Acceptance Sampling for the Clearance of Materials

A common activity associated with many decommissioning projects is the clearance (release) of materials for unrestricted use. Conventionally, the clearance process involves 100% survey of all the material being released. Survey activities include scans, direct measurements of total surface activity, and smears for removable activity. Surveying 100% of the material is time-consuming and expensive. It may be possible to employ a statistical approach to the release of materials. In fact, the recently finalized ANSI N13.12, “Surface and Volume Radioactivity Standards for Clearance,” recognizes that appropriate statistical methods for determining compliance with clearance levels may be used. One statistical approach may be to use acceptance samp ling, which can be defined as a collection of processes by which a lot of material is judged by its attributes—“residual radioactivity” in this context. Clearance survey designs can be evaluated using an operating characteristic curve that plots the probability of accepting the lot as a function of the probability of contamination in excess of release criteria.