Oklo Inc. tumbled the most in five months after announcing that director Michael Klein of Churchill Capital Corp. sold $6.7 million of his shares in the developer of advanced nuclear reactors.

Oklo slumped as much as 16% Thursday, the most in intraday trading since April 4, and was down 9.6% to $118.62 at 10:10 a.m. in New York. Klein sold 50,000 shares in the Santa Clara, California-based company in multiple transactions Monday, according to a filing.

The company’s market value has surged more than 450% this year, driven by growing interest in nuclear energy and its potential to supply carbon-free energy for data centers and factories. Still, it will be years before the slow-moving nuclear industry can connect a new reactor to the US power grid. Oklo has no systems in operation, though it broke ground this week on its first reactor.