Part-2: Turkey's Nuclear Energy Journey - Brief Information on NPP Physical Security
How a nuclear power plant works:
The functionality of every nuclear power facility relies on a regulated nuclear chain reaction. The nuclear fuel utilized in these plants is crafted from uranium ore, undergoing a process to extract natural uranium-238 (U238). Subsequently, this extracted uranium is enriched to achieve a uranium-235 (U235) content ranging from 3.5% to 5%, rendering it appropriate for application as fuel in thermal-neutron reactors, such as the VVER. A specialized tube, constructed from zirconium alloy, houses 350 uranium pellets deliberately. The choice of zirconium is not arbitrary; its presence is strategic. Zirconium, as the primary material, exerts minimal influence on the reaction, serving as the initial barrier that effectively contains radioactive substances, preventing their release into the environment. These tubes, numbering 313, are intricately connected through hexagonal grids, forming a cohesive unit known as a fuel assembly.
- The reactor core, in turn, accommodates a total of 163 such assemblies, collectively contributing to the operational dynamics of the nuclear facility.
- 700 train cars of hard coal are equivalent in energy capacity to one fuel assembly.
- The potential energy yield from 1 gram of uranium is substantial, enabling the production of 1 megawatt-hour of energy. This corresponds to 86.4 gigajoules of thermal energy or roughly 10,000 kilowatt-hours of electrical energy. The efficiency and energy density of uranium make it a potent source for generating significant power within a relatively compact amount of material.
VVER-1200 is the latest, most technologically advanced and safe Russian Generation III+ reactor.
- Achieving a 20% enhancement in electrical power output, while preserving the identical dimensions of the reactor pressure vessel as in the VVER-1000 reactors, represents a notable advancement in reactor efficiency. This improvement signifies a substantial leap forward in energy generation, demonstrating the capacity to harness more electricity within the existing spatial constraints. The innovation not only underscores technological progress but also underscores a more effective utilization of resources and infrastructure in power generation processes.
- The design service life has been increased by 2 times from 30 to 60 years, which can further be extended by another 20 years
- As a result of the nuclear chain reaction, a huge amount of thermal energy (3,312 MW) is released inside the reactor, which is carried by coolant.
Nestled within the reactor pressure vessel, a vertical cylindrical, hermetically sealed steel container, characterized by a spherical bottom and a securely sealed lid, houses the core of the nuclear reactor. Remarkably, the reactor sustains operations for up to eighteen months on a solitary fuel load. The heat generated during this period is staggering, equivalent to the thermal energy released by burning 124,500 train cars of coal. Notably, this massive energy production occurs without emitting carbon dioxide (CO2) into the atmosphere, underscoring the environmental advantages of nuclear power.
The VVER-type reactors employ chemically desalinated water as a coolant. This water undergoes high-pressure heating, reaching temperatures as high as 328.8 degrees Celsius as it traverses through the reactor, efficiently contributing to the controlled and optimized operation of the nuclear system.
Within the closed and sealed primary circuit, water circulates seamlessly, driven by robust circulation pumps known as reactor coolant pumps. These pumps play a pivotal role in maintaining the flow of water for effective heat transfer and reactor core cooling.
The heated water, enriched with thermal energy from the reactor, undergoes a crucial phase in the steam generators. Here, it imparts its heat to the water in the secondary circuit, prompting it to boil and transform into steam. This newly generated steam embarks on a journey through expansive steam lines, ultimately reaching the turbine. In the turbine's presence, the energy encapsulated in the steam manifests its power, setting in motion the rotation of the turbine shaft through a series of mechanical interactions. This transformative process highlights the pivotal role of nuclear energy in propelling the turbine, subsequently generating electricity through this well-orchestrated sequence of events.
The electricity generated by the generator goes to step-up transformers, after which it enters the switchgear via gas-insulated current conduits and is then fed into the grid.
