detector positions relative to each other, detector positions relative to the monitoring space, field of view positions and shape, container shape, container material, container position within the monitoring space, waste shape, waste material, waste position within the monitoring space.  
   
   
       26 . A method according to  claim 1  in which the simulation accounts for one or more of: the factors involved in the detection of emissions due to issues of geometry, the factors involved in the detection of emissions due to issues of attenuation, the factors involved in the detection of emissions due to issues of detector performance, the factors involved in the detection of emissions due to apparatus performance.  
   
   
       27 . A method according to  claim 1  in which the simulation includes introducing one or more simulated sources to one or more positions within the waste and consider the detector responses thereto.  
   
   
       28 . A method according to  claim 27  in which sensitivity values are derived from the detector response.  
   
   
       29 . A method according to  claim 2  in which the simulation is verified using the method of  claim 3 .  
   
   
       30 . Apparatus for monitoring a volume of waste for radioactive material, the apparatus comprising 
 a support, the support being provided with a plurality of detectors for radioactive material;    a monitoring space in which the volume of waste is provided; and    a data processor for calculating a monitoring result, for correcting the monitoring result for geometry and/or attenuation to give a corrected result and for providing a correction factor for correcting the monitoring result to give the corrected result;    wherein the correction factor is obtained by a method comprising: 
 providing a simulation of an equivalent volume of waste free of radioactive material in an equivalent monitoring space, with equivalent detectors;  
 providing a known activity radioactive source at one or more positions in the volume of waste; and  
 determining the detector response to the source in a position, a comparison of the response and known activity contributing to a correction function for that equal volume, one or more such correction functions providing the correction factor.  
   
   
   
       31 . Apparatus according to  claim 30  in which the simulation is a computer simulation.  
   
   
       32 . A method according to  claim 30  in which the simulation is a physical simulation.  
   
   
       33 . Apparatus according to  claim 30  wherein the correction factor is obtained by a method comprising: 
 providing an equivalent volume of waste free of radioactive material in an equivalent monitoring space, with an equivalent support provided with equivalent detectors;    dividing in one or more parts, the volume of waste into a plurality of equal volumes;    providing a known activity radioactive source at one or more positions in one or more of the equal volumes; and    monitoring the detector response to the source in a position in one of the equal volumes, a comparison of the response and known activity contributing to a correction function for that equal volume, one or more such correction functions providing the correction factor.