This paper might be good starting point for you to get more references on the design of steam radial turbine: Please just google it, it should be available online, otherwise I can send it to you.
T. Venkata Nagendra Kumar,Y.Rameswara Reddy. "DESIGN OF 20-30 MW RADIAL INFLOW STEAM TURBINE FOR POWER GENERATION". International Journal of Advance Engineering and Research. Development. Volume 4, Issue 12, December -2017
Dear Abdelkader Filali, Thank you for the advice , I already read this paper but in my modest opinion I think the paper is not clear and the published journal is less recognized.