Available Methods for Hydriding Zircaloy for Full-size Unirradiated CANDU Fuel and Surrogate Bundles

Abstract

In this study, various methods commonly used to hydrogen charge Zircaloy samples and specimens like tubing are described and reviewed in terms of their ability to hydride full-size non-irradiated CANDU fuel and surrogate bundles clad with Zircaloy metal. The purpose of hydriding full-size unirradiated fuel bundles is to have a cost-effective methodology to simulate irradiated fuel with these hydrided full-size bundles that can be used in various studies related to their handling such as in storage, transportation and DGR storage. Five well-known hydrogen charging techniques were considered:

1. Gaseous Hydrogen Charging
2. Electrolytic Cathodic Charging
3. Autoclave Corrosion by Lithium Hydroxide Solutions
4. Thermomechanical Method using Hydride Powder
5. Coulometric Titration Technique

Based on the requirements for these techniques, only two of the methods were found to be capable to hydrogen charge or hydride full-size CANDU fuel bundles: Gaseous Hydrogen Charging and Autoclave Corrosion by LiOH Solutions. Both processes require pressure vessels capable of withstanding pressures and temperatures up to 16 MPa and 400°C. The other three methods were screened out as not suitable for the purpose of hydrogen charging full-size bundles.

Further, among these two options, autoclaving in LiOH solutions was the preferred option because of the simplicity of the process and the elimination of time-consuming pre- and post- hydriding steps. In particular, annealing of the CANDU fuel bundle to homogenize the hydrides in the Zr alloy material is not required and yet the as-received microstructure of the material is preserved. As a result, the Autoclave Corrosion with LiOH solutions is recommended for hydriding non-irradiated CANDU fuel bundles or their surrogates.