Blaidd Drwg (Welsh for Bad Wolf) was the name of a nuclear power plant, planned for construction in central Cardiff. Behind the plans was Blon Fel-Fotch Passameer-Day Slitheen, posing as the new Lord Mayor of Cardiff, Margaret Blaine. The plans were to build the power plant on top of the Cardiff rift. The power plant would have a meltdown, causing the rift to open. According to Blaine she chose the name at random, thinking it sounded good. (DW: Boom Town). This was the first time the Doctor noticed that the phrase seemed to show up wherever they go.
The power station was built and became a functioning station. (TW: Everything Changes) Guy Wildman worked here and used his connections to steal six uranium cores for the Bruydac. (TWM: Another Life)