Nuclear fuel is stored in two ways after removal from a reactor: in a pool of water, or in dry
|Nuclear spent fuel pool|
Previously, articles in the Truth About Nuclear Power (TANP) series discussed economic disadvantages, and safety issues with nuclear power. The TANP series will have 30 articles, more or less, when complete.
Previous articles on The Truth About Nuclear Power emphasized the economic aspect by showing that (one) modern nuclear power plants are uneconomic to operate compared to natural gas and wind energy, (two) they produce preposterous pricing if they are the sole power source for a grid, (three) they cost far too much to construct, (four) use far more water for cooling, 4 times as much, than better alternatives, (five) nuclear fuel makes them difficult to shut down and requires very costly safeguards, (six) they are built to huge scale of 1,000 to 1,600 MWe or greater to attempt to reduce costs via economy of scale, (seven) an all-nuclear grid will lose customers to self-generation, (eight) smaller and modular nuclear plants have no benefits due to reverse economy of scale, (nine) large-scale plants have very long construction schedules even without lawsuits that delay construction, (ten) nuclear plants do not reach 50 or 60 years life because they require costly upgrades after 20 to 30 years that do not always perform as designed, (eleven) France has 85 percent of its electricity produced via nuclear power but it is subsidized, is still almost twice as expensive as prices in the US, and is only viable due to exporting power at night rather than throttling back the plants during low demand, (twelve) nuclear plants cannot provide cheap power on small islands, (thirteen) US nuclear plants are heavily subsidized but still cannot compete, (fourteen), projects are cancelled due to unfavorable economics, reactor vendors are desperate for sales, nuclear advocates tout low operating costs and ignore capital costs, nuclear utilities never ask for a rate decrease when building a new nuclear plant, and high nuclear costs are buried in a large customer base, (fifteen) safety regulations are routinely relaxed to allow the plants to continue operating without spending the funds to bring them into compliance, (sixteen) many, many near-misses occur each year in nuclear power, approximately one every 3 weeks, (seventeen) safety issues with short term, and long-term, storage of spent fuel, (eighteen) safety hazards of spent fuel reprocessing, (nineteen) health effects on people and other living things, (twenty) nuclear disaster at Chernobyl, (twenty-one) nuclear meltdown at Three Mile Island, (twenty-two) nuclear meltdowns at Fukushima, (twenty-three) near-disaster at San Onofre, (twenty-four) the looming disaster at St. Lucie, (twenty-five) the inherently unsafe characteristics of nuclear power plants required government shielding from liability, or subsidy, for the costs of a nuclear accident via the Price-Anderson Act, and (twenty-six) the serious public impacts of large-scale population evacuation and relocation after a major incident, or "extraordinary nuclear occurrence" in the language used by the Price-Anderson Act. Additional articles will include (twenty-seven) the future of nuclear fusion, (twenty-eight) future of thorium reactors, (twenty-nine) future of high-temperature gas nuclear reactors, and (thirty), a concluding chapter with a world-wide economic analysis of nuclear reactors and why countries build them.
Introduction to Storage
Nuclear fuel exists inside reactors in long, thin tubes known as fuel rods. The fuel rods are bundled together to make a fuel assembly, and the fuel assemblies are inserted into or removed from the reactor as necessary. After approximately 4-1/2 years in a reactor, each assembly is removed and stored until it is sufficiently cool for safe handling. As currently practiced in the US, a reactor is shut down for refueling approximately every 18 months. The refueling requires approximately 30 days. During refueling, only one-third of the fuel assemblies are removed, and those removed are replaced with fresh fuel assemblies. A bit of math shows, then, that after 40 years, 26 shutdowns for refueling will have occurred, with one-third of the assemblies removed at each shutdown. After a 40-year life, which most reactors are designed for, there will be a bit more than 8 full reactor-loads of spent fuel that must be stored. Adding in the final run, that presents 9 or a bit more reactor-loads that must be stored.
However, a spent fuel pool is not designed to store 8 or 9 full loads of spent fuel. The design is for a much shorter period. This leads to the first safety problem.
There are at least four safety problems with storing spent fuel in a pool: loss of cooling accident in the pool, overcrowding in the pool, sabotage or other attack, and natural disaster such as an earthquake or flood. Each of these four issues is discussed below.
Loss of Cooling Accident
Loss of cooling accident, LOCA, is not confined only to the reactor. LOCA also applies to the spent fuel pool. Pumps and cooling water systems are critical to remove residual heat from the hot fuel rod assemblies after being removed from the reactor. The fuel pellets inside the fuel rods are hot with high temperature caused by radioactive decay of the uranium and other elements. Some of the radioactive elements decay rapidly, so they no longer produce heat, others decay over thousands of years. The spent fuel pool typically holds the fuel assemblies for 3 to 5 years, with some being stored longer in the pool.
The safety problems occur as anything that can prevent cooling water from flowing into the pool. These could be electrical issues, mechanical problems with pumps, valves that will not work, leaking pipes, leaking heat exchangers, even leaks in the pool walls and floor. As seen in a previous article in TANP, see link, such electrical and mechanical issues are regular occurrences at nuclear power plants. These issues only get worse and more frequent as the plants get older. Even after the reactor shuts down after 40 years or longer, the spent fuel storage must continue operating far beyond that.
