Murphy Natural Resources worked with partners Costain on the £1.9m provision of essential decommissioning infrastructure solutions at the Magnox Nuclear power station, which has been providing National Grid with electricity for the past 45 years.
After four decades of successful and safe operations, on 30th December 2015 Wylfa nuclear power station closed down, marking the conclusion of Magnox reactor generation in the UK. As part of the site decommissioning Murphy Natural Resources was chosen to fabricate and install an active effluent discharge line (AEDL) - a pipeline connecting the power station underground to an outflow on the Irish Sea bed at Cemaes Bay, a distance of 320m.
A site of high security, coupled with a nearby coastal tourist Area of Outstanding Natural Beauty (AONB) meant considerable challenges for teams working onshore and offshore to minimise disruption and any environmental impact on the locale. An assortment of Site Stakeholder Groups (SSGs) included Magnox, the Nuclear Decommissioning Authority (NDA) and regulators as well as local councillors, non-governmental organisations and other interested stakeholders.
The site works followed on from the design and engineering study undertaken at Bromborough by Murphy in 2015 to determine the scope and complexity of the project. Fabrication and assembly of the pipe-in-pipe bundle took place at a site at Soldiers Quay, Holyhead, 17 miles from Wylfa. The 12m pipe lengths were delivered to the Holyhead site where they were welded together, using automatic butt-fusion technique, to form two individual strings of approximately 320m long.
Each pipe string was hydrostatically tested utilising Murphy’s in house testing facility PTS (Pipeline Testing Services). After dewatering the 125mm product pipe was fitted with pipe spacers every 3m and was then installed inside the 225mm sleeve pipe.
At the same time horizontal directional drilling (HDD) was employed by Murphy partners LMR Drilling, to form the route for the pipe.
Following completion of the pipe fabrication and the HDD borehole works, the pipe-in-pipe bundle was launched into Holyhead harbour and towed by tug to the LM Constructor (the Murphy work-barge), anchored off Wylfa within Cemaes Bay, Anglesey.
From within Wylfa power station, LMR’s HDD rig then pulled the pipeline into the hole drilled through the rock, with the pull-head arriving safely within the power station.
In an integrated approach Murphy carried out welding, hydrotesting, marine works, offshore hydrographic and onshore topographic surveys, tie-ins and engineering and design. A team of six onshore and 10 offshore engineers plus a subcontract SMS dive team and eight drilling technicians completed the project in three months, finishing in May 2016 successfully, on-schedule and without incident.