Three creative employees at the South Texas Project (STP) nuclear plant have received a US patent for an invention that cleans the bolts, or studs, that hold the head of a reactor in place between refuelings.
Cleaning studs is a difficult task to undertake by hand; each of the 72 studs in STP’s two reactors is two and a half metres long and weighs 750kg.
The Reactor Stud Cleaning Booth was created by John Griffin, an STP maintenance supervisor. Griffin conceptualised and designed the four metre-tall 2032kg device, and managed its production. Mechanic/welder William Mikulenka and machinist Alan Plunkett designed, fabricated and machined its components and controls, and assembled and tested the invention.
The booth has been in use at STP since 1997, and an application for a patent was filed after a global search determined that, although other stud cleaning devices exist, this particular machine was unique.
The STP invention has several features that its inventors claim are unique. It allows studs to be cleaned vertically, which eliminates the work, time and risk of manually lowering them onto their sides using chains and an A-frame hoist. The machine also cleans two machines at once: twice the capacity of other devices, and reduces cleaning time from three or four hours to 20 minutes or less per stud.
The machine also uses a cleaning agent in an enclosed system. Other cleaning devices entail manual brushing that generates airborne contamination and the associated low-level waste of cleaning rags, pads and brushes. The STP machine also has a filtering system that removes contaminants from the cleaning agent, which is then recirculated and reused.
By using the machine, staff at STP have reduced the work spent on stud cleaning from 750 to 144 labour-hours per refueling outage, and shortened the task’s timeline from more than five days to just one day. The associated cost savings, projected over the currently licensed life of the plant, exceed $2 million.
The invention won a Top Industry Practice Award from the national Nuclear Energy Institute when it was unveiled in 1999. The patent is the second to be awarded to the plant, and the first since the STP Nuclear Operating Company replaced Houston Lighting & Power as the plant’s manager in 1997. The earlier patent was granted for a special lifting device, which was also designed by an STP employee.