For decades, the proper disposal of nuclear waste has been an urgent environmental issue. The storage of radioactive waste over the long term presents substantial risks to both human health and the environment. Traditional approaches to nuclear waste disposal, like deep geological repositories (DGRs), have encountered various obstacles regarding cost, safety and public acceptance.

Molecular crystals have emerged as a promising alternative solution for nuclear waste storage. These structures -- based on cyclotetrabenzil hydrazones -- have the unique ability to capture and immobilize radioactive elements, such as iodine, in both organic and aqueous solutions. Let's explore the properties of molecular crystals that make them an ideal candidate for nuclear waste storage and how they can potentially revolutionize the way this global issue is handled.

The importance of reducing nuclear waste

Nuclear energy has been widely promoted as a cleaner alternative to fossil fuels, offering the potential to mitigate carbon emissions and address the urgent issue of climate change. Nevertheless, a significant concern persists regarding the handling and disposal of its by-product: radioactive waste.

Radioactive waste emits or contains radioactive particles. These particles can remain hazardous for thousands of years and have the potential to cause harm to human health and the environment if not properly managed. This is why it is critical to reduce nuclear waste as much as possible, in order to minimize its long-term impact.

Radioactive waste can be categorized into two main types: low-level waste and high-level waste. Low-level waste encompasses items like clothing, tools, and pipes that have come into contact with radioactive materials. This type of waste generally has a lower concentration of radioactivity and is relatively easier to manage and dispose of. Conversely, high-level waste is significantly more hazardous as it contains highly radioactive materials, such as spent nuclear fuel rods.

Managing high-level waste presents a formidable challenge due to its enduring radioactivity. To address this, a prevalent method involves storing it in DGRs, ensuring isolation from the environment for thousands of years. This approach effectively safeguards against potential hazards and ensures long-term containment.

Issues with deep geological repositories for nuclear waste

DGRs have long been proposed as a solution for the disposal of radioactive nuclear waste. The idea is to bury the waste deep underground in stable rock formations, away from human habitation and the environment. However, despite their widespread use, DGRs are not without their issues.

Long-term safety

The primary focus regarding DGRs is the long-term safety they provide. Considering that radioactive waste remains hazardous for thousands of years, it is crucial to develop storage solutions capable of effectively containing and isolating it from the environment over an extended duration.

One of the main concerns is the potential for groundwater contamination. If a DGR was to leak, it could contaminate groundwater, which would then spread and potentially affect human populations and ecosystems.

There is also the issue of seismic activity. While most DGRs are built in stable geological formations, there is always a chance of earthquakes or other natural disasters occurring.

Finally, there is the possibility of human error. DGRs are complex facilities that require strict adherence to safety protocols and maintenance procedures. However, as we have seen in the past with nuclear accidents, human error can never be completely eliminated. Any mistake or oversight in the operation of a DGR could have severe consequences.

Public perception

Another significant issue with DGRs is public perception and acceptance. Many people are uncomfortable with the idea of storing radioactive waste deep underground, even if it is deemed safe by experts. This reluctance is understandable given the potential risks involved, but it can also hinder progress in finding a long-term solution for radioactive waste management.

Public perception also plays a role in the regulatory and approval process for DGRs. Local communities and stakeholders may oppose the construction of a DGR near their homes, citing concerns about safety and environmental impact. This opposition can lead to delays or even cancellation of DGR projects, further complicating the issue of radioactive waste management.

Iodine capture with crystals

Iodine is a highly toxic and radioactive element that is commonly found in nuclear waste. It has a half-life of over 15 million years, making it one of the most challenging elements to deal with when it comes to nuclear waste storage and disposal. The release of iodine into the environment can have severe consequences, including causing radiation sickness and increasing the risk of cancer.

To address the issue of storing nuclear waste underground, University of Houston scientists have been searching for alternative methods to safely and effectively capture and store radioactive iodine. One promising solution that has been gaining traction is the use of crystals.

Crystals made from cyclotetrabenzil hydrazones exhibit exceptional iodine absorption capabilities, surpassing other materials like metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). Their remarkable iodine uptake capacity sets them apart in terms of efficiency and effectiveness.

But how exactly do these crystals capture iodine? These molecular crystals have a network of pores and channels in a ring-like structure that allow them to trap and store iodine molecules. The size and shape of these pores can be fine-tuned through chemical modifications, making them highly selective for iodine capture.

Why these types of crystals?

This particular type of crystal, based on cyclotetrabenzil hydrazones, serves various purposes. Firstly, the synthesis of these crystals is relatively straightforward and can be achieved using easily accessible elements such as carbon, hydrogen, and oxygen. Consequently, they are cost-effective to manufacture, with an approximate price of just $1 per gram.

But what makes these crystals so suitable for nuclear waste? The structure of these crystals plays a crucial role. Comprising of eight interconnected strands, these crystals form an intricate three-dimensional network. This unique architecture grants them a significant surface area, making them ideal for capturing and storing hazardous materials, including nuclear waste.

Furthermore, these crystals exhibit remarkable efficiency in capturing carbon dioxide (CO₂). Their unique capacity to bind with CO₂ molecules enables effective removal from the environment, mitigating further harm to our planet. Notably, these crystals surpass other materials currently employed in their superior CO₂ capture capacity.