As the one-year anniversary of the Fukushima Daiichi reactor accident is marked on March 11, a new paper by Peter C. Burns, Henry Massman Professor of Civil Engineering and Geological Sciences at the University of Notre Dame and colleagues from the University of Michigan and the University of California, Davis, stresses that we need much more knowledge about how nuclear fuel interacts with the environment during and after an accident.
In the paper, which appears in the March 9 editions of the journal Science, Burns and Rodney C. Ewing of the University of Michigan and Alexandra Navrotsky of the University of California-Davis call for increased research to help develop predictive models for future nuclear accidents.
A nine-magnitude earthquake near Japan on March 11triggered a tsunami that wiped out coastal towns, shut roads, severed communications and claimed thousands of lives. It also cut off all electricity to the Fukushima Daiichi nuclear power station, setting the stage for a series of explosions which released large quantities of radioactive substances into the surrounding environment.
"Reactors are designed to high safety standards, but on the anniversary of the accidents in Fukushima we are reminded that the forces of nature can produce unlikely events that can overcome the safety margins built into the reactor designs," Burns said. "A reactor core meltdown releases radioactive material from the fuel. If containment systems fail, as they did at Fukushima, radioactive material is then released into the environment."
Burns, Ewing and Navrotsky point out in their paper that accurate fundamental models for the prediction of release rates of radionuclides from damaged fuel, especially in contact with water, after an accident are limited.
"At Fukushima, a large amount of radioactive material was released when seawater was pumped onto the reactor cores that later leaked into the ocean and groundwater," Burns said. "Little is known about how radioactive fuel in a reactor accident interacts with water and releases radioactive material. This paper examines what is known, points to serious shortcomings in our understanding, and proposes a course of research to address the problem."
Although some of the needed research can be conducted using simulated core-melt events with fuel analogs that contain nonradioactive isotopes, Burns and his colleagues point out that some of the studies will need to be done with radioactive materials. Although such studies are both difficult and expensive, Burns points out that they are essential to reduce the risk associated with increasing reliance on nuclear energy.
"Nuclear power reactors, of which there are currently 440 operating worldwide, provide about 16 percent of the world's electricity," he said. "They also produce extremely radioactive used fuel.
"A growing reliance on nuclear energy in the world over the coming decades will make serious reactor accidents more likely, although they will remain rare events. To better protect humanity when accidents do occur, we need a much improved understanding of how water interacts with damaged fuel, and how the radioactive material is released and transported in water."
The research described in the Science paper was conducted under the auspicious of Notre Dame's Energy Frontier Research Center (EFRC), a U.S. Department of Energy-funded initiative established to pursue advanced scientific research on energy. Burns serves as director of the center.