National Nuclear Laboratory


Sunday 25 May 2014

Hot Stuff – Simulating the Evaporator

In this second part of six news items examining the unique contribution NNL makes to the onigoing operation of the HALES plants at Sellafield, we look at how we were able to replicate the effect of boiling highly active liquors and solids inside the plant.

NNLdesigned and built a boiling rig to replicate the effect of highly active liquor and solids boiling above the the metal base of the evaporator. As the corrosion rate of metals varies with temperature, data was collected on the temperature of the metalbase and the liquor and solids. This allowed an empirical model to be created of the temperature profile of the metal base and the effect of submerged depth on temperature. One successful outcome was that the rig validated previous modelling work.


In addition the work showed that the physical properties of the highly active solids were such that even at low heat fluxes, the boiling action was enough to lift the solids up from the base of the evaporator. As solids deposited on the base of the evaporatorwould have an impact on the metal temperatures in the evaporator, this meant that the effect of solids on corrosion was less than previously thought – valuable information to feed into the overall corrosion assessment.


The boiling rig also provided a useful visualisation of the behaviour of the boiling liquor and solids in the evaporator. Technologists, customers and regulators alike found this a very informative aid in their assessment of evaporator operating conditions.

NNL’s work in this area was largely possible due to our many years experience andunderstanding of highly active liquor chemistry. This enabled us to develop realistic simulants for the liquor and solids, which ensured our work was accurate and meaningful.

Find out more next time.