Volume measurement system for plutonium nitrate solution and its uncertainty to be used for nuclear materials accountancy proved by demonstration over fifteen years

Hosoma, Takashi   

An accurate volume measurement system for plutonium nitrate solution stored in an accountability tank with dip-tubes has been developed and demonstrated over fifteen years at Plutonium Conversion Development Facility of Japan Atomic Energy Agency. It was proved, as a result of calibrations during the demonstration, that measurement uncertainty practically achieved and maintained was less than 0.1% (systematic character) and 0.15% (random) as one sigma which was half of the current target uncertainty admitted internationally. It was also proved that discrepancy between measured density and analytically determined density was less than 0.002 gcm as one sigma. These uncertainties include effects by long term use of the accountability tank where plutonium throughput is six ton. The system consists of high precision differential pressure transducers and a dead weight tester, sequentially controlled valves for periodical zero adjustment, dampers to reduce pressure oscillation and a procedure to correct measurement biases. The sequence was also useful to carry out maintenances safely without contamination. Longevity of the transducer was longer than 15 years. Principles and essentials to determine solution volume and weight of plutonium, measurement biases and corrections, accurate pressure measurement system, maintenances and diagnostics, operational experiences, evaluation of measurement uncertainty are introduced.