The situation in Japan is serious. But, as of 1.30 3.00 9.30 pm PDT, there has been no “nuclear explosion” even though you may have seen headlines or tweets to that effect. Officials assume, but have not confirmed, a “partial meltdown” which does not appear to be either a “China Syndrome” (thank you, Hollywood) or a “Chernobyl” (thank you, media).

Four nuclear power plants in northern Japan have been affected by the earthquake-tsunami natural disaster. Here’s what we know about them, with minimal speculation. [Also, see this nuclear power explainer.]

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; residents have been evacuated in a 12.5-mile radius

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 from Units 1 and 3 to relieve pressure. Small amounts of radiation can escape, even though the steam is routed through a system of filters before reaching the atmosphere.

  • 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.

    Boing Water Reactor

    Status Of Fukashami Unit 1 From NEI

    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.

  • 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).

Fukushima Daini Nuclear Power Station

Located about 150 miles north of Tokyo
State of emergency at Units 1, 2 and 4
Residents have been evacuated in an approximate two mile radius

It has four reactors; Unit No. 3 is in “a safe, cold shutdown” and “Units 1, 2, and 4 at the Fukushima Daini retain off-site power.” However, the three reactors have had issues with cooling but there has been no venting of steam.

Tokyo, Japan to Onagawa

Tokyo, Japan to Onagawa

Onagawa Nuclear Power Plant

Located about 275 miles north of Tokyo
State of emergency

Reuters reported a fire at the facility on Friday. On Sunday, the government placed the area at emergency level one, the lowest state of emergency, due to a temporary elevation in radioactivity readings adjacent to the plant.


Tokyo, Japan to Ibaraki Prefecture

Tokyo, Japan to Ibaraki Prefecture

Tokai Daini Power Plant

Located about 75 miles north of Tokyo

On Sunday, news media reported that Unit No 2 cooling system pump had stopped working.


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KATHY GILL, Technology Policy Analyst
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