Japan's atomic power industry lost a record $46 billion since the Fukushima tsunami and meltdown last year, wiping out seven years of profit. Then came the bad news.

The government is preparing to force regional monopolies to spin off transmission assets from generation, under a July 13 announcement that helped cut 1.3 trillion yen ($17 billion) in market value in three weeks at the nine utilities from Tohoku Electric Power Co. to Kansai Electric Power Co. (9503) The overhaul, designed to spur competition, is the industry's biggest in post- war Japan.

Breaking the electricity model that powers the world's second-biggest economy, an experiment tried with some success by nations including Germany and Spain, risks shareholder value. The utilities will lose guaranteed access to distribution grids just as they struggle to replace idled nuclear reactors, a scenario threatening dividend payments that were 46 percent above the average of Nikkei 225 Stock Average companies in the five fiscal years to 2010.