Posted on 28 Mar 2011
Alarmingly high radiation levels were discovered in a flooded area inside Japan's stricken Fukushima Daiichi nuclear plant complex on Sunday, raising new questions about how and when cleanup workers could resume their tasks.
Plant operator Tokyo Electric Power Co. said the elevated radiation levels in the water, which had flooded the turbine buildings adjacent to the reactors at the plant, were at least four times the permissible exposure levels for workers at the plant and 100,000 times more than water ordinarily found at a nuclear facility.
That could mean crews seeking to determine damage and fix the problems at the plant, hit by a magnitude-9.0 earthquake and a tsunami more than two weeks ago, may not be able to even approach the most troubled parts of the complex until the water can be safely removed.
Tetsuo Iguchi, a professor in the department of quantum engineering at Nagoya University, said that at the sharply elevated levels of radiation, workers would be able to remain on the site for only about 15 minutes before health considerations required them to leave. That could hamper their efforts to restore power at the reactors, compromising attempts to bring the crisis under control.
Alarm over the radiation levels first intensified Thursday when two workers were burned after they stepped into highly radioactive water inside reactor No. 3 of the plant. Late Saturday, a worker trying to measure radiation levels of the water at another reactor, No. 2, saw the reading on his dosimeter jump beyond 1,000 millisieverts per hour, the highest reading so far. The worker left the scene immediately, said Takeo Iwamoto, a spokesman for the Tokyo Electric Power.
Michiaki Furukawa, a nuclear chemist and a board member of the Citizens’ Nuclear Information Center, a Tokyo-based watchdog group, said exposure to 1,000 millisieverts of radiation would induce nausea and vomiting, while exposure to triple that amount could be lethal.
There was no evacuation of the roughly 1,000 workers stationed at Daiichi after the high radiation levels were discovered. Naoki Sunoda, a spokesman for Tokyo Electric Power, said that since the crisis began, 19 workers had been exposed to radiation levels of 100 millisieverts.
Despite the new problem, Mr. Sunoda said, workers on Monday were still trying to determine a way to approach reactor No. 2, considered to be most troubled of the six.
“Radiation levels are high, but nothing will be resolved if we stay away,” Mr. Sunoda said. “Our objective is to restore power to all reactors so cooling functions can be restored.”
The Japanese government’s top spokesman, Yukio Edano, said in an afternoon press briefing on Sunday that it appeared the radioactive water had appeared when the No. 2 unit’s fuel rods had been exposed to air, but that “we don’t at this time believe they are melting. We’re confident that we are able to keep them cool.”
The higher levels may have suggested a leak from the reactor’s fuel rods — from either the suppression chamber under the rods or various piping — or even a breach in the pressure vessel that houses the rods, the Japanese nuclear regulator said earlier.
There was also deep concern early Sunday about initial readings of radioactive iodine 134, which has a half life of only 53 minutes and would not be present in large quantities unless fission had restarted. That would present the alarming possibility of an out-of-control reactor. Several hours after releasing the initial results, the plant operator said that those readings had been in error, and that retesting had shown negligible amounts of the isotope.
But the revised readings confirmed the overall high radiation readings at the plant, and utility officials continued to search for the exact source. And they still may need to retest for other radioactive isotopes that had been found in the seawater around the No. 2 reactor, including troubling quantities of cesium, barium, cobalt and lanthanum. The company has not yet been able to determine the source of those leaks, and confirming the isotopes’ exact levels could take much longer.