INTEGRATED WASTE ASSAY SYSTEM (IWAS) AND ANALYSIS ENHANCEMENTS

ABSTRACT

The Integrated Waste Assay System (IWAS) is a hybrid waste assay system developed to provide high throughput and improved data quality for characterization of transuranic wastes contained within 200 liter drums and 320 liter overpacks. The IWAS combines high efficiency passive neutron coincidence counting, active neutron interrogation and high resolution gamma-ray spectroscopy into a single assay cavity. The complementary nature of the multiple assay modes yields a higher success rate than any single assay mode alone allowing the system to accommodate a wide range of source and matrix types. Performance of the individual assay modes and performance of the combined analyses is discussed.

Modifications and enhancements of the traditional analysis algorithms for the passive and active neutron analyses were implemented in the IWAS. Reductions of the passive neutron detection levels of up to 50% have been achieved without the need to increase the neutron detection efficiency. Utilization of the Add-A-Source matrix correction measurement for determination of the active interrogation moderator index provided a means to implement a moderator correction for low Pu mass samples and uranium only samples. The modified algorithms and performance improvements are discussed.

The IWAS analysis makes use of data obtained from the three assay modalities to identify and flag problem waste drums. The analysis makes use of the Total Measurement Uncertainty (TMU) analysis for each assay modality to identify the mode providing the result that most likely represents the actual drum contents. The utility of this approach is discussed.

INTRODUCTION

The Integrated Waste Assay System [1] was designed to quantify plutonium and uranium in 220 liter (55 gallon drums) and 320 liter (85 gallon) over-packs. The IWAS provides passive and active neutron interrogation and quantitative gamma analysis allowing rapid characterization of TRU wastes for proper shipment and disposal. The system offers performance, speed and ease of use while using a fraction of the floor space of three independent systems.

Figure 1. Photograph of the Integrated Waste Assay System.

The IWAS is based on the Canberra High Efficiency Neutron Counter (HENC) [2] design with integrated active neutron interrogation mode using the Differential Die-Away (DDA) [3] analysis and Q2 style High Resolution Gamma-Ray Systems [4]. Results from individual assay modes are combined automatically by the system software to provide the best result for the item. Because all assays are performed by the same system in a single sequence there is no confusion over item identification or modification of drum contents between assays.

The IWAS is designed to be operated as an automated counting system which can process batches of drums, or can be incorporated in a facility process line. The following sections describe the various assay sub-systems, hardware, software and indicate typical performance characteristics.