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Spent nuclear fuel mismanagement poses a major threat to the United States. Here’s how.

Restricting its analyses to a severe earthquake scenario allowed the NRC to help allay public fears over the dangers of spent fuel pool accidents. There is good reason to question whether severe earthquakes pose the greatest threat to spent fuel pools.

Solar storms, physical attacks, and cyberattacks have the potential to cause a nightmare scenario …….

Bulletin, By Mark Leyse | April 2, 2024

Irradiated fuel assemblies—essentially bundles of fuel rods with zirconium alloy cladding sheathing uranium dioxide fuel pellets—that have been removed from a nuclear reactor (spent fuel) generate a great deal of heat from the radioactive decay of the nuclear fuel’s unstable fission products. This heat source is termed decay heat. Spent fuel is so thermally hot and radioactive that it must be submerged in circulating water and cooled in a storage pool (spent fuel pool) for several years before it can be moved to dry storage.

The dangers of reactor meltdowns are well known. But spent fuel can also overheat and burn in a storage pool if its coolant water is lost, thereby potentially releasing large amounts of radioactive material into the air. This type of accident is known as a spent fuel pool fire or zirconium fire, named after the fuel cladding. All commercial nuclear power plants in the United States—and nearly all in the world—have at least one spent fuel pool on site. A fire at an overloaded pool (which exist at many US nuclear power plants) could release radiation that dwarfs what the Chernobyl nuclear accident emitted.

Many analysts see very rare, severe earthquakes as the greatest threat to spent fuel pools; however, another far more likely event could threaten US nuclear sites: a widespread collapse of the power grid system. Such a collapse could be triggered by a variety of events, including solar storms, physical attacks, and cyberattacks—all of which are known, documented possibilities. Safety experts have warned for decades about the dangers of overloading spent fuel pools, but the Nuclear Regulatory Commission and Congress have refused to act.

The threat of overloaded spent fuel pools. Spent fuel pools at US nuclear plants are almost as densely packed with nuclear fuel as operating reactors—a hazard that has existed for decades and vastly increases the odds of having a major accident.

Spent fuel assemblies could ignite—starting a zirconium fire—if an overloaded pool were to lose a sizable portion or all of its coolant water. In a scenario in which coolant water boils off, uncovered zirconium cladding of fuel assemblies may overheat and chemically react with steam, generating explosive hydrogen gas. A substantial amount of hydrogen would almost certainly detonate, destroying the building that houses the spent fuel pool. (Only a small quantity of energy is required to ignite hydrogen gas, including electric sparks from equipment. It is speculated a ringing telephone initiated a hydrogen explosion that occurred during the Three Mile Island accident in 1979.)

A zirconium fire in an exposed spent fuel pool would have the potential to emit far more radioactive cesium 137 than the Chernobyl accident released. (The US Nuclear Regulatory Commission (NRC) has conducted analyses that found a zirconium fire at a densely packed pool could release as much as 24 megacuries of cesium 137; the Chernobyl accident is estimated to have released 2.3 megacuries of cesium 137.) Such a disaster could contaminate thousands of square miles of land in urban and rural areas, potentially exposing millions of people to large doses of ionizing radiation, many of whom could die from early or latent cancer.

In contrast, if a thinly packed pool were deprived of coolant water, its spent fuel assemblies would likely release about 1 percent of the radioactive material predicted to be released by a zirconium fire at a densely packed pool. A thinly packed pool has a much smaller inventory of radioactive material than a densely packed pool; it also contains much less zirconium. If such a limited amount of zirconium were to react with steam, most likely too little hydrogen would be generated to threaten the integrity of the spent fuel pool building.

After being cooled under water for a minimum of three years, spent fuel assemblies can be transferred from pools to giant, hermetically sealed canisters of reinforced steel and concrete that shield plant workers and the public from ionizing radiation. This liquid-free method of storage, which cools the spent fuel assemblies by passive air convection, is called “dry cask storage.”

A typical US storage pool for a 1,000-megawatt-electric reactor contains from 400 to 500 metric tons of spent fuel assemblies. (Dry casks can store 10 to 15 tons of spent fuel assemblies, so each cask contains a far lower amount of radioactive material than a storage pool.) Reducing the total inventories of spent fuel assemblies stored in US spent fuel pools by roughly 70 to 80 percent reduces their amount of radioactive cesium by about 50 percent. And the heat load in each pool drops by about 25 to 30 percent. With low-density storage, a pool’s spent fuel assemblies are separated from each other to an extent that greatly improves their ability to be cooled by air convection in the event that the pool loses its coolant water. Moreover, a dry cask storage area, which has passive cooling, is less vulnerable to either accidents or sabotage than a spent fuel pool.

