U.S. ITER is responsible for the design, engineering, and procurement of the Tokamak Cooling Water System (TCWS). TCWS is designed to provide cooling and baking for client systems that include the first wall/blanket, vacuum vessel, divertor, and neutral beam injector. Additional operations that support these primary functions include chemical control of water provided to client systems, draining and drying for maintenance, and leak detection/localization. TCWS interfaces with 27 systems including the secondary cooling system, which rejects this heat to the environment.
TCWS is complex because it serves vital functions for four primary clients whose performance is critical to ITER's success, and it interfaces with more than 20 additional ITER systems. Conceptual design of this one-of-a-kind cooling system has been completed; however, several issues remain that must be resolved before moving to the next stage of the design process. The 2004 baseline design indicated cooling loops that have no fault tolerance for component failures. During plasma operation each cooling loop relies on a single pump, a single pressurizer, and one heat exchanger. Consequently, failure of any of these would render TCWS inoperable, resulting in plasma shutdown. The application of reliability, availability, maintainability, and inspectability (RAMI) tools during the different stages of TCWS design is crucial for optimization purposes and for maintaining compliance with project requirements.
RAMI analysis indicates appropriate equipment redundancy that provides graceful degradation in the event of an equipment failure. Results from the study indicate that pump and heat exchanger reliability are key issues.
The ITER International Organization (ITER IO) RAMI group has proposed standardization for the pumps and heat exchangers to reduce fabrication risks of one-of-akind components. An aggressive maintenance/repair program should be an integral part of ITER operations. Preventive maintenance should be part of the maintenance system.
For equipment that is infrequently operated, it is suggested that the key components be tested on a regular basis. The analysis has indicated that the RAMI requirements have been exceeded at this point, allowing concentration on cost optimization.