A REVIEW OF RECENT IMPURITY MEASUREMENTS OF LANL MATERIAL

Abstract

The Applied Computational Engineering and Statistics (ACES) group of the Savannah River National Laboratory (SRNL) was asked to review recent measurements performed by the Los Alamos National Laboratory (LANL) on material from that facility that is being considered for processing through the Mixed Oxide (MOX) Fuel Fabrication Facility (MFFF) at the Savannah River Site (SRS). There are specification limits for impurities in the feed to the MOX facility: a maximum limit and an exceptional limit. The limits for an impurity apply to the population of concentration values for that impurity for a class of material that is to be processed through MOX. For the purposes of this report, these limits were defined as follows. The concentration of an elemental impurity, expressed as micrograms of the element per gram of plutonium ({micro}g/g Pu), is to be no more than the maximum limit for that element for 98% of the material coming through MOX; that is, 98% of the material processed at MOX is to have a concentration of the given element less than the maximum limit. In addition, the concentration for a given element is to be no more than the exceptional limit for that element for 99.9% of the materialmore » processed through MOX. The measurements evaluated as part of this study included LANL blend lots 1 through 29 and cover carbon (C), chlorine (Cl), fluorine (F), nitrogen (N), phosphorous (P), and sulfur (S). Note that all of the measurements for each impurity were below their respective maximum (and obviously, therefore, their exceptional) limits. Thus, there is no immediate concern regarding the LANL material being suitable for processing through MOX. Two approaches were used to investigate the quantiles of the impurity populations. The first approach used was a nonparametric approach. While the results from this approach did not indicate any problems for any of the impurities, there was too little data available to lead to confident statements about satisfying the maximum and exceptional limits. Impurity data from additional random samples of the LANL material would be needed to increase the confidence level associated with the results from a nonparametric approach for investigating the population quantiles of interest. For S, F, and Cl, only a nonparametric approach was used. A second approach, a parametric approach, was attempted for C, P, and N. However, the results for the P and N measurements indicated that each of their respective populations was not well modeled by a normal or by a lognormal distribution. Thus, the conclusions for the P and N populations were those provided by the nonparametric approach. From the parametric approach, the results for C indicated no issue in the LANL material meeting the maximum limit for this element assuming that the measurements for this element follow a lognormal distribution.« less