In short, they say at least one nuclear plant has lost containment integrity and is leaking radiation. The General Electric-designed plants have a Mark 1 (earliest) containment, with the fuel pool on the top floor. After the hydrogen explosion at the first (#1 unit) plant, the fuel pool opened to the environment, so years of spent fuel is not being cooled and is in direct contact with the air. The plants are releasing significant amounts of radiation that appears to be moving towards the Pacific Ocean. Like Three Mile Island (TMI), significant amounts of radiation has been detected around the plant: radioactive Cesium (lasts in the environment for 300 years and is absorbed by muscles in the human body, especially infant hearts). People near the plant are receiving as much radiation in an hour as they would normally receive in one year.
Today, the Institute for Energy and Environmental Research (IEER), also based in the U.S., addresses the same issue. John McGlynn, hot news editor, posted a summary and excerpt of the IEER report atThe Asia-Pacific Journal:
"Both reactors [Units 1 and 3] are of the Mark 1 Boiling Water Design. They do not have the sturdy secondary containment buildings of concrete that is several feet thick typical of later reactor designs.Aileen Mioko Smith of Green Action just reposted (via NHK) on the same issue:
A special feature of the Mark 1 design is that the used fuel, also called spent fuel [radioactive waste], is stored within the reactor building in a swimming pool like concrete structure near the top of the reactor vessel. When the reactor is refueled, the spent fuel is taken from the reactor by a large crane, transferred to the pool, and kept underwater for a few years. This spent fuel must be kept underwater to prevent severe releases of radioactivity, among other reasons. A meltdown or even a fire could occur if there is a loss of coolant from the spent fuel pool. The water in the spent fuel pool and the roof of the reactor building are the main barriers to release of radioactivity from the spent fuel pool."
NHK has now reported that the spent fuel pool at Fukushima Daiichi (Unit 3) does not have a roof over it since yesterday’s explosion.The Union of Concerned Scientists: fact-sheet on nuclear accidents.
There is no electric source, and there is a possibility that it has lost cooling ability. There is steam around the roof top. The connection between this and the other is unknown.