Challenges faced in selection, manufacture, quality assurance and qualification of the components for FBTR CRDM applications

Fast Breeder Test Reactor (FBTR) is a sodium cooled type experimental reactor. Six numbers of Control Rod Drive Mechanisms (CRDM) along with their B4C control rods perform reactor start up, controlled shutdown, reactivity control for power changing and burn-up compensation and to shut down the reactor by SCRAM action during abnormal conditions. Lower part of the CRDM which consists of translation tube, outer sheath and gripper is partially immersed in sodium. Nested Ripple type Welded Disc Bellows (NRWDB) called translation bellows prevents entry of sodium in the space between the translation tube and outer sheath and acts as primary leak tight barrier. Silicone bellows which is near ground level elevation acts as secondary leak tight barrier. Non standard Aluminium bronze rod was used as raw material for various drive components in CRDM. These components were imported earlier from FRANCE. Indigenous development of these items and bellows was taken up due to difficulties in procurement. Extensive studies were carried out on selection of materials, establishment of manufacturing procedures and stringent Quality Assurance Program (QAP) to ensure defect free component during indigenous development. Suitable methodology was arrived for qualification of these components. Successful development of silicone bellows and Aluminium bronze rods were completed as per our requirements and selection, establishment of manufacturing procedure and QAP were completed for (NRWDB). Prototype development of NRWDB is in progress. (author)