The authors exposed a radiatively cooled, lithium-filled tantalum heat pipe (HP) to a hydrogen plasma in DIFFER’s linear plasma source Magnum PSI continuously for ~2 hours. The beam made a saddle-shaped footprint along the side of the inclined ~195-mm-long HP. During several steps with constant overall heat load, we tilted the HP to vary the peak heat flux by a factor of two. The maximum was ~2.5 MWm². Diagnostics included near infra-red thermography from two orthogonal ports. Another paper [1] gives details of the experiment. The heat pipe operated at ~1000-1100° C. We stopped after a leak in the HP occurred near the beam axis intercept, and ~0.06 g of lithium formed a 6-mm-diameter nodule. A coating that covered roughly half of the area wetted by the beam was also present. The initial breach occurred at a site of prior material damage. A second breach occurred several seconds after the exposure was terminated. Fractography and post-test metallography show the mechanisms differed. With the second breach, a transverse crack, lithium flowed out quickly and wetted an area ~30 mm². At this point the HP was cooling. If creep and relaxation occurred during the exposure, then stress state reversed (tensile loading) during cooling. A tantalum disk annealed in a hydrogen furnace was available for comparative evidence of hydrogen embrittlement. Sandia had purchased an existing tantalum HP from Aavid-Thermacore, Inc. The test showed prolonged operation, gave useful data and we judged it a success. However, tantalum would not be the right choice for a future PFC. The paper also discusses the geometry and materials for future PFCs. [1] G.F. Matthews, R. Nygren, T. Morgan, S.A. Silburn, “Demonstration of the potential for exchangeable PFCs based on radiatively cooled lithium heat pipes in Magnum PSI,” this conference. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This work was also part-funded by the RCUK Energy Programme under grant EP/I501045.