Keeping nuclear components clean

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Derbyshire-based Paul Fabrications, a Unitech Aerospace company, has replaced solvent cleaning of nuclear fuel components with a multi-stage aqueous system.

For a long time the company used both aqueous and solvent systems to wash machined, pressed and fabricated stainless steel components for its customer, Springfields Fuels Limited, near Preston, which supplies fuel pellets for advanced gas-cooled reactors in the UK.

In 2017 it has phased out solvent cleaning, replacing it with a Turbex Pro 550 aqueous ultrasonic cleaning system.

The four-stage line is devoted to washing and drying all the nuclear components that support and hold the stainless steel tubes containing uranium fuel pellets in the core of advanced gas reactors in the UK. All these components were previously processed in a trichloroethylene closed system at the Castle Donington site.

Peter Tryner, Nuclear Operations Manager at Paul Fabrications said, “We clean the associated braces, which are heavier components, in an aqueous spray washer but the other support components are too lightweight for processing in the same machine, as they would be distorted and damaged.

“We had a number of trials carried out using different solvents, but all of them left some type of stain after the drying stage. This would mean the components being rejected or even scrapped.

“We decided we needed an aqueous tank system that would perform the final clean on the stainless steel components to nuclear required standard, without damage.”

Soils that need to be removed from the rings are principally press oil and coolant from machining centres. There is no or negligible swarf, as this is blown off before cleaning. Particularly important is that all traces of surface impurity, especially chlorine, are removed. The Turbex equipment achieves what Mr Tryner describes as a medical level of cleanliness and has received Springfields Fuels’ validation to clean the components in this way.

On receipt of the components and fabrications, Springfields Fuels visually inspects 20 per cent under magnification for cleanliness and also carries out dimensional checks to ensure that the drawing tolerances have been achieved.

In 2016, Paul Fabrications became the 100th UK manufacturing company to receive F4N accreditation through the Nuclear AMRC’s Fit For Nuclear programme.

www.unitech-aerospace.com

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