Year
1996
Abstract
A new neutron counter, the waste crate assay system (WCAS), has recently been installed in the Plutonium Facility at Los Alamos National Laboratory to assay non-compactible, plutonium-bearing waste packaged in oversized containers and crates. The instrument will be used for assaying both low-level waste (LLW) crates, which must be certified to contain less than 100 nCi/g, and transuranic (TRU) waste crates, which may contain up to a maximum of 325 g of plutonium minus two times the measurement uncertainty. The system consists of four slabs, each containing tsventy 152 cm-long He-3 tubes. To reduce the effects of nearby materials and changing background conditions on the measurements, the counter is configured to measure coincidence neutrons rather than totals, although the sensitivity is adversely affected in this mode. In the LLW measurement mode, the assay is performed with a variable count time based on the counting statistics. The LLW assay continues until sufficient information has been obtained to either certi& or fail the crate with a 95V0 confidence level. The performance of the WCAS for measurements of both LLW and TRU waste has been evaluated. The capabilities and limitations of the instrument, including measurement times and precision for various plutonium loadings, will be presented in this report.