Precise determination of plutonium in nuclear fuel process samples.

A REDOX-based analytical method was developed for determining the plutonium concentration. In this method, plutonium was oxidized to the +6-oxidation state using of ceric ammonium nitrate solution. The interference from ceric(IV) nitrate was suppressed by reducing its oxidation state from +4 to +3 with sodium nitrite. Hexavalent plutonium in this sample was then reduced to be tetravalent by adding a known volume of excess standard ferrous ammonium sulphate. The dichromate equivalence required for unreacted ferrous ammonium sulphate was determined to obtain the concentration of plutonium. Interference studies from chemicals envisaged to be present in the PUREX process stream, such as dissolved tri-n-butyl phosphate, uranium, and various reagents employed during analysis, were performed for the determination of plutonium concentration. The relative standard deviation was found and it is within ± 1.0% for an aliquot containing plutonium in a range of 0.7-2.5 mg.

Design and performance of an improved thermo-optometric equipment for the measurement of the solidus and liquidus at high temperatures.

Experimental determination of solidus and liquidus in reactive systems at very high-temperatures requires special equipment and is rather complex. In the present study, we describe setting up an experimental facility based on the "spot-technique." It was demonstrated that this setup could be used to measure phase transformation temperatures involving liquids in refractory systems that comprise reactive and radioactive components, in the range of 1273 K-2273 K, by using a thermo-optometric technique, namely, the "spot-technique." The equipment and the method were validated by measuring the melting points of high purity metals, namely, gold, copper, nickel, and zirconium. A measurement accuracy of ±2 K could be realized at temperatures as high as 2128 K. The solidus and liquidus temperatures of nuclear reactor fuels as well as some binary alloys were also measured by using this setup. The research involved in building this equipment and the key features of the equipment and method are described in detail.

Development of a semi-adiabatic isoperibol solution calorimeter.

A semi-adiabatic isoperibol solution calorimeter has been indigenously developed. The measurement system comprises modules for sensitive temperature measurement probe, signal processing, data collection, and joule calibration. The sensitivity of the temperature measurement module was enhanced by using a sensitive thermistor coupled with a lock-in amplifier based signal processor. A microcontroller coordinates the operation and control of these modules. The latter in turn is controlled through personal computer (PC) based custom made software developed with LabView. An innovative summing amplifier concept was used to cancel out the base resistance of the thermistor. The latter was placed in the dewar. The temperature calibration was carried out with a standard platinum resistance (PT100) sensor coupled with an 8½ digit multimeter. The water equivalent of this calorimeter was determined by using electrical calibration with the joule calibrator. The experimentally measured values of the quantum of heat were validated by measuring heats of dissolution of pure KCl (for endotherm) and tris (hydroxyl methyl) amino-methane (for exotherm). The uncertainity in the measurements was found to be within ±3%.