Tank 41H bounding uranium enrichment. Revision 1

The intent of this document is to combine data from salt samples and historical process information to bound the uranium (U-235) enrichment which could be expected in the upper portion of the salt in Tank 41H. This bounding enrichment will be used in another document to establish a nuclear safety basis for initial salt removal operations. Any number of mixing scenarios could have been examined for the components which fed the evaporator during the formation of the last five feet of salt. The scenario presented was designed to be conservative, while still incorporating process knowledge and available data where possible. In the scenario, the lowest enrichment seen in any feed material was for the L4 feed which was evaporated to form the top part of the salt in Tank 41H. The lowest enrichment of 17% is still higher than the 16% (95% confidence) maximum enrichment actually found at the salt surface (from sample results). This leads to the conclusion that the uranium enrichment of the material (L1) which was being fed to the evaporate when the last five feet began to form, was lower than 22%. The conservatism used in this analysis, combined with the available sample data are believed to provide a defensible basis for establishing an upper bounding enrichment of 22% for the top five feet of salt