Core on the Floor at Fukushima’s Nuclear Meltdown?

by Jim Riccio

May 13, 2011

Greenpeace Radiation Team

This morning Reuters reported that the damage at Fukushima Unit 1 was greater than expected by reactor owner TEPCO. This should not come as a surprise as TEPCO has, time and again, been slow to acknowledge the extent of the nuclear crisis in Japan.

TEPCO discovered that the water level in the pressure vessel that contains its uranium fuel rods had dropped about 5 meters  (16 ft) below the targeted level to cover the fuel under normal operating conditions.

“There must be a large leak,” Junichi Matsumoto, a general manager at the utility told a news conference.

“The fuel pellets likely melted and fell, and in the process may have damaged…the pressure vessel itself and created a hole,” he added.

When the reactor vessel is breached by the molten fuel this is commonly referred to by nuclear experts as “core on the floor”.

Dr. Ed Lyman of the Union of Concerned Scientists discussed this scenario over a month ago:

“While the authorities continue playing down the possibility of a breach of the primary containment at these reactors, I remain concerned.  Fukushima Dai-Ichi reactor Units 1, 2, and 3 are boiling water reactors with Mark I containments.  The Mark I is unusually vulnerable to containment failure in the event of a core-melt accident.  A recent study by Sandia National Laboratories shows that the likelihood of containment failure in this case is nearly 42% (see Table 4-7 on page 97). The most likely failure scenario involves the molten fuel burning through the reactor vessel, spilling onto the containment floor, and spreading until it contacts and breeches the steel containment-vessel wall.”

The situation in Japan highlights the inherent danger of nuclear power and that we should be using safe, clean and unlimited sources of energy like wind and solar. Let’s make that happen by telling the President and Congress that US tax payers should not on the risk of building new nuclear plants!

Jim Riccio

By Jim Riccio

Jim Riccio served as Greenpeace’s Nuclear Policy Analyst from 2001 to 2017 and has over two decades of nuclear activist experience. He has been quoted in the New York Times, Washington Post, Wall Street Journal, Los Angeles Times, and Boston Globe, and has appeared on ABC News, NBC News, Al Jazeera, CNN, the Discovery Channel and the History Channel.

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