Tokyo Electric shares plunged to a 34-year low of ¥696 on Monday after reports of highly radioactive water at the utility's quake-stricken nuclear power plant spurred selling.
Falling by the daily allowable limit of ¥150, or 17.7 percent, from Friday's close, shares of Tokyo Electric Power Co., better known as Tepco, closed at their lowest since February 1977.
The drop followed the utility's announcement early Monday that the concentration of a certain radioactive material in a pool of water found at the crippled Fukushima No. 1 complex was 100,000 times higher than what is usually found in a reactor core.
The news fueled concern it could further hinder workers' efforts to regain control of four reactors severely damaged by the March 11 earthquake and tsunami, brokers said.