Nuclear reactors and nuclear technology are widely used around the world. Some uses include energy production, isotope production, and thermal generators used in space probes. Nuclear technology has many features that make it dangerous to living beings (due to radiation). Because of the safety concerns surrounding nuclear technology and nuclear reactors, industry and science have developed and continue to develop many safety protocols and measures to avoid possible dangers and mitigate negative impacts.
If you’re interested, you can read up on the Chernobyl disaster. In 1986, a nuclear accident happened at the number four reactor of the Chernobyl Power Plant due to flaws with the reactor design and human error. During the initial emergency response, over 130 staff and firefighters absorbed very high doses of ionising radiation, and as a result, they experienced acute radiation syndrome. A sarcophagus (which was further enclosed recently) was built to reduce radioactive contamination.
Dangers of nuclear power
In nuclear technologies using radioactive isotopes, waste generation is one of the main challenges. If waste is not managed correctly, it can lead to nuclear contamination. Other problems include the possibility of out-of-control reactions in nuclear power plants, such as what happened in Chernobyl (USSR) and Three-Mile Island (USA). Another critical point in nuclear safety is the danger of others creating nuclear weapons (fissile material).
Fissile material is any isotope able to sustain a fission reaction, which consists of the breakaway of the isotope (atom) into lighter elements. The reaction emits large amounts of energy.
Let’s look at the above-mentioned challenges in more detail.
Nuclear contamination
Nuclear technology and reactors make use of materials that emit radiation. These materials are known as nuclear fuel. Radiation is dangerous for living beings as it can ionise atoms or molecules.
Ionisation happens when high-energy particles interact with an atom changing its electrical state by removing electrons out of their orbits.
In nuclear technology, any element that emits radiation is shielded by a dense wall of material that blocks the radiation. However, radiation can escape (if something fails in the structure, for example), causing nuclear contamination.
See our explanation on Alpha, Beta, and Gamma Radiation for more info on their ionising properties.
Nuclear waste
During nuclear reactions, heavy isotopes convert into lighter elements. Lighter elements from the nuclear reactions are, in some cases, radioactive too and are called residuals. Residuals cannot be used, and they are stored until their radiation emission decays to a point where they are no longer dangerous. Nuclear waste can also come from nuclear medicine that uses radiate isotopes for tracing, imaging techniques, and cancer therapy.
A certain degree of nuclear waste has a significant half-life and will be radioactive for thousands of years. Other waste is short-lived and is only radioactive for a few years. This short-life waste can be contained in near-surface burials. We can find facilities for this type of waste in Finland, Japan, the UK, and the USA. Waste with a longer decay period must be sent to deep geological store facilities.
If the waste is not stored correctly, it can cause nuclear contamination.
Check out our explanation on Half Life for more info on decay processes and storage.
Reactions out of control
Nuclear reactors in power plants use fission processes to convert thermal energy into electricity. Nuclear reactions depend on bombarding another heavy element (radioactive isotope) with neutrons in the reactor core. After absorbing the neutron, the heavy element breaks, creating two lighter elements. The reaction also releases alpha particles (alpha radiation) and free neutrons with high velocities.
The ejected neutrons are then partially slowed down so that other heavy atoms can absorb them and break. Fission processes increase the number of ejected neutrons that interact with other heavy elements. This, in turn, creates a chain reaction, which heats the nuclear core. As the heat and number of neutrons ejected rise, it is possible for an out-of-control reaction to occur.
On the left, an atom of uranium-236 breaks into two lighter elements (grey) and two neutrons, which are absorbed by atoms of uranium-235. The process converts the uranium-235 into uranium-236, which break again, which starts the reaction again.
In nuclear reactors, the core is made of densely packed fissile material (nuclear fuel). As soon as an isotope breaks away releasing neutrons, a chain reaction begins.
In nuclear reactors, rods are lifted to start the reactions. This design practice/working mechanism is used so that reactions always start at a minimum of activity. They are only lifted when more energy is needed.
The rods are made of materials that can absorb the neutrons from the nuclear reaction without entering into fission. The more neutrons they absorb, the fewer neutrons are available for the nuclear reaction.
