There are 65 nuclear power facilities in the U. S. They operate 104 reactors. Thirty-six of the plants have two or more reactors. They have generated nearly 20% of the nation’s electricity since 1990. The uranium fuel that is used eventually degrades and the plant output decreases. The spent fuel is replaced. The spent fuel is stored on site either in a deep pool of water or in secure metal casks in the open. Click the map for a larger version.
This post describes some basic information about their uranium fuel and what becomes of the spent fuel after is has been used in the reactor.
Description of Nuclear Fuel
Uranium rock ore is mined. The uranium is a radioactive element which means it can emit alpha, beta, and gamma forms of radiation. That can be the subject of another post. Uranium ore is weakly radioactive. It needs to be refined and enriched to make it useful in a reactor. The oxides of uranium form a yellow substance called yellowcake. This needs to be processed in secure facilities to extract the pure uranium atoms needed for a reactor to use.
The enriched and now highly radioactive uranium is fashioned into a ceramic pellet for ease of handling. The fuel pellet held in this image is not enriched. A stack of these enriched pellets is placed into a metal sleeve about 12 feet long. Many of these sleeves are grouped together into a bundle or fuel assembly. This assembly now has a large amount of uranium ready to be placed into the core of the reactor with many other fuel assemblies.
Neutrons are allowed to pass into the nuclei of the uranium in the core. The nuclei capture neutrons, become unstable, and then split, releasing more neutrons to continue the splitting process. The splitting process is called fission. It releases large amounts of heat energy to the surroundings. This heat is used to generate steam. The steam rotates turbines connected to electricity generators. The electricity is delivered to your home and office for you to use.
The energy from nuclear fuel is millions of times the amount contained in a similar mass of fossil fuel. No burning takes place. It is a clean and energy dense fuel in those terms. But, it doesn’t last forever in the core of the reactor. Eventually, a significant number of uranium nuclei are fissioned. The energy output decreases. The assemblies are removed and replaced with fresh ones. The spent fuel assemblies are placed into deep pools of water near the reactor core. They are hot and radioactive and not safe to be near.
Spent Fuel Storage in Pools
Most of us have heard much about the storage pools for spent fuel rods. The earthquake and tsunami in Japan and the resulting calamity at Fukushima put those pools in the news. Pool storage at the nuclear power facilities across the country is becoming a growing problem. The pools look pretty blue and calm. How could it be a problem? They are running out of room. They need to move the assemblies to a different storage method.
According to the U.S. Nuclear Regulatory Commission, these storage pools are safe with concrete and steel construction, deep water which serves as a coolant and shielding. As of the end of 2009, there were 62,683 metric tons of commercial spent fuel accumulated in the United States.
Of that total, 48,818 metric tons – or about 78 percent – were in pools, while 13,856 metric tons – or about 22 percent – were stored in dry casks. The total increases by 2000 to 2400 tons annually.
I visited a pool storage facility in the ’70s. At that time, the hope was for the continued development of spent nuclear fuel reprocessing which would allow the fuel pellets in the rods to be made into new enriched pellets for continued use. This was to mitigate the pool storage problem of them eventually filling up to capacity. That reprocessing program does not exist in this country. From the Union of Concerned Scientists…
The spent fuel rods are still highly radioactive and continue to generate significant heat for decades. The fuel assemblies, which consist of dozens to hundreds of fuel rods each, are moved to pools of water to cool. They are kept on racks in the pool, submerged in more than twenty feet of water, and water is continuously circulated to draw heat away from the rods and keep them at a safe temperature.
Because no permanent repository for spent fuel exists in the United States, reactor owners have kept spent fuel at the reactor sites. As the amount of spent fuel has increased, the Nuclear Regulatory Commission has authorized many power plant owners to increase the amount in their storage pools to as much as five times what they were designed to hold.
Nuclear Fuel Storage Casks
As pools fill with the cooling spent fuel rods, the older ones can be transferred to dry cask storage. This has been done as early as after 3 years in the pool. Regulations ask for 5 years of pool storage. The normal amount of time is 10 years. The Nuclear Regulatory Commission believes spent fuel pools and dry casks both provide adequate protection of the public health and safety and the environment. They see no pressing safety or security reason to mandate earlier transfer of fuel from pool to cask.
Here is a somewhat dated public relations video from the Yankee Atomic Electric Company when the Yankee Rowe power plant was decommissioned. It shows the steps involved in transferring the spent fuel assemblies from the storage pool into a metal and concrete cask that sits outdoors. The video is about 8 minutes long. You could skip ahead to the 3:30 mark to save some time.
Once the casks are secured and moved, they remain there. No plans are in place to move them from those sites. Here are dry storage casks at a different nuclear facility sitting on a 100 by 200-foot, three-foot-thick concrete pad. Each concrete cask has a three and a half-inch steel liner surrounded by 21 inches of reinforced concrete. Some casks are made with metal outer liners. Each storage cask, when loaded with the storage/transportation canister, weighs over 100 tons. There was a federal plan to move these to Yucca Mountain in Nevada for permanent deep underground storage. By April of 2009, that plan was cancelled.
How Long Are They Certified
According to the Spent Fuel Storage FAQ site, NRC regulations do not specify a maximum time for storing spent fuel in pool or cask.
The agency’s “waste confidence decision” expresses the Commission’s confidence that the fuel can be stored safely in either pool or cask for at least 60 years beyond the licensed life of any reactor without significant environmental effects. At current licensing terms (40 years of initial reactor operation plus 20 of extended operation), that would amount to at least 120 years of safe storage.
However, it is important to note that this does not mean NRC “allows” or “permits” storage for that period. Dry casks are licensed or certified for 20 years, with possible renewals of up to 40 years. This shorter licensing term means the casks are reviewed and inspected, and the NRC ensures the licensee has an adequate aging management program to maintain the facility.
Workers who transfer the rods to the casks and them move the casks to the storage pad receive about a quarter of their annual exposure of radiation. Workers avoid raising the casks directly over the fuel in the pools in case it fell. They also stop work with thunderstorms to avoid power outage problems. Once the casks are set in place outdoors on the concrete pad, maintenance is simple. They are checked twice a day to see that the air vents are not blocked. Cask manufacturers forecast a healthy future for their product.
What Are Your Thoughts? This lack of a plan for the future seems irresponsible. Eventually, the dry cask and pool facilities will both be full. Then what? If we had been following through on the reprocessing program from the 1970s, we could be keeping up with the spent fuel problem today. We shouldn’t just keep kicking the can down the road for another generation to fix.