Holdup and Survey Measurements in Support of the TA-18 Facility Hazard-Category Downgrade

After 60 years of operating as the most important criticality experimental facility in the U.S., the Los Alamos Critical Experiments Facility (LACEF), also known as Pajarito Site or Technical Area 18 at Los Alamos National Laboratory (LANL) is being deinventoried of nuclear material and prepared for removal from the list of operating nuclear facilities. The site supported many varied activities, including criticality experimental programs, safeguards research, and nuclear emergency-response activities. Most of the nuclear material has already been removed from the site, and the next step in decommissioning the site is to downgrade it from a hazard category-2 nuclear facility to a radiological facility. Several steps must be taken to downgrade the facility. These steps include performing a nuclear-material inventory, performing a site-wide radiological survey for unaccounted nuclear material and holdup, performing a chemical inventory, and performing a hazardous-metal inventory. The Safeguards Science and Technology group (N-1) at LANL was tasked with performing the sitewide radiological survey and holdup measurements. The site survey presented some challenging and unique constraints not seen in typical holdup campaigns. The entire site had to be surveyed for nuclear material in a short period of time, and the measurements needed to be sensitive to the limits for a hazard category-3 nuclear facility threshold. This required a quick qualitative survey of the entire site, followed by more intensive and quantitative measurements of any holdup and contamination that was found. The actual measurement uncertainty of the holdup measurements was not of major concern as long as the amount of activity was well below the hazard category-3 nuclear facility radiological threshold. In this paper, we will describe the overall measurement campaign, present the survey methodology, and show a selection of interesting results.