Critical Design Issues of the Tokamak Cooling Water System of ITER's Fusion Reactor

U.S. ITER is responsible for the design, engineering, and procurement of the Tokamak Cooling Water System. The TCWS transfers heat generated in the Tokamak to cooling water during nominal pulsed operation - 850 MW at up to 150°C and 4.2MPa water pressure. This water contains radionuclides because impurities (e.g., tritium) diffuse from in-vessel components and the vacuum vessel by water baking at 200–240°C at up to 4.4MPa, and corrosion products become activated by neutron. The complexity of the TCWS design and fabrication presents unique challenges. During completion of the conceptual design of this one-of-a-kind cooling system, several issues were identified because of complex system requirements. Those issues include flow balancing between over a hundred branch pipelines in parallel to supply cooling water to blankets, determination of optimum flow velocity while minimizing the potential for cavitation damage, design for freezing protection for cooling water flowing through the cryostat (freezing environment), requirements for high-energy piping design, and electromagnetic impact to piping and components. Although the TCWS consists of standard commercial components such as piping with valves and fittings, heat exchangers, and pumps, complex requirements present interesting design challenges. The TCWS conceptual design and strategies for resolving critical design issues are described.