The Akkuyu Nuclear Power Plant project incorporates a compact Arabelle low-speed turbine renowned for its exceptional efficiency, boasting rates of up to 38%. Teamed up with a cost-effective and dependable generator, this turbine stands as a pinnacle of power and reliability within its category on a global scale. The electricity produced by the generator undergoes a crucial transformation. First, it passes through step-up transformers, elevating its voltage. Subsequently, the power is directed into the switchgear via gas-insulated current conduits, ensuring a safe and efficient transmission process. Finally, the electricity seamlessly integrates into the grid, contributing to the overall energy supply with the high standards of performance and reliability synonymous with the Akkuyu NPP project.
Thus, in a nuclear power plant electricity is generated by converting nuclear energy into thermal energy, thermal energy into mechanical energy, and mechanical energy into electrical energy.
Brief information about security
The station is designed to withstand extreme loads:
- Fall of a large commercial aircraft weighing 400 tons
- Earthquake with a magnitude of up to 9.0 in the world.
- Tornadoes and hurricanes up to 60 m/s
- Explosion with a shock-wave of 30 kPa
- Tsunamis and waves up to 10 meters
Operation of passive safety systems is ensured even in the absence of power supply. The safety systems at the Akkuyu Nuclear Power Plant are meticulously crafted to address critical scenarios, encompassing emergency shutdown of the reactor, maintaining it in a subcritical state, emergency heat dissipation from the reactor, and controlling radioactive substances within defined limits. The design incorporates a comprehensive array of both active and passive safety systems, each playing a vital role in executing safety functions under diverse conditions.
The configuration of these active and passive safety systems is strategically devised to ensure optimal performance across a spectrum of situations. Notably, the efficiency of the passive systems is a standout feature, allowing for a minimum of 72 hours of uninterrupted safety functionality without the need for operator intervention, even in the event of complete power loss. This extended timeframe underscores the plant's commitment to safety and its ability to autonomously manage critical situations, further enhancing the reliability and robustness of the safety protocols in place.
Emergency control systems:
The rods of the reactor control and protection system are held above the reactor core by electromagnets. When the power is cut off, the rods are lowered by gravity into the reactor core in less than 2 seconds and put the reactor into subcritical state, stopping the nuclear reaction.
- Core catcher
One of the most important elements of the passive safety system, the core catcher is a steel vessel weighing 144 tons, which in the event of an emergency reliably holds the core melt fragments and does not allow them to escape beyond the containment of the reactor building
- Emergency core cooling system
Designed to cool the core with a volume of water many times larger than the volume of the reactor. Just as the reactor control and protection system, it will perform its function for 72 hours even in complete absence of power.
- Hermetic containment system
The design of the Akkuyu Nuclear Power Plant includes measures specifically tailored to prevent the dissemination of released radioactive substances and ionizing radiation beyond the confines of the accident confinement area. Additionally, these measures serve to shield systems that, if compromised, might contribute to the dispersion of radioactive substances into the environment.
A key component reinforcing the containment structure is the incorporation of high-strength reinforcement cables within the containment prestressing system, strategically positioned in specialized channels. These cables, when tensioned, generate compressive forces that act as a counterbalance, capable of mitigating potential loads in the event of a sudden surge in pressure within the containment. This additional layer of strength not only fortifies the containment's integrity but also enhances its ability to withstand and manage unexpected scenarios, underscoring the plant's commitment to safety and environmental protection.
Also:
- Passive heat removal system
Ensures removal of residual heat from the reactor core through the secondary circuit.
- System of emergency hydrogen removal in the accident area
The system performs functions to prevent formation of explosive hydrogen mixtures in the accident zone during accidents, including severe ones
- Overpressure protection system
The primary circuit overpressure protection system is designed to protect the reactor plant equipment and pipelines from an unacceptable increase of coolant pressure during accidents through operation of the pilot-operated safety valve, through which steam from the pressure compensator is discharged into the bubbler tank.
Today, I tried to provide brief information about the operational principles and physical security of the Akkuyu Nuclear Power Plant. I hope it has captured your interest.
Until the next article, wishing you enjoyable readings.
Previous articles:
1 - Akkuyu NPP - First Nuclear Power Plant of Türkiye
2 - Web3 Medium - Bulbapp
3 - Everything about Atatürk
4 - 100 Gretest Non-English Film
