Analysis of a radiological box monitor for source segregation

This study assesses the use of a Radiological Box Monitor (RBM) for source segregation of radioactively contaminated and uncontaminated solid waste generated at the Oak Ridge Y-12 site. The RBM is a monitoring device designed to screen bulky items such as trash bags for radioactive contamination. Prior studies of potentially radioactive waste in dumpsters revealed that 90% of the waste could be disposed of in the Y-12 sanitary landfill. Thus, waste segregation ranks high in the Y-12 waste minimization policy, and this is why Y-12 chose to investigate the use of RBMs for source segregation. The objectives of this study are to: (1) optimize counting times for maximum throughput and (2) determine lower limits of detection for various waste forms and source locations within the waste matrix. An evaluation to establish optimal counting times was performed using a 4 by 4 matrix of back-ground and sample count times ranging from 30 to 120 seconds. Thirty data points were collected for each of the 16 combinations of counting times. Results of the data collected to determine opti-mal counting times indicated that equal 60 second background and sample count times have the lowest standard deviation of all combinations tried. Performance of the instrument relative to waste composition and source location was evaluated by using five depleted uranium sources ranging in mass from 0.5 to 10 grams placed at nine locations in four waste matrices. The term "waste matrix" as used in this document refers to the composition of the waste form being examined. These waste forms include empty beverage cans, paper, ma-chine turnings, and an aggregate of trash. Data were obtained over a three week period in August of 1991 by randomly placing each of the sources, as well as a blank, in all nine positions of the waste matrices. Evaluation of data collected on performance of the instrument indicated that the RBM has lower limits of detection for depleted uranium below the existing action value of 35 pCi/g for all positions in the cavity and for all waste matrices studied. However, analysis of variance results suggest significant problems with the instruments reliability. If reliability of the instrument can be im-proved, it is expected that the Radiological Box Monitor will perform adequately on waste with minimal radioactive contamination.