Diffusion of gases in solids. Tritium diffusion in stainless steel, Zircaloy-2, and niobium. Period covered: November 1, 1972--October 31, 1973

Technical Report · Mon Jan 01 04:00:00 EST 1973

DOI:https://doi.org/10.2172/4381546· OSTI ID:4381546

Abraham, P. M.; Davis, J.; Pennington, C. W.; Elleman, T. S.; Verghese, K.

A surface effect which retards the release of recoil-injected tritium was observed for austenitic stainless steel, Zircaloy-2, and niobium. Tritium release from the surface is characterized by diffusion coefficients which are lower than the bulk diffusion coefficients by approximately two orders of magnitude in stainless steel and seven or eight orders of magnitude in Zircaloy-2 and niobium. The transport rate through the surface films appears to be the rate- limiting process for transport through thin specimens of the latter two materials. The effect appears to be associated with the transport through surface oxide films and is not simply a surface-absorption, desorption process. A two-region diffusion model was used to calculate apparent diffusion coefficients and activation energies for transport in the surface films. The surfacelayer diffusion coefficients determined for niobium exhibit a change in activation energy at temperatures above 500 deg C, an effect attributed to the dissolution of the oxide film at high temperatures. The niobium-release results are interpreted in terms of several possible models, and it is shown that the data can fit each model, thereby yielding tritium diffusion coefficients within the surface film and through the film. A three-region diffusion model, which includes the effect of surface films at both specimen faces, was applied to stainless steel and Zircaloy-2 reactor fuel cladding using typical reactor temperatures and times. Predicted tritium release was high for stainless steel- clad elements and low for Zircaloy cladding, in agreement with experimental observation. Tritium diffusion coefficients within the zirconium-oxide surface films on Zircaloy-2 were observed to be essentially independent of oxide film thickness. (16 figures, 30 references) (auth)

• Research Organization: North Carolina State Univ., Raleigh (USA). Dept. of Nuclear Engineering
• NSA Number: NSA-29-008281
• OSTI ID: 4381546
• Report Number(s): ORO--3508-9
• Country of Publication: United States
• Language: English

Related Subjects

*NIOBIUM-- SURFACE PROPERTIES
*STAINLESS STEELS-- SURFACE PROPERTIES
*TRITIUM-- DIFFUSION
*ZIRCALOY 2-- SURFACE PROPERTIES
ACTIVATION ENERGY
FUEL CANS
FUNCTIONAL MODELS
KINETICS
N50230* --Metals
Ceramics
& Other Materials--Metals & Alloys--Properties
Structure & Phase Studies
RECOILS ZIRCALOY-2