DESIGN, FABRICATION AND TESTING OF HELIUM-COOLED VANADIUM MODULE FOR FUSION APPLICATIONS

Vanadium alloys are attractive materials for fusion applications due to their low neutron activation and rapid decay of radioactivity with time. Design of high heat flux components with vanadium as the structural material is difficult due to its low thermal conductivity relative to copper and the lack of practical experience with fabrication of vanadium components. Similarly, helium is an attractive coolant for fusion power plants due to its chemical inertness, its transparency to neutrons, and stable heat transfer. However, there is a perceived difficulty that the use of helium as a coolant will limit the maximum heat flux on components. Reference 1 discusses the principle that heat transfer enhancement techniques reduce the pumping power for helium cooling, making it practical for cooling plasma facing components and General Atomics (GA) has demonstrated cooling of high heat flux components with helium coolant. A copper module designed by GA was successfully tested to a steady state heat flux level of 3200 W/cm 2 over small area and 1000 W/cm 2 over the entire 20 cm 2 area. As a continued effort to demonstrate practical application of fusion science, GA undertook the present effort to fabricate a vanadium module cooled with helium. Due to lower thermal conductivity of vanadium (6% of copper), this module will withstand about 300 W/cm 2 heat flux over the entire length. The module was fabricated from V-4Cr-4Ti alloy and is 228 mm long and 22.1 mm in diameter. The thickness of the vanadium tube is 1.76 mm. The internal flow path has been designed to enhance the heat transfer coefficient to a value of about 1 W/cm 2 −°C at a helium flow rate of 20 g/s. A thermal stress analysis of the design was performed to ensure that the stresses are within limits at a heat flux level of 300 W/cm 2 and a helium pressure of 4 MPa. The test module has been hydrostatically tested to 7 MPa pressure and helium leak checked. The module is ready to be tested at the helium loop (4 MPa pressure 20 g/s flow) at Sandia National Laboratory, Albuquerque. Future high heat flux testing is planned.