Input Plutonium Accountability Measurements at the Hanford Plutonium Uranium Extraction Facility by Isotopic Dilution Mass Spectrometry

Rockwell Hanford Operations' Analytical Laboratory is using Isotopic Dilution Mass Spectrometry (IDMS) to perform plutonium measurements on the input the Hanford Plutonium Uranium Extraction (PUREX) facility. A number of decisions were made in the design of the IDMS procedure to satisfy the requirements of highest possible accuracy, minimum number of analyses and minimum radiation exposure to personnel. Among the many steps in the 36-hour procedure, five have a critical effect on the accuracy of the method. Measurement controls include the analyses of duplicate and referee samples to monitor the system precision, National Bureau of Standards (NBS) Standard Reference Materials (SRMs) 946 and 947 for mass spectrometer calibration and NBS SRM 949f as the primary method standard providing traceability to a national data base. Plutonium (Pu)-244 (NBS SRM 996) is used as the isotopic diluent (spike). Continuous calibration of the spike solution Pu-244 concentation relative to the method control plutonium weight standard, using the same measurement system used for samples, minimizes the effect on accuracy of mass spectrometer calibration uncertainties and eliminates the dependence of accuracy on spike material certification. Experiences and performance achieved with the application of the IDMS technique to PUREX input plutonium accountability measurements are reported.