Inspection of Low-Level Radioactive Waste

Abstract

The accuracy of manual inspection of low-level radioactive waste (called dry active waste, or DAW) was determined in three studies conducted at two nuclear power plants. The project was conducted to determine the level of sorting accuracy in work settings given existing procedures, equipment, and technician characteristics. The research paradigm employed in each of the three studies included an unmodified waste stream of roughly 10 000 items and sorting by radioactive waste technicians using hand-held probes. Sorting performance was measured unobtrusively by intercepting the outflow from sorting stations and verifying the radioactivity of each piece of trash with a prototype semiautomated sorting table. In all, more than 30000 items of trash were examined, classified, counted, and verified. The results showed that between 1% and 19% of all items in each of the three DAW waste streams were contaminated at levels ≥100 corrected counts per minute. Sixty-two percent of the contaminated items in Study 1,87% of the contaminated items in Study 2, and 97% of the contaminated items in Study 3 were detected during inspection. False positive rates were very high in all three studies. The production rates and accuracy obtained on the semiautomated plastic scintillation sorting table used during the verification stages of this project greatly exceeded the rates for manual sorting.