Investigations on the availability of second shutdown system of Indian FBR

•Realisation of high availability for second shutdown system.•Development & qualification of sodium immersed EM clutch.•A new method for testing the ARDMs against flow induced vibrations.•In-situ cleaning of sodium immersed armature.•Alternative design concepts to further enhance the availability of ARDMs. Design and operating nuclear power plants with higher capacity factors is always desirable for improved economics and it is further more important in case of fast breeder reactors. It is well recognised that the availability of shutdown systems has an important bearing on the plant availability. In this paper, various investigations carried out on the availability of the second shutdown of Indian FBR are reported. The stability of the system performance against a range of anticipated disturbances was studied. Studies were designed to gain better technical insight into the system performance and to aid in finding out the performance bounds. Based on the design review of second shutdown system, in-house and international experiences, investigations related to the electromagnetic coupling, flow induced vibrations, subassembly bowing and the deterioration of electromagnet parting plane were carried out as part of the current experimental programme. Various innovative methods/schemes were adopted in the studies. These investigations helped in identifying the design vulnerabilities and thus in improving the system design, qualifying respective analytical/numerical studies, providing direction for further enhancement in system performance, demonstrating the margins available in the system design and more importantly much needed insights into various phenomenons to attend any unforeseen availability related issues of second shutdown system during their operation in reactor. Alternative design concepts were also discussed.