(480a) Development of a Liquid Jet Sludge Re-Suspension Model (Used on Pulse Jets or Jet Ballasts)

A performance prediction method has been developed for a radioactive or inactive liquid jet sludge re-suspension system. A model has been developed based on work by British Nuclear Group and previously published work at Savannah River, Hanford and others.

Nuclear fuel reprocessing is a complex operation involving many stages. In the final stages of treatment for the highly active components, material is stored in tanks to allow for cooling before final immobilisation. During this phase, solids are kept in suspension through the use of cyclic jet ballasts and airlifts. Settling of solids should be avoided since this may give rise to a highly tenacious sediment bed, where the energy required to re-suspend is much greater than the energy required to keep the bed in suspension.

The resuspension model has been successfully integrated into a physical model of the radioactive plant re-suspension system at Sellafield discussed above. It has been used operationally since 2001 to prevent solids accumulation. Operators use it to define optimum re-suspension conditions as the operational envelope changes and to support the plant safety case to external safety regulators. The model is important to the plant since sludge re-suspension can not be monitored visually due to the nature of the plant, although the extensive remote instrumentation on the plant can detect conditions of poor re-suspension performance.

Characterisation of the settling behaviour and the sediment has been performed in order to increase the flexibility and optimisation of the model and hence the process. Characterisation of the suspended solids is required in order to understand the impact of a wider operating envelope on suspended solids within potentially more complex chemical waste streams; in particular, flow curve rheology and sedimentation measurements, as well as particle size, shape and density.

In this paper we report the design, development and use of the model, and summaries the characterisation of a series of simulant materials through the measurement of fundamental properties.

Keywords: simulant, waste surrogate, rheology, settling, pulse jet mixing.