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A second comparison of procedures for the assay of low levels of gamma emitters in nuclear site waste.

Dean, J C J (2010) A second comparison of procedures for the assay of low levels of gamma emitters in nuclear site waste. NPL Report. IR 19

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A second ‘drum comparison’ exercise has been run by NPL. This involved two samples: Drum A and Drum B. Each sample consisted of a 200 L drum loaded with plastic bottles and vermiculite. Within each sample, one bottle was loaded with ionexchange resin containing a standardized mixture of 241Am, 137Cs and 60Co. The activity concentrations (averaged across the drum contents) were approximately 0.3 Bq g-1 for Drum A and 9 Bq g-1 for Drum B.
The participants were required to report the activity concentrations of the individual radionuclides in one (or both) samples. They were initially told which radionuclides were present, and were given ranges for the total activity concentration and details of the drum itself and the chemical composition of the contents. They were told neither the location of the activity in the drums nor the number of bottles containing the activity (the ‘hot volume’). Drum A was measured by 8 UK and 1 overseas laboratory and Drum B was measured by 12 UK and 2 overseas laboratories. After the initial results deadline, NPL revealed the location and size of the ‘hot volume’ in each drum and participants were invited to submit additional data. The exercise was followed by a workshop for discussion of the results.
Approximately 78 % of the initial results for Drum A were in agreement with the NPL value. After disclosure of the ‘hot volume’ details, a subset of the participants who had measured Drum A submitted additional data and approximately 56 % of these data agreed with NPL (n.b. approximately 76 % of the data submitted by this subset prior to disclosure agreed with NPL). For Drum B, the corresponding figures were: 56 % of initial data agreed with NPL; after disclosure, 74 % (from a subset of participants) agreed with NPL; 77 % of the initial data from the subset agreed with NPL.
The main findings were that (i) different approaches to efficiency modelling of the drums had been adopted and had produced different results (even using the same software) and (ii) the use of Segmented Gamma Scanners had in some cases produced discrepant results. Like the previous exercise, the participants again found the exercise a valuable test of their efficiency models and measurement systems.

Item Type: Report/Guide (NPL Report)
NPL Report No.: IR 19
Subjects: Ionising Radiation
Ionising Radiation > Radioactivity
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/4714

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