As happened at Fukushima, spent fuel in a pool that loses water can overheat, cause fires, and lead to radioactive releases.
Spent fuel pools are overcrowded; they have far more fuel assemblies at closer proximity to each other, than they were designed to handle. Part of this is due to nuclear plant owners' reluctance to remove fuel assemblies from the pool, and place them in expensive dry cask storage units. It is an economics issue. It costs the owner more money to purchase the dry casks and store them per NRC regulations on-site.
Only this week, the NRC board voted to allow owners to continue storing spent assemblies in the pools, instead of removing them to dry casks. see link
The overcrowding increases the severity of a LOCA, as more heat in a smaller space will cause water to boil sooner, and boil more rapidly, thus evaporating the pool and exposing even more fuel to the air. Overcrowding also has more fuel available to melt, and more mass of radioactive material that can escape into the environment.
Sabotage or Outside Attack
Nuclear plants have elaborate safeguards against security breaches, but as shown in article 16, see link, several security-related incidents occur each year. No details are publicly available on security breaches. It would not take much for sabotage to occur. Outside attack is a real possibility, as the NRC acknowledged not long ago by requiring all new reactors and plants to be designed and built to withstand an impact from a large passenger aircraft. The NRC requires the reactor building, spent fuel areas, and cooling systems to withstand such an impact. Notably, and ominously, this design requirement is not retroactive, it does not apply to the more than 100 operating or shutdown reactors in the US. Such an attack, if successful, could result in LOCA with disastrous results.
Natural Disaster - Earthquake, Flood, etc.
Natural disasters such as earthquake, floods, tornadoes, hurricanes, volcanic eruptions, tsunamis, etc. are all supposedly accounted for in the nuclear plant's design. However, even though the nuclear industry repeats the refrain that plants are safe, there is ample evidence that nature can and does surprise humans with events that are beyond our planning.
Earthquakes are the greatest risk. For example, four reactors in California (two each at San Onofre and Diablo Canyon) are in earthquake zones and are subject to tsunamis. Each was designed for certain earthquake stresses, and a tsunami of small scale. However, after being built, it was discovered that additional faults lay offshore from San Onofre. The tsunami that swamped Fukushima was far larger than was contemplated in its design. Even inland, other reactors in the US have had earthquakes rattle them, with attendant stresses. It is sobering to note that metal becomes brittle after long-term exposure to nuclear radiation, and will crack and even fall apart during an earthquake. Here is a link to an excellent article from Wall Street Journal, 2011, on nuclear plants and earthquakes. see link. A short excerpt from the WSJ article:
" In 1986, a magnitude 5.0 quake struck near the Perry nuclear plant in Ohio, causing minor damage but sparking concern among citizens' groups about potential damage from an even bigger temblor. The plant was shut down at the time, but was scheduled to be loaded with fresh fuel the next day. Small cracks in concrete and leaks in pipes were discovered, none critical.
In other words, the utilities' own experts reckoned there was an increased chance that an existing reactor could be struck by an earthquake that could overwhelm its ability to shut down safely." [emphasis added]
The Union of Concerned Scientists noted that approximately 30 US nuclear reactors are located where an upstream dam failure would create a flooding hazard. Even if a tsunami does not occur, dam failures can and do occur.
Hurricanes are routine events along the Gulf Coast and Atlantic coast, however thus far all nuclear plants in their path have survived the winds and waters. There are multiple plants in Florida, two reactors in Texas at South Texas Nuclear, plus reactors in Louisiana. Others exist along the Atlantic coast. The issue, though, is land subsidence in Texas and Louisiana, and levee protections in Louisiana.
Dry Cask Storage
Storage in dry casks is inherently safer, although curiously the NRC recently stated that
Even if spent fuel is stored in dry casks, the fuel must be guarded for a very long time. How long is much debated. Some of the long-lived transuranics will be spitting radioactivity for thousands of years. For example, plutonium Pu-239 has a half-life of 24,000 years. Nuclear power plants today are creating obligations on future generations, for thousands of years. Those future generations may not thank us for this.
It can be seen that there are serious safety issues with storage of spend nuclear fuel, whether in pools or dry casks. One solution, proposed by many, is to simply reprocess the fuel and concentrate the wicked components and recycle the usable parts. However, in the US we must deal with the law as it stands. Reprocessing is not allowed here.
The ever-present danger of LOCA in spent fuel pools is growing greater year after year, as more and more fuel is added, equipment ages and breaks down, and statistically at least, a natural disaster is more likely.
Part Fourteen - A Few More Reasons Nuclear Cannot Compete
Part Fifteen - Nuclear Safety Compromised by Bending the Rules
Part Sixteen - Near Misses on Meltdowns Occur Every 3 Weeks
Part Seventeen - this article
Part Twenty - Chernobyl Meltdown and Explosion
Part Twenty One - Three Mile Island Unit 2 Meltdown 1979
Part Twenty Two - Fukushima The Disaster That Could Not Happen
Part Twenty Three - San Onofre Shutdown Saga
Part Twenty Six - Evacuation Plans Required at Nuclear Plants
Part Twenty Seven - Power From Nuclear Fusion
Roger E. Sowell, Esq.
Marina del Rey, California