Thermal Analysis of Japan's Endangered Nuclear Reactors

Goryca, Jill, and Nihad Dukhan

The damaged reactors in Japan's Fukushima Dai-ichi power plant have released highly toxic plutonium into the soil outside, while the race to bring the power plant under control continues. Escaped radiation takes other circuitous route that depends on winds, rain and the half-life properties of the different materials. Radiation particles latch onto dust and drift with the winds. Some are dropped by rain, while others remain suspended. Traces of radioactive material are being detected in many areas in Japan, the United States and Iceland. Nuclear forensics scientists have used radioisotope signatures to identify gamma rays from isotopes of iodine-131, tellurium-132, cesium-134 and cesium-137. Iodine causes thyroid cancer, while Cesium-137 can be very dangerous because it is long-lived, with a half-life of 30 years.

These events come at a time of increasing discussion about nuclear plant safety and the future of nuclear energy, after the Chernobyl accident in 1986, and on the 32nd anniversary of another major nuclear accident, the Three-Mile Island meltdown in Pennsylvania. The impact on the environment not only could affect peoples' health, but it could also impact the economy.

Some of the radioactivity comes from damaged nuclear fuel rods.  In this presentation, a bundle of fuel rods is modeled as a cylinder having a known a diameter and height with a volumetric heat generation. Thermal analysis is performed taking into account the surrounding steam, steel casing and concrete enclosure.  The analysis assumes no active water cooling to mimic the actual scenario at the Fukushima Dai-ichi power plant.  It is revealed that the temperature inside the rods can reach extremely high levels.  At such temperatures, the steel would melt and the concrete would crumble.

When no cooling is present, and by treating the fuel rods bundle as a lumped system, transient analysis predicts that it would take for the steel to melt and for the concrete enclosure to deteriorate.