Performance evaluation and qualification of hard coatings used in absorber rod drive mechanism of Indian fast breeder reactor

Abstract

Prevention of surface damage at various guiding and bearing locations assumes high importance in ensuring reliable operation of Absorber Rod Drive Mechanisms (ARDM). Contact at an unintended location during any of the operating conditions, including seismic conditions, may cause unacceptable damage, reducing the availability of the ARDMs. Based on international and in-house experiences, the materials and surface coatings for mating surfaces and guiding locations were selected in the ARDMs of Indian Fast Breeder Reactors (FBR).Various mechanical and metallurgical investigations followed by integral assembly tests with full-scale components on hard face coatings were done to evaluate the performance of the hard coatings and to qualify them for reactor operation. In spite of detailed investigations, surface damage-related problems were faced during the initial stages of integral assembly testing, which severely delayed the qualification testing. Key lessons learned from the experimental program are that a holistic approach involving complete kinematics is necessary in the design of the systems to prevent unwanted surface damage-related issues. All these details are discussed in the present paper.From the qualification testing, it can be concluded that the performance of hard coatings for the ARDMs of Indian FBRs is satisfactory. The material and design selections made have formed the basis for the given applications in future FBRs in India.