2011-03-14 14:46

Q: What steps can be taken to prevent a meltdown?

A: The immediate key is reducing temperatures in all the reactor vessels. Another critical goal would be restoring regular electrical power.

Q: Why did the containment building at Dai-ichi Unit 1 explode?

A: When officials decided to vent steam from the reactor vessel to reduce the pressure, the hydrogen in the steam interacted with available oxygen. They knew it could cause a blast, but felt they had no choice. If the pressure kept building, the reactor vessel could have exploded, likely starting a meltdown scenario.

Q: How likely is it that one or more total meltdowns will occur?

A: That is very difficult to predict without detailed real-time measurements from inside the nuclear facilities. But admissions from Japanese officials that a partial meltdown may have already occurred are troubling.

Q: Why was the official announcement made late Sunday about something that occurred Friday?

A: Officials in Japan have been slow to provide information about the status of the nuclear plants. (There are 55 reactors on 17 sites throughout the country. Japan gets one-third of its electricity from nuclear plants.) The belated disclosures are often clouded in generalities. At times, new information has been available sooner from the International Atomic Energy Agency in Vienna. The UN organization posts updates at www.facebook.com/iaea.org

Q: How long will the crisis last?

A: One expert said cooling down all the reactors will "take days, not hours." But even if circumstances improve, conditions can still turn negative again.

Q: How about personal health danger?

A: Exposure to radioactive iodine released in a nuclear power accident can cause thyroid cancer.

Q: Is there a way to protect against the effects of radiation exposure?

A: Potassium iodide pills can help prevent thyroid cancer.

Q: So what is the worst-case scenario?

A: The attempts to cool the reactors fail, resulting in meltdowns and widespread radioactive contamination. If that occurs, everyone will be hoping the wind blows east, into the Pacific, as it usually does.

Q: The best-case?

A: Officials gain complete control of the temperature and pressure at the troubled reactors; then conditions will need to improve enough so it will be safe for workers to get close to assess the damage and restore normalcy.