Tokyo Electric Power Co. reported its second deadly radiation reading in as many days at its wrecked Fukushima nuclear plant north of Tokyo.

The utility known as Tepco said yesterday it detected 5 sieverts of radiation per hour in the No. 1 reactor building. On Aug. 1 in another area it recorded radiation of 10 sieverts per hour, enough to kill a person “within a few weeks” after a single exposure, according to the World Nuclear Association.

Radiation has impeded attempts to replace cooling systems to bring three melted reactors and four damaged spent fuel ponds under control after a tsunami on March 11 crippled the plant. The latest reading was taken on the second floor of the No. 1 reactor building and will stop workers entering the area.

“This does emphasize what care has to be taken,” Richard Wakeford, a visiting professor of epidemiology at the University of Manchester’s Dalton Nuclear Institute in England, said in a telephone interview. “They have to put robots into those areas where they might expect high radiation levels. It’s no real substitute for human access.”

The 10 sieverts of radiation detected on Aug. 1 outside reactor buildings was the highest the Geiger counters used were capable of reading, indicating the level could have been higher, Junichi Matsumoto, a general manager at the utility, said at a press conference.

“In the area surrounding the breach of containment you’d expect high levels of contamination and those high levels would be difficult to predict,” Wakeford said. “You can dig them up if they’re on the soil and contain it or wash it down if it’s on the side of a building.”

Tepco was forced to pump water into the three reactors after the March 11 earthquake and tsunami disabled cooling systems. The company in May estimated there would be 200,000 tons of radiated water in basements and other areas of the Fukushima Dai-Ichi plant by December.

“If nuclear fuels melted through containment chambers, Tepco will find even higher radiation readings after water in building basements is removed,” said Tetsuo Ito, the head of the Atomic Energy Research Institute at Kinki University.

Tepco has been criticized by the government for withholding radiation data and other missteps that have compounded the crisis, which led to 160,000 people being evacuated from near the plant.

Radiation leaks from the Fukushima reactors have spread over 600 square kilometers, Tomio Kawata, a fellow at the Nuclear Waste Management Organization of Japan, said in a research report published on May 24 and given to the government.

Radioactive soil in pockets of areas outside the exclusion zone around the plant have reached the same level as in Chernobyl following a reactor explosion in the former Soviet Union territory 25 years ago, the report said.

The threats to Japan’s food chain are also multiplying as radioactive cesium emissions from the Fukushima plant spread. Contaminated beef has been found on supermarket shelves around the country, forcing the government to ban cattle shipments from areas in northern Japan.

The latest high radiation readings are probably coming from materials released during early failed attempts to release pressure in containment vessels and vent hydrogen gas to prevent explosions that damaged reactor buildings, Matsumoto said. There were about 2,760 workers at the plant on Aug 1.

Tepco on April 17 set out a so-called road map to end the crisis by January, aiming to bring down radiation levels at the plant within three months and then achieve a so-called cold shutdown where reactor temperatures fall below 212 degrees Fahrenheit.