The effect of coatings on retention and permeation in SS 316L APT tritium production tubes

Abstract

The accelerator production of tritium (APT) design calls for thousands of thin-walled tubes to be filled with 3He gas. The reaction of the spallation neutrons with this gas will result in the bombardment of the interior of these tubes with energetic tritons and protons. For APT to be able to meet its tritium production goals, it is necessary that the holdup of the tritium in the tube walls be minimized. To examine the tritium retention characteristics of stainless steel, one of the tube reference materials, accelerator implantation experiments were performed. In these experiments, deuterium was used in place of tritium to eliminate the problem of tritium contamination. Deuterons with energies up to 200 keV and protons with energies up to 600 keV were implanted into stainless steel (SS 316L) samples to fluences as high as 5 × 10 22 D/m 2 and 5 × 10 22 p/m 2. Thermal desorption spectroscopy showed that approximately 3% of the deuterium was retained within the sample. Approximately 0.5% of the deuterium permeated through to the back surface of the sample where a zirconium getter trapped the deuterium. The deuterium trapped in the zirconium layer was measured by nuclear reaction analysis. Eight-micron thick copper and nickel coatings were applied to the implantation side of the stainless steel substrate in an attempt to reduce the retention and permeation of the deuterium. The copper-coated stainless steel was not successful in reducing the retention and permeation, however the nickel coated stainless steel reduced both the retention and permeation substantially.