There are serious problems at all reactors at the Fukushima Daiichi Nuclear Power Station. But, as of 10.00 pm PDT Monday, there has been no “nuclear explosion” even though you may have seen headlines or tweets that imply or say that. The challenge facing Fukushima is keeping the nuclear core covered with water, which is needed to cool the fuel rods, the heart of the reactor. The most serious damage appears to be at the Unit 2 reactor; TEPCO workers continue to pump sea water at units 1, 2 and 3.

This post is an update of Sunday’s recap but focuses exclusively on the status of reactors Fukushima Daiichi Nuclear Power Station. Also, see this nuclear power explainer for general background on nuclear power and the situation in Japan.

Precautionary Action: Evacuations and Iodine
On 12 March, the Japanese Prime Minister ordered the evacuation of residents living within 20 kilometres of the Fukushima Daiichi nuclear power plant. Japan has distributed 230,000 units of stable iodine to evacuation centers around the Fukushima Daiichi and Fukushima Daini nuclear power plants. According to the International Atomic Energy Commission, “the iodine has not yet been administered to residents; the distribution is a precautionary measure in the event that this is determined to be necessary.”

Fukushima Daiichi Nuclear Power Station

Located about 150 miles north of Tokyo
State of emergency at Units 1, 2 and 3
All six units shut down

This facility was the first to make headlines in western media. After the earthquake and tsunami, the facility lost external (grid) power and shifted to back up diesel generators. When those failed, it shifted to battery power. Whether the problem was loss of power or flooding, engineers struggled to maintain the water flow needed to keep cooling nuclear reactor core. The failure of the high pressure injection cooling system eventually led engineers to use sea water, mixed with boron, to continue cooling the reactor core. Engineers have vented steam to relieve pressure. Small amounts of radiation can escape, even though the steam is routed through a system of filters before reaching the atmosphere.

Unit 1 Reactor

On Saturday, there was an explosion at the building housing Unit No. 1; the explosion was probably caused by a build up of hydrogen gas, which can be a byproduct of cooling failure. The explosion was outside the primary containment vessel; four employees were injured. The explosion did not release radioactive material.

Also, officials detected caesium-137 and iodine-131 in the vicinity of Unit No. 1; radioactive cesium is created when uranium fuel is split. This detection also suggests cooling failure and “partial meltdown.” A “partial meltdown” results from over-heating and means a partial loss of integrity in the precise geometry of the rods at the center of the controlled nuclear reaction. The actuality and extent of any meltdown remains unknown.

Unit 2 Reactor

At 6.10 am Tuesday morning (Japan), there was an explosion at Unit 2. In a news conference, Chief Cabinet Secretary Yukio Edano said that the suppression pool had been damaged. The suppression pool is part of the containment system designed to prevent radioactive material from leaking outside. In addition, the Nuclear and Industrial Safety Agency said that nuclear fuel rods are exposed above water by about 2.7 meters, about half the length of the rods.

This is the first incident at the facility to be tied directly to human error, although the underlying cause remains the twin whammy of earthquake and tsunami. According to the LA Times:

Engineers had begun using fire hoses to pump seawater into the reactor — the third reactor at the Fukushima No. 1 complex to receive the last-ditch treatment — after the plant’s emergency cooling system failed. Company officials said workers were not paying sufficient attention to the process, however, and let the pump run out of fuel, allowing the fuel rods to become partially exposed to the air.

Once the pump was restarted and water flow was restored, another worker inadvertently closed a valve that was designed to vent steam from the containment vessel. As pressure built up inside the vessel, the pumps could no longer force water into it and the fuel rods were once more exposed.

The torus or suppression pool contains a large body of water and is where steam can be directed in an emergency to reduce pressure in the reactor system. If it is cracked, it cannot hold pressure and will release steam into the atmosphere.

Unit 3 Reactor

On Sunday, engineers vented steam from Unit No. 3 to relieve pressure inside the reactor. After the venting, “[r]adiation levels outside the plant, which had retreated overnight, shot up to 1,204 microsieverts per hour, or over twice Japan’s legal limit.” In addition, the emergency cooling system stopped working. According to Japan Live TV, Unit No 3 rods were exposed (~2.2 meters) above the water line.

On Monday at 11.01 am (Japan), there was an explosion in Unit 3, probably a hydrogen leak. Officials say that water is still being pumped to cool the reactor (press release).

Unit 4 Reactor

A fire on the Unit 4 reactor reactor building’s 4th floor was spotted at 9:38 AM Japan time on Tuesday. It was still burning at 7 pm PDT (11 am Japan). There is no fuel in the reactor, but there is spent fuel in the reactor (pool), which must be cooled.

Editorial Context

My inspiration to write these articles is the inflammatory, sound-bite focused headlines gracing western media websites, along with opportunistic political pandering. I am a former technical/science writer (now an educator) who happens to have friends in the nuclear power industry, friend willing to read drafts, answer questions and point me to resources. I am not an advocate for any particular form of energy, although I worry about US dependence on petroleum.

In talking with a friend today, I shared my frustration with what appears to be American paranoia regarding nuclear power. Her response: we are the nation that dropped nuclear bombs on Japan. Perhaps the horror of “the bomb” leaches into our fear of nuclear power, which is not the same thing (but most Americans probably don’t know that — after all, 1-in-5 thinks the sun revolves around the earth).

For anyone who thinks that US dependence on coal-fired power plants somehow makes us “safer” than the Japanese, please consider these facts, and remember that there are no “perfectly clean” sources of energy:

• The fly ash emitted by a coal-fired power plant “carries into the surrounding environment 100 times more radiation than a nuclear power plant producing the same amount of energy.” ~ Scientific American
• “Fukushima Daiichi Unit 1, is one of Japan’s oldest. It was two weeks from its 40-year expiration date when the quake hit. Similar plants in the United States have been upgraded to ensure that in the event of power failure, water can still be pumped in to cool them.” ~ Slate
• “The rate of direct fatalities per unit of energy production is 18 times worse for oil than it is for nuclear power.” ~ Slate
• “Even if you count all the deaths plausibly related to Chernobyl—9,000 to 33,000 over a 70-year period—that number is dwarfed by the death rate from burning fossil fuels. The OECD’s 2008 Environmental Outlook calculates that fine-particle outdoor air pollution caused nearly 1 million premature deaths in the year 2000, and 30 percent of this was energy-related. You’d need 500 Chernobyls to match that level of annual carnage. But outside Chernobyl, we’ve had zero fatal nuclear power accidents.” ~ Slate

Resources

• International Atomic Energy Agency Newscenter
• NY Times: Infographic provides visual insight into the situation at Fukushima Daichi
• Nuclear Energy Institute: Backgrounder: Radiation and the Japanese Nuclear Reactors
• Brave New Climate: Situation summary by Dr Josef Oehmen, MIT — detailed but understandable. Also at The Energy Collective
• TEPCO: Plant Status of Fukushima Daiichi Nuclear Power Station (as of 9pm March 13th) – press release archived here due to server issues in Japan (pdf)