The NRDC Nuclear Program's Notes on the Accident at Japan's Fukushima Daiichi Nuclear Power Plant
Over the last twenty days, the status of the nuclear accident on Japan’s Pacific Coast has changed dramatically. During the first week – in the direct aftermath of the earthquake and tsunami – explosions and fires damaged four of the six reactor units at the nuclear plant, more than one quarter million people evacuated from a 20 kilometer (12.4 mile) zone around Fukushima Daiichi and beyond, very high radiation levels were measured outside the reactor buildings, and in Tokyo – which is located 140 miles southwest – airborne radioactivity measurements peaked at twenty times normal levels. Despite new reports of radioactive contamination in drinking water, vegetables and milk across the region, the second week of the accident saw a growing optimism that control over the situation was imminent. No further explosions occurred, power lines were run to Fukushima Daiichi, equipment repair had begun, and radiation levels at the plant fell to a point where emergency cooling water could be consistently doused on the damaged reactor units using fire trucks and pumps.
In this the third week of the accident, however, efforts to bring these four reactor units under control by restoring automatic cooling has encountered a serious obstacle: entry and work within the plant buildings has uncovered a lot of highly radioactive water. In the face of this hazard, workers simply can’t spend more than a brief time in the environment, and so can’t get much done. But more gravely still, it appears that the emergency cooling of the reactors will have the effect of increasing radiation levels at the plant, as tons of water wash over damaged nuclear fuel and contaminated debris, pooling in tunnels, diesel generator buildings and elsewhere at Fukushima Daiichi.
Yukiya Amano, director general of the United Nation’s International Atomic Energy Agency (IAEA), said over the past weekend that Japan was “still far from the end of the accident.” At a Tokyo news conference on Sunday, March 27th, a vice president of TEPCO was asked for the company’s projected timeline for emerging from the crisis, and he responded: “We don’t have a concrete schedule.” On Tuesday, March 29th, Hidehiko Nishiyama, deputy director general of Japan’s Nuclear and Industrial Safety Agency, said: “We will have to continue cooling for quite a long period. We should be thinking years.”
There are several ways in which the Fukushima Daiichi nuclear accident is new territory for governments, industry and the public – different from Pennsylvania’s 1979 Three-Mile Island partial core meltdown and Ukraine’s 1986 Chernobyl reactor explosion and fire. First, the accident in Japan involves multiple reactors simultaneously, and is unfolding within the scope of a massive natural disaster of national scale. Secondly, at Fukushima Daiichi not only are fueled nuclear reactors at risk, but also pools within the reactor buildings where a greater quantity of discharged nuclear fuel is stored. Thirdly, mixed-oxide (MOX) fuel is loaded in the core of one of the reactors, a type of plutonium-rich fuel never before involved in a nuclear accident. And finally, radiation is being emitted both into the atmosphere and directly into the Pacific Ocean.
Iodine-131 Detected in US Milk
As part of the US Environmental Protection Agency (EPA)’s RADNET radiological monitoring program, the federal government analyzed milk samples obtained on March 25th from Spokane, Washington, and found levels of Iodine-131 to be 0.8 pCi/L. The EPA stated that "this level of radioactive iodine is “is more than 5,000 times lower than the Derived Intervention Level set by the U.S. Food and Drug Administration.” NRDC calculated the risk of getting cancer from drinking a gallon of milk at this level of iodine-131 contamination. According to EPA Federal Guidance, the risk of getting cancer from ingesting iodine-131 is 0.0000000000648 per pCi, and dying from the cancer caused by the exposure is about ten times smaller, or 0.00000000000685 per pCi (which are lifetime risks averaged over all age groups). Therefore drinking a gallon of milk contaminated to 0.8 pCi/L would increase your risk of getting cancer by about 1 in 100 billion, and increase your risk of dying from such cancer by about 1 in a trillion, which are very small risks. We are interested in following the iodine-131 measurements in US milk over time, reading that the EPA “has taken steps to increase the level of nationwide monitoring of milk, precipitation, drinking water, and other potential exposure routes.”
Information on the Fukushima Daiichi Nuclear Plant and Accident
The Tokyo Electric Power Company (TEPCO) owns and operates the Fukushima Daiichi nuclear power plant which has six reactor units. These six reactors are all Boiling Water Reactors (BWRs) which were brought online in the 1970’s (see table below for detailed information). About one-fifth of the operating reactors in the world are BWRs, which are the second most common type of reactor (the most common type of nuclear reactor is the Pressurized Water Reactor or PWR). In a BWR, the steam from the water that boils as it cools the reactor core is directly used to generate electricity in turbines. The group of damaged reactor units at Fukushima Daiichi is laid out in a line along Japan’s Pacific coast, with reactor units spaced about 250 feet apart: Unit 1 to the north and Unit 4 to the south. These reactors are approximately 140 miles from Tokyo, 3,000 miles from mainland Alaska, 4,000 miles from Hawaii and 5,000 miles from the U.S. West Coast.
