Probabilistic Approach to NDA of Container with Non-Uniform SNM Distribution

One of the most important parameters influencing the accuracy of NDA techniques is the dependence of the measured quantities on the spatial distribution of the nuclear material inside its container. Equal quantities of SNM with different spatial distribution may give rise to different inferred amounts of SNM. This paper addresses the problem of non-uniformity in two levels. First, a statistical measure is developed which defines the degree of homogeneity obtained by randomly loading SNM into a container (e.g., 55 gallon). For a given measured activity, a statistical formulation is presented to calculate the conditional probability that a certain mass is present in the container. This probability distribution quantitatively defines the uncertainty of the measurement. A computation procedure is formulated which is applied to both passive and active NDA techniques.