A comprehensive approach to Material Balance Evaluation

Material Balance Evaluation (MBE) is performed by nuclear safeguards inspectorates in order to gather assurance on the good management of nuclear materials by nuclear operators over the considered period and on the absence of nuclear materials diversion. More concretely, the MBE process intends to clarify whether measurement uncertainties can justify differences between physical and book inventories and differences between nuclear material amounts as declared by shippers and receivers. It also addresses any unjustified trends in these differences and the use of certain accountancy codes. The proposed approach is based on the use of nuclear operators' values of measurement uncertainty, differing from the current practice of using values as calculated by the inspectorate. The use of operators' uncertainty values brings the benefit of a tight control of the quality of measurements performed by nuclear operators. This control is achieved by means of traditional safeguards tools, such as independent measurement by the inspectorate, and by the use of innovative tools such as audits of the nuclear operators' measurement systems. The approach includes the assessment of the quality of nuclear operators' measurement systems and material balance tests procedures, the statistical analysis of shipper-receiver differences (SRD) and accumulated inventory differences, and the evaluation of specific accountancy codes. The European Commission is in the process of implementing this approach for European nuclear installations.