The Los Alamos National Laboratory Relative Risk Ranking and Expert
Judgement Approach for Prioritization of Disposition of Legacy Nuclear
Material Containers

The Los Alamos National Laboratory (LANL) incorporates results from a relative risk ranking (RRR) algorithm into a priority scoring (PS) algorithm to support risk-based prioritization decisions for legacy nuclear material container disposition and to report progress. Containers without an engineering design pedigree can present a risk for both workers and facility operations. Historically, there have been notable worker health impact incidents resulting in operational shutdowns and federal investigations. The RRR method utilizes both objective and subjective variables to assess the relative risk ranking of each container stored at LANL. These variables include measurable values such as container age, grams of nuclear material, dose conversion factors, respirable release fractions, etc.; along with expert judgement variables such as corrosivity, reactivity, pyrophoricity, and oxidative expansion potential. Los Alamos has been steadily addressing the disposition of legacy containers over time with continuous feedback and active management of relative risk. Recently, the risk ranking team identified 65 containers for accelerated repackaging, initially using the RRR method results and supplementing with expert judgement and information derived from container surveillance for similar container/content combinations. This assessment revealed opportunities for improving the RRR methodology, and identified several containers that the team viewed as equal or higher priority than those identified by RRR alone. The risk team concluded that although reduction in total RRR is a useful tool for reporting progress, additional considerations for prioritization should include other factors such as: 1) accounting for the polyvinyl chloride bag degradation, which off-gasses significant amounts of HCl for containers with high dose/heat load materials, 2) weighting older, non-pedigreed containers higher relative to younger pedigreed containers, and 3) researching details of containers and contents to supplement data from the nuclear material control and accountability database. An overview of the current RRR methodology, how it relates to the PS algorithm, and how it is used (including logistical and operational constraints) will be presented, along with the techniques used to assess and compile the 65 container list and how these may impact the RRR and PS methodology going forward.