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Refits add another dimension to nuclear safety

A Rockwell Automation - Allen-Bradley Guardmaster product story

Edited by the Engineeringtalk editorial team Nov 1, 2004

Allen Bradley-Guardmaster has completed two large projects to upgrade a total of 72 machine tools with the latest safety equipment at British Energy's Hunterston and Torness power stations.

Allen Bradley-Guardmaster has successfully completed two large projects to upgrade a total of 72 machine tools with the latest safety equipment at British Energy's Hunterston and Torness power stations.

The projects were secured as a result of AB-Guardmaster's ability to provide bespoke application solutions to specific safety issues.

They involved the company in the supply of a full range of safety equipment, including DC braking systems, safety interlocks, Safedge systems and emergency stops, and in the manufacture, installation and commissioning of physical guarding for the machines.

British Energy, one of the UK's largest electricity companies, has around 20% of the generation market.

The company owns and operates eight nuclear power stations in the UK with a combined capacity of approximately 9600MW.

Seven stations have twinned advanced gas cooled reactors (AGR); the eighth, a pressurised water reactor (PWR).

In 2002-03 the industrial safety accident rate for British Energy's Nuclear stations was one of the lowest ever at 0.48 accidents per 200kh worked.

However, despite this performance the company is devoting large resources in its efforts to achieve an injury free workplace.

Recently, the focus of these resources has been the Hunterston and Torness power stations in Scotland.

Because of the specialised nature of their operation, these stations have their own workshops complete with machine tools to perform specific machining and general maintenance tasks.

The Engineering Team Leader at Hunterston is Willie Welsh.

He is responsible for the general operation and operator safety of 25 machines - lathes, presses and drilling machines.

In late 2003, Welsh conducted a revised safety evaluation of the machines, which highlighted certain issues that he immediately flagged up to British Energy management.

This resulted in investment being made available to upgrade all machine stock at the Hunterston Station.

The supplier chosen to undertake the safety upgrade was AB-Guardmaster.

"They were able to provide the best solution to our requirements with a comprehensive safety package that included a wide range of different equipment types and the manufacture and fitment of movable guards", said Welsh.

"We also got good advice and good service, nothing was a problem".

Engineers from AB-Guardmaster fitted the machines with equipment such as Nelsa's Torklok: a DC injection braking system that provides operator safeguarding on machines, which in critical situations would otherwise not stop quickly enough to prevent serious injury.

The Torklok braking unit is designed for machinery such as radial and multispindle drills, horizontal borers and lathes, which is difficult to guard conventionally.

In these cases the only way to ensure sufficient operator protection is to provide a way of stopping the machine quickly if the operator gets into difficulties.

The DC injection braking provided by Torklok is the best and most reliable way of achieving this, the system providing a typical stopping time within one second when fitted to a radial drill.

Also fitted to many of the machines is AB-Guardmaster's Safedge, a pressure-sensitive safety device.

The Safedge strip is mounted right along the front of lathes used in the Hunterston workshop to prevent the risk of entanglement as a result of operators leaning over into the machine.

The action of leaning compresses the sensitive Safedge material, an action that energises the Torklok system to stop the machine in less than one second.

Engineers from AB Guardmaster also designed and installed movable guards on the chucks of the machine tools at Hunterston, and supplied and fitted all safety interlock and emergency stop switches.

The result of all this work is described by Welsh as the safest systems he has seen "in 30 years of engineering".

The success of the project at Hunterston has resulted in AB-Guardmaster providing a similar safety retrofit at Torness, another of British Energy's Scottish nuclear facilities.

The Torness project employed the same types of equipment and guarding systems as Hunterston, but was almost twice as large, with a total of 47 machines involved.