Chemically polished stainless steel tubing for tritium service

Abstract

The need for low carbon and protium inventory at the surfaces of tritium process vacuum components has previously been demonstrated: Radiolytic methane generation and hydrogen isotope exchange lead to contamination of the tritium gas. Significant lengths of small (less than 1/2 in.) stainless steel tubing have, however, been difficult to procure or prepare in an organic‐free, low surface area state. Chemical flow polishing now appears to be an appropriate method for preparation of such tubing. Three types of stainless steel (316) tubing—commercial supply house (SH), chromatography grade (CG), and flow‐polished (FP) samples—have been investigated by profilometry, SEM, and AES. Surface roughness of the SH, CG, and FP samples were 38, 22, and 7 μin. rms, respectively. Relative surface areas were approx. ≥10:10:1, as were relative total carbon inventories for the SH, CG, and FP surfaces, respectively. Some contamination of the surfaces by N, P, S, and Cl was noted. These elements were present at 1 to 3 at. % on the FP sample, but did not appear significantly concentrated along intergranular regions. Increased corrosion of FP tubing over SH or CG materials was considered unlikely. Growth data of protium and methane impurities into tritium gas from surfaces similar to those of SH and FP samples demonstrate the advantages of FP tubing in tritium service.