Steve Vick International Ltd was recently retained to carry out works at Chapelcross for the nuclear decommissioning company Magnox North.
The works required Steve Vick International engineers to seal off a number of redundant manholes – 43 in total – each containing between two to six inlet and outlet pipes of varying sizes from 20mm to 12”. The deepest manhole was 1.5 metres and the largest had a volume of 1.25 metres cubed.
The project was being carried out in order to secure a drainage system so that a sliplining operation could be carried out further downstream with no risk of flooding or contamination.
Following a site visit, Steve Vick engineers devised a solution based on the use of various techniques which the company has developed and which are used widely in the gas distribution and drainage industries. Adjustments needed to be made in the execution of the techniques as at no point were the engineers permitted to enter the manhole chambers. All stages in the sealing operation therefore had to be carried out from a remote position.
The proposal submitted to Magnox North was accepted and the Steve Vick International engineers attended a day’s safety induction at Chapelcross before commencing work. The two-man team worked for two to six hours per day dependant on weather and access availability and the project was completed in two weeks.
Fabric bags filled with polyurethane foam The DRAINBLOCK™ BAG technique, developed for use in the water sector for remotely sealing off disused drains and sewer laterals, was adapted and employed for sealing off the smaller inlet and outlet pipes at Chapelcross.
For the larger diameter pipes (up to 12”), a procedure developed for the gas distribution industry was employed. Known as Live Stub End Abandonment or SEAL™, the technique involves sealing off and securely abandoning short lengths of pipe which cannot be accessed directly. Both techniques use a specially tailored fabric bag which is remotely positioned in the pipe with the help of a CCTV camera where necessary. The bag is then injected with an expanding polyurethane foam which cures to form a permanent plug.
At Chapelcross, the Steve Vick team inserted the fabric bags into the open ended inlet/outlet pipes using a flexible nylon umbilical which also doubled as the foam supply tube. Once all the pipes were sealed off and the foam had cured (30 minutes), the Steve Vick engineers filled the redundant manhole chambers with the polyurethane foam to a position above the crown of the highest pipe in the manhole, thus stopping any egress or ingress of water into or out of the manhole chamber. The foam was injected in up to three stages depending on the chamber volume.
Manhole covers were silicon sealed into place by a Magnox North engineer once backfilling with foam was complete.
Martin Weeks, Head of Decommissioning Projects at Magnox North Chapelcross said, “Steve Vick offered us a competitive, engineered solution for our project and they delivered their service within the agreed timescales. We were impressed with the cooperation and flexibility that Steve Vick demonstrated under working arrangements that were clearly novel to them”
The project for Magnox North is the latest in a number of pipe and void sealing operations which Steve Vick International’s Special Contracts teams have carried out at other locations including Sellafield, Harwell and Winfrith.
Date Published – 26th October 2011