The nuclear power industry has lost a record $46 billion since the earthquake and tsunami disasters led to three meltdowns at the Fukushima No. 1 power plant last year, wiping out seven years of profit.

Then came the bad news.

Under a July 13 announcement that helped cut ¥1.3 trillion in market value in three weeks at the nine utility companies — from Tohoku Electric Power Co. to Kansai Electric Power Co. — the government is preparing to force regional monopolies to spin off transmission assets from generation. The overhaul, designed to spur competition, is the industry's biggest in postwar Japan.