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Trawsfynydd Nuclear Power Station - MOTS crane

As part of the decommissioning of Trawsfynydd Nuclear Power Station, SCX Special Projects supplied a crane system for handling 3m3 Nirex boxes containing low-level radioactive waste.

As part of the decommissioning of Trawsfynydd Nuclear Power Station, SCX Special Projects supplied a crane system for handling 3m3 Nirex boxes containing low-level radioactive waste.

The crane was to be used in the removal of the Nirex boxes from the on-site storage, so they could then be taken away by dedicated transfer vehicles into storage elsewhere.  This limited usage requirement meant that the crane needed to be a relatively cost-effective solution.

SCX Special Projects supplied a modified off the shelf (MOTS) crane to undertake this work; a commercial-off-the-shelf (COTS) crane, modified to meet nuclear industry requirements and incorporating a bespoke lifting grapple for handling the Nirex boxes.

Modified Street Crane heavy duty crab unit

The modified Street Crane heavy duty crab unit, designed and tested to cope with the high number of stops and starts associated with heavy duty industrial applications, provides increased reliability through robust construction and the use of standardised components.

A fail-safe hoist brake arrangement involves the brake being mounted directly onto the gearbox rather than onto the rear of the motors. Load cell monitoring on all ropes detects both slack rope and hoist overload past the SWL of 12tonnes. Absolute positioning of the crab unit is achieved using magnets, and an absolute angle encoder determines the position of the hoist, giving a positional accuracy of ±1mm.

The bespoke-designed grapple consists of a support plate housing four twist-lock connectors to couple with the Nirex boxes; the hoist will only operate once all four pins are fully engaged. Four wire ropes fed to the lifting grapple give a true vertical lift.

Lower levels of radiation in the working area enable the crane to be accessed directly by a person wearing appropriate PPE, but a remotely located control system with CCTV enhances safety for the operator. However, to keep the solution cost-effective, the built-in recovery system is designed to be operated manually, using pneumatic power tools to bring the crane back to a safe zone.

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SCX Special Projects Ltd
Roman Ridge Road,
Sheffield, S9 1GA
Tel: +44 (0)114 243 1142
Email: info@scx.co.uk
An SCX Company