Nuclear power safetyDeveloping nuclear cladding to withstand Fukushima-like meltdown conditions

Published 20 October 2015

Like much of the rest of the world, thousands of scientists and engineers watched in March 2011 as Japan’s Fukushima Daiichi nuclear reactors exploded. The fuel’s cladding, a zirconium alloy used to contain the fuel and radioactive fission products, reacted with boiling coolant water to form hydrogen gas, which then exploded, resulting in the biggest nuclear power-related disaster since Chernobyl. Challenged by this event, two research teams have made progress in developing fuel claddings that are capable of withstanding the high temperatures resulting from a Loss of Coolant Accident (LOCA), like that at Fukushima.

Like much of the rest of the world, thousands of scientists and engineers watched in March 2011 as Japan’s Fukushima Daiichi nuclear reactors exploded. The chain of events began when a magnitude 9.0 earthquake off the coast of Tohoku caused a tsunami that destroyed the ability to cool the fuel elements in the reactors.

The fuel’s cladding, a zirconium alloy used to contain the fuel and radioactive fission products, reacted with boiling coolant water to form hydrogen gas, which then exploded, resulting in the biggest nuclear power-related disaster since Chernobyl.

Challenged by this event, two research teams have made progress in developing fuel claddings that are capable of withstanding the high temperatures resulting from a Loss of Coolant Accident (LOCA), like that at Fukushima. AVS reports that both teams are presenting their results at the AVS 62nd International Symposium and Exhibition, held18-23 October in San Jose, California.

Testing new fuel claddings — merging models and experiments
At the Illinois Institute of Technology, Jeff Terry and colleagues are seeking to determine whether silicon carbide could be an adequate cladding, while reducing the possibility of hydrogen explosions. Nuclear fuel cladding prevents radioactive fission products from escaping into the coolant, and must hold up under the extreme conditions that might be present during accidents. To that end, the researchers have conducted one of the first experiments to describe the physical and chemical properties of radioactive elements in silicon carbide under accident conditions.

Terry’s approach combines theory and experiment, using resources from several national labs and institutions to bridge the gap between the predictions of models and experimental data from earlier, more applied, measurements. “These complex environments are often difficult to predict theoretically. Our collaborators at Oak Ridge National Laboratory have done wonderful work predicting the reactivity of fission products on model single crystal silicon carbide surfaces,” Terry explained.

What Terry needed was a way to measure the actual position of elements in the materials, so that the accuracy of the models could be tested. At IIT, the group can both create the model materials used in the calculations and experimentally determine the environment of each element, both in the model materials and in irradiated fuel claddings.

“It is no longer practical to test every element in a nuclear reactor to failure,” said Terry. “We need to have models that predict what will actually happen.” To advance the development of more reliable models, the research team used IIT’s pulsed laser