Table: Detailed Technical Information on Fukushima Daiichi Reactor Units (data are from the 2008 World Nuclear Industry Handbook, Nuclear Engineering International).
|Fukushima Daiichi Reactor||Date of Start of Construction||Date of First Power||Reactor Model||Net Electric Capacity in Megawatts||Fuel Inventory: Tons of Heavy Metal in Reactor Core||Containment Design Pressure (kilograms per square centimeter)||Number of Reactor Control Rods||Maximum Fuel Cladding Temperature (degrees Celsius)||Maximum Fuel Centerline Temperature (degrees Celsius)|
|Unit 1||1966||Nov. 1970||BWR 3||439||68||4.35||97||360°||1690°|
|Unit 2||Jan. 1969||Dec. 1973||BWR 4||760||94||3.92||137||310°||1740°|
|Unit 3||Jan. 1970||Oct. 1974||BWR 4||760||94||3.92||137||310°||1740°|
|Unit 4||Jan. 1972||Feb. 1978||BWR 4||760||94||3.92||137||310°||1740°|
|Unit 5||Jan. 1972||Sept. 1977||BWR 4||760||94||3.92||137||310°||1740°|
|Unit 6||Jan. 1972||May 1979||BWR 5||1067||132||2.85||185||310°||1740°|
According to the International Atomic Energy Agency (IAEA), Fukushima Daiichi Unit 4 was shut down for a routine, planned maintenance on November 30, 2010, when all the fuel from the reactor (94 tons, see table above) was transferred to the spent fuel pool. In total 647 tons of spent fuel are reported to be stored in spent fuel pools at the tops of the six reactor buildings, and a further 1,097 tons of spent fuel are stored in another pool at the plant separate from the reactor building.
Just after the earthquake on March 11th, ten Japanese reactors performed an emergency shutdown. Of the six units at Fukushima Daiichi, only three were operating at the time of the earthquake (Units 1, 2 and 3), and these were successfully shut down – the fission chain reactions in the cores were stopped. Trouble began an hour later when the tsunami swept over the station and flooded the backup diesel generating capacity. The flow of cooling water to the reactor cores could not be maintained because of what is called a “station blackout,” when both off-site power and on-site emergency diesel generator backup power was lost, and then subsequently the reserve batteries were exhausted. As cooling systems failed in the reactors, the cores heated up, water surrounding the fuel evaporated, nuclear fuel became exposed to air, and the fuel temperature continued to rise. Hydrogen gas was produced by the hot exposed fuel, this chemical reaction itself producing more heat in the reactor core, and caused the three explosions at Fukushima Daiichi. The explosions damaged the reactor cores, containment, equipment, buildings and – importantly – also damaged the spent fuel pools located at the tops of the reactor buildings.
Radiation Releases in Japan
The highest radiation measurements reported by the Japanese government in the first days of the accident were taken within the plant boundary adjacent to the damaged reactors, and were very high dose rates – sufficient to cause severe radiation sickness in addition to genetic damage and heightened cancer risk over a period of hours or less. Even at the plant boundary, reported radiation levels last week were such that the threshold of the annual limit for nuclear plant workers would be reached in a matter of hours. Off site, the Japanese government confirmed radioactive Iodine-131and Cesium-137 has been detected in the water supplies of Fukushima city, neighboring prefectures, and in Tokyo 140 miles southeast from the reactors. Fallout (surface deposition of radioactivity) from the reactor disaster has been measured in twelve prefectures surrounding Fukushima Daiichi, and is accumulating over time. Last week higher than normal levels of radioactivity in spinach and milk – unhealthy levels – were measured at farms up to 90 miles away from the reactors – this was the first report of radioactive materials in Japan’s food supply, and low levels of radioactivity were also detected in a shipments of produce and container cargo to China. TEPCO has stated that high levels of radioactive substances were found in seawater near the plant.
Radiation Releases to the United States
US Government radiation detectors have picked up signals from radioactive strontium, cesium, iodine and xenon consistent with a signal from a reactor accident in monitoring stations located in Alaska, Washington State, and California, but at a maximum intensity 1/100,000th of normal background levels. These low levels are not of a health concern to individuals, and reflect dilution and dispersal over the eastward drift from Fukushima Daiichi to the United States.
Developments for US Nuclear Power Related to the Fukushima Daiichi Accident
The United States currently has the largest number of nuclear reactors of any country: 104 reactors, or about one-quarter of the world’s total operating reactors. More than two-dozen US reactors are similar in design to the units at Fukushima Daichii.
The NRC will begin a “90-Day Effort” soon to evaluate information from the Japanese event, and use that information to evaluate the 104 operating US reactors, looking at: natural disasters, station blackouts, severe accidents and spent fuel accident projection, and radiological consequent analysis. The result of the 90-Day Effort will be a “Quick Look” report with “limited stakeholder involvement.” There is no start date yet for a nine month review by the NRC, although this is generally planned, which will be inter-agency (for example including FEMA) and have “significant stakeholder involvement.”
Tokyo Electric Power Company: Press Releases Describing Work at the Damaged Nuclear Plant
Japanese Nuclear Industrial and Safety Agency: Data on Radiation Measurements in the Environment
International Atomic Energy Agency: Fukushima Nuclear Accident Update Log
World Health Organization: Daily Situation Reports
US Nuclear Regulatory Commission: NRC Actions on Japan’s Emergency
US Department of Energy: The Situation in Japan
US Environmental Protection Agency: EPA's Radnet Air Monitoring Data
US Centers for Disease Control and Prevention: 2011 Earthquake, Tsunami, and Radiation Release in Japan: Travel Information