Tokyo (CNN) -- Radiation levels in pooled water tested in the No. 2 nuclear reactor's turbine building at the Fukushima Daiichi power plant are 10 million times normal, utility company and government officials said Sunday.
Hidehiko Nishiyama, an official with Japan's nuclear and industrial safety agency, said the surface water showed 1,000 millisieverts of radiation. By comparison, an individual in a developed country is naturally exposed to 3 millisieverts per year, though Japan's health ministry has set a 250 millisievert per year cumulative limit before workers must leave the plant.
The 10-million-times normal reading applies to radioactive iodine-134 found in the No. 2 building's pooled water, according to the nuclear safety agency. This isotope loses half its radioactive atoms every 53 minutes, compared to a half-life of every eight days for radioactive iodine-131 that has also been detected in recent days.
This exponentially dwindling amount of radiation means, according to Nishiyama, that it's unlikely that sealife -- and, several steps down the line, humans who might eat once contaminated seafood -- will suffer greatly from the iodine-134 exposure.
"Certainly, we have to be concerned about the fact that the level of radiation is increasing," said Nishiyama. "But at this point, we do not ... envisage negative health impacts."
There was no indication either of harm done to the two people working in and around the No. 2 reactor when the test result became known. Those two subsequently left, and work in the turbine building has stopped until the government signs off on the power company's plan to address the issue, according to an official with the Tokyo Electric Power Company, which runs the plant.
That said, a Tokyo Electric official noted Sunday that people continued to work in other buildings -- including a control room, which got power and light for the first time in weeks the previous afternoon -- in the No. 2 reactor's complex.
Work has similar ceased at the No. 3 reactor's turbine building, where tests earlier indicated radiation 10,000 times normal in that structure's basement.
Eventually, authorities want to pump the pooled, and contaminated, water from both these 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.
Authorities are still trying to pinpoint the relationship, if any, between these alarming readings from inside all these buildings to a continued spike in radiation detected in seawater just offshore.
A Japanese nuclear safety official said Sunday that levels of radiation were 1,850 times normal at a monitoring post situated 330 meters (361 yards) into the Pacific Ocean. This is near the discharge canal for the Nos. 1, 2, 3 and 4 reactors.
On Saturday, similar readings from the same monitoring posts showed readings were 1,250 times above normal. The previous day, they'd been lower -- at 104 times more than a typical level.
This substance is a biproduct during the nuclear energy process, and officials suspect the seawater contamination may be a direct result of problems at the plant.
These setbacks notwithstanding, a Tokyo Electric official said that fresh water -- and not seawater, as had been done earlier -- is still being injected into the reactor cores and the spent nuclear fuel pools for the Nos. 1, 2 and 3 units.
That is critical as it suggests that measures continue to ensure that nuclear fuel rods there are kept cool, in order to prevent overheating and the release of more airborne radiation.
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.
On Sunday, 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 the 24th, after the three workers were exposed to between 173 to 181 millisieverts of radiation.
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."
As 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.
"We need to be sure that (Tokyo Electric) isn't going to act in a way that will create distrust," Edano said.
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.
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 (and, thus, the only ones with nuclear fuel rods in the reactor cores) when the March 11 earthquake and subsequent tsunami hit.
Authorities have been trying to restart a steady supply of electricity to power the cooling systems, in order to control the temperatures of nuclear fuel and prevent further radioactive emissions, for that reactor and several other in the nuclear facility.
This has already occurred in the Nos. 5 and 6 units, which are considered stable. These units have fuel rods in spent fuel pools, but not in their reactor cores.