Reduction of fluctuation and small bias observed in continuous volume monitoring taken in an annular tank for plutonium nitrate

Hosoma, Takashi   ; Mukai, Yasunobu ; Tanaka, Hideki 

Accurate measurement of density and volume by dip-tubes in an annular tank for plutonium nitrate solution is indispensable for material accountancy and safeguards in a reprocessing and conversion plant. The principle of this method is to measure true hydrostatic pressure at the tip of the tube, which postulates that solution in a tank is motionless during measurement. Such condition is satisfied by short time measurement for material accountancy. However, solution is normally being agitated continuously for safety reasons. Therefore, the solution flows and causes some fluctuation and possibly some small bias on hydrostatic pressure measurement. Continuous volume monitoring data is very important information for safeguards, but some apparent change in volume is observed due to the above situation. The reason of fluctuation and small bias is estimated that the effect of solution flow on pressure measurement is not compensating between the density tube (several millimeter higher than the bottom) and the level tube (close to the bottom where solution flow is stagnated), thus measured density fluctuates. In principle, measured volume decreases when measured density increases. We focused attention to the solution mass simply calculated by volume multiplied by density measured coincidentally. As a result, fluctuation and small bias is significantly reduced in mass monitoring.