Industry first: machining completed on live nuclear reactor pipework26 October 2018
Machining specialist Hydratight reports that it has “become the first company to use electrical discharge machining (EDM) for maintenance work on a live nuclear reactor pipework system.”
The company completed the “technically challenging campaign” at a US nuclear power plant as part of post-Fukushima upgrades. The use of EDM avoided an expensive unplanned shutdown of the reactor for the operator and took 48 hours off the reactor outage schedule, Hydratight says.
Hydratight’s EDM process used a heated solid electrode to accurately cut a hole within the reactor feed water line then removed microscopic cuttings using back-flushing and vacuums. It prevented 99.5% of foreign material exclusion (FME) particles, such as drill cuttings and debris, from entering the reactor.
Mike Riordan, Hydratight’s nuclear speciality services manager, said: “This was a milestone achievement on a live nuclear reactor pipeline system and has resulted in safety enhancements in line with the industry’s post-Fukushima requirements.
The work has created another way to feed water into the main line if there is ever a power loss to the reactor.”
The line had water pressure of 120 psi and electrical conductance exceeding 3500 micro-siemens.
Hydratight deployed customised tooling to negotiate a 15 inch long, 1 inch wide pipe as an entry point to reach the spot where the 3⁄4 inch EDM penetration was to take place.
EDM is typically deployed as an alternative to mechanical methods, such as drilling and hot-tapping, during planned outages. As well as preventing FME particles from entering process piping, the cutting is highly accurate and can maintain a tolerance of .002 in when making the hole in the pipe.
“Material contaminations are a major concern for most facilities and electrical discharge machining is a highly accurate and safe way of machining,” noted Mike Riordan. “Tool pressure was also a concern on this particular project, so we were able to use a method which was completely contactless.”