Engineering change management during replacement and up-gradation of reactor systems of Dhruva

Dhruva, 100 MWth, tank type research reactor has been operating since 1985 at Mumbai, India with maximum thermal neutron flux of 1.8 Χ 1014 n/cm2/sec. Natural metallic uranium is used as fuel and heavy water as coolant, moderator and reflector. The reactor has been well utilized for over 27 years with high availability and excellent safety record. Initial design of SSCs of Dhruva was carried out with stringent specifications and strict quality control to assure safe and reliable operation for the entire service life. During operational phase, a well formulated in service inspection and surveillance programme has been put in place to provide timely feedback on the healthiness of systems, structures and components (SSC) important to safety. Based on systematic inservice inspection (ISI) programme, insights from regular surveillance programme and structured system performance monitoring and review, certain incipient degradations in the reactor systems could be noted in time and replacement of certain systems/components, like secondary coolant heat exchangers, certain portion of emergency cooling water pipelines have been undertaken. Technological obsolescence has necessitated some of the replacement/up-gradation actions for power supply and controls and instrumentation systems of the reactor. Replacement of 150 kVA class II MA set with 250 kVA MA set, up-gradation of 20 kVA class II inverters, complete up-gradation of control room and fuelling machine instrumentation was taken up, without significantly affecting the reactor availability. While implementing these changes in the reactor systems, although the initial and the final system configuration were well analyzed and well established, during the transition phase adequate care had to be exercised in order to ensure that the system configuration does not lead to an unsafe state, taking into account various possible failures in the system under commissioning. Further, in order to ensure this requirement, the system change protocol followed a multitier review and approval procedure with adequate quality control during execution of these changes. This paper provides an overview of engineering change management during replacement and up gradation of the reactor components/systems of Dhruva