The one advantage that Fukushima has over Chornobyl is that it is located on the water and for most of the time as the disaster unfolded the wind was blowing out to sea. Nonetheless, about 80 percent of the airborne contamination wound up in the ocean, while the remaining 20 percent, which was at first dispersed in the mountains, was washed into the ocean by rain and snow. Moreover, roughly four hundred tons of groundwater each day is entering through the cracks in the building, where the nuclear fuel remains on the floor. The Japanese are building tanks for this highly contaminated water—one every two and a half days. These tanks are placed in a large tank farm, where they are pumping water from the basements into the seismically unqualified tanks. Liquid releases will continue for years and years into the future. We already know that the liquid releases are ten times those at Chornobyl.
At what point do the risks of a technology become unacceptable? Sooner or later in any foolproof system, the fools are going to exceed the proofs.
13
Management of Spent-Fuel Pools and Radioactive Waste
Robert Alvarez
When I was in the Department of Energy, we looked at a spent-fuel pool problem at the Hanford nuclear site that had been ignored for decades. At the closing briefing we asked what would happen if there was an earthquake and the water drained. There was a hem and haw, and then an old-timer said, “Well, there would be a fire that would make Chornobyl look like a pimple on a pumpkin.”
The accident at Fukushima has clearly demonstrated the dangers of spent nuclear fuel storage. Each pool contains irradiated fuel from several years of operations. They contain not one reactor core but several, and there is no secondary barrier of concrete and steel like that which covers the reactor. As a result of the explosions, several pools are now completely open to the atmosphere. The pools of this particular design are more than one hundred feet above the ground, and their structural integrity is now in serious question. They are basically temporary storage structures never intended to hold the quantities they are now holding. Further earthquakes might cause drainage or topple the pools. If they were to drain, there would be a point at which the radiation levels would become so prohibitively high that they would prevent emergency crews from intervening without being exposed to lethal dose rates of five hundred roentgens per hour at fifty to seventy yards. The loss of water could result in overheating from the fuel decay, which could cause melting or an exothermic reaction. The zirconium metal cladding or the metal tubing around the fuel could be set alight, which would result in a large deposit of radioactive material over hundreds of miles.
Irradiated fuel, or spent fuel, is extremely radioactive. An unprotected human one meter away from a single freshly removed spent-fuel assembly would receive a lethal dose of radiation within seconds. This waste contains materials that are radiotoxic, meaning that they create biological damage based on their radioactive properties alone. The U.S. government considers spent nuclear fuel to be one of the most hazardous substances on Earth. This radiotoxic detritus has placed a serious environmental safety and public health burden on our shoulders for tens of thousands of years to come.
The spent-fuel pool at Fukushima Unit 4 contains roughly 37 million curies of cesium-137—about ten times the amount released by the Chornobyl accident. Removing one hundred tons of fuel will not be easy. It is not simply a matter of lifting it out with a crane as if it were cargo on a ship. The basic infrastructure that allows for the safe removal of the spent fuel was destroyed and must be repaired or replaced. All the spent fuel has to be removed underwater with nuclear-safety-rated cranes. It must be transferred into a network of other pools, including a staging pool and an upper pool, which usually remain empty and are required only when moving material in and out. Not only must these pools be repaired, the structural integrity of the building must also be shored up.
Assuming everything proceeded smoothly, it would take time and effort. The rate of transfer of the 1,331 assemblies would be nine or ten assemblies each time. Those assemblies would then be placed in a dry casket—a walled concrete and steel container. Once it is dry, it would be lifted out by a very large crane, placed in a transport facility, and moved to the central pool, which would have to be thinned out to fit the spent fuel and the radioactive ruins.
Pressurized-water reactors do not have elevated pools. Instead, the pools tend to be in buildings adjacent to the reactor. Many of the spent-fuel pool storage areas have cavities underneath them, which could lead to rapid drainage.
Since the early 1980s, the U.S. Nuclear Regulatory Commission (NRC) has approved high-density storage with the expectation that the United States would open a permanent repository for the disposal of spent fuel and defense-level radioactive waste. These pools are now storing four to five times more spent fuel than they were originally designed to hold. The pools were originally intended to be temporary storage facilities for a period of five years and therefore did not require nuclear-safety-rated defense and depth requirements. These pools do not have secondary containments. Some of these pools have buildings with tin roofs—structures you might find at a Costco, a Walmart, or a Ford dealership. They are not required to have redundant power or independent water makeup capability. Only after the Fukushima accident did the Nuclear Regulatory Commission implement requirements that reactor operators have instrumentation in their control rooms to monitor the water levels, water chemistry, and water temperature of the pools. Before that, at some reactors, plant workers had to go and look in the room. There has been at least one occasion when workers did not do this and later discovered that the water level had dropped dramatically.
The spent-fuel pools in the United States contain more spent fuel than in Japan. This is because of indefinite-storage modes, which the nuclear industry has adopted to save money. Furthermore, since the 1990s, U.S. reactor operators are permitted by the NRC to effectively double the amount of time nuclear fuel can be irradiated in a reactor by approving an increase in the percentage of uranium-235, the key fissionable material that generates energy. In doing so, the NRC has bowed to the wishes of nuclear reactor operators, motivated more by economics than spent nuclear fuel storage and disposal. The nuclear power fleet is allowed to operate at the highest burn-up rates in the world. According to engineers from the National Research Council, “the technical basis for the spent fuel currently being discharged and the high-utilization burn-up fuels is not well established. In addition, spent fuel that may have degraded after extended storage may present new obstacles to safe transport.”
The reactors operate in turbulent environments. They contain debris. They churn and vibrate, which causes wear and tear on the cladding of the fuel. The cladding, which is only between 0.04 millimeters and 0.08 millimeters thick, becomes thinner and elongated, and the efficient gas pressure inside is two to three times higher. Some types of reactors experience large amounts of grid-to-rod fretting from the high burn-ups.
Spent-fuel pools in the United States are going to run out of room for storage by 2015, which is forcing the nuclear power industry to adopt dry storage but not to thin out their pools. The industry looks as though it will maintain high-density wet storage to the bitter end. It will keep these pools filled to the brim by packing hot spent-fuel assemblies closer together. When there is no longer any room, the industry will start building dry casks.