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Posted by on Mar 16, 2011 in International, Science & Technology | 0 comments

Japan’s Nuclear Headache : Timeline and Reactor Status at Fukushima

In the wake of Friday’s earthquake and tsunami, the challenge facing Fukushima has been keeping the nuclear cores covered with water, which is needed to cool the fuel rods, the heart of a reactor. The most serious damage is at the Unit 2 reactor, where there was a hydrogen explosion on Tuesday; the suppression pool has been damaged.

Only 50 employees remain on site, and they have been exposed to high levels of radiation. However, news reports indicate that radiation levels drop quickly once leaving the vicinity of the power plant. A spike on Wednesday, which led to suspended operations, followed a decrease in detectable radiation Tuesday.

This post follows two other updates focused on the status of reactors (Sunday and Tuesday). 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. Later, residents living in a 20-30 kilometer radius were advised to stay inside.

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.” Treatment with potassium iodide helps keep the thyroid, which requires iodine to function, from absorbing radioactive iodine.

Tokyo, Japan to Okuma

Tokyo, Japan to Okuma, Fukushima Prefecture

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

Boing Water Reactor

Status Of Fukashami Unit 1 From NEI

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.

As of 19.00 March 15 (Japan, pdf unless otherwise indicated):

  • Fuel Integrity : 70% damaged
  • Containment Integrity : not damaged
  • Core cooling : not functional
  • Water level in pressure vessel : about half full
  • Pressure in pressure vessel : stable
  • Sea water injection into the core : ongoing

Unit 2 Reactor

Boiling Water Reactor - Torus

The Unit 2 Suppression Pool May Be Damaged

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 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.

It is believed to be the source of this surge:

The Nuclear and Industrial Safety Agency told reporters on Wednesday that the level of radiation near the plant’s main gate rose to 10 millisieverts per hour at 10:40 AM, but dropped to 2.7 millisieverts per hour within 30 minutes.

As of 19.00 March 15 (Japan, pdf unless otherwise indicated):

  • Fuel Integrity : 33% damaged
  • Containment Integrity : damaged
  • Core cooling : not functional
  • Water level in pressure vessel : recovering after going dry
  • Pressure in pressure vessel : fluctuating
  • Sea water injection into the core : ongoing

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).

As of 19.00 March 15 (Japan, pdf unless otherwise indicated):

  • Fuel Integrity : damaged
  • Containment Integrity : possible damage
  • Core cooling : not functional
  • Water level in pressure vessel : about half full
  • Pressure in pressure vessel : stable
  • Sea water injection into the core : ongoing

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. After being contained, it began burning again Wednesday (for two hours). The source of the fire: an oil leak in a cooling water pump. The fire was not in the spent fuel pool, despite media reports making this assertion.

There is no fuel in the reactor, but there is spent fuel in the reactor (pool), which must be cooled; there are concerns that this water is boiling.

All of the fuel rods had been moved from reactor 4 to the spent fuel pool due to the maintenance work.

As of 19.00 March 15 (Japan, pdf unless otherwise indicated):

  • Fuel Integrity : not damaged
  • Containment Integrity : not damaged
  • Core cooling : not needed
  • Water level in pressure vessel : safel
  • Pressure in pressure vessel : safe
  • Sea water injection into the core : not necessary

Units 5 and 6

Reactor Unit 5 and 6 were not in use at the time of the earthquake. As of 15 March, there have been reports rising temperatures in the water (ponds) that house spent fuel rods. About one-third of the fuel rods in reactors 5 and 6 had been removed as part of maintenance and refueling activities.

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


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