China has completed the basic technology research and published a development roadmap for a Generation IV demonstration supercritical-water-cooled reactor that could be commissioned in 2022.
This reactor could achieve costs that are up to half the cost of current reactors and have higher efficiency.
They could be low cost enough to displace all future coal plant construction in China starting in 2025-2030.
$900 per kilowatt is over three times cheaper than the estimated overnight cost of advanced nuclear reactors ($3100 per kilowatt) estimated by the US department of energy
In China, water-cooled reactors are and will be the main reactor concept for the generation of nuclear power. China’s experience and the technology developed in the design, manufacture, construction, and operation of nuclear power plants are mainly concentrated on water-cooled reactors. Thus, the development of SCWRs is a smooth extension of the existing nuclear power generation park in China. From a technological point of view, an SCWR is a combination of the water-cooled reactor technology and the supercritical fossil-fired power generation technology. Hence, SCWRs ensure the technological availability.
The Nuclear Power Institute of China said the SCR-1000 reactor block will have a capacity of about 1,000 megawatts.
The institute will work on the demonstration unit as part of the Generation IV International Forum (GIF), which sees 13 countries and regions collaborate in the development of Generation IV nuclear energy systems.
The institute said it had identified four stages of development, continuing until 2025. Further technology development will begin this year, followed by engineering research and development from 2017-2021, construction from 2019 -2023, and commissioning between 2022 and 2025.
SCWR core is operated above the critical pressure of water (22.1MPa), where reactor coolant experiences no phase change and the coolant temperature can exceed the pseudo-critical temperature, which corresponds to the boiling temperature at subcritical pressure.
The potential technical advantages of the SCWR over current water-cooled reactors are derived from the above-mentioned features as follows:
• High thermal efficiency
High temperature and high pressure of turbine inlet steam lead to high thermal efficiency. Inlet pressures of current light water reactors (LWRs) and pressurized heavy water reactors (PHWRs) are usually at around 7MPa and their temperatures are at or near the saturation temperature. Turbine inlet steam pressure and temperature of SCWR are much higher. The thermal efficiency of SCWRs is expected to be 1.2 to 1.4 times higher than that of current water cooled reactors.
• Simplification of plant system and low capacity components
Without phase change in the core, the SCWR plant system can be simplified by eliminating recirculation system and steam-water separation system in BWR, or steam generators and a pressurizer in PWR. The reactor coolant flow rate of SCWR is much smaller than that of BWR and PWR because the enthalpy rise in the core is much larger, which results in low capacity components of the primary system.
Furthermore, the SCWR incorporates advances from supercritical fossil power plant technologies that have been operating successfully for more than 40 years. The main fossil power plant technology that will be used in the SCWR is supercritical turbines that can be incorporated in a direct thermodynamic cycle to increase thermal efficiency
. The R&D task for developing the balance of power (BOP) of the SCWR would be very limited or almost none. In addition, using a direct cycle at supercritical conditions simplifies the plant system and eliminates certain components, which results in significant reduction in capital cost.
These technical advantages would lead to considerable reduction of the capital cost. The construction cost of SCWR plants has been targeted at $900/kW in the GIF Roadmap
A mixed core design (SCWR-M) was being developed at Shanghai Jiao Tong University in China. It is a pressure vessel concept, and the core is divided into thermal-spectrum and fast-spectrum zones. The coolant entering the pressure vessel flows downwards through the thermal zone at first and then flows upwards through the fast zone.
The reactor is one of six reactor systems chosen by GIF for “further research and development”.
GIF says Generation-IV designs will use fuel more efficiently, reduce waste production, be economically competitive, and meet stringent standards of safety and proliferation resistance.
Some 100 experts evaluated 130 reactor concepts before GIF chose the final six. They are the gas-cooled fast reactor (GFR), the lead-cooled fast reactor (LFR), the molten salt reactor (MSR), the sodium-cooled fast reactor (SFR), the very high temperature reactor (VHTR) and the supercritical-water-cooled reactor (SCWR).
SCWRs are high temperature, high-pressure, light-water-cooled reactors that operate above the thermodynamic critical point of water. They have the potential of lower capital costs for a given electric power of the plant and of better fuel utilisation, GIF said.
However, there are several technological challenges associated with the development of the SCWR, particularly the need to validate transient heat transfer models (for describing the depressurisation from supercritical to sub-critical conditions), qualification of materials (advanced steels for cladding), and demonstration of the passive safety systems.
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