Nope, it became one when it was clear that too many incidents were impeding industrial production. The WP article states it clearly: it "was a nuclear power st

Nope, it became one when it was clear that too many incidents were impeding industrial production. The WP article states it clearly: it "was a nuclear power station prototype", it means that there was hope to decline it, not that it was a lab. It was a "1,242 MWe" reactor, which sort of lab uses such a monster? It was meant to be "an economical generator of power on its own." As for its success: "Construction began in 1974 but suffered from a series of cost overruns, delays and enormous public protests.", and it "demonstrated very poor reliability and had a historical capacity factor of less than 7%." (after being connected to the grid for 20+ years). The nuke industry claims that it was dumped for political reasons, completely ignoring its industrial and technical failures.