A million pound contract to demonstrate the applicability of using laser beams in the decommissioning of nuclear facilities has been won by TWI.
'Our task is to use industrially hardened fibre laser sources using optical fibre delivery of the laser power, and set up realistic demonstrations to show how a one centimetre deep skin of concrete can be removed from pre-castspecimens, a process known as scabbling says project manager Colin Walters. 'The concept uses a diffused laser beam, about 100mm in diameter, to rapidly heat the material and cause differential expansion between the coarse aggregate and the fine cementitious matrix. This results in the surface spalling away from the bulk of the material. The demonstration facility, to be established at TWI's headquarters in Cambridge, will be as representative as possible using un-contaminated concrete to simulate the procedures.'
When decommissioning a nuclear facility the vast majority of the concrete is 'clean' so if this can be separated from the contaminated fraction, the costs in terms of nuclear waste disposal can be greatly reduced.
'The cost savings are incredible' says Walters. 'The laser technique can treat approximately one square metre per hour. Nuclear decommissioning has never been a hurried process.'
Removal by high pressure water jet is a competing process, however this creates significant quantities of secondary waste because the used water becomes contaminated and has to be disposed of separately.
Although laser scabbling was first demonstrated almost two decades ago, lasers at that time were unreliable and high powers could not be transmitted via optical fibres. However the recent advent of the fibre laser now offers a robust, easily deployable, tool that is suitable for use in nuclear decommissioning environments. The laser source is ideal for remote operations and allows the use of a small process head on a lightweight manipulator.
'The present Nuclear Decommissioning Authority contract is for 12 months' says Walters. 'And we hope to be demonstrating the process to potential end-users within nine months.'
An added bonus of laser scabbling is that by changing the process head, the laser is capable of being focused for cutting pipework and other metallic objects requiring size reduction.
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