Toshiba’s $5.4bn purchase of Westinghouse, the US nuclear company, has been good for Norio Sasaki. He led that deal in 2006, and its successful completion led to a rapid ascent through the executive ranks, which culminated on Wednesday when he became Toshiba’s president.

Yet the Westinghouse purchase still has a lot to prove. Toshiba paid a full price when it was already clear that climate change was prompting a nuclear resurgence. Like nuclear power itself, meanwhile, the true costs and benefits of the investment will not be clear for years, because of the decades it takes for a reactor to go from glint in a politician’s eye to concrete-and-steel reality.