Advancing towards Universal Affordable Energy

Affordable energy is key to the development of a country’s economy, education and healthcare, but more than 670 million people in developing countries still lack access to electricity, according to the United Nations.

The need to increase access to affordable electricity through new green sources has sparked many developing countries’ interest in nuclear energy. The International Atomic Energy Agency (IAEA) accompanies its member states during the long process of nuclearization and ensures that their practices comply with the Agency’s standards in important domains such as nuclear safety and security. 

The IAEA has been working together with ICTP to provide key training to scientists from developing countries, many of which are not yet members of the IAEA. The latest joint ICTP-IAEA initiative was the “Workshop on Modelling for Encapsulated Intermediate Level Waste (ILW) and High Level Waste (HLW) During Long-Term Storage” that took place in Trieste from 26 February to 1 March 2024.

The workshop included both lectures and practical simulations sessions, and it focused on helping scientists with the use of computer codes to model ionizing radiation (that arises from radionuclide decay) on the properties of a waste form and use this information to design long-term storage facilities and management procedures. The event gathered about 60 participants, including both students and more experienced researchers from countries all over the world, including Nigeria, Ghana, Sudan, Congo, Egypt, India and Iran, some of whom attended online.

Willie Meyer, Predisposal specialist at the IAEA, was an organiser and a speaker at the workshop and he agreed to answer a few questions about the event organised in collaboration with ICTP.

What was the workshop about and what motivated it?

The IAEA promotes the safe and peaceful uses of nuclear energy including the management of radioactive waste according to nationally and internationally agreed principles and standards with safe disposal as endpoint for all waste types. During the operation of nuclear research reactors and nuclear power plants  nuclear waste arises that must be safely managed by countries planning for these activities.

 Ionizing radiation, that arises from radionuclide decay will interact with waste form materials, resulting in collision cascades, defects, dislocations and phase separation that could influence  the long-term stability and integrity of the waste form should be specified in the safety case. Underpinning the safety case are mathematical models that can predict the durability of waste packages during long term storage and in the disposal environment.

The workshop was meant to train scientists to the use of computer codes to model ionizing radiation on the properties of a waste form and use this information to design long-term storage facilities and management procedures. Collaborating with ICTP has been important for the Agency, as that gives us access to scientists from developing countries who are not yet member states. By making them aware of the technologies that are available and of the current practices we provide them with important information that helps them advise the stakeholders in their countries to ensure the establishing of an integrated management plan before embarking on nuclear activities.

Let’s start from the basics. Can you tell us more about the different types of nuclear waste?

Nuclear reactors generate waste that can be classified into three different categories: low, intermediate and high-level waste, depending on their level of radioactivity.

Low-level waste includes paper, garments and cleaning materials, with low radioactivity, but that still need to be stored safely before disposal in designated facilities.

Intermediate-level waste has much higher radioactivity. Examples include the resins that are used to purify the water from the reactor’s cooling system. These types of waste are conditioned (encapsulated) into for examples glass, composite materials and ceramics to provide a engineered safety barrier during long term storage and disposal.

High-level waste is for instance metallic core waste (reactor parts that are replaced) that is highly radioactive due to the neutron activation of impurities inside the metals. This waste is stored in special containers inside special facilities and will be disposed in deep engineered designed geological facilities as they will be highly radioactive for even thousands of years.

How do these different types of nuclear waste need to be managed?

Nuclear power plants (NPPs) and research reactors are designed to ensure minimal waste arising during operation and waste management processes ensure that radioactive waste can be managed safely and cost effectively. However, within legally binding regulations and license conditions, NNP operators continue to explore options for further avoidance and minimization of waste arisings thereby accumulating experience in cost effectively minimizing (optimizing) waste.

The radioactive waste arisings during a NPP’s lifetime operation need to be controlled in terms of volume, weight and activity by using appropriate design measures and technologies. This is made possible by establishing explicit waste minimization programs, selection of appropriate minimization technologies (including early segregation), control of construction and operational material and the implementation of appropriate facility operation procedures in terms of radioactive discharges and radioactive waste.

The IAEA and its member states promote the safe disposal of radioactive waste as endpoint for all waste types.

How is nuclear waste managed in the meantime?

