“Probable impossibilities are to be preferred to improbable possibilities.” — Aristotle

An unimaginable natural disaster that was a combination of a monster 9.0 earthquake and an ensuing powerful tsunami triggered unprecedented “secondary” and “tertiary” effects of reactors meltdown, fire and radiation release at the Fukushima Daiichi Nuclear Power Station in Japan.

What is unfolding is the realization of probable impossibilities: The compromise of a nuclear power plant, as a result of a tsunami caused by an earthquake, would be a creative mind’s scenario in a Hollywood disaster movie. Yet is happening before our own eyes. And it is a rude awakening to reconsider seriously our wishful assumptions of our systems’ reliability and the vulnerability of the redundant safety systems to common mode failures.

Out of the six nuclear reactors at the Fukushima plant, two have had partial meltdowns, accompanied by powerful hydrogen explosions. Thankfully, their primary containment vessels, made of concrete and steel and able to prevent radiation from escaping, were mostly holding on (at least for five of the six reactors), despite the very strong motions from the earthquake. (Reactor number 2 suffered a minor breach of the primary containment.) These reactors are not out of the danger zone yet as their fuel rods contain residual heat and they need to be cooled. Most likely this will be accomplished by dumping more seawater into the vessel, then venting the resulting steam to the atmosphere and continuing this process of “feed and bleed” until they can be stabilized.

But at present, the gravest danger at the Fukushima plant is the dire condition of the spent fuel storage facilities that contain tons of still highly radioactive and “hot” spent fuel rods. Spent fuel (otherwise known as nuclear waste) has been of a secondary concern prior to this impending disaster, despite its immense importance. In many of the nuclear plants around the world, the practice is for old rods to be stored in 30- to 40-feet-deep body of water pools with a cooling system to dissipate the intense heat they give off. These pools are located in the containment area. However, loss of water or its circulation could convert the pools to a wet “lethal sauna” with rising levels of radioactive steam. An explosion last Tuesday damaged the building of Reactor No. 4, its roof and, according to last Wednesday’s Congress testimony of the chairman of the U.S. Nuclear Regulatory Commission, resulted in all the water in these pools to boil dry. In his words: The radiation levels are extremely high, which “impact the ability to take corrective measures.”

Spent fuel pools currently are in use at all 65 sites with operating commercial nuclear power reactors in the United States. The unfolding nightmare in Fukushima tells us that these are major safety and security sitting ducks in 33 states of the union. A major study by the National Research Council in 2005 on the safety and security of spent fuel storage found that an accidental or a terrorist attack that “partially or completely drained the spent fuel pool could lead to a propagating zirconium cladding fire and the release of large quantities of radioactive materials to the environment.” It recommended that “the NRC should ensure that power plant operators take prompt and effective measures to reduce the consequences of loss-of-pool-coolant event in spent fuel pools that could result in propagating zirconium cladding fires.”

More ominously, these spent fuel pools are gradually approaching their full capacity, and it is projected that up to three or four nuclear power plants will reach full capacity in their spent fuel pools, each year for at least the next 11 years.

The Japan disaster notwithstanding, and just to highlight the urgency to paying serious attention to this issue in the United States, one can point to the dangerous safety condition of the spent fuel pool at the Unit 1 of the Millstone nuclear power plant in Connecticut, which was the subject of a protracted and controversial investigation by the NRC and was the topic of a special investigation and article in Time magazine. This case, according to the article, resulted in some major policy changes in the NRC, as well the inclusion of all Millstone reactors in the NRC’s “hall of shame,” which is the high-scrutiny “watch list” of troublesome reactors.

We have to learn lessons from Fukushima and count our blessings in the United States. And urgently start, before it is again too late, decommissioning the highly risky spent fuel pools, now scattered all over the country in 33 states. This can be accomplished by reactivating the Yucca Mountain deep geologic disposal site for high-level nuclear waste, the study of which has been going on for more than 25 years with the staggering cost of $38 billion to date.

Making Yucca Mountain the solution to the nuclear waste disposal problem is a vital public policy issue that requires bold leadership from the administration and bipartisan support. It is fortuitous that in this critical juncture, Dr. Steven Chu, a Nobel physicist, is leading the U.S. Department of Energy. In light of what’s happening in Japan, he ought to lead the effort to reconsider the decision to withdraw Yucca Mountain’s license application from the NRC, restore its funding, and urgently reactivate the project.

In the age of probable impossibilities, we cannot afford to stick to wishful thinking or romantic fascination of the improbable failure of even a single one of these 65 dangerous sites. Exhibit A: Fukushima.

Najmedin Meshkati is a professor of civil/environmental and industrial and systems engineering at the University of Southern California.