Mix of old and new ideas lead to savings on pipeline project

October 25, 2011

Significant time and cost-savings have been made on a major project to decommission redundant active drains on the RSRL Harwell site. With the project now halfway through, if the work continues at its present pace, engineers will have cut the decommissioning time by a remarkable two-thirds, considerably reducing costs.

Commissioned in 1987, RSRL Harwell’s New Active Drain System (NMAD) used to carry low level liquid effluent from the major facilities on the site to the Liquid Effluent Treatment Plant (LETP). With this function no longer needed, work has begun to decommission the 4000 metre-long drain system, which extends across the site and includes a series of delay tanks and 55 manhole access chambers.

The drain line itself consists of two pipes, one inside the other, the outer pipe made of bitumen-coated cast iron, the inner pipe of polypropylene. Senior project manager Paul Atyeo explained further:

“The outer pipe is there to provide back-up containment in case of leaks. The inner pipe does not have joints except within the chambers, greatly reducing the chance of leakage or trapped radioactivity.  When the system was built, the original engineers envisaged the decommissioning process would reverse the construction process. That is, access ramps would be dug and the pipe pulled out and cut up on the surface – like giant spaghetti. But, after much thought, consultation and preliminary investigations by RSRL, the team came up with an idea which we thought would work better.”

The plan the team devised is to gain access to the chambers, feeding the inner pipe out in 0.9 metre sections, so that it can be cut up underground.

“This new method means completing many thousands of cutting operations underground, but practical methods were developed to do this. We found this revised approach much quicker, more efficient and therefore more cost-effective method,” said Paul Atyeo. “And, because less excavation is required, there is less potential for any disruption to underground services.”

Contracts were placed in Jan 2011; work began on site in May 2011 and is expected to be completed soon after Christmas, less than a year from when it started. Since the estimated timescale for the project was three years, this represents a huge saving in both time and cost.

But the savings don’t stop there. Further cost-cutting has been achieved by recycling equipment from Harwell’s sister site at Winfrith.

With the new decommissioning method, the drain system’s outer pipe and access chambers stay in situ. Since they are to be left underground, they have to be proved to be uncontaminated, posing no liability to people or the environment.

“Proving the pipeline is clean requires a specialist health physics drain probe, which can crawl down the pipe, taking measurements and sending back images of what it finds,” said Paul Atyeo. "Luckily for us, just such a probe was designed and built at Winfrith some time ago."

“So, we dusted off the so-called dRover probe, refurbished and re-commissioned it, and put it to work. It is performing perfectly to date.”

A network of contractors has been involved in this project, collaborating with the RSRL team.

“The teamwork and co-operation of the people at EDS, the primary contractor, alongside those at Nuclear Technologies and Aurora, have been important components in the success of this project so far,” said Paul Atyeo. “It is thanks to them, the RSRL project team – and dRover – that we have been able to deliver great value to our customer.”

For more information please contact Angela Vincent, RSRL Communications Manager