The IAEA and its member states promote the safe disposal of radioactive waste as endpoint for all waste types. Most developed countries dispose of radioactive waste but for countries that are currently establishing disposal facilities, as interim, nuclear waste is stored in special designed facilities.

The storage of radioactive wastes is an integral part of all stages of waste management of fully conditioned waste packages awaiting final disposal. The purpose of a storage facility or structure is to contain the packaged radioactive waste safely and securely in an organized and retrievable fashion for a defined time that is supposed to be less than the facility design life, while ensuring that the radiation protection of workers, the public and the environment are properly addressed according to applicable regulations and the ALARA principle (a principle of radioprotection stating that whenever ionizing radiation has to be applied to humans, animals or materials exposure should be as low as reasonably achievable).

The workshop we organised at ICTP focused on the use of computer models of ionizing radiation on the properties of a waste form and the storage facilities during long-term storage and to use this information to design facilities and management procedures  to ensure that the waste is safely stored. Management of well-designed and well-constructed storage facilities together with the use of suitable waste packages has demonstrated that radioactive wastes can be stored satisfactorily and safely for extended periods of time.

Why do we need models to predict what happens to encapsulated nuclear waste?

Nuclear  waste is radioactive and during decay it will interact with waste form materials, resulting in collision cascades, defects, dislocations and phase separation that could influence  the long-term stability and integrity of the waste form.

Unfortunately as the waste is conditioned into special matrixes to ensure safety, it is difficult to perform durability experiments in laboratories on these large structures for 60 years continuously and hope that the current analytical instrument will be able to observe any changes during 60 years of experimentation. This will be difficult as these waste packages are designed to be durable for at least 300-10 000 years and longer and to see any changes during the lifetime of the researcher will be impossible.

Only mathematical models can confirm the safety of the stored waste by predicting the durability of waste packages during long term storage and in the disposal environment.

What can the models tell us about the waste?

The models help answer fundamental questions that are also the focus of the workshop.

The radiation induced models using the TRIM software will provide information regarding how the waste form is damaged by radiation during the long storage period and if the designed safety margins (low waste loading) will ensure the durability of the waste packages for disposal in the future. Basically it means must the waste container be placed inside another container to ensure transportation to the disposal site.

The ORIGEN and ORIGAMI codes in SCALE-6.2 and 6.3 provide us with reliable information on what happens to the waste composition over time: as the radionuclides  decay, their chemical composition changes, thus producing what are called daughter products, whose typical decay time, chemical composition and radiation  could be different from the original radioisotope.

The radiation transport code MCNP6.2 can accurately model the decay of the radioisotopes and the radioactivity arising from this transition to ensure that the dose rate (amount of radioactivity the human body encounters) from the surface of the waste packages is within prescribed safety values for the workers and even the public when monitoring the waste before disposal. This model also calculated the heat generated inside the waste during these decay processes to determine if ventilation will be required.

The combined outputs of the models indicates the maximum amount of waste you can put into those waste form to ensure that it can safely stored for a long time period without having any safety concerns to any stakeholder.

How reliable are the models?

The models we used in this workshop  were developed  decades ago and have continued to be validated and updated using data collected over the past 50/60 years. They are a very reliable tool for predicting the evolution of waste over periods of up to about 100 years. They have not been validated beyond this time scale though accuracy should remain very high.

What is the interest of organising these training events in collaboration with ICTP?

IAEA assists member countries during and after the nuclearization process, but collaborating with ICTP helps us reach developing countries that are not yet members of the IAEA. At the moment many of these countries, especially in Africa, are interested in generating energy using  nuclear power plants. Researchers who participate in these workshops will have the skills to provide solid and reliable information to the stakeholders in their countries, which will help them take better informed decisions. For example, for many developing countries the idea that they can build a nuclear reactor comes from their experience with research reactors. However, they need to be fully aware that nuclear research reactors are very small compared to nuclear power plants and that security and nuclear waste management also need to be upscaled. These things need to be considered well in advance and collaborating with ICTP is a way for the IAEA to ensure that relevant information reaches developing countries through their scientific community and is taken into account during the decision making process. Nuclear energy can be an important source of electricity as we collectively try to move away from fossil fuel, as long as the decision makers are fully aware of the challenges  and of the measures that need to be taken in order to prevent them.