The Nuclear Decommissioning Authority

 

A £4.2 million project to divert key pipework that provides cooling water at Wylfa has been completed on time and within budget.

The two-year sea water ring main diversion work was described as "a highly successful project" by Wylfa Site Programme Manager, Glenn Vaughan. He added that the team had responded well to the challenge of completing the diversion within the original schedule and therefore minimising the impact on generation which provides vital revenue support for the NDA.

 

The project was accompanied by some impressive statistics:

• a project team of 45 people including: eight safety case personnel, 6 engineering staff, 6 project management personnel and 25 contractors and subcontractors
• 2,000 tons of spoil were excavated, mainly by hand as the area was too sensitive for machinery
• approximately 70,000 man hours were spent during the work on the re-route alone.

The ring main pumps sea water to cool the reactor pressure vessel and ancillary equipment.  Buried six metres underground, the one-metre diameter pipework runs around the perimeter of the reactor building.

In April 2007, an incident at Hartlepool power station led to automatic safety checks at other power stations and revealed a potential challenge to the Wylfa's Seismic Safety Case due to location of the sea water ring main close to the tertiary feed tank, which contains back-up cooling water.

In April 2008 - during the Reactor Two outage – the first phase of the project began, installing a back-up sea water cooling supply to allow internal inspections of the south sea water cooling supply main.

In May 2008, the Independent Nuclear Safety Assessor (INSA) and Nuclear Installations Inspectorate (NII) agreed to the revised strategy of installing a re-routed sea water cooling supply main.

 

A contract was awarded to Doosan Babcock, with TJ Pritchard, a local contractor acting as civil sub-contractor. In January 2009, excavation work started in two phases. As the sea water ring main was in service, phase one consisted of non-intrusive excavations only. Phase two included full depth excavations of six metres, revealing and cutting into the existing ring main and constructing an underground seismic chamber. It also included the internal inspection of the north sea water cooling supply main and again the installation of a back-up sea water cooling system. Phase two had to be completed before the end of the Reactor One outage. Any delays would have cost Magnox £500,000 per day in lost generation.

Project Lead Gafyn Jones commented:

"The re-routed ring main has now been in service for five months with no detrimental effects on the performance of the system and having mitigated the risk to the tertiary-fed system, fully restores the station's Seismic Safety Case."