Monitors for process control

It is shown how the PUREX process in an industrial reprocessing plant can be controlled by suitable monitors and what experience was gained during testing such monitors in the WAK reprocessing plant. For the control of criticality a monitor provides a non-destructive determination of the criticality parameter k∞max by a combination of active and passive neutron measurements. By the same combination the residual fissile material content of high active waste solutions can be determined. The detection of fissile material can also be performed by a simple passive neutron measurement, as shown by the results obtained with a passive neutron monitor installed at the dissolver of the WAK plant. The on-line control of uranium and plutonium concentrations during extraction can either be done by a simple measurement of the temperature profile along the extraction apparatus or again by a passive neutron measurement. X-ray-fluorescence is used as an additional method for determination of low residual uranium concentrations in waste streams. (orig.)