Tokyo Electric Power Company says it measured radiation of 1,800 millisieverts at the plant . The reading came from near a tank holding contaminated water . The previous highest reading around that tank was 2,200 millisieverts on a day . Last month , TEPCO said one of the tanks at the site had leaked 300 tons of toxic water , prompting Japan 's nuclear regulator to declare the situation a Level 3 serious incident , its gravest assessment since the reactor meltdowns at the plant in 2011 . Those levels are strong enough to kill an unprotected person within hours .
Tokyo Electric Power Company says it measured radiation of 1,800 millisieverts at the plant . The reading came from near a tank holding contaminated water . The previous highest reading around that tank was 2,200 millisieverts on a day . Those levels are strong enough to kill an unprotected person within hours .