Evaluation of Real Balance Data Using a Detailed Realistic Measurement Model

Near-Real Time Accountancy (NRTA) appears to be an adequate tool to achieve the IAEA's safeguarding criteria in future large scale plants. R&D work related to this subject are going on in several countries. In the framework of the Karlsruhe Project Reprocessing and Waste Treatmentt a computer program called PROSA was developed capable to apply truncated sequential tests to a given sequence of material accounting periods. The determination of the measurement model of the process considered is essential for the application of NRTA procedures. After some first investigations related to a \"one-block model\" which led to encouraging results, this report describes the next step of the analysis which is the determination of a detailed realistic measurement model. Thereby, the plant is in a non-steady operating state. The method of establishing the measurement model includes about 70 plant components containing Plutonium which relate to about 100 single measurements for determination of the total Plutonium inventory. The results of the evaluation of real balance data based on this detailed measurement model demonstrate that the NRTA tests included in PROSA are not only able to detect timely a possible loss of nuclear material but also to test the underlying measurement model. That means, in a non-loss situation significant results indicate that the underlying measurement model does not adequately describe the real magnitude of error sizes and propagations. Real operational data accompanied by appropriate statistical methods are necessary to develop step by step the model for the \"true\" measurement system of the facility under consideration.