Dynamic limits of error for inventory differences at the Savannah River Site

Limits of error for inventory differences (LEIDs) using variance propagation techniques have been discussed in previous INMM meetings. However, using the variance propagation methodology with a large number of actual inventory measurements on a monthly basis requires the use of an automated LEID program and a means of inputting the data into the program. Currently, there is no standard program being used at DOE facilities. A standard program should be flexible and easy to use but general enough to handle all required measurement combinations and error models to generate the correct LEID. Previously, the Savannah River Site (SRS) used static (inventory snapshot) variance propagated limits or limits based on historical inventory differences (IDs). SRS now uses the software program Materials Accounting with Sequential Testing (MAWST), developed at Los Alamos National Laboratory, to calculate dynamic LEIDs on a monthly basis in order to have limits that reflect the current measurements and measurement errors. The MAWST program depends on realistic estimates of measurement errors, the ability to model the errors, and the proper input of measurements for the software to correctly calculate the measurement LEID. This paper will describe the SRS experience in modeling the measurement system for monthly IDs using the MAWST software and using historical inventories to evaluate the software.