As workers at the Fukushima Daiichi power plant scrambled to prevent a meltdown of cores of several reactors on Tuesday, a new problem emerged: the failure of cooling systems for several pools containing spent fuel rods. Late Tuesday, Japan’s nuclear watchdog said that the water meant to cool spent fuel in three reactors was becoming dangerously hot. If the water evaporates and the rods become dry, they could overheat and catch fire, potentially spreading radioactive materials in dangerous clouds.
To understand the danger posed by spent fuels, Ecocentric has put together a fact sheet with the help of Dr. Ferenc Dalnoki-Veress, a Research Scientist at the James Martin Center for Nonproliferation Studies (CNS) at the Monterey Institute of International Studies.
What is spent fuel?
Spent fuel are fuel assemblies that have been used in the nuclear reactor to produce electricity and are no longer useful. Spent fuel is taken out of the reactor and replaced by new fuel. Nuclear power plants do this periodically—in some cases, every year. Once they are removed, however, spent nuclear fuel is very “hot and dirty”–it’s physically hot, but it also emits lots of nasty radiation. So you have to cool it in a special pool for 5 to 10 years to let the radioactivity fade.
So what could go wrong?
If you don’t keep circulating the water in the pool, it won’t provide enough cooling. It will start boiling. When that happens, steam is released that is radioactive. That makes it very dangerous for workers to approach the pool and fix the problem. Some reports from Japan suggests that might be the current situation. At a press conference on Tuesday covered by the New York Times, a spokesman from the plant’s operator Tokyo Power Company said that “The only ideas we have right now are using a helicopter to spray water from above, or inject water from below. We believe action must be taken by tomorrow or the day after.”
What could happen if cooling fails?
If you don’t cool the spent fuel, the temperature will rise and there may be a swift chain reaction that leads to spontaneous combustion–an explosion and fire of the spent fuel assemblies. Such a scenario would emit radioactive particles into the atmosphere.
The nuclear industry has said that spent fuel storage is safe and that the risk of fire is low in part because the spent fuel contains relatively little energy compared to the fuel inside the reactor. In addition, industry officials have said, plant workers only need to replace about 25 gallons of water each day to the fuel pool to maintain water levels.
Would a spent fuel fire be worse than a meltdown of the reactor core?
Pick your poison. Fresh fuel is hotter and more radioactive, but is only one fuel assembly. A pool of spent fuel will have dozens of assemblies. One report from Sankei News said that there are over 700 fuel assemblies stored in one pool at Fukushima. If they all caught fire, radioactive particles—including those lasting for as long as a decade—would be released into the air and eventually contaminate the land or, worse, be inhaled by people. “To me, the spent fuel is scarier. All those spent fuel assemblies are still extremely radioactive,” Dalnoki-Veress says.
Why hasn’t there been concern over spent fuel safety in the past?
There has been. The spent fuel is related to a nagging issue for the nuclear industry: what to do with nuclear waste. Right now, there is no approved long-term storage of spent fuel. Storage in certain geological structures would safely house spent fuel for centuries, but it’s difficult to get nearby communities to accept such geological repositories. So, as an interim measure, nuclear power companies are storing more spent fuel assemblies in pools.
Interestingly, the people who have raised the most concern about this is nuclear terrorism experts, rather than nuclear safety campaigners. That’s because combustion of spent fuel was something that most people only thought could be possible following sabotage by terrorists. “This is the worst case scenario that ‘[terrorism experts] thought about happening. We envisaged scenarios such as terrorists stopping the cooling at a spent fuel pond. And now it seems to be happening without terrorists,” Dalnoki-Veress says.
Perhaps the most troubling warning about the dangers of spent fuel came in a 2003 article in the journal “Science and Global Security” by Robert Alvarez, Senior Scholar, Institute for Policy Studies, called “Reducing the Hazards from Stored Spent Power-Reactor Fuel in the United States.” Its first paragraph reads:
Because of the unavailability of off-site storage for spent power-reactor fuel, the U.S Nuclear Regulatory Commission has allowed high-density storage of spent fuel in pools originally designed to hold much smaller inventories….It has been known for more than two decades that, in case of a loss of water in the pool, convective air cooling would be relatively ineffective in such a “dense-packed” pool. Spent fuel recently discharged from a reactor could heat up relatively rapidly to temperatures at which the zircaloy fuel cladding could catch fire and the fuel’s volatile fission product, including 30-year half-life Cs, would be released. The fire could well spread to older spent fuel. The long-term land-contamination consequences of such an event could be significantly worse than those from Chernobyl.
