Vessels used for keeping the used nuclear waste [Image Source: Wikimedia Commons]
Radioactive materials are some of the most volatile compounds on the face of the planet. Yet with the right technology, even a train cannot penetrate the impressive shields that safeguard them from any danger on the road, track, or sea. Through decades of refined engineering, scientists developed mechanically robust nuclear transportation flasks. These flasks are capable of withstanding the most potential and devastating dangers imposed while being transported all across the world. Though many people question the safety systems and measures put in place to protect the nuclear waste from the environment, and everything else from the potential dangers of radiation.
Constructing a flask to carry the world’s most dangerous material is no easy task. The flask must be heavy enough to provide adequate shielding to prevent radiation* from penetrating the walls of the container. Though the container must still be tough enough to withstand the most severe of accidents. However, not all types of radioactive materials emit the same forms of radiation. Engineers must accommodate and manufacture different radioactive transportation flasks to contain various types of radioactive material. Radioactive material spans much further than just spent nuclear fuel. It comes in many states ranging from gasses, to liquids and solids.
Nuclear waste is typically the material which is left after nuclear fuel becomes depleted. Although, since nuclear fuel is so energy rich, it does not produce much nuclear waste. For example, if the entire US population solely relied on nuclear power, each person would generate 39.5 grams of nuclear waste. In equivalence, if the energy was obtained by burning wood, each individual would end up with 10,000 kg.
Different forms of radiation requires different types of protection
Radioactive materials are classified based on the element responsible for emitting the radiation. Generally, the heavier the element, the higher the radioactive energy is. There are also two forms of radiation, ionizing, and non-ionizing. Non-ionizing radiation gives the atom more energy but does not cause it to change physically. The most common forms of non-ionizing radiation are visible light, infrared, microwaves, and so on. Though they are radioactive, typically they do not pose much danger. Ionizing radiation, on the other hand, causes physical changes in molecules, forcing them to lose electrons, or break apart completely. Breaking an atom apart results in an absurd amount of radiation to be released. While the radiation can be controlled and used for magnificent things, it must be contained in the world’s strongest containers.
Creating a flask worthy of protecting nuclear employees, the general public, and the environment from decades of contamination requires being made with the highest level of precision and stringent quality to prevent a disaster.
*Radiation is energy that is launched out of an atom. It travels as an electromagnetic wave (just like a sun ray), or as a subatomic particle that is traveling incredibly fast. When radiation hits another atom, it gives all of its energy away to the atom and can cause it to heat up. It’s what lets us see and keeps us warm, and sometimes to power all of our electronics.
Types of Flasks
Not all radioactive substances emit the same levels of radiation and therefore require varying degrees of protection constructed from different materials. The flasks vary in purposes such as the small leak-tight containers which are engineered to be used for transporting radioactive gasses and medical isotopes. Shipping spent nuclear fuel requires the most protection. Nuclear transportation flasks can be more than over 50 tons!
Nuclear Waste Container [Image Source: Wikimedia Commons]
The level of protection depends on two main variables: how much material is being transported, and the type of radiation that is being emitted.
Small radioactive particles emit lower energy radiation, generally of beta particle emitters. Beta particle emitters are easily contained with minimal radiation shielding. Since the particles are so small, the largest issue arises from the potential of having a fracture or imperfection. A fracture could allow the small particles to leak from the container and out into the world. Though, the containers are not required to be as tough as other forms of ionizing radiation.
Heavier atoms emit higher energy like gamma radiation. Gamma rays require significantly more shielding since they are the highest energy rays of all radiation. Large atoms, like uranium, generate the most gamma radiation. Within the center of the atom are the protons and neutrons. Neutrons are excellent absorbers of gamma radiation making them great shields against gamma rays. The more neutrons, the better the container which is why extremely heavy elements are used to contain the high-energy radiation. Steel, lead, concrete, and sometimes even depleted uranium are used to fabricate the containers- the largest of which have dry weights upwards of 50 tons.
Constructing an impenetrable shield
The walls of the container can be over 35 centimeters thick to ensure no gamma radiation escapes. A seamless flask is formed to contain gamma radiation by forging the body out of a solid unit of steel. Somewhat ironically, gamma radiation is used to inspect every inch of the flask before it enters service. Government personnel holds extremely high safety codes and practices which are strictly enforced.
Some radioactive materials need to be surrounded by a thick layer of lead. Lead is one of the softest metals, though one of the best at absorbing radiation. Lead shields prevent radiation from coming into contact with the outer flask. While gamma radiation is easy to contain, it can ionize other particles and force them to release more dangerous forms of radiation. Though, to ensure the flasks are adequate, government personnel uphold the most strict safety procedures to prevent an accident from happening.
How Radioactive Materials are Prepped and Transported
The sheer weight of the nuclear flasks prevents most nuclear waste from being shipped by air. Most radioactive material uses the same transportation routes traveled by the general public, specifically by train.
Once nuclear fuel is spent, it still contains 96% uranium, 1% plutonium and 3% of fission products (from the nuclear reaction) as well as a small amount of transuranics (what remains once the uranium decays). During operation, a nuclear reactor works at about 300-degrees. Though, inside the reactor core, the temperatures can exceed 1000-degrees. Once spent, the fuel is still extremely hot. It must be cooled in a spent fuel storage bay for months before it can be safely shipped in a transportation flask. The spent fuel bays are typically massive cooling pools which house the radioactive material until it reaches a sustainable level.
Once cooled, the fuel is placed in a suitable cask. Some casks can hold spent fuel for up to 120 years! However, occasionally the fuel is required to be transported over long distances. Though it may have spent months cooling down, the fuel is still immensely hot.
Most shipping flasks are filled with water to absorb some of the thermal energy. Although, in the confined region, water alone is often not enough. Cooling fins are typically integrated on the outside of the shipping container to disperse heat into the atmosphere. The flask is continually moving once placed on a vehicle to provide a continuous flow of air. Continuous transportation also limits the amount of time the flask is exposed in a more vulnerable container, though the flasks are practically impenetrable.
How dangerous is shipping?
Shipping radioactive is a precise and impeccably safe operation which is executed daily across the globe without incident. According to the World Nuclear Association about 20 million consignments of all sizes containing radioactive materials are routinely transported worldwide annually on public roads, railways and ships. Through the years, radioactive material has been shipped millions of kilometers across the world. Though there have been minor accidents over the decades, there has never been a container with highly radioactive equipment leak into the environment.
Ensuring safety through vigorous testing
While nuclear engineering specialists are competent in their work, nothing is left to chance. International nuclear protocols require all agencies to perform extensive testing on any shipping container before it is implemented into the real world.
One such test conducted in 1984 by British Nuclear Fuels investigated the strength of their nuclear containers in “Operation Smash Hit”. The most unlikely events were put to the test on the most extreme level in the worst conditions to see how well the flasks can perform and contain nuclear waste.
The flask which underwent most of the testing failed during one of the 8-meter drop tests. A small amount of water was released as the container smashed into the ground with an incredible amount of force. While the spray would contain nearly no radiation and poses no threat to the environment, Sellafield Ltd (formally known as British Nuclear Fuels) reengineered the flask to withstand the force entirely before it was to be used with real spent fuel. The following experiments successfully proved the competence of the container as it was hammered by the most extreme situations.
There is always an inherent risk involved when dealing with radioactive material. However, the strict policies governing any aspect dealing with radioactive material as well as precise engineering practices significantly reduce the chances of an accident occurring. Nuclear policies are constantly being revised and reformed to ensure the safety of the public.