The rods are so effective that in the case of emergency, they can be dropped suddenly, and, when necessary, they shut down the reactor completely. Below is a figure showing the event of dropping the rods suddenly.
A shows the moment when the reactor rods are partially removed so that the reactor can gain power. B shows when the rods are suddenly dropped so that the reaction slows down.
Nuclear proliferation
Nuclear material can be used to create nuclear weapons. The International Atomic Energy Agency and the United Nations Office for Disarmament Affairs deter the use of nuclear material for nuclear weapons by detecting early misuse of nuclear technology and actively enforcing and promoting treaties to ban nuclear proliferation.
Safety measures in nuclear power
Nuclear power and technologies have high regulations for safety. This includes the way reactors are built and how waste is managed.
Precautions taken to prevent a nuclear accident
Nuclear reactors have many safety measures to ensure their correct inner workings. Here are some of these measures:
- Control rods. The reactors use control rods to reduce the number of neutrons in the core.
- Remote refuelling. Reactor refuelling should be done remotely, and the refuelling of reactors can vary depending on the plant and design.
- Structural containment with an extensive lifespan. The structural components of a nuclear power plant should be able to stand seismic activity and heavy impacts on the outer side. On the internal side, heat and radiation will degrade the materials used in the reactor core construction. As a result, materials that withstand these conditions during longer periods than the plant lifecycle must be used.
- Diverse sensors, including cameras, thermal sensors, and radiation sensors, analyse collected information, which is then used to update the reactor crew.
- Many mechanical and electrical systems are made redundant. Having duplicates or triplicates is essential, so a failure of one component will not affect the plant.
Nuclear waste storage
Nuclear waste storage is a technique used to isolate waste material. Nuclear waste can be divided into low-level waste, high-level waste, and transuranic waste, which can emit alpha particles and consist of elements heavier than uranium.
Each type of containment is different and depends on the type of radiation and how long the waste remains radioactive. Low-level waste can sometimes be placed in faraway locations isolated in shallow burials.
High-level waste needs a deeper burial known as deep geological repositories. The depths of the burials can reach up to one kilometre. These burials are designed for long-time containment without maintenance. One example of these systems is the one under construction at Onkalo in Finland.
Deep geological repositories are constructed in geological places with large temporal stability, which ensures they will not undergo geological changes that can cause leaks. The materials are packed in a tight container that is sealed and shielded.
Although they are still being built, deep burial sites are still under research. Because nuclear material can create high temperatures at deep depths, the rock type must withstand the large temperatures and time period. Granite is one of the main candidates as it is an erosion-resistant rock that can last for hundreds of millions of years.
Future of Fission
Nuclear power plants can be named third-generation power plants. Despite their current safety measures, they can still be improved. As a result, future plants classify as fourth-generation plants. Their designs incorporate a process known as reprocessing. Reprocessing is the ability to recover used nuclear fuel, making the process more efficient. Proponents claim that there will be less waste with a shorter decay period.
Other reactor designs with more significant safety measures include molten salt reactors (which, in theory, could prevent nuclear accidents). Molten salt reactors function with fuel that is in a molten state and at lower pressures, which decreases the risk of dangerous meltdowns.
Safety of Nuclear Reactors - Key takeaways
- Nuclear technology poses many challenges that need increased safety measures. Some of these challenges are nuclear waste, nuclear contamination, the control of nuclear reactions, and the proliferation of nuclear weapons.
- Nuclear waste can be classified into low-level waste, high-level waste, and also transuranic materials. The type of storage, radioactivity, and life span depends on the type of waste.
- High-level waste is stored in deep geological reservoirs that are geologically stable (but research for this is still happening).
- Control rods are used to reduce or even stop the reaction at a nuclear reactor core. They do so by absorbing the neutrons in the nuclear reaction.
- Nuclear reactor construction must withstand long periods without degradation.
- Nuclear proliferation is another danger of nuclear technology. Countries and organisations have signed treaties to stop nuclear weapon creation.
Explanations 
Textbooks 
Exams 
Magazine 
