Steve Vick International has been involved in a pipe sealing project at Sellafield where “a complex set of decommissioning challenges” exist in dealing with the 60 year old First Generations Magnox Storage Pond (FGMSP).
The scope of the work covered the removal of redundant pipework in a high radiation area and then cleaning and sealing a contaminated pond wall.
The redundant 10cm diameter pipework posed a significant risk. In order to seal off the pipes so that they could safely be removed, Steve Vick International supplied a quantity of their High Integrity FOAMBAG™ kits which are based on a patented system first developed over 30 years ago for use in the safety-critical gas distribution network. In recent years these fabric bags and the expanding polyurethane resin foam with which they are injected, have been specially adapted for use in nuclear decommissioning.
A bespoke robotic arm, supplied by specialist contractors SA Robotics, was developed especially for the project to work in the high radiation area where it was unsafe for operatives. Software, originally developed for NASA, was used to control the robot or Powered Remote Manipulator (PRM) arm.
“The operation demanded surgical precision in an industrial context”, said Paul Farran, Head of Projects FGMSP. “The completion of this vital piece of work helps us to get on with the job of retrieving nuclear wastes from the pond”, he continued.
High Integrity FOAMBAG™
The High Integrity FOAMBAG™ kits supplied by Steve Vick International and used at Sellafield comprised a semi-porous fabric bag with four circumferential pockets, filled with an underwater resin, equally spaced along its surface. The bags were inserted by the PRM into the pipes at strategic points. Each bag was then injected, remotely, with a two-part polyurethane resin which was mixed just prior to insertion.
As the foam expands it fills the bag and a small quantity seeps through the fabric to adhere to the inner wall of the pipe. The underwater resin contained in the circumferential pockets is squeezed through the semi porous pocket material by the expansion of the foam and provides a secondary seal against the internal wall of the pipe being decommissioned.
The National Nuclear Laboratory has carried out tests on the cured foam used in Steve Vick International’s FOAMBAG™ and have rated it as having an 8 to 10 year lifespan in an area with a background radiation level of 7 to 9Sv.
Once the pipework had been sealed off in this way, it could be removed to allow the robotic arm to scabble the pond wall and apply a specialist coating to seal the concrete.
Preparation for the project included the construction of a full scale mock-up of the facility in Whitehaven to test the equipment, techniques and safety of the procedure and to provide a low risk environment in which to train the operatives.
Mark Steele of the Nuclear Decommissioning Authority and Head of Programme for Sellafield, said, “Sellafield faces a complex set of decommissioning challenges in dealing with the legacy facilities on the site. Often innovative approaches and techniques are needed to overcome them.”
The FOAMBAG™ technique has been used at other sites including Chapel Cross, Winfrith and Harwell.