Safely Stripping Uranium Vessel Liners

Walco Industries Ltd. was asked to provide a solution to a unique task. This was to strip a liner from a large vessel that houses uranium product. The obvious main concern was how to remove or reduce the allowable exposure (micro-sieverts) to stay within federal regulations and secondly to complete the project within an aggressive timeframe.

Two methods the company is familiar with are the use of robotics and 3-D tooling. Approval was given to use the 3-D tooling as the cost for decontamination or replacement of the robotics was high for such a short job. However, by going to the 3-D tooling method, the allowable exposure time for the beginning phase of the project would limit the exposure time to 15 minutes per day per person.

The areas of the vessel were mapped out and access points were created to gain access to the top of the vessel. The tooling would then be dropped in with extension arms and set to rotate for a given amount of time until the area had successfully stripped the liner in that zone. The 3-D tooling was then lowered to the next zone remotely and the process would be repeated until the zone was completed and the tooling had to be moved to the next section. Visual confirmation was made to confirm the cleanliness before rigging to the next area of the vessel.

One of the lessons learned was that as the liner fell to the floor and piled up, it greatly increased the radiation hazards to the workers. Where at first the levels were at an acceptable level to allow for 15 minutes it had now decreased exposure levels to 45 seconds at the vessel entrance near the floor.

The customer was responsible for removing any debris on the floor on the off-shift. Every day as the debris was removed the allowable time to work around the tank increased. After 95% of the liner had been removed the workers were now able to enter for more than 2 hours at a time to complete touch-ups. The men water jetting within the vessel had to adhere to a strict PPE requirement. No radiation particles were to contact the skin! This was done by wearing Tychem, full face with PAPR 100 filters, full rubber gear and nitrile gloves. Proper donning and doffing procedures were followed upon leaving the vessel. The use of decontamination rooms and daily urination screening was completed. Crews working within the building housing the vessels had to wear a personal dosimeter (EPD). All equipment to leave the site had to adhere to Canadian Nuclear Standards, thus, it was decontaminated and scanned for radiation particles before leaving the site.

The project was successfully completed with 100% of the liner removed within the time frame allowed and no health and safety incidents. With the help from the customer and the supporting members of the team, the project went off without any concerns.