Radioisotope tracer study in a sludge hygienization research irradiator (SHRI)

A radioisotope tracer study has been carried out in a batch type sludge hyg ienization research irradiator with flow from top to bottom, the objective being to measure flow rate, circulation and mixing times and to investigate the hydrodynamic behaviour of the irradiator for identifying the cause(s) of malfunction. A stimulus-response technique with (NH4Br)-Br-82 as a trace r was used to measure the above parameters. Experiments were carried out at three different flow rates, i.e 1.0, 0.64 and 0.33 m(3)/min. Three combine d models based on a set of differential equations are proposed and used to simulate the measured tracer concentration curves. The obtained parameters were used to estimate dead volume and analyse hydrodynamic behaviour of the irradiator. The nonlinear regression problem of model parameter estimation was solved using the Marquardt-Levenberg method. The measured flow rate wa s found to be in good agreement with the values shown by the flow meter. Th e circulation times were found to be half of the mixing times. A simple app roach for estimation of dose based on a known vertical dose-rate profile in side the irradiator is presented. About one-fourth of the volume of the irr adiator was found to be dead at lower flow rates and this decreased with in crease in flow rate. At higher flow rates, a semi stagnant volume was found with slow exchange of flow between the active and dead volumes. (C) 2000 E lsevier Science Ltd. All rights reserved.