In the aftermath of the March 2011 Fukushima Daiichi accident in Japan, in which there was a risk of spent fuel assemblies igniting, the NRC considered forcing US utilities to expedite the transfer of all sufficiently-cooled spent fuel assemblies stored in overloaded pools to dry cask storage. The NRC decided against implementing such a safety measure.

To help justify its decision, the NRC chose to analyze only one scenario that might lead to a zirconium fire: a severe earthquake. In 2014, the NRC claimed that a severe earthquake with a magnitude “expected to occur once in 60,000 years” is the prototypical initiating event that would lead to a zirconium fire in a boiling water reactor’s spent fuel pool.

The NRC’s 2014 study concluded that the type of earthquake it selected for its analyses would cause a zirconium fire and a large radiological release to occur at a densely packed spent fuel pool once every nine million years (or even less frequently). Restricting its analyses to a severe earthquake scenario allowed the NRC to help allay public fears over the dangers of spent fuel pool accidents. (At the time of the Fukushima Daiichi accident, the New York Times and other news outlets warned that a zirconium fire could break out in the plant’s Unit 4 spent fuel pool, causing global public concern.)

There is good reason to question whether severe earthquakes pose the greatest threat to spent fuel pools. A widespread collapse of the US power grid system that would last for a period of months to years—estimated to occur once in a century—may be far more likely to lead to a zirconium fire than a severe earthquake. The prospect that a widespread, long-term blackout will occur within the next 100 years should prompt US utilities to expedite the transfer of spent fuel from pools to dry cask storage. Utilities in other nations, including in Japan, that have overloaded pools should follow suit.

Solar storms, physical attacks, and cyberattacks have the potential to cause a nightmare scenario in which the US power grid collapses, along with other vital infrastructures—leading to reactor meltdowns and spent fuel pool fires, whose radioactive emissions would aggravate the disaster.

Vulnerability to solar storms……………………………………………………………………………………………………………………..

Vulnerability to physical attacks.……………………………………………………………………………………………………….

Vulnerability to cyberattacks. …………………………………………………………………………………………………………….

Insufficient public safety.…………………………………………………………………………………….

Overloading spent fuel pools should be outlawed. Safety analysts have warned about the dangers of overloading spent fuel pools since the 1970s. For decades, experts and organizations have argued that in order to improve safety, sufficiently cooled spent fuel assemblies should be removed from high-density spent fuel pools and transferred to passively cooled dry cask storage. Sadly, the NRC has not heeded their advice.

In the face of the NRC’s inaction, Sen. Edward Markey of Massachusetts introduced The Dry Cask Storage Act in 2014, calling for the thinning out of spent fuel pools. The act, which Senator Markey has reintroduced in subsequent congressional sessions, has not passed into law.

The relatively high probability of a nationwide grid collapse, which would lead to multiple nuclear disasters, emphasizes the need to expedite the transfer of spent fuel to dry cask storage. According to Frank von Hippel, a professor of public and international affairs emeritus at Princeton University, the impact of a single accident at an overstocked spent fuel pool has the potential to be two orders of magnitude more devastating in terms of radiological releases than the three Fukushima Daiichi meltdowns combined. If the US grid collapses for a lengthy period of time, society would likely descend into chaos, as uncooled nuclear fuel burned at multiple sites and spewed radioactive plumes into the environment.

The value of preventing the destruction of US society and untold human suffering is incalculable. So, on the issue of protecting people and the environment from spent fuel pool fires, it is surprising when one learns that promptly transferring the nationwide inventories of spent fuel assemblies that have been cooled for at least five years from US pools to dry cask storage would be “relatively inexpensive”—less than (in 2012 dollars) a total of $4 billion ($5.4 billion in today’s dollars). That is far, far less than the monetary toll of losing vast tracts of urban and rural land for generations to come because of radioactive contamination.

One should also consider that plant owners are required, as part of the decommissioning process, to transfer spent fuel assemblies from storage pools to dry cask storage after nuclear plants are permanently shut down. So, in accordance with industry protocols, all spent fuel assemblies at plant sites are intended to eventually be placed in dry cask storage (before ultimately being transported to a long-term surface storage site or a permanent geologic repository).  https://thebulletin.org/2024/04/spent-nuclear-fuel-mismanagement-poses-a-major-threat-to-the-united-states-heres-how/

April 5, 2024 Posted by Christina Macpherson | Reference, safety, USA, wastes | 1 Comment