Comparison of the Performance of Different Uranium Enrichment Analysis Codes Using a Range of Detector Types

ABSTRACT

This paper describes the results of a set of measurements carried out to assess the state of the practice of relative uranium enrichment measurements by gamma ray spectrometry and to compare a range of approaches by carrying out measurements on a set of uranium samples with known enrichments. Measurements made by a team from Canberra Industries were carried out using two detector/counting chain combinations. The data were collected in such a way as to allow it to be analyzed using different uranium enrichment analysis methods. The results obtained using different detector and enrichment analysis method combinations were compared with each other and with the known values for each sample. Results of these measurements show that in controlled experimental conditions the total uncertainty of reported enrichment is below the procedural upper reporting limit of ±20%. Measurements tend to be better with a BeGe detector over a coaxial detector.

INTRODUCTION

Canberra Oak Ridge, LLC is the Nondestructive Assay/Nondestructive Examination (NDA/NDE) Services Subcontractor to Bechtel Jacobs Company , the Environmental Management and Enrichment Facilities Management and Integration Contractor at Oak Ridge. The main focus of the contract was originally for NDA waste measurements in fixed facilities such as K-1423 at the East Tennessee Technology Park (ETTP), Building 9720-32 at the Y-12 Site, and the Waste Examination Assay Facility at the Oak Ridge National Laboratory. Outside this main contract, Canberra also performs numerous field measurements of waste containers at the three Oak Ridge Reservation sites. Waste characterization is one of the vital functions performed at these sites and NDA of waste containers is the primary method used for waste characterization. 

An important part of the NDA measurements is the determination of uranium enrichment in the assayed samples. Historically, the total measurement uncertainty (TMU) of +/- 20% (relative) in the presence of +/- 50% absolute uncertainty has been reported at the Oak Ridge K-25 site for ²³⁵U enrichment. This estimated uncertainty bound was established in the early 1990s by Martin Marietta Energy System’s NDA measurement organization at the K-25 Site. Interviews with a former employee revealed that it was based on data analyses from a series of NDA measurements of known uranium sources. Unfortunately, documentation of this evaluation has not been found. In the mean time, the signal processing hardware and the enrichment analysis methods have evolved since the early 1990s. Therefore, we have conducted a series of new NDA test measurements of known uranium sources using presently available hardware and software to re-establish this estimated uncertainty bound.