Thermal and Structural Assessments
In this fourth part of six news items examining the unique contribution NNL makes to the ongoing operation of the HALES plants at Sellafield, we look at how our expert modellers were able to provide extremely accurate models of what happens in the HALES plant.
Sellafield Ltd. asked for a thermal assessment to provide a means of predicting temperatures throughout the evaporators under a range of conditions. This information could be used to translate the temperatures seen in the evaporators to metal loss from the evaporators using a corrosion rate relationship. NNL needed to create a thermal model of the evaporator in order to carry out this work.
The model created was later validated by the boiling rig and was able toreplicate the transient operating conditions in the evaporator. This information provided Sellafield Ltd. with valuable information on the current conditions in the evaporators and the changes in temperatures likely to occur during their remaining lifetime.
National Nuclear Laboratory created a finite element model to calcluate the minimum acceptable thickness of the evaporator vessel to meet safety standards. The model used the information taken from the thermal assessment and combined it with vessel drawings and information on construction methods to calculate the stresses across the evaporator during operations. The model identified metal loss due to corrosion and also provided information on what would happen under different operating conditions.
Next time: The Centrepiece – The Corrosion Assessment