Tokyo (CNN) -- Radiation levels remain extremely high in part of the No. 2 reactor complex at the earthquake-damaged Fukushima Daiichi nuclear power plant although an earlier, even more alarming reading was incorrect, its owner said early Monday.
Water pooling in the reactor's turbine building was still giving off radioactivity at a level of 1,000 milliSieverts per hour, the Tokyo Electric Power Company told reporters. That's more than 330 times the dose an average person in a developed country receives per year, and four times the top dose Japan's health ministry has set for emergency workers struggling to prevent a meltdown at the damaged plant.
But Tokyo Electric said that figure is a mere 100,000 times normal levels for reactor coolant, not the 10 million times normal reported Sunday.
Tokyo Electric said Sunday that the water had contained a sharply elevated level of iodine-134, a short-lived isotope produced in a nuclear reaction. But after Japanese regulators questioned the readings, the utility conducted new tests that found a minimal level of the substance, the company said.
However, high radiation levels persisted in the Pacific Ocean waters near the seaside power plant, however, with one monitoring post reporting levels 1,850 times normal Sunday. And tests at the No. 3 reactor building suggested sharply elevated radiation levels as well, the utility said.
Experts suspect that three of the six reactors at Fukushima Daiichi, located about 240 km (190 miles) north of Tokyo, suffered damage to their radioactive cores after the March 11 earthquake. The magnitude 9 quake and the tsunami that followed knocked out backup generators that ran their coolant systems and damaged water pumps at the plant, forcing workers to scramble to prevent a meltdown.
Hydrogen explosions severely damaged the buildings housing the No. 1 and No. 3 reactors in the days following the quake, while an explosion also may have occurred inside No. 2 -- the source of the extremely high readings Sunday.
"The radioactive material that is found in that water is either from the reactor itself or the spent fuel pool," said Hidehiko Nishiyama, a NISA spokesman. "At the moment, we consider that the possibilities are higher that the water is from reactor."
Nishiyama said earlier that NISA considered Sunday's extremely high radiation figures "a bit odd," based on a high ratio of iodine-134 to a more common reactor byproduct, iodine-131. He said the pressure vessel surrounding the core of the No. 2 reactor was not believed to have been damaged -- but the water could be leaking from valves or pipes connecting the reactor to other parts of the plant.
Nishiyama told reporters it was "not possible" that radioactive water was leaking into the ocean from the plant. He suggested runoff from the area around the damaged plant may have carried radioactive particles into the ocean, but said no definite source had been identified.
Sunday's test results stopped work at the No. 2 reactor, but there was no indication of harm done to the two people working in and around the turbine house. Tokyo Electric said crews continued working in other buildings in the No. 2 reactor's complex, including a control room, which got power and light for the first time in weeks Saturday afternoon.
Eventually, authorities want to pump the pooled, contaminated water the reactors' turbine buildings. This happened again Sunday in the No. 1 reactor's turbine building, where tests had showed some radioactive contamination, although nowhere as high as in the other two locales.
But high radiation levels also stopped work at the No. 3 reactor's turbine building, where tests earlier indicated radiation 10,000 times normal in that structure's basement. And 19 plant workers have received doses of radiation of more than 100 millisieverts, both the utility and the Nuclear and Industrial Safety Agency reported Sunday.
Tokyo Electric said fresh water -- and not seawater, as had been done earlier -- was still being injected into the reactor cores and the spent nuclear fuel pools for the Nos. 1, 2 and 3 units.
Up until Sunday, the potential for contamination from the No. 3 reactor had been a primary concern. This unit, which has had a building severely damaged by a hydrogen explosion and that an official said last week might have leaked radiation from its reactor core, is the only one of the facility's six reactors to use a combination of uranium and plutonium fuel, called MOX. Experts say this mix is considered more dangerous than the pure uranium fuel used in other reactors.
Three men laying cable in the No. 3 unit turbine building's basement have been hospitalized after stepping in the highly radioactive water there on Thursday. But Japanese Chief Cabinet Secretary Yukio Edano confirmed that these workers would likely be released Monday from the hospital, which he characterized as a "good development."
An official with Tokyo Electric Power Company, which runs the plant, apologized Saturday, saying the exposure might have been avoided with better communication.
Hideyuki Koyama, the company's associate director, said pooled water had been discovered in the basement of the No. 1 reactor six days earlier. But a sample was not taken for analysis until March 24, after the three workers were exposed to between 173 to 181 millisieverts of radiation.
Koyama told reporters that radiation alarms went off while the three men were working, but they continued with their mission for 40 to 50 minutes after assuming it was a false alarm.
s important, the chief secretary said, was the need for Tokyo Electric to be upfront with the Japanese -- millions of whom get power from the company and millions more of whom have been affected by radioactive emissions from the crisis.
Edano told reporters Saturday the company has been given "stronger instructions" to fully and quickly disclose information about the plant's conditions, so the government can ensure "proper safety measures." A
"We need to be sure that (Tokyo Electric) isn't going to act in a way that will create distrust," Edano said.
This continued debate about the working conditions for the roughly 500 individuals -- among them utility workers, Japanese soldiers and firefighters from several cities -- comes as work continued Sunday to cool nuclear fuel at the plant and prevent the further emission of radioactive material into the air and sea.
The Nos. 1, 2 and 3 units have been authorities' chief focus, since they were the only ones operating when the March 11 earthquake hit. Units 5 and 6 are considered shut down and stable, while Unit 4's fuel rods had been removed before the quake.
Authorities have expressed concern about the spent fuel from Unit 4, which was placed in a cooling pool adjacent to the reactor. That pool has been the target of repeated efforts to spray water into the reactor housing, which was damaged by a fire March 15.
CNN's Whitney Hurst contributed to this report.