| Turbine technology
Arabelle 75in LSB: going to new lengths in LP half speed blade development
The two Arabelle steam turbine trains at Hinkley Point C in the UK, currently under construction, will each be capable of producing an astonishing 1770 MW (gross). A key contributor to this unprecedented power output is the deployment of 75in last stage blades in the LP modules, the longest LSBs ever made. The size of the LSBs, coupled with strict limits on their weight, posed significant challenges for the development team, requiring new design tools and manufacturing processes. The result: a high performance last stage, manufacturable at moderate cost
Ivan McBean Principal Engineer, Aerodynamics, Arabelle Solutions, Baden, Switzerland
The Arabelle turbine platform has been developed for nuclear half speed applications and can be deployed with different reactor types and for different cooling water temperatures. Some typical PWR applications include Akkuyu in Turkey, Flamanville in France, and Taishan in China. The Arabelle turbine trains for these power plants have a high- pressure (HP) and intermediate-pressure (IP) module as well as multiple low-pressure (LP) turbine modules. In the LP turbines, the last stage blades have a length of 69in. More recent applications have been identified that involve even lower cooling water temperatures and higher steam volume flows at the LP turbine exhaust. This has led to the development of a 75in last stage blade to accommodate the required increase in LP exhaust area. This increase in last stage blade length posed a significant challenge to the design team in the development process due to the strict limits on last stage blade weight.
Turbine configurations for nuclear power plants
The main two categories of turbine configuration for nuclear power plants are referred to as half-speed (rotating at half of the grid frequency, 1500 RPM for a 50 Hz grid and 1800 RPM for a 60 Hz grid) and full speed (rotating at the grid frequency, 3000 RPM or
Rendering of Arabelle LP module (source Arabelle Solutions)
3600 RPM). Although there is a current trend to develop smaller reactors and full speed turbine designs, the economics of nuclear power plant design still require a high steam volume. A comparison of half-speed versus full-speed configurations for a given power plant output shows that the half speed layout involves a reduced number of LP turbine modules and a requirement for only one train, whereas at large
power outputs the full-speed layout requires two trains. Clearly these are not the only considerations when designing the plant, and the plant economics vary over time and depend on the geographic location and power market. Nonetheless, the half speed train configuration remains the most cost competitive solution for very large powers, when one considers only the cost of the turbine train itself.
About Arabelle Solutions
Owned by EDF Group, Arabelle Solutions operates as a standalone business dedicated to providing nuclear turbine island solutions. The business was acquired by EDF Group from GE Vernova in May 2024, and provides turbine island technology for new nuclear power plants around the globe as well as maintenance and upgrade activities in all regions other than the Americas. Tracing its heritage back to the industry’s early years, the firms’ technology ranges
from the world’s most powerful steam turbine in operation, to pioneering modular designs optimised for SMRs, as well as generators, pumps, heat-exchangers, and controls. Arabelle Solutions has around 3300 employees and is headquartered in Boulogne-Billancourt, France.
A solution for Hinkley Point C As countries transition away from fossil fuel fired power plants to alternatives, many have chosen to extend or replace their nuclear power plant fleet. In the UK it was decided to build a new nuclear power plant next to the existing one at Hinkley Point B on the Bristol channel, as this latter plant was coming to the end of its operational life.
The first new nuclear power plant in the UK in a generation, the requirement was for a large power output, over 3 GW, for which the Arabelle turbine platform is well suited.
The cooling water temperature at the Hinkley Point site is relatively low compared to existing
www.modernpowersystems.com | September 2024 | 19
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