Characterising Containment Weld Integrity of Product Storage Cans

Abstract

By-product from spent nuclear fuel is currently being stored in product storage cans made from type 316L stainless steel. Since these cans are needed for long-term storage, the integrity of the welding technique used to seal the cans needs to be understood, particularity in environments containing HCl because some of the product being stored was placed in PVC, which over time may have degraded. This is of particular interest since the can design is set to be changed to provide long-term storage of up to 100 years. This research looks to compare the welding and can designs using microstructural and 3D techniques, whilst also seeking to understand the behaviour of type 316L stainless steel, resistance seam welding (RSW) and tungsten inert gas (TIG) welding when exposed to chloride containing environments at high relative humidity and low relative humidity. The microstructural analysis shows the difference in microstructure of the base material, the RSW can and the TIG welded can to identify if the difference in microstructure has a bearing on the corrosion resistance. X-ray tomography is utilised to visualise the presence of defects within the RSW and microstructural analysis was used alongside this to determine the cause of the defect. Electrochemical techniques have been used to provide information about the corrosion response and corrosion resistance of these welding processes. Due to the presence of passive films and weld oxide layers, the pitting information varies from sample to sample and a comparison has been drawn between the materials. Individual areas of the weldments were isolated and their electrochemical response measured using the EC-pen to see if the weldment was more susceptible to corrosion as the weld scale changes. The droplet tests were used to simulate the conditions on the inside of the can and how difference HCl concentrations can impact corrosion. These tests showed the extent and type of corrosion when type 316L coupons were exposed to varying %RH and varying chloride concentrations inside a sealed container. The discussion of results uses the comparison of the RSW to the TIG weld to see how the factors mentioned above play a part in the weld integrity of the old can design and the new 100-year-can design.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Dirk Engelberg (Supervisor) & Andrey Jivkov (Supervisor)