THE BLOG

Conflicting Stories Surround Fukushima Fuel Pool #4

The tragedy at the Fukushima reactors and the misery in Japan continues to unfold. We can only feel sorrow for our brothers and sisters in Japan. The media frenzy in the U.S. is reaching new heights and has started to take leave of its senses. Consider the fuel pool at reactor #4. This sits 70 to 80 feet above the ground, near the top of the reactor. Is it dry, as NRC Chairman Jaczko has stated in Congress on Thursday? Is the zirconium fuel cladding on fire, as CNN has graphically shown? To this and more, I say, no.

Earthquake and Tsunami of Biblical Proportions

When the 9.0 earthquake struck off shore, and 30 foot waves washed out ten thousand lives and tens of thousands of homes, Fukushima reactors 1, 2 and 3 were operating, and reactors 4, 5 and 6 were shut down for maintenance, and had been since the end of November. The fuel in those reactors had been transferred to the fuel pools. When the tsunami washed out off-site power and backup power from diesel generators, nuclear fuel from reactors 4, 5 and 6 had already cooled for 100 days. But now, all pumps and water circulation ceased.

Heroic Workers and Measures

The immediate problem was the three operating reactors 1, 2 and 3. On immediate shutdown, the fuel in those reactors was more than 100 times more heat-generating than the fuel in pools, 4, 5 and 6. Without pumps, workers had to pump water into the reactors, and let the pressure out before more water could be pumped. "Feed and bleed" it was called, likened to pumping water into a balloon. But hydrogen was created in the process; the bleed exploded. Over 2 dozen workers have been injured, while the radiation fields continued to rise. Cesium, a semi-volatile metal and gaseous iodine, were released. At one point, only 50 workers remained on the site. Tokyo Electric (TEPCO) acknowledges that reactors 1, 2 and 3 had partial meltdowns. TEPCO is in the process of bringing in external power and pumps to begin properly circulating cooling water. But the melted fuel will likely not allow unfettered cooling.

Fuel Pool at #4 Reactor

Meanwhile, two fires occurred at reactor #4, partially destroying the roof and side panels of the building. The fuel pool is a deep pool of water, approximately 40 feet deep, with a lattice work to hold the fuel assemblies that are approximately 12 feet long. The water cover is 20', enough to cool and shield the fuel. The International Atomic Energy Agency says the water had reached 84 oC, about 1½ days after the accident. My calculations show that it would take almost 3 days for the water to reach 100 oC. Steam has been seen emanating from the pool. It would then take less than two weeks for the fuel to become uncovered. As the water levels declined and the vaporization increased, the radiation dose rate above the pool would increase. When five feet of cover remained, the dose rate would begin to increase precipitously. When the fuel becomes uncovered, a zirconium fire would ensue. The heat and radiation levels, including released radioactivity, would be enormous. I estimate, using the standard software, Microshield, dose rates on the order of 3000 rems/hour, 200 meters above the fuel pool. Less than one minute in this dose field would be grave.

Conflicting Reports

The New York Times acknowledges Friday afternoon that there are conflicting versions of what is taking place. On the one hand, Union of Concerned Scientists and the Nuclear Regulatory Commission claim that fuel pool #4 is dry and that zirconium fires have taken place, releasing cesium and iodine to the environment. On the other hand, TEPCO says the #4 fuel pool has water. Who's right? The NRC is right, if the fuel pool had a leak and water drained out. But if the steel liner and concrete walls remained intact, TEPCO is right and there is time to bring the #4 pool situation under control. In this conflict, I agree with TEPCO, and hope that the company quickly resolves the problem. The alternative is unthinkable.