PNNL

Abstract

Co-deposition of carbon atoms with hydrogen isotopes and hydrogenated carbon radicals and molecules has been investigated and recognized as the main mechanism for tritium retention in the first wall of tokamak fusion devices. This has emerged as a serious constraint for safe and economic long-term operation of future fusion test reactors and fusion energy systems. Similar deposits on the surface of the engineered components in Tritium-Producing Burnable Absorber Rods (TPBARs) are observed. Characterization of the deposits can help understand the tritium transport, accumulation history and distribution in TPBARs. This study reports our recent results from post-irradiation examinations of carbonaceous deposits on an aluminide-coated cladding in the lower plenum of a TPBAR following neutron irradiation. The observed deposits are amorphous in nature, consisting of flakes of interconnected nanoscale features. They contain mostly double-bonded carbon (e.g., alkene) and carbonyl carbon, as well as a minor fraction of aliphatic carbon, all of which are likely tritiated. A similar co-deposition process that occurs in fusion devices is responsible for the formation and growth of the carbonaceous deposits.