Inuktun Sighting #18: Magnox goes Modular

Located within the Snowdonia National Park in North Wales, the Trawsfynydd nuclear power plant generated up to 470MW for the United Kingdom between 1965 and 1991 and was defueled between 1993 and 1995. The station is now well into the process of being decommissioned.

As with any nuclear site, the decommissioning process requires both painstakingly slow and monumentally precise operations, including visual inspections of numerous key components. Between September 2011 and July 2013, the two most significant components of Trawsfynydd, the twin Magnox reactor pressure vessels, were visually inspected.

According to a technical paper by Magnox Ltd., the company responsible for the inspection, the team tasked with performing the job had no previous experience undertaking an RPV inspection. Although this type of inspection had not been performed at Trawsfynydd since the 1990s, access was known to be limited through one of the reactor’s bioshields. Therefore, as with many nuclear inspections, a mock-up was made to allow the team to better understand the challenges.

Pantograph mounted on Inuktun platform

Pantograph mounted on Inuktun platform

In answer to the challenge, the team tapped into Inuktun’s modular technology to procure a set of Minitracs™, Microtracs™ and a Spectrum 45™ camera, which in turn became the key components for their custom inspection vehicle.

The Microtracs™ and Minitracs™ were both fitted with a pantograph created by BICO Ltd. that provided the ability to lift the camera 1.5 metres from the floor level and pitch it 1.2 metres forward to access the vent holes in the RPV skirt. Generally, the Microtracs™ were used below the sub-floor while the Minitracs™ were used above. The Spectrum 45™ was deployed using a tether above the charge pan of the first pressure vessel.

Spectrum 90 drop camera deployment

Spectrum 90 drop camera deployment

The result was what the team had hoped for. The robots and camera provided proof of the good condition of the pressure vessels, confirming the presence of an anticipated amount of corrosion. Diagrid supports, torsion bars, debris ducts, cold gas ducts and other infrastructure were all inspected and also showed no unanticipated corrosion issues.

The information gathered over the course of the inspection will be used as a point of reference for the teams responsible for the long-term care of the station.

In January 2017, Trawsfynydd is scheduled to enter a period of care and maintenance. After this time, the site is designed to be in a passive state until the final site clearance begins in 2076.

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