Long-term stability of hybrid K-edge/K-XRF densitometer

Destructive assay methods such as potentiometric titration and mass spectrometry have been generally applied to the analyses of uranium and plutonium concentration in a solution sample for the purpose of the accountancy and safeguards for nuclear materials in a facility. Recently, it has been strongly expected to establish a non-destructive assay instead of the destructive assay from the viewpoints of the timeliness requirement for safeguards, the speed-up for the analysis and the decrease of quantity of liquid waste arising from the analysis. For these purposes, a hybrid K-edge/K-XRF densitometer was installed in the Nuclear Fuel Cycle Safety Engineering Research Facility (NUCEF) of the Japan Atomic Energy Research Institute (JAERI) under the JAERI-U.S. DOE cooperation program. JAERI has developed the techniques on the non-destructive assay of uranium and plutonium in cooperation with U.S. DOE. This instrument is expected to be also applied to an inspection at NUCEF in the future. It is necessary to make sure that the instrument can analyze with the same accuracy compared with the destructive assay instrument and can keep the stable measurement over a long term for that purpose. Furthermore, whenever an inspector uses the instrument the performance of the system will be first checked with the standard material whose concentration is known. Facility's side must prepare the standard material which is steady over a long time for that purpose. This report presents the long-term stability of the instrument and uranium standard material and the effect of change of X-ray tube voltage on uranium concentration measurement. (author)