Pressurized Water Reactors (PWRs) and High-Temperature Gas-Cooled Reactors (HTGRs) from Different Generation
Nuclear reactors have improved in various aspects from generation to generation (Figure 1). In the last Generation IV, the major goals are:
• Sustainability is achieved by efficient fuel use, waste reduction (particularly for long-term aspects), and clean air goals
• economics, which should be competitive with other energy and reflect a comparable degree of financial risk
• safety and reliability, which should be based on modern risk assessment methodologies and include passive and inherent safety measures.
• proliferation resistance, preventing the abuse of nuclear materials and installations, and physical security against terrorist attacks.
Next, this will be discussed PWR and HTGR designs form different reactor generations.
Pressurized Water Reactors (PWRs)
Pressurized Water Reactors (PWR) are a type of light nuclear reactor and are one of the most common types of reactors in the world. PWR is a generation II reactor that began operating at the end of 1960. PWR uses enriched uranium as fuel and light water as coolant and moderator. PWR is known for its reliability and long experience in operation, making it a technology very ready for use in the field of nuclear energy. PWR experienced several improvements and innovations in Generation III in several aspects. The AP1000 is a two-loop pressurized water reactor (PWR) designed by Westinghouse Electric Company. The reactor is considered a Generation III+ nuclear reactor, combining advanced passive safety features and improved economics over previous generations. Several differences in PWR between Generations II and III can be seen from various aspects.
1. Improved design, as an implementation of inherent safety from the aspect of limiting effects
Generation III reactors provide an evolution in terms of design, including improved fuel technology, improved safety systems, and longer operational life. This reactor is designed for an operating life of 60 years, which can be extended to more than 100 years compared to Generation II reactors which are designed for an operating life of 40 years which can only be extended to more than 60 years.
2. Safety features, as an implementation of built-in safety
The Generation III+ reactor design is an evolutionary development of the Generation III reactor, offering improved safety over the Generation III design.
3. Operational Life, as an implementation of inherent safety from the error tolerance aspect
Generation III reactors are intended to have a longer operational life compared to Generation II reactors. This is achieved through improved materials, design and safety systems, allowing for longer operational periods.
4. Economic considerations, as an implementation of inherent safety from the aspects of intensification, substitution, attenuation and simplification
Generation III reactors are designed to be less expensive to build, operate, and maintain compared to Generation II reactors. In Generation III, simplifications were made in safety systems, normal operating systems, construction techniques, and instrumentation and control systems, resulting in large savings in investment capital and reduced operating and maintenance costs.
From the various aspects above, it can be concluded that Generation III PWRs, offer a sophisticated design compared to Generation II reactors, offering better safety features, longer operational life and cost effectiveness. Compared to the previous generation II PWR design, the AP1000 has 50% fewer safety-related valves, 35% fewer pumps, and 80% less safety-related piping, demonstrating an inclusive and innovative approach to safety and design.
High-Temperature Gas-Cooled Reactors (HTGRs)
HTGRs are graphite-moderated, helium-cooled nuclear reactors that employ uranium fuel to reach extremely high reactor core output temperatures. The Very High Temperature Reactor (VHTR) is a Generation IV reactor that represents an evolution of typical gas-cooled reactors. Several differences in HTGR between Generations III and IV can be seen from various aspects.
1. Design evolution
The VHTR is an improvement of traditional Generation III+ gas-cooled reactors. The VHTR, on the other hand, is a Generation IV reactor that is scheduled to be installed between 2015 and 2025 and has been recognized as being inexpensive, safe, efficient, and proliferation resistant.
2. Coolant temperature and efficiency
The VHTR has two benefits over existing Generation III reactor designs in terms of coolant temperature and efficiency. The high temperature of the coolant exiting the reactor core allows for excellent thermal efficiency in power generation and may also be used as process heat in hydrogen synthesis. This capacity to operate at high temperatures distinguishes VHTRs from Generation III reactors.
3. Fuel Configuration
VHTRs can be built with either a prismatic block core or a pebble-bed core. The two designs mostly are related to the fuel arrangement.
4. Application
VHTRs feature inherent safety, high thermal efficiency, process heat application capabilities, low operating and maintenance costs, and modular construction. They can provide nuclear heat and energy at core outlet temperatures ranging from 700 to 950°C, and maybe even more than 1000°C in the future.
The VHTR, as a Generation IV reactor, represents a significant advancement in nuclear reactor technology, offering high thermal efficiency, inherent safety, and the potential for diverse applications such as electricity generation and hydrogen production, distinguishing it from Generation III reactors.
Reference:
https://medium.com/@6unpnp/safety-by-design-an-intro-856eef425724
https://en.wikipedia.org/wiki/Generation_II_reactor
https://en.wikipedia.org/wiki/Generation_III_reactor
https://en.wikipedia.org/wiki/Pressurized_water_reactor
https://www.westinghousenuclear.com/energy-systems/ap1000-pwr/overview
https://en.wikipedia.org/wiki/AP1000
http://large.stanford.edu/courses/2013/ph241/kallman1/
Very-High-Temperature Reactor (VHTR), https://www.gen-4.org/gif/jcms/c_42153/very-high-temperature-reactor-vhtr
https://www.energy.gov/sites/default/files/2016/03/f30/QTR2015-4J-High-Temperature-Reactors.pdf
https://en.wikipedia.org/wiki/High-temperature_gas-cooled_reactor
