Tokyo, April 12, 2011 — The accident at Fukushima Daiichi nuclear power plant in Japan is now ranked as a level 7 major accident, which is the same ranking assigned to the Chernobyl disaster.
Japan’s nuclear energy watchdog, the Nuclear and Industrial Safety Agency, issued the new rating April 12, and has formally submitted the finding to the International Atomic Energy Agency.
A level 7 “major accident” on the IAEA‘s own ranking system for nuclear accidents — called the International Nuclear and Radiological Event Scale or INES — is used for events characterized by, “A major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures”.
This rating encompasses the reactor damage and radiation release from Fukushima Units No, 1, 2 and 3. Those units were previously ranked as a level 5 accident on the INES scale.
The NISA INES rating applied to Unit 4, where the heat level of the spent fuel ponds remains a concern, stands at level 3 — or “serious incident.”
INES is used to communicate to the public the safety significance of events associated with sources of radiation. The scale runs from 0 (deviation) to 7 (major accident).
The revised accident ranking is based on NISA’s estimate of radioactivity released from the Fukushima plant into the surrounding area. So far, the agency estimates that Fukushima Daiichi has released about 10 percent of the radiation that was released by Chernobyl in 1986.
The Chernobyl disaster is the only other event to earn a level 7 INES ranking. The Three Mile Island accident was ranked as a level 5 event, denoting an accident with wider consequences.
Japanese authorities have said they may revise the rankings again as more information surfaces.
After Japan raised the ranking of the disaster, Prime Minister Naoto Kan took to the airwaves in a TV address to tell Japanese citizens that the situation is stabilizing. The amount of radiation leaking from the site is in decline, Kan said.
Officials with NISA confirmed this view, reporting that the amount of radiation being released into he atmosphere peaked from March 15 to 16, adding that a smaller amount of radiation is still being released.
In other new developments from Fukushima, plant operators released about 11,500 tons of radioactive water into the Pacific Ocean
Plant operator Tokyo Electric Power Co. confirmed the release of three radioactive materials, or nuclides: Cesium-134, Cesium-137 and Iodine-131.
TEPCO reported that following the 6.3 magnitude earthquake that struck near Fukushima on April 12, pumping activities had to temporarily halt as workers were evacuated. The utility then said that no equipment was damaged during the earthquake and that crews had resumed pumping water into Units 1, 2 and 3.
In the U.S., heavy equipment manufacturer Putzmeister America recently shipped by air two of the world’s largest concrete boom pumps to Japan to assist the effort to cool down the reactors.
Each of the 70Z-meter pumps sent from the U.S. weighs about 190,000 pounds and has a boom reach over 227 feet. The pumps are traveling on Russian Antonov cargo jets, among the world’s largest aircraft, and two technicians are accompanying each pump to provide training and ensure operators are comfortable using the equipment.